date_picker.dart 103 KB
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// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:math' as math;

import 'package:flutter/gestures.dart' show DragStartBehavior;
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'package:flutter/widgets.dart';

import 'app_bar.dart';
import 'back_button.dart';
import 'calendar_date_picker.dart';
import 'color_scheme.dart';
import 'date.dart';
import 'debug.dart';
import 'dialog.dart';
import 'dialog_theme.dart';
import 'divider.dart';
import 'icon_button.dart';
import 'icons.dart';
import 'ink_well.dart';
import 'input_border.dart';
import 'input_date_picker_form_field.dart';
import 'input_decorator.dart';
import 'material.dart';
import 'material_localizations.dart';
import 'scaffold.dart';
import 'text_button.dart';
import 'text_field.dart';
import 'text_theme.dart';
import 'theme.dart';

const Size _calendarPortraitDialogSize = Size(330.0, 518.0);
const Size _calendarLandscapeDialogSize = Size(496.0, 346.0);
const Size _inputPortraitDialogSize = Size(330.0, 270.0);
const Size _inputLandscapeDialogSize = Size(496, 160.0);
const Size _inputRangeLandscapeDialogSize = Size(496, 164.0);
const Duration _dialogSizeAnimationDuration = Duration(milliseconds: 200);
const double _inputFormPortraitHeight = 98.0;
const double _inputFormLandscapeHeight = 108.0;

/// Shows a dialog containing a Material Design date picker.
///
/// The returned [Future] resolves to the date selected by the user when the
/// user confirms the dialog. If the user cancels the dialog, null is returned.
///
/// When the date picker is first displayed, it will show the month of
/// [initialDate], with [initialDate] selected.
///
/// The [firstDate] is the earliest allowable date. The [lastDate] is the latest
/// allowable date. [initialDate] must either fall between these dates,
/// or be equal to one of them. For each of these [DateTime] parameters, only
/// their dates are considered. Their time fields are ignored. They must all
/// be non-null.
///
/// The [currentDate] represents the current day (i.e. today). This
/// date will be highlighted in the day grid. If null, the date of
/// `DateTime.now()` will be used.
///
/// An optional [initialEntryMode] argument can be used to display the date
/// picker in the [DatePickerEntryMode.calendar] (a calendar month grid)
/// or [DatePickerEntryMode.input] (a text input field) mode.
/// It defaults to [DatePickerEntryMode.calendar] and must be non-null.
///
/// An optional [selectableDayPredicate] function can be passed in to only allow
/// certain days for selection. If provided, only the days that
/// [selectableDayPredicate] returns true for will be selectable. For example,
/// this can be used to only allow weekdays for selection. If provided, it must
/// return true for [initialDate].
///
/// The following optional string parameters allow you to override the default
/// text used for various parts of the dialog:
///
///   * [helpText], label displayed at the top of the dialog.
///   * [cancelText], label on the cancel button.
///   * [confirmText], label on the ok button.
///   * [errorFormatText], message used when the input text isn't in a proper date format.
///   * [errorInvalidText], message used when the input text isn't a selectable date.
///   * [fieldHintText], text used to prompt the user when no text has been entered in the field.
///   * [fieldLabelText], label for the date text input field.
///
/// An optional [locale] argument can be used to set the locale for the date
/// picker. It defaults to the ambient locale provided by [Localizations].
///
/// An optional [textDirection] argument can be used to set the text direction
/// ([TextDirection.ltr] or [TextDirection.rtl]) for the date picker. It
/// defaults to the ambient text direction provided by [Directionality]. If both
/// [locale] and [textDirection] are non-null, [textDirection] overrides the
/// direction chosen for the [locale].
///
/// The [context], [useRootNavigator] and [routeSettings] arguments are passed to
/// [showDialog], the documentation for which discusses how it is used. [context]
/// and [useRootNavigator] must be non-null.
///
/// The [builder] parameter can be used to wrap the dialog widget
/// to add inherited widgets like [Theme].
///
/// An optional [initialDatePickerMode] argument can be used to have the
/// calendar date picker initially appear in the [DatePickerMode.year] or
/// [DatePickerMode.day] mode. It defaults to [DatePickerMode.day], and
/// must be non-null.
///
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/// {@macro flutter.widgets.RawDialogRoute}
///
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/// ### State Restoration
///
/// Using this method will not enable state restoration for the date picker.
/// In order to enable state restoration for a date picker, use
/// [Navigator.restorablePush] or [Navigator.restorablePushNamed] with
/// [DatePickerDialog].
///
/// For more information about state restoration, see [RestorationManager].
///
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/// {@macro flutter.widgets.RestorationManager}
///
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/// {@tool dartpad}
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/// This sample demonstrates how to create a restorable Material date picker.
/// This is accomplished by enabling state restoration by specifying
/// [MaterialApp.restorationScopeId] and using [Navigator.restorablePush] to
/// push [DatePickerDialog] when the button is tapped.
///
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/// ** See code in examples/api/lib/material/date_picker/show_date_picker.0.dart **
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/// {@end-tool}
///
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/// See also:
///
///  * [showDateRangePicker], which shows a material design date range picker
///    used to select a range of dates.
///  * [CalendarDatePicker], which provides the calendar grid used by the date picker dialog.
///  * [InputDatePickerFormField], which provides a text input field for entering dates.
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///  * [DisplayFeatureSubScreen], which documents the specifics of how
///    [DisplayFeature]s can split the screen into sub-screens.
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///  * [showTimePicker], which shows a dialog that contains a material design time picker.
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///
Future<DateTime?> showDatePicker({
  required BuildContext context,
  required DateTime initialDate,
  required DateTime firstDate,
  required DateTime lastDate,
  DateTime? currentDate,
  DatePickerEntryMode initialEntryMode = DatePickerEntryMode.calendar,
  SelectableDayPredicate? selectableDayPredicate,
  String? helpText,
  String? cancelText,
  String? confirmText,
  Locale? locale,
  bool useRootNavigator = true,
  RouteSettings? routeSettings,
  TextDirection? textDirection,
  TransitionBuilder? builder,
  DatePickerMode initialDatePickerMode = DatePickerMode.day,
  String? errorFormatText,
  String? errorInvalidText,
  String? fieldHintText,
  String? fieldLabelText,
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  TextInputType? keyboardType,
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  Offset? anchorPoint,
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}) async {
  assert(context != null);
  assert(initialDate != null);
  assert(firstDate != null);
  assert(lastDate != null);
  initialDate = DateUtils.dateOnly(initialDate);
  firstDate = DateUtils.dateOnly(firstDate);
  lastDate = DateUtils.dateOnly(lastDate);
  assert(
    !lastDate.isBefore(firstDate),
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    'lastDate $lastDate must be on or after firstDate $firstDate.',
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  );
  assert(
    !initialDate.isBefore(firstDate),
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    'initialDate $initialDate must be on or after firstDate $firstDate.',
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  );
  assert(
    !initialDate.isAfter(lastDate),
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    'initialDate $initialDate must be on or before lastDate $lastDate.',
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  );
  assert(
    selectableDayPredicate == null || selectableDayPredicate(initialDate),
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    'Provided initialDate $initialDate must satisfy provided selectableDayPredicate.',
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  );
  assert(initialEntryMode != null);
  assert(useRootNavigator != null);
  assert(initialDatePickerMode != null);
  assert(debugCheckHasMaterialLocalizations(context));

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  Widget dialog = DatePickerDialog(
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    initialDate: initialDate,
    firstDate: firstDate,
    lastDate: lastDate,
    currentDate: currentDate,
    initialEntryMode: initialEntryMode,
    selectableDayPredicate: selectableDayPredicate,
    helpText: helpText,
    cancelText: cancelText,
    confirmText: confirmText,
    initialCalendarMode: initialDatePickerMode,
    errorFormatText: errorFormatText,
    errorInvalidText: errorInvalidText,
    fieldHintText: fieldHintText,
    fieldLabelText: fieldLabelText,
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    keyboardType: keyboardType,
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  );

  if (textDirection != null) {
    dialog = Directionality(
      textDirection: textDirection,
      child: dialog,
    );
  }

  if (locale != null) {
    dialog = Localizations.override(
      context: context,
      locale: locale,
      child: dialog,
    );
  }

  return showDialog<DateTime>(
    context: context,
    useRootNavigator: useRootNavigator,
    routeSettings: routeSettings,
    builder: (BuildContext context) {
      return builder == null ? dialog : builder(context, dialog);
    },
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    anchorPoint: anchorPoint,
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  );
}

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/// A Material-style date picker dialog.
///
/// It is used internally by [showDatePicker] or can be directly pushed
/// onto the [Navigator] stack to enable state restoration. See
/// [showDatePicker] for a state restoration app example.
///
/// See also:
///
///  * [showDatePicker], which is a way to display the date picker.
class DatePickerDialog extends StatefulWidget {
  /// A Material-style date picker dialog.
  DatePickerDialog({
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    Key? key,
    required DateTime initialDate,
    required DateTime firstDate,
    required DateTime lastDate,
    DateTime? currentDate,
    this.initialEntryMode = DatePickerEntryMode.calendar,
    this.selectableDayPredicate,
    this.cancelText,
    this.confirmText,
    this.helpText,
    this.initialCalendarMode = DatePickerMode.day,
    this.errorFormatText,
    this.errorInvalidText,
    this.fieldHintText,
    this.fieldLabelText,
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    this.keyboardType,
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    this.restorationId,
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  }) : assert(initialDate != null),
       assert(firstDate != null),
       assert(lastDate != null),
       initialDate = DateUtils.dateOnly(initialDate),
       firstDate = DateUtils.dateOnly(firstDate),
       lastDate = DateUtils.dateOnly(lastDate),
       currentDate = DateUtils.dateOnly(currentDate ?? DateTime.now()),
       assert(initialEntryMode != null),
       assert(initialCalendarMode != null),
       super(key: key) {
    assert(
      !this.lastDate.isBefore(this.firstDate),
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      'lastDate ${this.lastDate} must be on or after firstDate ${this.firstDate}.',
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    );
    assert(
      !this.initialDate.isBefore(this.firstDate),
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      'initialDate ${this.initialDate} must be on or after firstDate ${this.firstDate}.',
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    );
    assert(
      !this.initialDate.isAfter(this.lastDate),
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      'initialDate ${this.initialDate} must be on or before lastDate ${this.lastDate}.',
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    );
    assert(
      selectableDayPredicate == null || selectableDayPredicate!(this.initialDate),
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      'Provided initialDate ${this.initialDate} must satisfy provided selectableDayPredicate',
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    );
  }

  /// The initially selected [DateTime] that the picker should display.
  final DateTime initialDate;

  /// The earliest allowable [DateTime] that the user can select.
  final DateTime firstDate;

  /// The latest allowable [DateTime] that the user can select.
  final DateTime lastDate;

  /// The [DateTime] representing today. It will be highlighted in the day grid.
  final DateTime currentDate;

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  /// The initial mode of date entry method for the date picker dialog.
  ///
  /// See [DatePickerEntryMode] for more details on the different data entry
  /// modes available.
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  final DatePickerEntryMode initialEntryMode;

  /// Function to provide full control over which [DateTime] can be selected.
  final SelectableDayPredicate? selectableDayPredicate;

  /// The text that is displayed on the cancel button.
  final String? cancelText;

  /// The text that is displayed on the confirm button.
  final String? confirmText;

  /// The text that is displayed at the top of the header.
  ///
  /// This is used to indicate to the user what they are selecting a date for.
  final String? helpText;

  /// The initial display of the calendar picker.
  final DatePickerMode initialCalendarMode;

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  /// The error text displayed if the entered date is not in the correct format.
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  final String? errorFormatText;

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  /// The error text displayed if the date is not valid.
  ///
  /// A date is not valid if it is earlier than [firstDate], later than
  /// [lastDate], or doesn't pass the [selectableDayPredicate].
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  final String? errorInvalidText;

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  /// The hint text displayed in the [TextField].
  ///
  /// If this is null, it will default to the date format string. For example,
  /// 'mm/dd/yyyy' for en_US.
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  final String? fieldHintText;

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  /// The label text displayed in the [TextField].
  ///
  /// If this is null, it will default to the words representing the date format
  /// string. For example, 'Month, Day, Year' for en_US.
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  final String? fieldLabelText;

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  /// The keyboard type of the [TextField].
  ///
  /// If this is null, it will default to [TextInputType.datetime]
  final TextInputType? keyboardType;

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  /// Restoration ID to save and restore the state of the [DatePickerDialog].
  ///
  /// If it is non-null, the date picker will persist and restore the
  /// date selected on the dialog.
  ///
  /// The state of this widget is persisted in a [RestorationBucket] claimed
  /// from the surrounding [RestorationScope] using the provided restoration ID.
  ///
  /// See also:
  ///
  ///  * [RestorationManager], which explains how state restoration works in
  ///    Flutter.
  final String? restorationId;

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  @override
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  State<DatePickerDialog> createState() => _DatePickerDialogState();
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}

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class _DatePickerDialogState extends State<DatePickerDialog> with RestorationMixin {
  late final RestorableDateTime _selectedDate = RestorableDateTime(widget.initialDate);
  late final _RestorableDatePickerEntryMode _entryMode = _RestorableDatePickerEntryMode(widget.initialEntryMode);
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  final _RestorableAutovalidateMode _autovalidateMode = _RestorableAutovalidateMode(AutovalidateMode.disabled);
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  @override
  String? get restorationId => widget.restorationId;
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  @override
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  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
    registerForRestoration(_selectedDate, 'selected_date');
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    registerForRestoration(_autovalidateMode, 'autovalidateMode');
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    registerForRestoration(_entryMode, 'calendar_entry_mode');
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  }

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  final GlobalKey _calendarPickerKey = GlobalKey();
  final GlobalKey<FormState> _formKey = GlobalKey<FormState>();

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  void _handleOk() {
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    if (_entryMode.value == DatePickerEntryMode.input || _entryMode.value == DatePickerEntryMode.inputOnly) {
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      final FormState form = _formKey.currentState!;
      if (!form.validate()) {
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        setState(() => _autovalidateMode.value = AutovalidateMode.always);
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        return;
      }
      form.save();
    }
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    Navigator.pop(context, _selectedDate.value);
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  }

  void _handleCancel() {
    Navigator.pop(context);
  }

  void _handleEntryModeToggle() {
    setState(() {
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      switch (_entryMode.value) {
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        case DatePickerEntryMode.calendar:
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          _autovalidateMode.value = AutovalidateMode.disabled;
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          _entryMode.value = DatePickerEntryMode.input;
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          break;
        case DatePickerEntryMode.input:
          _formKey.currentState!.save();
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          _entryMode.value = DatePickerEntryMode.calendar;
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          break;
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        case DatePickerEntryMode.calendarOnly:
        case DatePickerEntryMode.inputOnly:
          assert(false, 'Can not change entry mode from _entryMode');
          break;
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      }
    });
  }

  void _handleDateChanged(DateTime date) {
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    setState(() {
      _selectedDate.value = date;
    });
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  }

  Size _dialogSize(BuildContext context) {
    final Orientation orientation = MediaQuery.of(context).orientation;
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    switch (_entryMode.value) {
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      case DatePickerEntryMode.calendar:
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      case DatePickerEntryMode.calendarOnly:
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        switch (orientation) {
          case Orientation.portrait:
            return _calendarPortraitDialogSize;
          case Orientation.landscape:
            return _calendarLandscapeDialogSize;
        }
      case DatePickerEntryMode.input:
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      case DatePickerEntryMode.inputOnly:
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        switch (orientation) {
          case Orientation.portrait:
            return _inputPortraitDialogSize;
          case Orientation.landscape:
            return _inputLandscapeDialogSize;
        }
    }
  }

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  static const Map<ShortcutActivator, Intent> _formShortcutMap = <ShortcutActivator, Intent>{
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    // Pressing enter on the field will move focus to the next field or control.
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    SingleActivator(LogicalKeyboardKey.enter): NextFocusIntent(),
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  };

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colorScheme = theme.colorScheme;
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final Orientation orientation = MediaQuery.of(context).orientation;
    final TextTheme textTheme = theme.textTheme;
    // Constrain the textScaleFactor to the largest supported value to prevent
    // layout issues.
    final double textScaleFactor = math.min(MediaQuery.of(context).textScaleFactor, 1.3);

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    final String dateText = localizations.formatMediumDate(_selectedDate.value);
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    final Color onPrimarySurface = colorScheme.brightness == Brightness.light
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      ? colorScheme.onPrimary
      : colorScheme.onSurface;
    final TextStyle? dateStyle = orientation == Orientation.landscape
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      ? textTheme.headline5?.copyWith(color: onPrimarySurface)
      : textTheme.headline4?.copyWith(color: onPrimarySurface);
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    final Widget actions = Container(
      alignment: AlignmentDirectional.centerEnd,
      constraints: const BoxConstraints(minHeight: 52.0),
      padding: const EdgeInsets.symmetric(horizontal: 8),
      child: OverflowBar(
        spacing: 8,
        children: <Widget>[
          TextButton(
            onPressed: _handleCancel,
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            child: Text(widget.cancelText ?? localizations.cancelButtonLabel),
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          ),
          TextButton(
            onPressed: _handleOk,
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            child: Text(widget.confirmText ?? localizations.okButtonLabel),
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          ),
        ],
      ),
    );

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    CalendarDatePicker calendarDatePicker() {
      return CalendarDatePicker(
        key: _calendarPickerKey,
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        initialDate: _selectedDate.value,
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        firstDate: widget.firstDate,
        lastDate: widget.lastDate,
        currentDate: widget.currentDate,
        onDateChanged: _handleDateChanged,
        selectableDayPredicate: widget.selectableDayPredicate,
        initialCalendarMode: widget.initialCalendarMode,
      );
    }

    Form inputDatePicker() {
      return Form(
        key: _formKey,
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        autovalidateMode: _autovalidateMode.value,
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        child: Container(
          padding: const EdgeInsets.symmetric(horizontal: 24),
          height: orientation == Orientation.portrait ? _inputFormPortraitHeight : _inputFormLandscapeHeight,
          child: Shortcuts(
            shortcuts: _formShortcutMap,
            child: Column(
              children: <Widget>[
                const Spacer(),
                InputDatePickerFormField(
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                  initialDate: _selectedDate.value,
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                  firstDate: widget.firstDate,
                  lastDate: widget.lastDate,
                  onDateSubmitted: _handleDateChanged,
                  onDateSaved: _handleDateChanged,
                  selectableDayPredicate: widget.selectableDayPredicate,
                  errorFormatText: widget.errorFormatText,
                  errorInvalidText: widget.errorInvalidText,
                  fieldHintText: widget.fieldHintText,
                  fieldLabelText: widget.fieldLabelText,
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                  keyboardType: widget.keyboardType,
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                  autofocus: true,
                ),
                const Spacer(),
              ],
            ),
          ),
        ),
      );
    }

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    final Widget picker;
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    final Widget? entryModeButton;
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    switch (_entryMode.value) {
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      case DatePickerEntryMode.calendar:
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        picker = calendarDatePicker();
        entryModeButton = IconButton(
          icon: const Icon(Icons.edit),
          color: onPrimarySurface,
          tooltip: localizations.inputDateModeButtonLabel,
          onPressed: _handleEntryModeToggle,
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        );
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        break;

      case DatePickerEntryMode.calendarOnly:
        picker = calendarDatePicker();
        entryModeButton = null;
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        break;

      case DatePickerEntryMode.input:
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        picker = inputDatePicker();
        entryModeButton = IconButton(
          icon: const Icon(Icons.calendar_today),
          color: onPrimarySurface,
          tooltip: localizations.calendarModeButtonLabel,
          onPressed: _handleEntryModeToggle,
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        );
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        break;

      case DatePickerEntryMode.inputOnly:
        picker = inputDatePicker();
        entryModeButton = null;
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        break;
    }

    final Widget header = _DatePickerHeader(
      helpText: widget.helpText ?? localizations.datePickerHelpText,
      titleText: dateText,
      titleStyle: dateStyle,
      orientation: orientation,
      isShort: orientation == Orientation.landscape,
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      entryModeButton: entryModeButton,
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    );

    final Size dialogSize = _dialogSize(context) * textScaleFactor;
    return Dialog(
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      insetPadding: const EdgeInsets.symmetric(horizontal: 16.0, vertical: 24.0),
      clipBehavior: Clip.antiAlias,
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      child: AnimatedContainer(
        width: dialogSize.width,
        height: dialogSize.height,
        duration: _dialogSizeAnimationDuration,
        curve: Curves.easeIn,
        child: MediaQuery(
          data: MediaQuery.of(context).copyWith(
            textScaleFactor: textScaleFactor,
          ),
          child: Builder(builder: (BuildContext context) {
            switch (orientation) {
              case Orientation.portrait:
                return Column(
                  mainAxisSize: MainAxisSize.min,
                  crossAxisAlignment: CrossAxisAlignment.stretch,
                  children: <Widget>[
                    header,
                    Expanded(child: picker),
                    actions,
                  ],
                );
              case Orientation.landscape:
                return Row(
                  mainAxisSize: MainAxisSize.min,
                  crossAxisAlignment: CrossAxisAlignment.stretch,
                  children: <Widget>[
                    header,
                    Flexible(
                      child: Column(
                        mainAxisSize: MainAxisSize.min,
                        crossAxisAlignment: CrossAxisAlignment.stretch,
                        children: <Widget>[
                          Expanded(child: picker),
                          actions,
                        ],
                      ),
                    ),
                  ],
                );
            }
          }),
        ),
      ),
    );
  }
}

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// A restorable [DatePickerEntryMode] value.
//
// This serializes each entry as a unique `int` value.
class _RestorableDatePickerEntryMode extends RestorableValue<DatePickerEntryMode> {
  _RestorableDatePickerEntryMode(
    DatePickerEntryMode defaultValue,
  ) : _defaultValue = defaultValue;

  final DatePickerEntryMode _defaultValue;

  @override
  DatePickerEntryMode createDefaultValue() => _defaultValue;

  @override
  void didUpdateValue(DatePickerEntryMode? oldValue) {
    assert(debugIsSerializableForRestoration(value.index));
    notifyListeners();
  }

  @override
  DatePickerEntryMode fromPrimitives(Object? data) => DatePickerEntryMode.values[data! as int];

  @override
  Object? toPrimitives() => value.index;
}

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// A restorable [AutovalidateMode] value.
//
// This serializes each entry as a unique `int` value.
class _RestorableAutovalidateMode extends RestorableValue<AutovalidateMode> {
  _RestorableAutovalidateMode(
      AutovalidateMode defaultValue,
      ) : _defaultValue = defaultValue;

  final AutovalidateMode _defaultValue;

  @override
  AutovalidateMode createDefaultValue() => _defaultValue;

  @override
  void didUpdateValue(AutovalidateMode? oldValue) {
    assert(debugIsSerializableForRestoration(value.index));
    notifyListeners();
  }

  @override
  AutovalidateMode fromPrimitives(Object? data) => AutovalidateMode.values[data! as int];

  @override
  Object? toPrimitives() => value.index;
}

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/// Re-usable widget that displays the selected date (in large font) and the
/// help text above it.
///
/// These types include:
///
/// * Single Date picker with calendar mode.
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/// * Single Date picker with text input mode.
/// * Date Range picker with text input mode.
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///
/// [helpText], [orientation], [icon], [onIconPressed] are required and must be
/// non-null.
class _DatePickerHeader extends StatelessWidget {

  /// Creates a header for use in a date picker dialog.
  const _DatePickerHeader({
    Key? key,
    required this.helpText,
    required this.titleText,
    this.titleSemanticsLabel,
    required this.titleStyle,
    required this.orientation,
    this.isShort = false,
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    this.entryModeButton,
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  }) : assert(helpText != null),
       assert(orientation != null),
       assert(isShort != null),
       super(key: key);

  static const double _datePickerHeaderLandscapeWidth = 152.0;
  static const double _datePickerHeaderPortraitHeight = 120.0;
  static const double _headerPaddingLandscape = 16.0;

  /// The text that is displayed at the top of the header.
  ///
  /// This is used to indicate to the user what they are selecting a date for.
  final String helpText;

  /// The text that is displayed at the center of the header.
  final String titleText;

  /// The semantic label associated with the [titleText].
  final String? titleSemanticsLabel;

  /// The [TextStyle] that the title text is displayed with.
  final TextStyle? titleStyle;

  /// The orientation is used to decide how to layout its children.
  final Orientation orientation;

  /// Indicates the header is being displayed in a shorter/narrower context.
  ///
  /// This will be used to tighten up the space between the help text and date
  /// text if `true`. Additionally, it will use a smaller typography style if
  /// `true`.
  ///
  /// This is necessary for displaying the manual input mode in
  /// landscape orientation, in order to account for the keyboard height.
  final bool isShort;

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  final Widget? entryModeButton;
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  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colorScheme = theme.colorScheme;
    final TextTheme textTheme = theme.textTheme;

    // The header should use the primary color in light themes and surface color in dark
    final bool isDark = colorScheme.brightness == Brightness.dark;
    final Color primarySurfaceColor = isDark ? colorScheme.surface : colorScheme.primary;
    final Color onPrimarySurfaceColor = isDark ? colorScheme.onSurface : colorScheme.onPrimary;

    final TextStyle? helpStyle = textTheme.overline?.copyWith(
      color: onPrimarySurfaceColor,
    );

    final Text help = Text(
      helpText,
      style: helpStyle,
      maxLines: 1,
      overflow: TextOverflow.ellipsis,
    );
    final Text title = Text(
      titleText,
      semanticsLabel: titleSemanticsLabel ?? titleText,
      style: titleStyle,
      maxLines: orientation == Orientation.portrait ? 1 : 2,
      overflow: TextOverflow.ellipsis,
    );

    switch (orientation) {
      case Orientation.portrait:
        return SizedBox(
          height: _datePickerHeaderPortraitHeight,
          child: Material(
            color: primarySurfaceColor,
            child: Padding(
              padding: const EdgeInsetsDirectional.only(
                start: 24,
                end: 12,
              ),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  const SizedBox(height: 16),
                  help,
                  const Flexible(child: SizedBox(height: 38)),
                  Row(
                    children: <Widget>[
                      Expanded(child: title),
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                      if (entryModeButton != null)
                        entryModeButton!,
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                    ],
                  ),
                ],
              ),
            ),
          ),
        );
      case Orientation.landscape:
        return SizedBox(
          width: _datePickerHeaderLandscapeWidth,
          child: Material(
            color: primarySurfaceColor,
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                const SizedBox(height: 16),
                Padding(
                  padding: const EdgeInsets.symmetric(
                    horizontal: _headerPaddingLandscape,
                  ),
                  child: help,
                ),
                SizedBox(height: isShort ? 16 : 56),
                Expanded(
                  child: Padding(
                    padding: const EdgeInsets.symmetric(
                      horizontal: _headerPaddingLandscape,
                    ),
                    child: title,
                  ),
                ),
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                if (entryModeButton != null)
                  Padding(
                    padding: const EdgeInsets.symmetric(horizontal: 4),
                    child: entryModeButton,
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                  ),
              ],
            ),
          ),
        );
    }
  }
}

/// Shows a full screen modal dialog containing a Material Design date range
/// picker.
///
/// The returned [Future] resolves to the [DateTimeRange] selected by the user
/// when the user saves their selection. If the user cancels the dialog, null is
/// returned.
///
/// If [initialDateRange] is non-null, then it will be used as the initially
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/// selected date range. If it is provided, `initialDateRange.start` must be
/// before or on `initialDateRange.end`.
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///
/// The [firstDate] is the earliest allowable date. The [lastDate] is the latest
/// allowable date. Both must be non-null.
///
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/// If an initial date range is provided, `initialDateRange.start`
/// and `initialDateRange.end` must both fall between or on [firstDate] and
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/// [lastDate]. For all of these [DateTime] values, only their dates are
/// considered. Their time fields are ignored.
///
/// The [currentDate] represents the current day (i.e. today). This
/// date will be highlighted in the day grid. If null, the date of
/// `DateTime.now()` will be used.
///
/// An optional [initialEntryMode] argument can be used to display the date
/// picker in the [DatePickerEntryMode.calendar] (a scrollable calendar month
/// grid) or [DatePickerEntryMode.input] (two text input fields) mode.
/// It defaults to [DatePickerEntryMode.calendar] and must be non-null.
///
/// The following optional string parameters allow you to override the default
/// text used for various parts of the dialog:
///
///   * [helpText], the label displayed at the top of the dialog.
///   * [cancelText], the label on the cancel button for the text input mode.
///   * [confirmText],the  label on the ok button for the text input mode.
///   * [saveText], the label on the save button for the fullscreen calendar
///     mode.
///   * [errorFormatText], the message used when an input text isn't in a proper
///     date format.
///   * [errorInvalidText], the message used when an input text isn't a
///     selectable date.
///   * [errorInvalidRangeText], the message used when the date range is
///     invalid (e.g. start date is after end date).
///   * [fieldStartHintText], the text used to prompt the user when no text has
///     been entered in the start field.
///   * [fieldEndHintText], the text used to prompt the user when no text has
///     been entered in the end field.
///   * [fieldStartLabelText], the label for the start date text input field.
///   * [fieldEndLabelText], the label for the end date text input field.
///
/// An optional [locale] argument can be used to set the locale for the date
/// picker. It defaults to the ambient locale provided by [Localizations].
///
/// An optional [textDirection] argument can be used to set the text direction
/// ([TextDirection.ltr] or [TextDirection.rtl]) for the date picker. It
/// defaults to the ambient text direction provided by [Directionality]. If both
/// [locale] and [textDirection] are non-null, [textDirection] overrides the
/// direction chosen for the [locale].
///
/// The [context], [useRootNavigator] and [routeSettings] arguments are passed
/// to [showDialog], the documentation for which discusses how it is used.
/// [context] and [useRootNavigator] must be non-null.
///
/// The [builder] parameter can be used to wrap the dialog widget
/// to add inherited widgets like [Theme].
///
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/// {@macro flutter.widgets.RawDialogRoute}
///
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/// ### State Restoration
///
/// Using this method will not enable state restoration for the date range picker.
/// In order to enable state restoration for a date range picker, use
/// [Navigator.restorablePush] or [Navigator.restorablePushNamed] with
/// [DateRangePickerDialog].
///
/// For more information about state restoration, see [RestorationManager].
///
/// {@macro flutter.widgets.RestorationManager}
///
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/// {@tool sample}
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/// This sample demonstrates how to create a restorable Material date range picker.
/// This is accomplished by enabling state restoration by specifying
/// [MaterialApp.restorationScopeId] and using [Navigator.restorablePush] to
/// push [DateRangePickerDialog] when the button is tapped.
///
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/// ** See code in examples/api/lib/material/date_picker/show_date_range_picker.0.dart **
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/// {@end-tool}
///
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/// See also:
///
///  * [showDatePicker], which shows a material design date picker used to
///    select a single date.
///  * [DateTimeRange], which is used to describe a date range.
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///  * [DisplayFeatureSubScreen], which documents the specifics of how
///    [DisplayFeature]s can split the screen into sub-screens.
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Future<DateTimeRange?> showDateRangePicker({
  required BuildContext context,
  DateTimeRange? initialDateRange,
  required DateTime firstDate,
  required DateTime lastDate,
  DateTime? currentDate,
  DatePickerEntryMode initialEntryMode = DatePickerEntryMode.calendar,
  String? helpText,
  String? cancelText,
  String? confirmText,
  String? saveText,
  String? errorFormatText,
  String? errorInvalidText,
  String? errorInvalidRangeText,
  String? fieldStartHintText,
  String? fieldEndHintText,
  String? fieldStartLabelText,
  String? fieldEndLabelText,
  Locale? locale,
  bool useRootNavigator = true,
  RouteSettings? routeSettings,
  TextDirection? textDirection,
  TransitionBuilder? builder,
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  Offset? anchorPoint,
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}) async {
  assert(context != null);
  assert(
    initialDateRange == null || (initialDateRange.start != null && initialDateRange.end != null),
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    'initialDateRange must be null or have non-null start and end dates.',
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  );
  assert(
    initialDateRange == null || !initialDateRange.start.isAfter(initialDateRange.end),
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    "initialDateRange's start date must not be after it's end date.",
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  );
  initialDateRange = initialDateRange == null ? null : DateUtils.datesOnly(initialDateRange);
  assert(firstDate != null);
  firstDate = DateUtils.dateOnly(firstDate);
  assert(lastDate != null);
  lastDate = DateUtils.dateOnly(lastDate);
  assert(
    !lastDate.isBefore(firstDate),
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    'lastDate $lastDate must be on or after firstDate $firstDate.',
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  );
  assert(
    initialDateRange == null || !initialDateRange.start.isBefore(firstDate),
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    "initialDateRange's start date must be on or after firstDate $firstDate.",
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  );
  assert(
    initialDateRange == null || !initialDateRange.end.isBefore(firstDate),
985
    "initialDateRange's end date must be on or after firstDate $firstDate.",
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  );
  assert(
    initialDateRange == null || !initialDateRange.start.isAfter(lastDate),
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    "initialDateRange's start date must be on or before lastDate $lastDate.",
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  );
  assert(
    initialDateRange == null || !initialDateRange.end.isAfter(lastDate),
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    "initialDateRange's end date must be on or before lastDate $lastDate.",
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  );
  currentDate = DateUtils.dateOnly(currentDate ?? DateTime.now());
  assert(initialEntryMode != null);
  assert(useRootNavigator != null);
  assert(debugCheckHasMaterialLocalizations(context));

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  Widget dialog = DateRangePickerDialog(
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    initialDateRange: initialDateRange,
    firstDate: firstDate,
    lastDate: lastDate,
    currentDate: currentDate,
    initialEntryMode: initialEntryMode,
    helpText: helpText,
    cancelText: cancelText,
    confirmText: confirmText,
    saveText: saveText,
    errorFormatText: errorFormatText,
    errorInvalidText: errorInvalidText,
    errorInvalidRangeText: errorInvalidRangeText,
    fieldStartHintText: fieldStartHintText,
    fieldEndHintText: fieldEndHintText,
    fieldStartLabelText: fieldStartLabelText,
    fieldEndLabelText: fieldEndLabelText,
  );

  if (textDirection != null) {
    dialog = Directionality(
      textDirection: textDirection,
      child: dialog,
    );
  }

  if (locale != null) {
    dialog = Localizations.override(
      context: context,
      locale: locale,
      child: dialog,
    );
  }

  return showDialog<DateTimeRange>(
    context: context,
    useRootNavigator: useRootNavigator,
    routeSettings: routeSettings,
    useSafeArea: false,
    builder: (BuildContext context) {
      return builder == null ? dialog : builder(context, dialog);
    },
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    anchorPoint: anchorPoint,
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  );
}

/// Returns a locale-appropriate string to describe the start of a date range.
///
/// If `startDate` is null, then it defaults to 'Start Date', otherwise if it
/// is in the same year as the `endDate` then it will use the short month
/// day format (i.e. 'Jan 21'). Otherwise it will return the short date format
/// (i.e. 'Jan 21, 2020').
String _formatRangeStartDate(MaterialLocalizations localizations, DateTime? startDate, DateTime? endDate) {
  return startDate == null
    ? localizations.dateRangeStartLabel
    : (endDate == null || startDate.year == endDate.year)
      ? localizations.formatShortMonthDay(startDate)
      : localizations.formatShortDate(startDate);
}

/// Returns an locale-appropriate string to describe the end of a date range.
///
/// If `endDate` is null, then it defaults to 'End Date', otherwise if it
/// is in the same year as the `startDate` and the `currentDate` then it will
/// just use the short month day format (i.e. 'Jan 21'), otherwise it will
/// include the year (i.e. 'Jan 21, 2020').
String _formatRangeEndDate(MaterialLocalizations localizations, DateTime? startDate, DateTime? endDate, DateTime currentDate) {
  return endDate == null
    ? localizations.dateRangeEndLabel
    : (startDate != null && startDate.year == endDate.year && startDate.year == currentDate.year)
      ? localizations.formatShortMonthDay(endDate)
      : localizations.formatShortDate(endDate);
}

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/// A Material-style date range picker dialog.
///
/// It is used internally by [showDateRangePicker] or can be directly pushed
/// onto the [Navigator] stack to enable state restoration. See
/// [showDateRangePicker] for a state restoration app example.
///
/// See also:
///
///  * [showDateRangePicker], which is a way to display the date picker.
class DateRangePickerDialog extends StatefulWidget {
  /// A Material-style date range picker dialog.
  const DateRangePickerDialog({
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    Key? key,
    this.initialDateRange,
    required this.firstDate,
    required this.lastDate,
    this.currentDate,
    this.initialEntryMode = DatePickerEntryMode.calendar,
    this.helpText,
    this.cancelText,
    this.confirmText,
    this.saveText,
    this.errorInvalidRangeText,
    this.errorFormatText,
    this.errorInvalidText,
    this.fieldStartHintText,
    this.fieldEndHintText,
    this.fieldStartLabelText,
    this.fieldEndLabelText,
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    this.restorationId,
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  }) : super(key: key);

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  /// The date range that the date range picker starts with when it opens.
  ///
  /// If an initial date range is provided, `initialDateRange.start`
  /// and `initialDateRange.end` must both fall between or on [firstDate] and
  /// [lastDate]. For all of these [DateTime] values, only their dates are
  /// considered. Their time fields are ignored.
  ///
  /// If [initialDateRange] is non-null, then it will be used as the initially
  /// selected date range. If it is provided, `initialDateRange.start` must be
  /// before or on `initialDateRange.end`.
1116
  final DateTimeRange? initialDateRange;
1117 1118

  /// The earliest allowable date on the date range.
1119
  final DateTime firstDate;
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  /// The latest allowable date on the date range.
1122
  final DateTime lastDate;
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  /// The [currentDate] represents the current day (i.e. today).
  ///
  /// This date will be highlighted in the day grid.
  ///
  /// If `null`, the date of `DateTime.now()` will be used.
1129
  final DateTime? currentDate;
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  /// The initial date range picker entry mode.
  ///
  /// The date range has two main modes: [DatePickerEntryMode.calendar] (a
  /// scrollable calendar month grid) or [DatePickerEntryMode.input] (two text
  /// input fields) mode.
  ///
  /// It defaults to [DatePickerEntryMode.calendar] and must be non-null.
1138
  final DatePickerEntryMode initialEntryMode;
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  /// The label on the cancel button for the text input mode.
  ///
  /// If null, the localized value of
  /// [MaterialLocalizations.cancelButtonLabel] is used.
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  final String? cancelText;
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  /// The label on the "OK" button for the text input mode.
  ///
  /// If null, the localized value of
  /// [MaterialLocalizations.okButtonLabel] is used.
1150
  final String? confirmText;
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  /// The label on the save button for the fullscreen calendar mode.
  ///
  /// If null, the localized value of
  /// [MaterialLocalizations.saveButtonLabel] is used.
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  final String? saveText;
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  /// The label displayed at the top of the dialog.
  ///
  /// If null, the localized value of
  /// [MaterialLocalizations.dateRangePickerHelpText] is used.
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  final String? helpText;
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  /// The message used when the date range is invalid (e.g. start date is after
  /// end date).
  ///
  /// If null, the localized value of
  /// [MaterialLocalizations.invalidDateRangeLabel] is used.
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  final String? errorInvalidRangeText;
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  /// The message used when an input text isn't in a proper date format.
  ///
  /// If null, the localized value of
  /// [MaterialLocalizations.invalidDateFormatLabel] is used.
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  final String? errorFormatText;
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  /// The message used when an input text isn't a selectable date.
  ///
  /// If null, the localized value of
  /// [MaterialLocalizations.dateOutOfRangeLabel] is used.
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  final String? errorInvalidText;
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  /// The text used to prompt the user when no text has been entered in the
  /// start field.
  ///
  /// If null, the localized value of
  /// [MaterialLocalizations.dateHelpText] is used.
1188
  final String? fieldStartHintText;
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  /// The text used to prompt the user when no text has been entered in the
  /// end field.
  ///
  /// If null, the localized value of [MaterialLocalizations.dateHelpText] is
  /// used.
1195
  final String? fieldEndHintText;
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  /// The label for the start date text input field.
  ///
  /// If null, the localized value of [MaterialLocalizations.dateRangeStartLabel]
  /// is used.
1201
  final String? fieldStartLabelText;
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  /// The label for the end date text input field.
  ///
  /// If null, the localized value of [MaterialLocalizations.dateRangeEndLabel]
  /// is used.
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  final String? fieldEndLabelText;

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  /// Restoration ID to save and restore the state of the [DateRangePickerDialog].
  ///
  /// If it is non-null, the date range picker will persist and restore the
  /// date range selected on the dialog.
  ///
  /// The state of this widget is persisted in a [RestorationBucket] claimed
  /// from the surrounding [RestorationScope] using the provided restoration ID.
  ///
  /// See also:
  ///
  ///  * [RestorationManager], which explains how state restoration works in
  ///    Flutter.
  final String? restorationId;

1223
  @override
1224
  State<DateRangePickerDialog> createState() => _DateRangePickerDialogState();
1225 1226
}

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class _DateRangePickerDialogState extends State<DateRangePickerDialog> with RestorationMixin {
  late final _RestorableDatePickerEntryMode _entryMode = _RestorableDatePickerEntryMode(widget.initialEntryMode);
  late final RestorableDateTimeN _selectedStart = RestorableDateTimeN(widget.initialDateRange?.start);
  late final RestorableDateTimeN _selectedEnd = RestorableDateTimeN(widget.initialDateRange?.end);
  final RestorableBool _autoValidate = RestorableBool(false);
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  final GlobalKey _calendarPickerKey = GlobalKey();
  final GlobalKey<_InputDateRangePickerState> _inputPickerKey = GlobalKey<_InputDateRangePickerState>();

  @override
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  String? get restorationId => widget.restorationId;

  @override
  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
    registerForRestoration(_entryMode, 'entry_mode');
    registerForRestoration(_selectedStart, 'selected_start');
    registerForRestoration(_selectedEnd, 'selected_end');
    registerForRestoration(_autoValidate, 'autovalidate');
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  }

  void _handleOk() {
1247
    if (_entryMode.value == DatePickerEntryMode.input || _entryMode.value == DatePickerEntryMode.inputOnly) {
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      final _InputDateRangePickerState picker = _inputPickerKey.currentState!;
      if (!picker.validate()) {
        setState(() {
1251
          _autoValidate.value = true;
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        });
        return;
      }
    }
    final DateTimeRange? selectedRange = _hasSelectedDateRange
1257
        ? DateTimeRange(start: _selectedStart.value!, end: _selectedEnd.value!)
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        : null;

    Navigator.pop(context, selectedRange);
  }

  void _handleCancel() {
    Navigator.pop(context);
  }

  void _handleEntryModeToggle() {
    setState(() {
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      switch (_entryMode.value) {
1270
        case DatePickerEntryMode.calendar:
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          _autoValidate.value = false;
          _entryMode.value = DatePickerEntryMode.input;
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          break;

        case DatePickerEntryMode.input:
        // Validate the range dates
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          if (_selectedStart.value != null &&
              (_selectedStart.value!.isBefore(widget.firstDate) || _selectedStart.value!.isAfter(widget.lastDate))) {
            _selectedStart.value = null;
1280
            // With no valid start date, having an end date makes no sense for the UI.
1281
            _selectedEnd.value = null;
1282
          }
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          if (_selectedEnd.value != null &&
              (_selectedEnd.value!.isBefore(widget.firstDate) || _selectedEnd.value!.isAfter(widget.lastDate))) {
            _selectedEnd.value = null;
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          }
          // If invalid range (start after end), then just use the start date
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          if (_selectedStart.value != null && _selectedEnd.value != null && _selectedStart.value!.isAfter(_selectedEnd.value!)) {
            _selectedEnd.value = null;
1290
          }
1291
          _entryMode.value = DatePickerEntryMode.calendar;
1292
          break;
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        case DatePickerEntryMode.calendarOnly:
        case DatePickerEntryMode.inputOnly:
          assert(false, 'Can not change entry mode from $_entryMode');
          break;
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      }
    });
  }

  void _handleStartDateChanged(DateTime? date) {
1303
    setState(() => _selectedStart.value = date);
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  }

  void _handleEndDateChanged(DateTime? date) {
1307
    setState(() => _selectedEnd.value = date);
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  }

1310
  bool get _hasSelectedDateRange => _selectedStart.value != null && _selectedEnd.value != null;
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  @override
  Widget build(BuildContext context) {
    final MediaQueryData mediaQuery = MediaQuery.of(context);
    final Orientation orientation = mediaQuery.orientation;
    final double textScaleFactor = math.min(mediaQuery.textScaleFactor, 1.3);
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
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    final ColorScheme colors = Theme.of(context).colorScheme;
    final Color onPrimarySurface = colors.brightness == Brightness.light
      ? colors.onPrimary
      : colors.onSurface;
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    final Widget contents;
    final Size size;
    ShapeBorder? shape;
    final double elevation;
    final EdgeInsets insetPadding;
1328
    final bool showEntryModeButton =
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      _entryMode.value == DatePickerEntryMode.calendar ||
      _entryMode.value == DatePickerEntryMode.input;
    switch (_entryMode.value) {
1332
      case DatePickerEntryMode.calendar:
1333
      case DatePickerEntryMode.calendarOnly:
1334 1335
        contents = _CalendarRangePickerDialog(
          key: _calendarPickerKey,
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          selectedStartDate: _selectedStart.value,
          selectedEndDate: _selectedEnd.value,
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          firstDate: widget.firstDate,
          lastDate: widget.lastDate,
          currentDate: widget.currentDate,
          onStartDateChanged: _handleStartDateChanged,
          onEndDateChanged: _handleEndDateChanged,
          onConfirm: _hasSelectedDateRange ? _handleOk : null,
          onCancel: _handleCancel,
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          entryModeButton: showEntryModeButton
            ? IconButton(
                icon: const Icon(Icons.edit),
                padding: EdgeInsets.zero,
                color: onPrimarySurface,
                tooltip: localizations.inputDateModeButtonLabel,
                onPressed: _handleEntryModeToggle,
              )
            : null,
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          confirmText: widget.saveText ?? localizations.saveButtonLabel,
          helpText: widget.helpText ?? localizations.dateRangePickerHelpText,
        );
        size = mediaQuery.size;
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        insetPadding = EdgeInsets.zero;
1359
        shape = const RoundedRectangleBorder();
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        elevation = 0;
        break;

      case DatePickerEntryMode.input:
1364
      case DatePickerEntryMode.inputOnly:
1365
        contents = _InputDateRangePickerDialog(
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          selectedStartDate: _selectedStart.value,
          selectedEndDate: _selectedEnd.value,
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          currentDate: widget.currentDate,
          picker: Container(
            padding: const EdgeInsets.symmetric(horizontal: 24),
            height: orientation == Orientation.portrait
                ? _inputFormPortraitHeight
                : _inputFormLandscapeHeight,
            child: Column(
              children: <Widget>[
                const Spacer(),
                _InputDateRangePicker(
                  key: _inputPickerKey,
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                  initialStartDate: _selectedStart.value,
                  initialEndDate: _selectedEnd.value,
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                  firstDate: widget.firstDate,
                  lastDate: widget.lastDate,
                  onStartDateChanged: _handleStartDateChanged,
                  onEndDateChanged: _handleEndDateChanged,
                  autofocus: true,
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                  autovalidate: _autoValidate.value,
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                  helpText: widget.helpText,
                  errorInvalidRangeText: widget.errorInvalidRangeText,
                  errorFormatText: widget.errorFormatText,
                  errorInvalidText: widget.errorInvalidText,
                  fieldStartHintText: widget.fieldStartHintText,
                  fieldEndHintText: widget.fieldEndHintText,
                  fieldStartLabelText: widget.fieldStartLabelText,
                  fieldEndLabelText: widget.fieldEndLabelText,
                ),
                const Spacer(),
              ],
            ),
          ),
          onConfirm: _handleOk,
          onCancel: _handleCancel,
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          entryModeButton: showEntryModeButton
            ? IconButton(
                icon: const Icon(Icons.calendar_today),
                padding: EdgeInsets.zero,
                color: onPrimarySurface,
                tooltip: localizations.calendarModeButtonLabel,
                onPressed: _handleEntryModeToggle,
              )
            : null,
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          confirmText: widget.confirmText ?? localizations.okButtonLabel,
          cancelText: widget.cancelText ?? localizations.cancelButtonLabel,
          helpText: widget.helpText ?? localizations.dateRangePickerHelpText,
        );
        final DialogTheme dialogTheme = Theme.of(context).dialogTheme;
        size = orientation == Orientation.portrait ? _inputPortraitDialogSize : _inputRangeLandscapeDialogSize;
        insetPadding = const EdgeInsets.symmetric(horizontal: 16.0, vertical: 24.0);
        shape = dialogTheme.shape;
        elevation = dialogTheme.elevation ?? 24;
        break;
    }

    return Dialog(
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      insetPadding: insetPadding,
      shape: shape,
      elevation: elevation,
      clipBehavior: Clip.antiAlias,
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      child: AnimatedContainer(
        width: size.width,
        height: size.height,
        duration: _dialogSizeAnimationDuration,
        curve: Curves.easeIn,
        child: MediaQuery(
          data: MediaQuery.of(context).copyWith(
            textScaleFactor: textScaleFactor,
          ),
          child: Builder(builder: (BuildContext context) {
            return contents;
          }),
        ),
      ),
    );
  }
}

class _CalendarRangePickerDialog extends StatelessWidget {
  const _CalendarRangePickerDialog({
    Key? key,
    required this.selectedStartDate,
    required this.selectedEndDate,
    required this.firstDate,
    required this.lastDate,
    required this.currentDate,
    required this.onStartDateChanged,
    required this.onEndDateChanged,
    required this.onConfirm,
    required this.onCancel,
    required this.confirmText,
    required this.helpText,
1460
    this.entryModeButton,
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  }) : super(key: key);

  final DateTime? selectedStartDate;
  final DateTime? selectedEndDate;
  final DateTime firstDate;
  final DateTime lastDate;
  final DateTime? currentDate;
  final ValueChanged<DateTime> onStartDateChanged;
  final ValueChanged<DateTime?> onEndDateChanged;
  final VoidCallback? onConfirm;
  final VoidCallback? onCancel;
  final String confirmText;
  final String helpText;
1474
  final Widget? entryModeButton;
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  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colorScheme = theme.colorScheme;
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final Orientation orientation = MediaQuery.of(context).orientation;
    final TextTheme textTheme = theme.textTheme;
    final Color headerForeground = colorScheme.brightness == Brightness.light
        ? colorScheme.onPrimary
        : colorScheme.onSurface;
    final Color headerDisabledForeground = headerForeground.withOpacity(0.38);
    final String startDateText = _formatRangeStartDate(localizations, selectedStartDate, selectedEndDate);
    final String endDateText = _formatRangeEndDate(localizations, selectedStartDate, selectedEndDate, DateTime.now());
    final TextStyle? headlineStyle = textTheme.headline5;
    final TextStyle? startDateStyle = headlineStyle?.apply(
1491
        color: selectedStartDate != null ? headerForeground : headerDisabledForeground,
1492 1493
    );
    final TextStyle? endDateStyle = headlineStyle?.apply(
1494
        color: selectedEndDate != null ? headerForeground : headerDisabledForeground,
1495 1496
    );
    final TextStyle saveButtonStyle = textTheme.button!.apply(
1497
        color: onConfirm != null ? headerForeground : headerDisabledForeground,
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    );

    return SafeArea(
      top: false,
      left: false,
      right: false,
      child: Scaffold(
        appBar: AppBar(
          leading: CloseButton(
            onPressed: onCancel,
          ),
          actions: <Widget>[
1510 1511
            if (orientation == Orientation.landscape && entryModeButton != null)
              entryModeButton!,
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            TextButton(
              onPressed: onConfirm,
              child: Text(confirmText, style: saveButtonStyle),
            ),
            const SizedBox(width: 8),
          ],
          bottom: PreferredSize(
1519
            preferredSize: const Size(double.infinity, 64),
1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560
            child: Row(children: <Widget>[
              SizedBox(width: MediaQuery.of(context).size.width < 360 ? 42 : 72),
              Expanded(
                child: Semantics(
                  label: '$helpText $startDateText to $endDateText',
                  excludeSemantics: true,
                  child: Column(
                    crossAxisAlignment: CrossAxisAlignment.start,
                    children: <Widget>[
                      Text(
                        helpText,
                        style: textTheme.overline!.apply(
                          color: headerForeground,
                        ),
                      ),
                      const SizedBox(height: 8),
                      Row(
                        children: <Widget>[
                          Text(
                            startDateText,
                            style: startDateStyle,
                            maxLines: 1,
                            overflow: TextOverflow.ellipsis,
                          ),
                          Text(' – ', style: startDateStyle,
                          ),
                          Flexible(
                            child: Text(
                              endDateText,
                              style: endDateStyle,
                              maxLines: 1,
                              overflow: TextOverflow.ellipsis,
                            ),
                          ),
                        ],
                      ),
                      const SizedBox(height: 16),
                    ],
                  ),
                ),
              ),
1561
              if (orientation == Orientation.portrait && entryModeButton != null)
1562 1563
                Padding(
                  padding: const EdgeInsets.symmetric(horizontal: 8.0),
1564
                  child: entryModeButton,
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                ),
            ]),
          ),
        ),
        body: _CalendarDateRangePicker(
          initialStartDate: selectedStartDate,
          initialEndDate: selectedEndDate,
          firstDate: firstDate,
          lastDate: lastDate,
          currentDate: currentDate,
          onStartDateChanged: onStartDateChanged,
          onEndDateChanged: onEndDateChanged,
        ),
      ),
    );
  }
}

const Duration _monthScrollDuration = Duration(milliseconds: 200);

const double _monthItemHeaderHeight = 58.0;
const double _monthItemFooterHeight = 12.0;
const double _monthItemRowHeight = 42.0;
const double _monthItemSpaceBetweenRows = 8.0;
const double _horizontalPadding = 8.0;
const double _maxCalendarWidthLandscape = 384.0;
const double _maxCalendarWidthPortrait = 480.0;

/// Displays a scrollable calendar grid that allows a user to select a range
/// of dates.
class _CalendarDateRangePicker extends StatefulWidget {
  /// Creates a scrollable calendar grid for picking date ranges.
  _CalendarDateRangePicker({
    Key? key,
    DateTime? initialStartDate,
    DateTime? initialEndDate,
    required DateTime firstDate,
    required DateTime lastDate,
    DateTime? currentDate,
    required this.onStartDateChanged,
    required this.onEndDateChanged,
  }) : initialStartDate = initialStartDate != null ? DateUtils.dateOnly(initialStartDate) : null,
       initialEndDate = initialEndDate != null ? DateUtils.dateOnly(initialEndDate) : null,
       assert(firstDate != null),
       assert(lastDate != null),
       firstDate = DateUtils.dateOnly(firstDate),
       lastDate = DateUtils.dateOnly(lastDate),
       currentDate = DateUtils.dateOnly(currentDate ?? DateTime.now()),
       super(key: key) {
    assert(
      this.initialStartDate == null || this.initialEndDate == null || !this.initialStartDate!.isAfter(initialEndDate!),
1616
      'initialStartDate must be on or before initialEndDate.',
1617 1618 1619
    );
    assert(
      !this.lastDate.isBefore(this.firstDate),
1620
      'firstDate must be on or before lastDate.',
1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702
    );
  }

  /// The [DateTime] that represents the start of the initial date range selection.
  final DateTime? initialStartDate;

  /// The [DateTime] that represents the end of the initial date range selection.
  final DateTime? initialEndDate;

  /// The earliest allowable [DateTime] that the user can select.
  final DateTime firstDate;

  /// The latest allowable [DateTime] that the user can select.
  final DateTime lastDate;

  /// The [DateTime] representing today. It will be highlighted in the day grid.
  final DateTime currentDate;

  /// Called when the user changes the start date of the selected range.
  final ValueChanged<DateTime>? onStartDateChanged;

  /// Called when the user changes the end date of the selected range.
  final ValueChanged<DateTime?>? onEndDateChanged;

  @override
  _CalendarDateRangePickerState createState() => _CalendarDateRangePickerState();
}

class _CalendarDateRangePickerState extends State<_CalendarDateRangePicker> {
  final GlobalKey _scrollViewKey = GlobalKey();
  DateTime? _startDate;
  DateTime? _endDate;
  int _initialMonthIndex = 0;
  late ScrollController _controller;
  late bool _showWeekBottomDivider;

  @override
  void initState() {
    super.initState();
    _controller = ScrollController();
    _controller.addListener(_scrollListener);

    _startDate = widget.initialStartDate;
    _endDate = widget.initialEndDate;

    // Calculate the index for the initially displayed month. This is needed to
    // divide the list of months into two `SliverList`s.
    final DateTime initialDate = widget.initialStartDate ?? widget.currentDate;
    if (!initialDate.isBefore(widget.firstDate) &&
        !initialDate.isAfter(widget.lastDate)) {
      _initialMonthIndex = DateUtils.monthDelta(widget.firstDate, initialDate);
    }

    _showWeekBottomDivider = _initialMonthIndex != 0;
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  void _scrollListener() {
    if (_controller.offset <= _controller.position.minScrollExtent) {
      setState(() {
        _showWeekBottomDivider = false;
      });
    } else if (!_showWeekBottomDivider) {
      setState(() {
        _showWeekBottomDivider = true;
      });
    }
  }

  int get _numberOfMonths => DateUtils.monthDelta(widget.firstDate, widget.lastDate) + 1;

  void _vibrate() {
    switch (Theme.of(context).platform) {
      case TargetPlatform.android:
      case TargetPlatform.fuchsia:
        HapticFeedback.vibrate();
        break;
1703 1704 1705 1706
      case TargetPlatform.iOS:
      case TargetPlatform.linux:
      case TargetPlatform.macOS:
      case TargetPlatform.windows:
1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816
        break;
    }
  }

  // This updates the selected date range using this logic:
  //
  // * From the unselected state, selecting one date creates the start date.
  //   * If the next selection is before the start date, reset date range and
  //     set the start date to that selection.
  //   * If the next selection is on or after the start date, set the end date
  //     to that selection.
  // * After both start and end dates are selected, any subsequent selection
  //   resets the date range and sets start date to that selection.
  void _updateSelection(DateTime date) {
    _vibrate();
    setState(() {
      if (_startDate != null && _endDate == null && !date.isBefore(_startDate!)) {
        _endDate = date;
        widget.onEndDateChanged?.call(_endDate);
      } else {
        _startDate = date;
        widget.onStartDateChanged?.call(_startDate!);
        if (_endDate != null) {
          _endDate = null;
          widget.onEndDateChanged?.call(_endDate);
        }
      }
    });
  }

  Widget _buildMonthItem(BuildContext context, int index, bool beforeInitialMonth) {
    final int monthIndex = beforeInitialMonth
      ? _initialMonthIndex - index - 1
      : _initialMonthIndex + index;
    final DateTime month = DateUtils.addMonthsToMonthDate(widget.firstDate, monthIndex);
    return _MonthItem(
      selectedDateStart: _startDate,
      selectedDateEnd: _endDate,
      currentDate: widget.currentDate,
      firstDate: widget.firstDate,
      lastDate: widget.lastDate,
      displayedMonth: month,
      onChanged: _updateSelection,
    );
  }

  @override
  Widget build(BuildContext context) {
    const Key sliverAfterKey = Key('sliverAfterKey');

    return Column(
      children: <Widget>[
        _DayHeaders(),
        if (_showWeekBottomDivider) const Divider(height: 0),
        Expanded(
          child: _CalendarKeyboardNavigator(
            firstDate: widget.firstDate,
            lastDate: widget.lastDate,
            initialFocusedDay: _startDate ?? widget.initialStartDate ?? widget.currentDate,
            // In order to prevent performance issues when displaying the
            // correct initial month, 2 `SliverList`s are used to split the
            // months. The first item in the second SliverList is the initial
            // month to be displayed.
            child: CustomScrollView(
              key: _scrollViewKey,
              controller: _controller,
              center: sliverAfterKey,
              slivers: <Widget>[
                SliverList(
                  delegate: SliverChildBuilderDelegate(
                    (BuildContext context, int index) => _buildMonthItem(context, index, true),
                    childCount: _initialMonthIndex,
                  ),
                ),
                SliverList(
                  key: sliverAfterKey,
                  delegate: SliverChildBuilderDelegate(
                    (BuildContext context, int index) => _buildMonthItem(context, index, false),
                    childCount: _numberOfMonths - _initialMonthIndex,
                  ),
                ),
              ],
            ),
          ),
        ),
      ],
    );
  }
}

class _CalendarKeyboardNavigator extends StatefulWidget {
  const _CalendarKeyboardNavigator({
    Key? key,
    required this.child,
    required this.firstDate,
    required this.lastDate,
    required this.initialFocusedDay,
  }) : super(key: key);

  final Widget child;
  final DateTime firstDate;
  final DateTime lastDate;
  final DateTime initialFocusedDay;

  @override
  _CalendarKeyboardNavigatorState createState() => _CalendarKeyboardNavigatorState();
}

class _CalendarKeyboardNavigatorState extends State<_CalendarKeyboardNavigator> {

1817 1818 1819 1820 1821 1822
  final Map<ShortcutActivator, Intent> _shortcutMap = const <ShortcutActivator, Intent>{
    SingleActivator(LogicalKeyboardKey.arrowLeft): DirectionalFocusIntent(TraversalDirection.left),
    SingleActivator(LogicalKeyboardKey.arrowRight): DirectionalFocusIntent(TraversalDirection.right),
    SingleActivator(LogicalKeyboardKey.arrowDown): DirectionalFocusIntent(TraversalDirection.down),
    SingleActivator(LogicalKeyboardKey.arrowUp): DirectionalFocusIntent(TraversalDirection.up),
  };
1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187
  late Map<Type, Action<Intent>> _actionMap;
  late FocusNode _dayGridFocus;
  TraversalDirection? _dayTraversalDirection;
  DateTime? _focusedDay;

  @override
  void initState() {
    super.initState();

    _actionMap = <Type, Action<Intent>>{
      NextFocusIntent: CallbackAction<NextFocusIntent>(onInvoke: _handleGridNextFocus),
      PreviousFocusIntent: CallbackAction<PreviousFocusIntent>(onInvoke: _handleGridPreviousFocus),
      DirectionalFocusIntent: CallbackAction<DirectionalFocusIntent>(onInvoke: _handleDirectionFocus),
    };
    _dayGridFocus = FocusNode(debugLabel: 'Day Grid');
  }

  @override
  void dispose() {
    _dayGridFocus.dispose();
    super.dispose();
  }

  void _handleGridFocusChange(bool focused) {
    setState(() {
      if (focused) {
        _focusedDay ??= widget.initialFocusedDay;
      }
    });
  }

  /// Move focus to the next element after the day grid.
  void _handleGridNextFocus(NextFocusIntent intent) {
    _dayGridFocus.requestFocus();
    _dayGridFocus.nextFocus();
  }

  /// Move focus to the previous element before the day grid.
  void _handleGridPreviousFocus(PreviousFocusIntent intent) {
    _dayGridFocus.requestFocus();
    _dayGridFocus.previousFocus();
  }

  /// Move the internal focus date in the direction of the given intent.
  ///
  /// This will attempt to move the focused day to the next selectable day in
  /// the given direction. If the new date is not in the current month, then
  /// the page view will be scrolled to show the new date's month.
  ///
  /// For horizontal directions, it will move forward or backward a day (depending
  /// on the current [TextDirection]). For vertical directions it will move up and
  /// down a week at a time.
  void _handleDirectionFocus(DirectionalFocusIntent intent) {
    assert(_focusedDay != null);
    setState(() {
      final DateTime? nextDate = _nextDateInDirection(_focusedDay!, intent.direction);
      if (nextDate != null) {
        _focusedDay = nextDate;
        _dayTraversalDirection = intent.direction;
      }
    });
  }

  static const Map<TraversalDirection, int> _directionOffset = <TraversalDirection, int>{
    TraversalDirection.up: -DateTime.daysPerWeek,
    TraversalDirection.right: 1,
    TraversalDirection.down: DateTime.daysPerWeek,
    TraversalDirection.left: -1,
  };

  int _dayDirectionOffset(TraversalDirection traversalDirection, TextDirection textDirection) {
    // Swap left and right if the text direction if RTL
    if (textDirection == TextDirection.rtl) {
      if (traversalDirection == TraversalDirection.left)
        traversalDirection = TraversalDirection.right;
      else if (traversalDirection == TraversalDirection.right)
        traversalDirection = TraversalDirection.left;
    }
    return _directionOffset[traversalDirection]!;
  }

  DateTime? _nextDateInDirection(DateTime date, TraversalDirection direction) {
    final TextDirection textDirection = Directionality.of(context);
    final DateTime nextDate = DateUtils.addDaysToDate(date, _dayDirectionOffset(direction, textDirection));
    if (!nextDate.isBefore(widget.firstDate) && !nextDate.isAfter(widget.lastDate)) {
      return nextDate;
    }
    return null;
  }

  @override
  Widget build(BuildContext context) {
    return FocusableActionDetector(
      shortcuts: _shortcutMap,
      actions: _actionMap,
      focusNode: _dayGridFocus,
      onFocusChange: _handleGridFocusChange,
      child: _FocusedDate(
        date: _dayGridFocus.hasFocus ? _focusedDay : null,
        scrollDirection: _dayGridFocus.hasFocus ? _dayTraversalDirection : null,
        child: widget.child,
      ),
    );
  }
}

/// InheritedWidget indicating what the current focused date is for its children.
///
/// This is used by the [_MonthPicker] to let its children [_DayPicker]s know
/// what the currently focused date (if any) should be.
class _FocusedDate extends InheritedWidget {
  const _FocusedDate({
    Key? key,
    required Widget child,
    this.date,
    this.scrollDirection,
  }) : super(key: key, child: child);

  final DateTime? date;
  final TraversalDirection? scrollDirection;

  @override
  bool updateShouldNotify(_FocusedDate oldWidget) {
    return !DateUtils.isSameDay(date, oldWidget.date) || scrollDirection != oldWidget.scrollDirection;
  }

  static _FocusedDate? of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<_FocusedDate>();
  }
}


class _DayHeaders extends StatelessWidget {
  /// Builds widgets showing abbreviated days of week. The first widget in the
  /// returned list corresponds to the first day of week for the current locale.
  ///
  /// Examples:
  ///
  /// ```
  /// ┌ Sunday is the first day of week in the US (en_US)
  /// |
  /// S M T W T F S  <-- the returned list contains these widgets
  /// _ _ _ _ _ 1 2
  /// 3 4 5 6 7 8 9
  ///
  /// ┌ But it's Monday in the UK (en_GB)
  /// |
  /// M T W T F S S  <-- the returned list contains these widgets
  /// _ _ _ _ 1 2 3
  /// 4 5 6 7 8 9 10
  /// ```
  List<Widget> _getDayHeaders(TextStyle headerStyle, MaterialLocalizations localizations) {
    final List<Widget> result = <Widget>[];
    for (int i = localizations.firstDayOfWeekIndex; true; i = (i + 1) % 7) {
      final String weekday = localizations.narrowWeekdays[i];
      result.add(ExcludeSemantics(
        child: Center(child: Text(weekday, style: headerStyle)),
      ));
      if (i == (localizations.firstDayOfWeekIndex - 1) % 7)
        break;
    }
    return result;
  }

  @override
  Widget build(BuildContext context) {
    final ThemeData themeData = Theme.of(context);
    final ColorScheme colorScheme = themeData.colorScheme;
    final TextStyle textStyle = themeData.textTheme.subtitle2!.apply(color: colorScheme.onSurface);
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final List<Widget> labels = _getDayHeaders(textStyle, localizations);

    // Add leading and trailing containers for edges of the custom grid layout.
    labels.insert(0, Container());
    labels.add(Container());

    return Container(
      constraints: BoxConstraints(
        maxWidth: MediaQuery.of(context).orientation == Orientation.landscape
          ? _maxCalendarWidthLandscape
          : _maxCalendarWidthPortrait,
        maxHeight: _monthItemRowHeight,
      ),
      child: GridView.custom(
        shrinkWrap: true,
        gridDelegate: _monthItemGridDelegate,
        childrenDelegate: SliverChildListDelegate(
          labels,
          addRepaintBoundaries: false,
        ),
      ),
    );
  }
}

class _MonthItemGridDelegate extends SliverGridDelegate {
  const _MonthItemGridDelegate();

  @override
  SliverGridLayout getLayout(SliverConstraints constraints) {
    final double tileWidth = (constraints.crossAxisExtent - 2 * _horizontalPadding) / DateTime.daysPerWeek;
    return _MonthSliverGridLayout(
      crossAxisCount: DateTime.daysPerWeek + 2,
      dayChildWidth: tileWidth,
      edgeChildWidth: _horizontalPadding,
      reverseCrossAxis: axisDirectionIsReversed(constraints.crossAxisDirection),
    );
  }

  @override
  bool shouldRelayout(_MonthItemGridDelegate oldDelegate) => false;
}

const _MonthItemGridDelegate _monthItemGridDelegate = _MonthItemGridDelegate();

class _MonthSliverGridLayout extends SliverGridLayout {
  /// Creates a layout that uses equally sized and spaced tiles for each day of
  /// the week and an additional edge tile for padding at the start and end of
  /// each row.
  ///
  /// This is necessary to facilitate the painting of the range highlight
  /// correctly.
  const _MonthSliverGridLayout({
    required this.crossAxisCount,
    required this.dayChildWidth,
    required this.edgeChildWidth,
    required this.reverseCrossAxis,
  }) : assert(crossAxisCount != null && crossAxisCount > 0),
       assert(dayChildWidth != null && dayChildWidth >= 0),
       assert(edgeChildWidth != null && edgeChildWidth >= 0),
       assert(reverseCrossAxis != null);

  /// The number of children in the cross axis.
  final int crossAxisCount;

  /// The width in logical pixels of the day child widgets.
  final double dayChildWidth;

  /// The width in logical pixels of the edge child widgets.
  final double edgeChildWidth;

  /// Whether the children should be placed in the opposite order of increasing
  /// coordinates in the cross axis.
  ///
  /// For example, if the cross axis is horizontal, the children are placed from
  /// left to right when [reverseCrossAxis] is false and from right to left when
  /// [reverseCrossAxis] is true.
  ///
  /// Typically set to the return value of [axisDirectionIsReversed] applied to
  /// the [SliverConstraints.crossAxisDirection].
  final bool reverseCrossAxis;

  /// The number of logical pixels from the leading edge of one row to the
  /// leading edge of the next row.
  double get _rowHeight {
    return _monthItemRowHeight + _monthItemSpaceBetweenRows;
  }

  /// The height in logical pixels of the children widgets.
  double get _childHeight {
    return _monthItemRowHeight;
  }

  @override
  int getMinChildIndexForScrollOffset(double scrollOffset) {
    return crossAxisCount * (scrollOffset ~/ _rowHeight);
  }

  @override
  int getMaxChildIndexForScrollOffset(double scrollOffset) {
    final int mainAxisCount = (scrollOffset / _rowHeight).ceil();
    return math.max(0, crossAxisCount * mainAxisCount - 1);
  }

  double _getCrossAxisOffset(double crossAxisStart, bool isPadding) {
    if (reverseCrossAxis) {
      return
        ((crossAxisCount - 2) * dayChildWidth + 2 * edgeChildWidth) -
        crossAxisStart -
        (isPadding ? edgeChildWidth : dayChildWidth);
    }
    return crossAxisStart;
  }

  @override
  SliverGridGeometry getGeometryForChildIndex(int index) {
    final int adjustedIndex = index % crossAxisCount;
    final bool isEdge = adjustedIndex == 0 || adjustedIndex == crossAxisCount - 1;
    final double crossAxisStart = math.max(0, (adjustedIndex - 1) * dayChildWidth + edgeChildWidth);

    return SliverGridGeometry(
      scrollOffset: (index ~/ crossAxisCount) * _rowHeight,
      crossAxisOffset: _getCrossAxisOffset(crossAxisStart, isEdge),
      mainAxisExtent: _childHeight,
      crossAxisExtent: isEdge ? edgeChildWidth : dayChildWidth,
    );
  }

  @override
  double computeMaxScrollOffset(int childCount) {
    assert(childCount >= 0);
    final int mainAxisCount = ((childCount - 1) ~/ crossAxisCount) + 1;
    final double mainAxisSpacing = _rowHeight - _childHeight;
    return _rowHeight * mainAxisCount - mainAxisSpacing;
  }
}

/// Displays the days of a given month and allows choosing a date range.
///
/// The days are arranged in a rectangular grid with one column for each day of
/// the week.
class _MonthItem extends StatefulWidget {
  /// Creates a month item.
  _MonthItem({
    Key? key,
    required this.selectedDateStart,
    required this.selectedDateEnd,
    required this.currentDate,
    required this.onChanged,
    required this.firstDate,
    required this.lastDate,
    required this.displayedMonth,
    this.dragStartBehavior = DragStartBehavior.start,
  }) : assert(firstDate != null),
       assert(lastDate != null),
       assert(!firstDate.isAfter(lastDate)),
       assert(selectedDateStart == null || !selectedDateStart.isBefore(firstDate)),
       assert(selectedDateEnd == null || !selectedDateEnd.isBefore(firstDate)),
       assert(selectedDateStart == null || !selectedDateStart.isAfter(lastDate)),
       assert(selectedDateEnd == null || !selectedDateEnd.isAfter(lastDate)),
       assert(selectedDateStart == null || selectedDateEnd == null || !selectedDateStart.isAfter(selectedDateEnd)),
       assert(currentDate != null),
       assert(onChanged != null),
       assert(displayedMonth != null),
       assert(dragStartBehavior != null),
       super(key: key);

  /// The currently selected start date.
  ///
  /// This date is highlighted in the picker.
  final DateTime? selectedDateStart;

  /// The currently selected end date.
  ///
  /// This date is highlighted in the picker.
  final DateTime? selectedDateEnd;

  /// The current date at the time the picker is displayed.
  final DateTime currentDate;

  /// Called when the user picks a day.
  final ValueChanged<DateTime> onChanged;

  /// The earliest date the user is permitted to pick.
  final DateTime firstDate;

  /// The latest date the user is permitted to pick.
  final DateTime lastDate;

  /// The month whose days are displayed by this picker.
  final DateTime displayedMonth;

  /// Determines the way that drag start behavior is handled.
  ///
  /// If set to [DragStartBehavior.start], the drag gesture used to scroll a
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  /// date picker wheel will begin at the position where the drag gesture won
  /// the arena. If set to [DragStartBehavior.down] it will begin at the position
  /// where a down event is first detected.
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  ///
  /// In general, setting this to [DragStartBehavior.start] will make drag
  /// animation smoother and setting it to [DragStartBehavior.down] will make
  /// drag behavior feel slightly more reactive.
  ///
  /// By default, the drag start behavior is [DragStartBehavior.start].
  ///
  /// See also:
  ///
  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for
  ///    the different behaviors.
  final DragStartBehavior dragStartBehavior;

  @override
  _MonthItemState createState() => _MonthItemState();
}

class _MonthItemState extends State<_MonthItem> {
  /// List of [FocusNode]s, one for each day of the month.
  late List<FocusNode> _dayFocusNodes;

  @override
  void initState() {
    super.initState();
    final int daysInMonth = DateUtils.getDaysInMonth(widget.displayedMonth.year, widget.displayedMonth.month);
    _dayFocusNodes = List<FocusNode>.generate(
        daysInMonth,
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        (int index) => FocusNode(skipTraversal: true, debugLabel: 'Day ${index + 1}'),
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    );
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    // Check to see if the focused date is in this month, if so focus it.
    final DateTime? focusedDate = _FocusedDate.of(context)?.date;
    if (focusedDate != null && DateUtils.isSameMonth(widget.displayedMonth, focusedDate)) {
      _dayFocusNodes[focusedDate.day - 1].requestFocus();
    }
  }

  @override
  void dispose() {
    for (final FocusNode node in _dayFocusNodes) {
      node.dispose();
    }
    super.dispose();
  }

  Color _highlightColor(BuildContext context) {
    return Theme.of(context).colorScheme.primary.withOpacity(0.12);
  }

  void _dayFocusChanged(bool focused) {
    if (focused) {
      final TraversalDirection? focusDirection = _FocusedDate.of(context)?.scrollDirection;
      if (focusDirection != null) {
        ScrollPositionAlignmentPolicy policy = ScrollPositionAlignmentPolicy.explicit;
        switch (focusDirection) {
          case TraversalDirection.up:
          case TraversalDirection.left:
            policy = ScrollPositionAlignmentPolicy.keepVisibleAtStart;
            break;
          case TraversalDirection.right:
          case TraversalDirection.down:
            policy = ScrollPositionAlignmentPolicy.keepVisibleAtEnd;
            break;
        }
        Scrollable.ensureVisible(primaryFocus!.context!,
          duration: _monthScrollDuration,
          alignmentPolicy: policy,
        );
      }
    }
  }

  Widget _buildDayItem(BuildContext context, DateTime dayToBuild, int firstDayOffset, int daysInMonth) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colorScheme = theme.colorScheme;
    final TextTheme textTheme = theme.textTheme;
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final TextDirection textDirection = Directionality.of(context);
    final Color highlightColor = _highlightColor(context);
    final int day = dayToBuild.day;

    final bool isDisabled = dayToBuild.isAfter(widget.lastDate) || dayToBuild.isBefore(widget.firstDate);

    BoxDecoration? decoration;
    TextStyle? itemStyle = textTheme.bodyText2;

    final bool isRangeSelected = widget.selectedDateStart != null && widget.selectedDateEnd != null;
    final bool isSelectedDayStart = widget.selectedDateStart != null && dayToBuild.isAtSameMomentAs(widget.selectedDateStart!);
    final bool isSelectedDayEnd = widget.selectedDateEnd != null && dayToBuild.isAtSameMomentAs(widget.selectedDateEnd!);
    final bool isInRange = isRangeSelected &&
      dayToBuild.isAfter(widget.selectedDateStart!) &&
      dayToBuild.isBefore(widget.selectedDateEnd!);

    _HighlightPainter? highlightPainter;

    if (isSelectedDayStart || isSelectedDayEnd) {
      // The selected start and end dates gets a circle background
      // highlight, and a contrasting text color.
      itemStyle = textTheme.bodyText2?.apply(color: colorScheme.onPrimary);
      decoration = BoxDecoration(
        color: colorScheme.primary,
        shape: BoxShape.circle,
      );

      if (isRangeSelected && widget.selectedDateStart != widget.selectedDateEnd) {
        final _HighlightPainterStyle style = isSelectedDayStart
          ? _HighlightPainterStyle.highlightTrailing
          : _HighlightPainterStyle.highlightLeading;
        highlightPainter = _HighlightPainter(
          color: highlightColor,
          style: style,
          textDirection: textDirection,
        );
      }
    } else if (isInRange) {
      // The days within the range get a light background highlight.
      highlightPainter = _HighlightPainter(
        color: highlightColor,
        style: _HighlightPainterStyle.highlightAll,
        textDirection: textDirection,
      );
    } else if (isDisabled) {
      itemStyle = textTheme.bodyText2?.apply(color: colorScheme.onSurface.withOpacity(0.38));
    } else if (DateUtils.isSameDay(widget.currentDate, dayToBuild)) {
      // The current day gets a different text color and a circle stroke
      // border.
      itemStyle = textTheme.bodyText2?.apply(color: colorScheme.primary);
      decoration = BoxDecoration(
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        border: Border.all(color: colorScheme.primary),
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        shape: BoxShape.circle,
      );
    }

    // We want the day of month to be spoken first irrespective of the
    // locale-specific preferences or TextDirection. This is because
    // an accessibility user is more likely to be interested in the
    // day of month before the rest of the date, as they are looking
    // for the day of month. To do that we prepend day of month to the
    // formatted full date.
    String semanticLabel = '${localizations.formatDecimal(day)}, ${localizations.formatFullDate(dayToBuild)}';
    if (isSelectedDayStart) {
      semanticLabel = localizations.dateRangeStartDateSemanticLabel(semanticLabel);
    } else if (isSelectedDayEnd) {
      semanticLabel = localizations.dateRangeEndDateSemanticLabel(semanticLabel);
    }

    Widget dayWidget = Container(
      decoration: decoration,
      child: Center(
        child: Semantics(
          label: semanticLabel,
          selected: isSelectedDayStart || isSelectedDayEnd,
          child: ExcludeSemantics(
            child: Text(localizations.formatDecimal(day), style: itemStyle),
          ),
        ),
      ),
    );

    if (highlightPainter != null) {
      dayWidget = CustomPaint(
        painter: highlightPainter,
        child: dayWidget,
      );
    }

    if (!isDisabled) {
      dayWidget = InkResponse(
        focusNode: _dayFocusNodes[day - 1],
        onTap: () => widget.onChanged(dayToBuild),
        radius: _monthItemRowHeight / 2 + 4,
        splashColor: colorScheme.primary.withOpacity(0.38),
        onFocusChange: _dayFocusChanged,
        child: dayWidget,
      );
    }

    return dayWidget;
  }

  Widget _buildEdgeContainer(BuildContext context, bool isHighlighted) {
    return Container(color: isHighlighted ? _highlightColor(context) : null);
  }

  @override
  Widget build(BuildContext context) {
    final ThemeData themeData = Theme.of(context);
    final TextTheme textTheme = themeData.textTheme;
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final int year = widget.displayedMonth.year;
    final int month = widget.displayedMonth.month;
    final int daysInMonth = DateUtils.getDaysInMonth(year, month);
    final int dayOffset = DateUtils.firstDayOffset(year, month, localizations);
    final int weeks = ((daysInMonth + dayOffset) / DateTime.daysPerWeek).ceil();
    final double gridHeight =
        weeks * _monthItemRowHeight + (weeks - 1) * _monthItemSpaceBetweenRows;
    final List<Widget> dayItems = <Widget>[];

    for (int i = 0; true; i += 1) {
      // 1-based day of month, e.g. 1-31 for January, and 1-29 for February on
      // a leap year.
      final int day = i - dayOffset + 1;
      if (day > daysInMonth)
        break;
      if (day < 1) {
        dayItems.add(Container());
      } else {
        final DateTime dayToBuild = DateTime(year, month, day);
        final Widget dayItem = _buildDayItem(
          context,
          dayToBuild,
          dayOffset,
          daysInMonth,
        );
        dayItems.add(dayItem);
      }
    }

    // Add the leading/trailing edge containers to each week in order to
    // correctly extend the range highlight.
    final List<Widget> paddedDayItems = <Widget>[];
    for (int i = 0; i < weeks; i++) {
      final int start = i * DateTime.daysPerWeek;
      final int end = math.min(
        start + DateTime.daysPerWeek,
        dayItems.length,
      );
      final List<Widget> weekList = dayItems.sublist(start, end);

      final DateTime dateAfterLeadingPadding = DateTime(year, month, start - dayOffset + 1);
      // Only color the edge container if it is after the start date and
      // on/before the end date.
      final bool isLeadingInRange =
        !(dayOffset > 0 && i == 0) &&
        widget.selectedDateStart != null &&
        widget.selectedDateEnd != null &&
        dateAfterLeadingPadding.isAfter(widget.selectedDateStart!) &&
        !dateAfterLeadingPadding.isAfter(widget.selectedDateEnd!);
      weekList.insert(0, _buildEdgeContainer(context, isLeadingInRange));

      // Only add a trailing edge container if it is for a full week and not a
      // partial week.
      if (end < dayItems.length || (end == dayItems.length && dayItems.length % DateTime.daysPerWeek == 0)) {
        final DateTime dateBeforeTrailingPadding =
        DateTime(year, month, end - dayOffset);
        // Only color the edge container if it is on/after the start date and
        // before the end date.
        final bool isTrailingInRange =
          widget.selectedDateStart != null &&
          widget.selectedDateEnd != null &&
          !dateBeforeTrailingPadding.isBefore(widget.selectedDateStart!) &&
          dateBeforeTrailingPadding.isBefore(widget.selectedDateEnd!);
        weekList.add(_buildEdgeContainer(context, isTrailingInRange));
      }

      paddedDayItems.addAll(weekList);
    }

    final double maxWidth = MediaQuery.of(context).orientation == Orientation.landscape
      ? _maxCalendarWidthLandscape
      : _maxCalendarWidthPortrait;
    return Column(
      children: <Widget>[
        Container(
          constraints: BoxConstraints(maxWidth: maxWidth),
          height: _monthItemHeaderHeight,
          padding: const EdgeInsets.symmetric(horizontal: 16),
          alignment: AlignmentDirectional.centerStart,
          child: ExcludeSemantics(
            child: Text(
              localizations.formatMonthYear(widget.displayedMonth),
              style: textTheme.bodyText2!.apply(color: themeData.colorScheme.onSurface),
            ),
          ),
        ),
        Container(
          constraints: BoxConstraints(
            maxWidth: maxWidth,
            maxHeight: gridHeight,
          ),
          child: GridView.custom(
            physics: const NeverScrollableScrollPhysics(),
            gridDelegate: _monthItemGridDelegate,
            childrenDelegate: SliverChildListDelegate(
              paddedDayItems,
              addRepaintBoundaries: false,
            ),
          ),
        ),
        const SizedBox(height: _monthItemFooterHeight),
      ],
    );
  }
}

/// Determines which style to use to paint the highlight.
enum _HighlightPainterStyle {
  /// Paints nothing.
  none,

  /// Paints a rectangle that occupies the leading half of the space.
  highlightLeading,

  /// Paints a rectangle that occupies the trailing half of the space.
  highlightTrailing,

  /// Paints a rectangle that occupies all available space.
  highlightAll,
}

/// This custom painter will add a background highlight to its child.
///
/// This highlight will be drawn depending on the [style], [color], and
/// [textDirection] supplied. It will either paint a rectangle on the
/// left/right, a full rectangle, or nothing at all. This logic is determined by
/// a combination of the [style] and [textDirection].
class _HighlightPainter extends CustomPainter {
  _HighlightPainter({
    required this.color,
    this.style = _HighlightPainterStyle.none,
    this.textDirection,
  });

  final Color color;
  final _HighlightPainterStyle style;
  final TextDirection? textDirection;

  @override
  void paint(Canvas canvas, Size size) {
    if (style == _HighlightPainterStyle.none) {
      return;
    }

    final Paint paint = Paint()
      ..color = color
      ..style = PaintingStyle.fill;

    final Rect rectLeft = Rect.fromLTWH(0, 0, size.width / 2, size.height);
    final Rect rectRight = Rect.fromLTWH(size.width / 2, 0, size.width / 2, size.height);

    switch (style) {
      case _HighlightPainterStyle.highlightTrailing:
        canvas.drawRect(
          textDirection == TextDirection.ltr ? rectRight : rectLeft,
          paint,
        );
        break;
      case _HighlightPainterStyle.highlightLeading:
        canvas.drawRect(
          textDirection == TextDirection.ltr ? rectLeft : rectRight,
          paint,
        );
        break;
      case _HighlightPainterStyle.highlightAll:
        canvas.drawRect(
          Rect.fromLTWH(0, 0, size.width, size.height),
          paint,
        );
        break;
      case _HighlightPainterStyle.none:
        break;
    }
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => false;
}

class _InputDateRangePickerDialog extends StatelessWidget {
  const _InputDateRangePickerDialog({
    Key? key,
    required this.selectedStartDate,
    required this.selectedEndDate,
    required this.currentDate,
    required this.picker,
    required this.onConfirm,
    required this.onCancel,
    required this.confirmText,
    required this.cancelText,
    required this.helpText,
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    required this.entryModeButton,
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  }) : super(key: key);

  final DateTime? selectedStartDate;
  final DateTime? selectedEndDate;
  final DateTime? currentDate;
  final Widget picker;
  final VoidCallback onConfirm;
  final VoidCallback onCancel;
  final String? confirmText;
  final String? cancelText;
  final String? helpText;
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  final Widget? entryModeButton;
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  String _formatDateRange(BuildContext context, DateTime? start, DateTime? end, DateTime now) {
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final String startText = _formatRangeStartDate(localizations, start, end);
    final String endText = _formatRangeEndDate(localizations, start, end, now);
    if (start == null || end == null) {
      return localizations.unspecifiedDateRange;
    }
    if (Directionality.of(context) == TextDirection.ltr) {
      return '$startText$endText';
    } else {
      return '$endText$startText';
    }
  }

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final ColorScheme colorScheme = theme.colorScheme;
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final Orientation orientation = MediaQuery.of(context).orientation;
    final TextTheme textTheme = theme.textTheme;

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    final Color onPrimarySurfaceColor = colorScheme.brightness == Brightness.light
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        ? colorScheme.onPrimary
        : colorScheme.onSurface;
    final TextStyle? dateStyle = orientation == Orientation.landscape
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        ? textTheme.headline5?.apply(color: onPrimarySurfaceColor)
        : textTheme.headline4?.apply(color: onPrimarySurfaceColor);
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    final String dateText = _formatDateRange(context, selectedStartDate, selectedEndDate, currentDate!);
    final String semanticDateText = selectedStartDate != null && selectedEndDate != null
        ? '${localizations.formatMediumDate(selectedStartDate!)}${localizations.formatMediumDate(selectedEndDate!)}'
        : '';

    final Widget header = _DatePickerHeader(
      helpText: helpText ?? localizations.dateRangePickerHelpText,
      titleText: dateText,
      titleSemanticsLabel: semanticDateText,
      titleStyle: dateStyle,
      orientation: orientation,
      isShort: orientation == Orientation.landscape,
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      entryModeButton: entryModeButton,
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    );

    final Widget actions = Container(
      alignment: AlignmentDirectional.centerEnd,
      constraints: const BoxConstraints(minHeight: 52.0),
      padding: const EdgeInsets.symmetric(horizontal: 8),
      child: OverflowBar(
        spacing: 8,
        children: <Widget>[
          TextButton(
            onPressed: onCancel,
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            child: Text(cancelText ?? localizations.cancelButtonLabel),
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          ),
          TextButton(
            onPressed: onConfirm,
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            child: Text(confirmText ?? localizations.okButtonLabel),
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          ),
        ],
      ),
    );

    switch (orientation) {
      case Orientation.portrait:
        return Column(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            header,
            Expanded(child: picker),
            actions,
          ],
        );

      case Orientation.landscape:
        return Row(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            header,
            Flexible(
              child: Column(
                mainAxisSize: MainAxisSize.min,
                crossAxisAlignment: CrossAxisAlignment.stretch,
                children: <Widget>[
                  Expanded(child: picker),
                  actions,
                ],
              ),
            ),
          ],
        );
    }
  }
}

/// Provides a pair of text fields that allow the user to enter the start and
/// end dates that represent a range of dates.
class _InputDateRangePicker extends StatefulWidget {
  /// Creates a row with two text fields configured to accept the start and end dates
  /// of a date range.
  _InputDateRangePicker({
    Key? key,
    DateTime? initialStartDate,
    DateTime? initialEndDate,
    required DateTime firstDate,
    required DateTime lastDate,
    required this.onStartDateChanged,
    required this.onEndDateChanged,
    this.helpText,
    this.errorFormatText,
    this.errorInvalidText,
    this.errorInvalidRangeText,
    this.fieldStartHintText,
    this.fieldEndHintText,
    this.fieldStartLabelText,
    this.fieldEndLabelText,
    this.autofocus = false,
    this.autovalidate = false,
  }) : initialStartDate = initialStartDate == null ? null : DateUtils.dateOnly(initialStartDate),
       initialEndDate = initialEndDate == null ? null : DateUtils.dateOnly(initialEndDate),
       assert(firstDate != null),
       firstDate = DateUtils.dateOnly(firstDate),
       assert(lastDate != null),
       lastDate = DateUtils.dateOnly(lastDate),
       assert(firstDate != null),
       assert(lastDate != null),
       assert(autofocus != null),
       assert(autovalidate != null),
       super(key: key);

  /// The [DateTime] that represents the start of the initial date range selection.
  final DateTime? initialStartDate;

  /// The [DateTime] that represents the end of the initial date range selection.
  final DateTime? initialEndDate;

  /// The earliest allowable [DateTime] that the user can select.
  final DateTime firstDate;

  /// The latest allowable [DateTime] that the user can select.
  final DateTime lastDate;

  /// Called when the user changes the start date of the selected range.
  final ValueChanged<DateTime?>? onStartDateChanged;

  /// Called when the user changes the end date of the selected range.
  final ValueChanged<DateTime?>? onEndDateChanged;

  /// The text that is displayed at the top of the header.
  ///
  /// This is used to indicate to the user what they are selecting a date for.
  final String? helpText;

  /// Error text used to indicate the text in a field is not a valid date.
  final String? errorFormatText;

  /// Error text used to indicate the date in a field is not in the valid range
  /// of [firstDate] - [lastDate].
  final String? errorInvalidText;

  /// Error text used to indicate the dates given don't form a valid date
  /// range (i.e. the start date is after the end date).
  final String? errorInvalidRangeText;

  /// Hint text shown when the start date field is empty.
  final String? fieldStartHintText;

  /// Hint text shown when the end date field is empty.
  final String? fieldEndHintText;

  /// Label used for the start date field.
  final String? fieldStartLabelText;

  /// Label used for the end date field.
  final String? fieldEndLabelText;

  /// {@macro flutter.widgets.editableText.autofocus}
  final bool autofocus;

  /// If true, this the date fields will validate and update their error text
  /// immediately after every change. Otherwise, you must call
  /// [_InputDateRangePickerState.validate] to validate.
  final bool autovalidate;

  @override
  _InputDateRangePickerState createState() => _InputDateRangePickerState();
}

/// The current state of an [_InputDateRangePicker]. Can be used to
/// [validate] the date field entries.
class _InputDateRangePickerState extends State<_InputDateRangePicker> {
  late String _startInputText;
  late String _endInputText;
  DateTime? _startDate;
  DateTime? _endDate;
  late TextEditingController _startController;
  late TextEditingController _endController;
  String? _startErrorText;
  String? _endErrorText;
  bool _autoSelected = false;

  @override
  void initState() {
    super.initState();
    _startDate = widget.initialStartDate;
    _startController = TextEditingController();
    _endDate = widget.initialEndDate;
    _endController = TextEditingController();
  }

  @override
  void dispose() {
    _startController.dispose();
    _endController.dispose();
    super.dispose();
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    if (_startDate != null) {
      _startInputText = localizations.formatCompactDate(_startDate!);
      final bool selectText = widget.autofocus && !_autoSelected;
      _updateController(_startController, _startInputText, selectText);
      _autoSelected = selectText;
    }

    if (_endDate != null) {
      _endInputText = localizations.formatCompactDate(_endDate!);
      _updateController(_endController, _endInputText, false);
    }
  }

  /// Validates that the text in the start and end fields represent a valid
  /// date range.
  ///
  /// Will return true if the range is valid. If not, it will
  /// return false and display an appropriate error message under one of the
  /// text fields.
  bool validate() {
    String? startError = _validateDate(_startDate);
    final String? endError = _validateDate(_endDate);
    if (startError == null && endError == null) {
      if (_startDate!.isAfter(_endDate!)) {
        startError = widget.errorInvalidRangeText ?? MaterialLocalizations.of(context).invalidDateRangeLabel;
      }
    }
    setState(() {
      _startErrorText = startError;
      _endErrorText = endError;
    });
    return startError == null && endError == null;
  }

  DateTime? _parseDate(String? text) {
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    return localizations.parseCompactDate(text);
  }

  String? _validateDate(DateTime? date) {
    if (date == null) {
      return widget.errorFormatText ?? MaterialLocalizations.of(context).invalidDateFormatLabel;
    } else if (date.isBefore(widget.firstDate) || date.isAfter(widget.lastDate)) {
      return widget.errorInvalidText ?? MaterialLocalizations.of(context).dateOutOfRangeLabel;
    }
    return null;
  }

  void _updateController(TextEditingController controller, String text, bool selectText) {
    TextEditingValue textEditingValue = controller.value.copyWith(text: text);
    if (selectText) {
      textEditingValue = textEditingValue.copyWith(selection: TextSelection(
        baseOffset: 0,
        extentOffset: text.length,
      ));
    }
    controller.value = textEditingValue;
  }

  void _handleStartChanged(String text) {
    setState(() {
      _startInputText = text;
      _startDate = _parseDate(text);
      widget.onStartDateChanged?.call(_startDate);
    });
    if (widget.autovalidate) {
      validate();
    }
  }

  void _handleEndChanged(String text) {
    setState(() {
      _endInputText = text;
      _endDate = _parseDate(text);
      widget.onEndDateChanged?.call(_endDate);
    });
    if (widget.autovalidate) {
      validate();
    }
  }

  @override
  Widget build(BuildContext context) {
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final InputDecorationTheme inputTheme = Theme.of(context).inputDecorationTheme;
    return Row(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        Expanded(
          child: TextField(
            controller: _startController,
            decoration: InputDecoration(
              border: inputTheme.border ?? const UnderlineInputBorder(),
              filled: inputTheme.filled,
              hintText: widget.fieldStartHintText ?? localizations.dateHelpText,
              labelText: widget.fieldStartLabelText ?? localizations.dateRangeStartLabel,
              errorText: _startErrorText,
            ),
            keyboardType: TextInputType.datetime,
            onChanged: _handleStartChanged,
            autofocus: widget.autofocus,
          ),
        ),
        const SizedBox(width: 8),
        Expanded(
          child: TextField(
            controller: _endController,
            decoration: InputDecoration(
              border: inputTheme.border ?? const UnderlineInputBorder(),
              filled: inputTheme.filled,
              hintText: widget.fieldEndHintText ?? localizations.dateHelpText,
              labelText: widget.fieldEndLabelText ?? localizations.dateRangeEndLabel,
              errorText: _endErrorText,
            ),
            keyboardType: TextInputType.datetime,
            onChanged: _handleEndChanged,
          ),
        ),
      ],
    );
  }
}