selectable_text.dart

// Copyright 2019 The Chromium 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 'package:flutter/cupertino.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';

import 'feedback.dart';
import 'text_selection.dart';
import 'theme.dart';

/// An eyeballed value that moves the cursor slightly left of where it is
/// rendered for text on Android so its positioning more accurately matches the
/// native iOS text cursor positioning.
///
/// This value is in device pixels, not logical pixels as is typically used
/// throughout the codebase.
const int iOSHorizontalOffset = -2;

class _TextSpanEditingController extends TextEditingController {
  _TextSpanEditingController({@required TextSpan textSpan}):
    assert(textSpan != null),
    _textSpan = textSpan,
    super(text: textSpan.toPlainText());

  final TextSpan _textSpan;

  @override
  TextSpan buildTextSpan({TextStyle style ,bool withComposing}) {
    // TODO(chunhtai): Implement composing.
    return TextSpan(
      style: style,
      children: <TextSpan>[_textSpan],
    );
  }

  @override
  set text(String newText) {
    // TODO(chunhtai): Implement value editing.
  }
}

class _SelectableTextSelectionGestureDetectorBuilder extends TextSelectionGestureDetectorBuilder {
  _SelectableTextSelectionGestureDetectorBuilder({
    @required _SelectableTextState state,
  }) : _state = state,
      super(delegate: state);

  final _SelectableTextState _state;

  @override
  void onForcePressStart(ForcePressDetails details) {
    super.onForcePressStart(details);
    if (delegate.selectionEnabled && shouldShowSelectionToolbar) {
      editableText.showToolbar();
    }
  }

  @override
  void onForcePressEnd(ForcePressDetails details) {
    // Not required.
  }

  @override
  void onSingleLongTapMoveUpdate(LongPressMoveUpdateDetails details) {
    if (delegate.selectionEnabled) {
      switch (Theme.of(_state.context).platform) {
        case TargetPlatform.iOS:
          renderEditable.selectPositionAt(
            from: details.globalPosition,
            cause: SelectionChangedCause.longPress,
          );
          break;
        case TargetPlatform.android:
        case TargetPlatform.fuchsia:
          renderEditable.selectWordsInRange(
            from: details.globalPosition - details.offsetFromOrigin,
            to: details.globalPosition,
            cause: SelectionChangedCause.longPress,
          );
          break;
      }
    }
  }

  @override
  void onSingleTapUp(TapUpDetails details) {
    editableText.hideToolbar();
    if (delegate.selectionEnabled) {
      switch (Theme.of(_state.context).platform) {
        case TargetPlatform.iOS:
          renderEditable.selectWordEdge(cause: SelectionChangedCause.tap);
          break;
        case TargetPlatform.android:
        case TargetPlatform.fuchsia:
          renderEditable.selectPosition(cause: SelectionChangedCause.tap);
          break;
      }
    }
    if (_state.widget.onTap != null)
      _state.widget.onTap();
  }

  @override
  void onSingleLongTapStart(LongPressStartDetails details) {
    if (delegate.selectionEnabled) {
      switch (Theme.of(_state.context).platform) {
        case TargetPlatform.iOS:
          renderEditable.selectPositionAt(
            from: details.globalPosition,
            cause: SelectionChangedCause.longPress,
          );
          break;
        case TargetPlatform.android:
        case TargetPlatform.fuchsia:
          renderEditable.selectWord(cause: SelectionChangedCause.longPress);
          Feedback.forLongPress(_state.context);
          break;
      }
    }
  }
}

/// A run of selectable text with a single style.
///
/// The [SelectableText] widget displays a string of text with a single style.
/// The string might break across multiple lines or might all be displayed on
/// the same line depending on the layout constraints.
///
/// The [style] argument is optional. When omitted, the text will use the style
/// from the closest enclosing [DefaultTextStyle]. If the given style's
/// [TextStyle.inherit] property is true (the default), the given style will
/// be merged with the closest enclosing [DefaultTextStyle]. This merging
/// behavior is useful, for example, to make the text bold while using the
/// default font family and size.
///
/// {@tool sample}
///
/// ```dart
/// SelectableText(
///   'Hello! How are you?',
///   textAlign: TextAlign.center,
///   style: TextStyle(fontWeight: FontWeight.bold),
/// )
/// ```
/// {@end-tool}
///
/// Using the [SelectableText.rich] constructor, the [SelectableText] widget can
/// display a paragraph with differently styled [TextSpan]s. The sample
/// that follows displays "Hello beautiful world" with different styles
/// for each word.
///
/// {@tool sample}
///
/// ```dart
/// const SelectableText.rich(
///   TextSpan(
///     text: 'Hello', // default text style
///     children: <TextSpan>[
///       TextSpan(text: ' beautiful ', style: TextStyle(fontStyle: FontStyle.italic)),
///       TextSpan(text: 'world', style: TextStyle(fontWeight: FontWeight.bold)),
///     ],
///   ),
/// )
/// ```
/// {@end-tool}
///
/// ## Interactivity
///
/// To make [SelectableText] react to touch events, use callback [onTap] to achieve
/// the desired behavior.
///
/// See also:
///
///  * [Text], which is the non selectable version of this widget.
///  * [TextField], which is the editable version of this widget.
class SelectableText extends StatefulWidget {
  /// Creates a selectable text widget.
  ///
  /// If the [style] argument is null, the text will use the style from the
  /// closest enclosing [DefaultTextStyle].
  ///

  /// The [showCursor], [autofocus], [dragStartBehavior], and [data] parameters
  /// must not be null. If specified, the [maxLines] argument must be greater
  /// than zero.
  const SelectableText(
    this.data, {
    Key key,
    this.focusNode,
    this.style,
    this.strutStyle,
    this.textAlign,
    this.textDirection,
    this.showCursor = false,
    this.autofocus = false,
    ToolbarOptions toolbarOptions,
    this.maxLines,
    this.cursorWidth = 2.0,
    this.cursorRadius,
    this.cursorColor,
    this.dragStartBehavior = DragStartBehavior.start,
    this.enableInteractiveSelection = true,
    this.onTap,
    this.scrollPhysics,
    this.textWidthBasis,
  }) :  assert(showCursor != null),
        assert(autofocus != null),
        assert(dragStartBehavior != null),
        assert(maxLines == null || maxLines > 0),
        assert(
          data != null,
          'A non-null String must be provided to a SelectableText widget.',
        ),
        textSpan = null,
        toolbarOptions = toolbarOptions ??
          const ToolbarOptions(
            selectAll: true,
            copy: true,
          ),
        super(key: key);

  /// Creates a selectable text widget with a [TextSpan].
  ///
  /// The [textSpan] parameter must not be null and only contain [TextSpan] in
  /// [textSpan.children]. Other type of [InlineSpan] is not allowed.
  ///
  /// The [autofocus] and [dragStartBehavior] arguments must not be null.
  const SelectableText.rich(
    this.textSpan, {
    Key key,
    this.focusNode,
    this.style,
    this.strutStyle,
    this.textAlign,
    this.textDirection,
    this.showCursor = false,
    this.autofocus = false,
    ToolbarOptions toolbarOptions,
    this.maxLines,
    this.cursorWidth = 2.0,
    this.cursorRadius,
    this.cursorColor,
    this.dragStartBehavior = DragStartBehavior.start,
    this.enableInteractiveSelection = true,
    this.onTap,
    this.scrollPhysics,
    this.textWidthBasis,
  }) :  assert(showCursor != null),
    assert(autofocus != null),
    assert(dragStartBehavior != null),
    assert(maxLines == null || maxLines > 0),
    assert(
      textSpan != null,
      'A non-null TextSpan must be provided to a SelectableText.rich widget.',
    ),
    data = null,
    toolbarOptions = toolbarOptions ??
      const ToolbarOptions(
        selectAll: true,
        copy: true,
      ),
    super(key: key);

  /// The text to display.
  ///
  /// This will be null if a [textSpan] is provided instead.
  final String data;

  /// The text to display as a [TextSpan].
  ///
  /// This will be null if [data] is provided instead.
  final TextSpan textSpan;

  /// Defines the focus for this widget.
  ///
  /// Text is only selectable when widget is focused.
  ///
  /// The [focusNode] is a long-lived object that's typically managed by a
  /// [StatefulWidget] parent. See [FocusNode] for more information.
  ///
  /// To give the focus to this widget, provide a [focusNode] and then
  /// use the current [FocusScope] to request the focus:
  ///
  /// ```dart
  /// FocusScope.of(context).requestFocus(myFocusNode);
  /// ```
  ///
  /// This happens automatically when the widget is tapped.
  ///
  /// To be notified when the widget gains or loses the focus, add a listener
  /// to the [focusNode]:
  ///
  /// ```dart
  /// focusNode.addListener(() { print(myFocusNode.hasFocus); });
  /// ```
  ///
  /// If null, this widget will create its own [FocusNode].
  final FocusNode focusNode;

  /// The style to use for the text.
  ///
  /// If null, defaults [DefaultTextStyle] of context.
  final TextStyle style;

  /// {@macro flutter.widgets.editableText.strutStyle}
  final StrutStyle strutStyle;

  /// {@macro flutter.widgets.editableText.textAlign}
  final TextAlign textAlign;

  /// {@macro flutter.widgets.editableText.textDirection}
  final TextDirection textDirection;

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

  /// {@macro flutter.widgets.editableText.maxLines}
  final int maxLines;

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

  /// {@macro flutter.widgets.editableText.cursorWidth}
  final double cursorWidth;

  /// {@macro flutter.widgets.editableText.cursorRadius}
  final Radius cursorRadius;

  /// The color to use when painting the cursor.
  ///
  /// Defaults to the theme's `cursorColor` when null.
  final Color cursorColor;

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

  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
  final DragStartBehavior dragStartBehavior;

  /// Configuration of toolbar options.
  ///
  /// Paste and cut will be disabled regardless.
  ///
  /// If not set, select all and copy will be enabled by default.
  final ToolbarOptions toolbarOptions;

  /// {@macro flutter.rendering.editable.selectionEnabled}
  bool get selectionEnabled {
    return enableInteractiveSelection;
  }

  /// Called when the user taps on this selectable text.
  ///
  /// The selectable text builds a [GestureDetector] to handle input events like tap,
  /// to trigger focus requests, to move the caret, adjust the selection, etc.
  /// Handling some of those events by wrapping the selectable text with a competing
  /// GestureDetector is problematic.
  ///
  /// To unconditionally handle taps, without interfering with the selectable text's
  /// internal gesture detector, provide this callback.
  ///
  /// To be notified when the text field gains or loses the focus, provide a
  /// [focusNode] and add a listener to that.
  ///
  /// To listen to arbitrary pointer events without competing with the
  /// selectable text's internal gesture detector, use a [Listener].
  final GestureTapCallback onTap;

  /// {@macro flutter.widgets.edtiableText.scrollPhysics}
  final ScrollPhysics scrollPhysics;

  /// {@macro flutter.painting.textPainter.textWidthBasis}
  final TextWidthBasis textWidthBasis;

  @override
  _SelectableTextState createState() => _SelectableTextState();

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<String>('data', data, defaultValue: null));
    properties.add(DiagnosticsProperty<FocusNode>('focusNode', focusNode, defaultValue: null));
    properties.add(DiagnosticsProperty<TextStyle>('style', style, defaultValue: null));
    properties.add(DiagnosticsProperty<bool>('autofocus', autofocus, defaultValue: false));
    properties.add(DiagnosticsProperty<bool>('showCursor', showCursor, defaultValue: false));
    properties.add(IntProperty('maxLines', maxLines, defaultValue: null));
    properties.add(EnumProperty<TextAlign>('textAlign', textAlign, defaultValue: null));
    properties.add(EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
    properties.add(DoubleProperty('cursorWidth', cursorWidth, defaultValue: 2.0));
    properties.add(DiagnosticsProperty<Radius>('cursorRadius', cursorRadius, defaultValue: null));
    properties.add(DiagnosticsProperty<Color>('cursorColor', cursorColor, defaultValue: null));
    properties.add(FlagProperty('selectionEnabled', value: selectionEnabled, defaultValue: true, ifFalse: 'selection disabled'));
    properties.add(DiagnosticsProperty<ScrollPhysics>('scrollPhysics', scrollPhysics, defaultValue: null));
  }
}

class _SelectableTextState extends State<SelectableText> with AutomaticKeepAliveClientMixin implements TextSelectionGestureDetectorBuilderDelegate {
  EditableTextState get _editableText => editableTextKey.currentState;

  _TextSpanEditingController _controller;

  FocusNode _focusNode;
  FocusNode get _effectiveFocusNode => widget.focusNode ?? (_focusNode ??= FocusNode());

  bool _showSelectionHandles = false;

  _SelectableTextSelectionGestureDetectorBuilder _selectionGestureDetectorBuilder;

  // API for TextSelectionGestureDetectorBuilderDelegate.
  @override
  bool forcePressEnabled;

  @override
  final GlobalKey<EditableTextState> editableTextKey = GlobalKey<EditableTextState>();

  @override
  bool get selectionEnabled => widget.selectionEnabled;
  // End of API for TextSelectionGestureDetectorBuilderDelegate.

  @override
  void initState() {
    super.initState();
    _selectionGestureDetectorBuilder = _SelectableTextSelectionGestureDetectorBuilder(state: this);
    _controller = _TextSpanEditingController(
        textSpan: widget.textSpan ?? TextSpan(text: widget.data)
    );
  }

  @override
  void didUpdateWidget(SelectableText oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (widget.data != oldWidget.data || widget.textSpan != oldWidget.textSpan) {
      _controller = _TextSpanEditingController(
          textSpan: widget.textSpan ?? TextSpan(text: widget.data)
      );
    }
    if (_effectiveFocusNode.hasFocus && _controller.selection.isCollapsed) {
      _showSelectionHandles = false;
    }
  }

  @override
  void dispose() {
    _focusNode?.dispose();
    super.dispose();
  }

  void _handleSelectionChanged(TextSelection selection, SelectionChangedCause cause) {
    final bool willShowSelectionHandles = _shouldShowSelectionHandles(cause);
    if (willShowSelectionHandles != _showSelectionHandles) {
      setState(() {
        _showSelectionHandles = willShowSelectionHandles;
      });
    }

    switch (Theme.of(context).platform) {
      case TargetPlatform.iOS:
        if (cause == SelectionChangedCause.longPress) {
          _editableText?.bringIntoView(selection.base);
        }
        return;
      case TargetPlatform.android:
      case TargetPlatform.fuchsia:
      // Do nothing.
    }
  }

  /// Toggle the toolbar when a selection handle is tapped.
  void _handleSelectionHandleTapped() {
    if (_controller.selection.isCollapsed) {
      _editableText.toggleToolbar();
    }
  }

  bool _shouldShowSelectionHandles(SelectionChangedCause cause) {
    // When the text field is activated by something that doesn't trigger the
    // selection overlay, we shouldn't show the handles either.
    if (!_selectionGestureDetectorBuilder.shouldShowSelectionToolbar)
      return false;

    if (_controller.selection.isCollapsed)
      return false;

    if (cause == SelectionChangedCause.keyboard)
      return false;

    if (cause == SelectionChangedCause.longPress)
      return true;

    if (_controller.text.isNotEmpty)
      return true;

    return false;
  }

  @override
  bool get wantKeepAlive => true;

  @override
  Widget build(BuildContext context) {
    super.build(context); // See AutomaticKeepAliveClientMixin.
    assert(() {
      return _controller._textSpan.visitChildren((InlineSpan span) => span.runtimeType == TextSpan);
    }(), 'SelectableText only supports TextSpan; Other type of InlineSpan is not allowed');
    assert(debugCheckHasMediaQuery(context));
    assert(debugCheckHasDirectionality(context));
    assert(
      !(widget.style != null && widget.style.inherit == false &&
          (widget.style.fontSize == null || widget.style.textBaseline == null)),
      'inherit false style must supply fontSize and textBaseline',
    );

    final ThemeData themeData = Theme.of(context);
    final FocusNode focusNode = _effectiveFocusNode;

    TextSelectionControls textSelectionControls;
    bool paintCursorAboveText;
    bool cursorOpacityAnimates;
    Offset cursorOffset;
    Color cursorColor = widget.cursorColor;
    Radius cursorRadius = widget.cursorRadius;

    switch (themeData.platform) {
      case TargetPlatform.iOS:
        forcePressEnabled = true;
        textSelectionControls = cupertinoTextSelectionControls;
        paintCursorAboveText = true;
        cursorOpacityAnimates = true;
        cursorColor ??= CupertinoTheme.of(context).primaryColor;
        cursorRadius ??= const Radius.circular(2.0);
        cursorOffset = Offset(iOSHorizontalOffset / MediaQuery.of(context).devicePixelRatio, 0);
        break;

      case TargetPlatform.android:
      case TargetPlatform.fuchsia:
        forcePressEnabled = false;
        textSelectionControls = materialTextSelectionControls;
        paintCursorAboveText = false;
        cursorOpacityAnimates = false;
        cursorColor ??= themeData.cursorColor;
        break;
    }

    final DefaultTextStyle defaultTextStyle = DefaultTextStyle.of(context);
    TextStyle effectiveTextStyle = widget.style;
    if (widget.style == null || widget.style.inherit)
      effectiveTextStyle = defaultTextStyle.style.merge(widget.style);
    if (MediaQuery.boldTextOverride(context))
      effectiveTextStyle = effectiveTextStyle.merge(const TextStyle(fontWeight: FontWeight.bold));
    final Widget child = RepaintBoundary(
      child: EditableText(
        key: editableTextKey,
        style: effectiveTextStyle,
        readOnly: true,
        textWidthBasis: widget.textWidthBasis ?? defaultTextStyle.textWidthBasis,
        showSelectionHandles: _showSelectionHandles,
        showCursor: widget.showCursor,
        controller: _controller,
        focusNode: focusNode,
        strutStyle: widget.strutStyle ?? StrutStyle.disabled,
        textAlign: widget.textAlign ?? defaultTextStyle.textAlign ?? TextAlign.start,
        textDirection: widget.textDirection,
        autofocus: widget.autofocus,
        forceLine: false,
        toolbarOptions: widget.toolbarOptions,
        maxLines: widget.maxLines ?? defaultTextStyle.maxLines,
        selectionColor: themeData.textSelectionColor,
        selectionControls: widget.selectionEnabled ? textSelectionControls : null,
        onSelectionChanged: _handleSelectionChanged,
        onSelectionHandleTapped: _handleSelectionHandleTapped,
        rendererIgnoresPointer: true,
        cursorWidth: widget.cursorWidth,
        cursorRadius: cursorRadius,
        cursorColor: cursorColor,
        cursorOpacityAnimates: cursorOpacityAnimates,
        cursorOffset: cursorOffset,
        paintCursorAboveText: paintCursorAboveText,
        backgroundCursorColor: CupertinoColors.inactiveGray,
        enableInteractiveSelection: widget.enableInteractiveSelection,
        dragStartBehavior: widget.dragStartBehavior,
        scrollPhysics: widget.scrollPhysics,
      ),
    );

    return Semantics(
      onTap: () {
        if (!_controller.selection.isValid)
          _controller.selection = TextSelection.collapsed(offset: _controller.text.length);
        _effectiveFocusNode.requestFocus();
      },
      onLongPress: () {
        _effectiveFocusNode.requestFocus();
      },
      child: _selectionGestureDetectorBuilder.buildGestureDetector(
        behavior: HitTestBehavior.translucent,
        child: child,
      ),
    );
  }
}