text_selection.dart

// 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/widgets.dart';

import 'debug.dart';
import 'material_localizations.dart';
import 'text_selection_theme.dart';
import 'text_selection_toolbar.dart';
import 'text_selection_toolbar_text_button.dart';
import 'theme.dart';

const double _kHandleSize = 22.0;

// Padding between the toolbar and the anchor.
const double _kToolbarContentDistanceBelow = _kHandleSize - 2.0;
const double _kToolbarContentDistance = 8.0;

/// Android Material styled text selection controls.
///
/// The [materialTextSelectionControls] global variable has a
/// suitable instance of this class.
class MaterialTextSelectionControls extends TextSelectionControls {
  /// Returns the size of the Material handle.
  @override
  Size getHandleSize(double textLineHeight) => const Size(_kHandleSize, _kHandleSize);

  /// Builder for material-style copy/paste text selection toolbar.
  @override
  Widget buildToolbar(
    BuildContext context,
    Rect globalEditableRegion,
    double textLineHeight,
    Offset selectionMidpoint,
    List<TextSelectionPoint> endpoints,
    TextSelectionDelegate delegate,
    ClipboardStatusNotifier? clipboardStatus,
    Offset? lastSecondaryTapDownPosition,
  ) {
    return _TextSelectionControlsToolbar(
      globalEditableRegion: globalEditableRegion,
      textLineHeight: textLineHeight,
      selectionMidpoint: selectionMidpoint,
      endpoints: endpoints,
      delegate: delegate,
      clipboardStatus: clipboardStatus,
      handleCut: canCut(delegate) ? () => handleCut(delegate) : null,
      handleCopy: canCopy(delegate) ? () => handleCopy(delegate) : null,
      handlePaste: canPaste(delegate) ? () => handlePaste(delegate) : null,
      handleSelectAll: canSelectAll(delegate) ? () => handleSelectAll(delegate) : null,
    );
  }

  /// Builder for material-style text selection handles.
  @override
  Widget buildHandle(BuildContext context, TextSelectionHandleType type, double textHeight, [VoidCallback? onTap]) {
    final ThemeData theme = Theme.of(context);
    final Color handleColor = TextSelectionTheme.of(context).selectionHandleColor ?? theme.colorScheme.primary;
    final Widget handle = SizedBox(
      width: _kHandleSize,
      height: _kHandleSize,
      child: CustomPaint(
        painter: _TextSelectionHandlePainter(
          color: handleColor,
        ),
        child: GestureDetector(
          onTap: onTap,
          behavior: HitTestBehavior.translucent,
        ),
      ),
    );

    // [handle] is a circle, with a rectangle in the top left quadrant of that
    // circle (an onion pointing to 10:30). We rotate [handle] to point
    // straight up or up-right depending on the handle type.
    switch (type) {
      case TextSelectionHandleType.left: // points up-right
        return Transform.rotate(
          angle: math.pi / 2.0,
          child: handle,
        );
      case TextSelectionHandleType.right: // points up-left
        return handle;
      case TextSelectionHandleType.collapsed: // points up
        return Transform.rotate(
          angle: math.pi / 4.0,
          child: handle,
        );
    }
  }

  /// Gets anchor for material-style text selection handles.
  ///
  /// See [TextSelectionControls.getHandleAnchor].
  @override
  Offset getHandleAnchor(TextSelectionHandleType type, double textLineHeight) {
    switch (type) {
      case TextSelectionHandleType.left:
        return const Offset(_kHandleSize, 0);
      case TextSelectionHandleType.right:
        return Offset.zero;
      case TextSelectionHandleType.collapsed:
        return const Offset(_kHandleSize / 2, -4);
    }
  }

  @override
  bool canSelectAll(TextSelectionDelegate delegate) {
    // Android allows SelectAll when selection is not collapsed, unless
    // everything has already been selected.
    final TextEditingValue value = delegate.textEditingValue;
    return delegate.selectAllEnabled &&
           value.text.isNotEmpty &&
           !(value.selection.start == 0 && value.selection.end == value.text.length);
  }
}

// The label and callback for the available default text selection menu buttons.
class _TextSelectionToolbarItemData {
  const _TextSelectionToolbarItemData({
    required this.label,
    required this.onPressed,
  });

  final String label;
  final VoidCallback onPressed;
}

// The highest level toolbar widget, built directly by buildToolbar.
class _TextSelectionControlsToolbar extends StatefulWidget {
  const _TextSelectionControlsToolbar({
    required this.clipboardStatus,
    required this.delegate,
    required this.endpoints,
    required this.globalEditableRegion,
    required this.handleCut,
    required this.handleCopy,
    required this.handlePaste,
    required this.handleSelectAll,
    required this.selectionMidpoint,
    required this.textLineHeight,
  });

  final ClipboardStatusNotifier? clipboardStatus;
  final TextSelectionDelegate delegate;
  final List<TextSelectionPoint> endpoints;
  final Rect globalEditableRegion;
  final VoidCallback? handleCut;
  final VoidCallback? handleCopy;
  final VoidCallback? handlePaste;
  final VoidCallback? handleSelectAll;
  final Offset selectionMidpoint;
  final double textLineHeight;

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

class _TextSelectionControlsToolbarState extends State<_TextSelectionControlsToolbar> with TickerProviderStateMixin {
  void _onChangedClipboardStatus() {
    setState(() {
      // Inform the widget that the value of clipboardStatus has changed.
    });
  }

  @override
  void initState() {
    super.initState();
    widget.clipboardStatus?.addListener(_onChangedClipboardStatus);
  }

  @override
  void didUpdateWidget(_TextSelectionControlsToolbar oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (widget.clipboardStatus != oldWidget.clipboardStatus) {
      widget.clipboardStatus?.addListener(_onChangedClipboardStatus);
      oldWidget.clipboardStatus?.removeListener(_onChangedClipboardStatus);
    }
  }

  @override
  void dispose() {
    super.dispose();
    widget.clipboardStatus?.removeListener(_onChangedClipboardStatus);
  }

  @override
  Widget build(BuildContext context) {
    // If there are no buttons to be shown, don't render anything.
    if (widget.handleCut == null && widget.handleCopy == null
        && widget.handlePaste == null && widget.handleSelectAll == null) {
      return const SizedBox.shrink();
    }
    // If the paste button is desired, don't render anything until the state of
    // the clipboard is known, since it's used to determine if paste is shown.
    if (widget.handlePaste != null
        && widget.clipboardStatus?.value == ClipboardStatus.unknown) {
      return const SizedBox.shrink();
    }

    // Calculate the positioning of the menu. It is placed above the selection
    // if there is enough room, or otherwise below.
    final TextSelectionPoint startTextSelectionPoint = widget.endpoints[0];
    final TextSelectionPoint endTextSelectionPoint = widget.endpoints.length > 1
      ? widget.endpoints[1]
      : widget.endpoints[0];
    final double topAmountInEditableRegion = startTextSelectionPoint.point.dy - widget.textLineHeight;
    final double anchorTop = math.max(topAmountInEditableRegion, 0) + widget.globalEditableRegion.top - _kToolbarContentDistance;

    final Offset anchorAbove = Offset(
      widget.globalEditableRegion.left + widget.selectionMidpoint.dx,
      anchorTop,
    );
    final Offset anchorBelow = Offset(
      widget.globalEditableRegion.left + widget.selectionMidpoint.dx,
      widget.globalEditableRegion.top + endTextSelectionPoint.point.dy + _kToolbarContentDistanceBelow,
    );

    // Determine which buttons will appear so that the order and total number is
    // known. A button's position in the menu can slightly affect its
    // appearance.
    assert(debugCheckHasMaterialLocalizations(context));
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final List<_TextSelectionToolbarItemData> itemDatas = <_TextSelectionToolbarItemData>[
      if (widget.handleCut != null)
        _TextSelectionToolbarItemData(
          label: localizations.cutButtonLabel,
          onPressed: widget.handleCut!,
        ),
      if (widget.handleCopy != null)
        _TextSelectionToolbarItemData(
          label: localizations.copyButtonLabel,
          onPressed: widget.handleCopy!,
        ),
      if (widget.handlePaste != null
          && widget.clipboardStatus?.value == ClipboardStatus.pasteable)
        _TextSelectionToolbarItemData(
          label: localizations.pasteButtonLabel,
          onPressed: widget.handlePaste!,
        ),
      if (widget.handleSelectAll != null)
        _TextSelectionToolbarItemData(
          label: localizations.selectAllButtonLabel,
          onPressed: widget.handleSelectAll!,
        ),
    ];

    // If there is no option available, build an empty widget.
    if (itemDatas.isEmpty) {
      return const SizedBox.shrink();
    }

    return TextSelectionToolbar(
      anchorAbove: anchorAbove,
      anchorBelow: anchorBelow,
      children: itemDatas.asMap().entries.map((MapEntry<int, _TextSelectionToolbarItemData> entry) {
        return TextSelectionToolbarTextButton(
          padding: TextSelectionToolbarTextButton.getPadding(entry.key, itemDatas.length),
          onPressed: entry.value.onPressed,
          child: Text(entry.value.label),
        );
      }).toList(),
    );
  }
}

/// Draws a single text selection handle which points up and to the left.
class _TextSelectionHandlePainter extends CustomPainter {
  _TextSelectionHandlePainter({ required this.color });

  final Color color;

  @override
  void paint(Canvas canvas, Size size) {
    final Paint paint = Paint()..color = color;
    final double radius = size.width/2.0;
    final Rect circle = Rect.fromCircle(center: Offset(radius, radius), radius: radius);
    final Rect point = Rect.fromLTWH(0.0, 0.0, radius, radius);
    final Path path = Path()..addOval(circle)..addRect(point);
    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(_TextSelectionHandlePainter oldPainter) {
    return color != oldPainter.color;
  }
}

/// Text selection controls that follow the Material Design specification.
final TextSelectionControls materialTextSelectionControls = MaterialTextSelectionControls();