text_selection.dart

// Copyright 2017 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 'dart:math' as math;
import 'dart:ui' as ui;

import 'package:flutter/widgets.dart';
import 'package:flutter/rendering.dart';

import 'button.dart';
import 'colors.dart';
import 'localizations.dart';
import 'theme.dart';

// Read off from the output on iOS 12. This color does not vary with the
// application's theme color.
const double _kSelectionHandleOverlap = 1.5;
// Extracted from https://developer.apple.com/design/resources/.
const double _kSelectionHandleRadius = 6;

// Minimal padding from all edges of the selection toolbar to all edges of the
// screen.
const double _kToolbarScreenPadding = 8.0;
// Minimal padding from tip of the selection toolbar arrow to horizontal edges of the
// screen. Eyeballed value.
const double _kArrowScreenPadding = 26.0;

// Vertical distance between the tip of the arrow and the line of text the arrow
// is pointing to. The value used here is eyeballed.
const double _kToolbarContentDistance = 8.0;
// Values derived from https://developer.apple.com/design/resources/.
// 92% Opacity ~= 0xEB

// Values extracted from https://developer.apple.com/design/resources/.
// The height of the toolbar, including the arrow.
const double _kToolbarHeight = 43.0;
const Size _kToolbarArrowSize = Size(14.0, 7.0);
const Radius _kToolbarBorderRadius = Radius.circular(8);
// Colors extracted from https://developer.apple.com/design/resources/.
// TODO(LongCatIsLooong): https://github.com/flutter/flutter/issues/41507.
const Color _kToolbarBackgroundColor = Color(0xEB202020);
const Color _kToolbarDividerColor = Color(0xFF808080);


const TextStyle _kToolbarButtonFontStyle = TextStyle(
  inherit: false,
  fontSize: 14.0,
  letterSpacing: -0.15,
  fontWeight: FontWeight.w400,
  color: CupertinoColors.white,
);

// Eyeballed value.
const EdgeInsets _kToolbarButtonPadding = EdgeInsets.symmetric(vertical: 10.0, horizontal: 18.0);

/// An iOS-style toolbar that appears in response to text selection.
///
/// Typically displays buttons for text manipulation, e.g. copying and pasting text.
///
/// See also:
///
/// * [TextSelectionControls.buildToolbar], where [CupertinoTextSelectionToolbar]
///   will be used to build an iOS-style toolbar.
@visibleForTesting
class CupertinoTextSelectionToolbar extends SingleChildRenderObjectWidget {
  const CupertinoTextSelectionToolbar._({
    Key key,
    double barTopY,
    double arrowTipX,
    bool isArrowPointingDown,
    Widget child,
  }) : _barTopY = barTopY,
       _arrowTipX = arrowTipX,
       _isArrowPointingDown = isArrowPointingDown,
       super(key: key, child: child);

  // The y-coordinate of toolbar's top edge, in global coordinate system.
  final double _barTopY;

  // The y-coordinate of the tip of the arrow, in global coordinate system.
  final double _arrowTipX;

  // Whether the arrow should point down and be attached to the bottom
  // of the toolbar, or point up and be attached to the top of the toolbar.
  final bool _isArrowPointingDown;

  @override
  _ToolbarRenderBox createRenderObject(BuildContext context) => _ToolbarRenderBox(_barTopY, _arrowTipX, _isArrowPointingDown, null);

  @override
  void updateRenderObject(BuildContext context, _ToolbarRenderBox renderObject) {
    renderObject
      ..barTopY = _barTopY
      ..arrowTipX = _arrowTipX
      ..isArrowPointingDown = _isArrowPointingDown;
  }
}

class _ToolbarParentData extends BoxParentData {
  // The x offset from the tip of the arrow to the center of the toolbar.
  // Positive if the tip of the arrow has a larger x-coordinate than the
  // center of the toolbar.
  double arrowXOffsetFromCenter;
  @override
  String toString() => 'offset=$offset, arrowXOffsetFromCenter=$arrowXOffsetFromCenter';
}

class _ToolbarRenderBox extends RenderShiftedBox {
  _ToolbarRenderBox(
    this._barTopY,
    this._arrowTipX,
    this._isArrowPointingDown,
    RenderBox child,
  ) : super(child);


  @override
  bool get isRepaintBoundary => true;

  double _barTopY;
  set barTopY(double value) {
    if (_barTopY == value) {
      return;
    }
    _barTopY = value;
    markNeedsLayout();
    markNeedsSemanticsUpdate();
  }

  double _arrowTipX;
  set arrowTipX(double value) {
    if (_arrowTipX == value) {
      return;
    }
    _arrowTipX = value;
    markNeedsLayout();
    markNeedsSemanticsUpdate();
  }

  bool _isArrowPointingDown;
  set isArrowPointingDown(bool value) {
    if (_isArrowPointingDown == value) {
      return;
    }
    _isArrowPointingDown = value;
    markNeedsLayout();
    markNeedsSemanticsUpdate();
  }

  final BoxConstraints heightConstraint = const BoxConstraints.tightFor(height: _kToolbarHeight);

  @override
  void setupParentData(RenderObject child) {
    if (child.parentData is! _ToolbarParentData) {
      child.parentData = _ToolbarParentData();
    }
  }

  @override
  void performLayout() {
    size = constraints.biggest;

    if (child == null) {
      return;
    }
    final BoxConstraints enforcedConstraint = constraints
      .deflate(const EdgeInsets.symmetric(horizontal: _kToolbarScreenPadding))
      .loosen();

    child.layout(heightConstraint.enforce(enforcedConstraint), parentUsesSize: true,);
    final _ToolbarParentData childParentData = child.parentData;

    // The local x-coordinate of the center of the toolbar.
    final double lowerBound = child.size.width/2 + _kToolbarScreenPadding;
    final double upperBound = size.width - child.size.width/2 - _kToolbarScreenPadding;
    final double adjustedCenterX = _arrowTipX.clamp(lowerBound, upperBound);

    childParentData.offset = Offset(adjustedCenterX - child.size.width / 2, _barTopY);
    childParentData.arrowXOffsetFromCenter = _arrowTipX - adjustedCenterX;
  }

  // The path is described in the toolbar's coordinate system.
  Path _clipPath() {
    final _ToolbarParentData childParentData = child.parentData;
    final Path rrect = Path()
      ..addRRect(
        RRect.fromRectAndRadius(
          Offset(0, _isArrowPointingDown ? 0 : _kToolbarArrowSize.height,)
          & Size(child.size.width, child.size.height - _kToolbarArrowSize.height),
          _kToolbarBorderRadius,
        ),
      );

    final double arrowTipX = child.size.width / 2 + childParentData.arrowXOffsetFromCenter;

    final double arrowBottomY = _isArrowPointingDown
      ? child.size.height - _kToolbarArrowSize.height
      : _kToolbarArrowSize.height;

    final double arrowTipY = _isArrowPointingDown ? child.size.height : 0;

    final Path arrow = Path()
      ..moveTo(arrowTipX, arrowTipY)
      ..lineTo(arrowTipX - _kToolbarArrowSize.width / 2, arrowBottomY)
      ..lineTo(arrowTipX + _kToolbarArrowSize.width / 2, arrowBottomY)
      ..close();

    return Path.combine(PathOperation.union, rrect, arrow);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child == null) {
      return;
    }

    final _ToolbarParentData childParentData = child.parentData;
    context.pushClipPath(
      needsCompositing,
      offset + childParentData.offset,
      Offset.zero & child.size,
      _clipPath(),
      (PaintingContext innerContext, Offset innerOffset) => innerContext.paintChild(child, innerOffset),
    );
  }

  Paint _debugPaint;

  @override
  void debugPaintSize(PaintingContext context, Offset offset) {
    assert(() {
      if (child == null) {
        return true;
      }

      _debugPaint ??= Paint()
      ..shader = ui.Gradient.linear(
        const Offset(0.0, 0.0),
        const Offset(10.0, 10.0),
        <Color>[const Color(0x00000000), const Color(0xFFFF00FF), const Color(0xFFFF00FF), const Color(0x00000000)],
        <double>[0.25, 0.25, 0.75, 0.75],
        TileMode.repeated,
      )
      ..strokeWidth = 2.0
      ..style = PaintingStyle.stroke;

      final _ToolbarParentData childParentData = child.parentData;
      context.canvas.drawPath(_clipPath().shift(offset + childParentData.offset), _debugPaint);
      return true;
    }());
  }
}

/// Draws a single text selection handle with a bar and a ball.
class _TextSelectionHandlePainter extends CustomPainter {
  const _TextSelectionHandlePainter(this.color);

  final Color color;

  @override
  void paint(Canvas canvas, Size size) {
    final Paint paint = Paint()
        ..color = color
        ..strokeWidth = 2.0;
    canvas.drawCircle(
      const Offset(_kSelectionHandleRadius, _kSelectionHandleRadius),
      _kSelectionHandleRadius,
      paint,
    );
    // Draw line so it slightly overlaps the circle.
    canvas.drawLine(
      const Offset(
        _kSelectionHandleRadius,
        2 * _kSelectionHandleRadius - _kSelectionHandleOverlap,
      ),
      Offset(
        _kSelectionHandleRadius,
        size.height,
      ),
      paint,
    );
  }

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

class _CupertinoTextSelectionControls extends TextSelectionControls {
  /// Returns the size of the Cupertino handle.
  @override
  Size getHandleSize(double textLineHeight) {
    return Size(
      _kSelectionHandleRadius * 2,
      textLineHeight + _kSelectionHandleRadius * 2 - _kSelectionHandleOverlap,
    );
  }

  /// Builder for iOS-style copy/paste text selection toolbar.
  @override
  Widget buildToolbar(
    BuildContext context,
    Rect globalEditableRegion,
    double textLineHeight,
    Offset position,
    List<TextSelectionPoint> endpoints,
    TextSelectionDelegate delegate,
  ) {
    assert(debugCheckHasMediaQuery(context));
    final MediaQueryData mediaQuery = MediaQuery.of(context);

    // The toolbar should appear below the TextField when there is not enough
    // space above the TextField to show it, assuming there's always enough space
    // at the bottom in this case.
    final double toolbarHeightNeeded = mediaQuery.padding.top
      + _kToolbarScreenPadding
      + _kToolbarHeight
      + _kToolbarContentDistance;
    final double availableHeight = globalEditableRegion.top + endpoints.first.point.dy - textLineHeight;
    final bool isArrowPointingDown = toolbarHeightNeeded <= availableHeight;

    final double arrowTipX = (position.dx + globalEditableRegion.left).clamp(
      _kArrowScreenPadding + mediaQuery.padding.left,
      mediaQuery.size.width - mediaQuery.padding.right - _kArrowScreenPadding,
    );

    // The y-coordinate has to be calculated instead of directly quoting postion.dy,
    // since the caller (TextSelectionOverlay._buildToolbar) does not know whether
    // the toolbar is going to be facing up or down.
    final double localBarTopY = isArrowPointingDown
      ? endpoints.first.point.dy - textLineHeight - _kToolbarContentDistance - _kToolbarHeight
      : endpoints.last.point.dy + _kToolbarContentDistance;

    final List<Widget> items = <Widget>[];
    final Widget onePhysicalPixelVerticalDivider =
    SizedBox(width: 1.0 / MediaQuery.of(context).devicePixelRatio);
    final CupertinoLocalizations localizations = CupertinoLocalizations.of(context);
    final EdgeInsets arrowPadding = isArrowPointingDown
      ? EdgeInsets.only(bottom: _kToolbarArrowSize.height)
      : EdgeInsets.only(top: _kToolbarArrowSize.height);

    void addToolbarButtonIfNeeded(
      String text,
      bool Function(TextSelectionDelegate) predicate,
      void Function(TextSelectionDelegate) onPressed,
    ) {
      if (!predicate(delegate)) {
        return;
      }

      if (items.isNotEmpty) {
        items.add(onePhysicalPixelVerticalDivider);
      }

      items.add(CupertinoButton(
        child: Text(text, style: _kToolbarButtonFontStyle),
        color: _kToolbarBackgroundColor,
        minSize: _kToolbarHeight,
        padding: _kToolbarButtonPadding.add(arrowPadding),
        borderRadius: null,
        pressedOpacity: 0.7,
        onPressed: () => onPressed(delegate),
      ));
    }

    addToolbarButtonIfNeeded(localizations.cutButtonLabel, canCut, handleCut);
    addToolbarButtonIfNeeded(localizations.copyButtonLabel, canCopy, handleCopy);
    addToolbarButtonIfNeeded(localizations.pasteButtonLabel, canPaste, handlePaste);
    addToolbarButtonIfNeeded(localizations.selectAllButtonLabel, canSelectAll, handleSelectAll);

    return CupertinoTextSelectionToolbar._(
      barTopY: localBarTopY + globalEditableRegion.top,
      arrowTipX: arrowTipX,
      isArrowPointingDown: isArrowPointingDown,
      child: items.isEmpty ? null : DecoratedBox(
        decoration: const BoxDecoration(color: _kToolbarDividerColor),
        child: Row(mainAxisSize: MainAxisSize.min, children: items),
      ),
    );
  }

  /// Builder for iOS text selection edges.
  @override
  Widget buildHandle(BuildContext context, TextSelectionHandleType type, double textLineHeight) {
    // We want a size that's a vertical line the height of the text plus a 18.0
    // padding in every direction that will constitute the selection drag area.
    final Size desiredSize = getHandleSize(textLineHeight);

    final Widget handle = SizedBox.fromSize(
      size: desiredSize,
      child: CustomPaint(
        painter: _TextSelectionHandlePainter(CupertinoTheme.of(context).primaryColor),
      ),
    );

    // [buildHandle]'s widget is positioned at the selection cursor's bottom
    // baseline. We transform the handle such that the SizedBox is superimposed
    // on top of the text selection endpoints.
    switch (type) {
      case TextSelectionHandleType.left:
        return handle;
      case TextSelectionHandleType.right:
        // Right handle is a vertical mirror of the left.
        return Transform(
          transform: Matrix4.identity()
            ..translate(desiredSize.width / 2, desiredSize.height / 2)
            ..rotateZ(math.pi)
            ..translate(-desiredSize.width / 2, -desiredSize.height / 2),
          child: handle,
        );
      // iOS doesn't draw anything for collapsed selections.
      case TextSelectionHandleType.collapsed:
        return const SizedBox();
    }
    assert(type != null);
    return null;
  }

  /// Gets anchor for cupertino-style text selection handles.
  ///
  /// See [TextSelectionControls.getHandleAnchor].
  @override
  Offset getHandleAnchor(TextSelectionHandleType type, double textLineHeight) {
    final Size handleSize = getHandleSize(textLineHeight);
    switch (type) {
      // The circle is at the top for the left handle, and the anchor point is
      // all the way at the bottom of the line.
      case TextSelectionHandleType.left:
        return Offset(
          handleSize.width / 2,
          handleSize.height,
        );
      // The right handle is vertically flipped, and the anchor point is near
      // the top of the circle to give slight overlap.
      case TextSelectionHandleType.right:
        return Offset(
          handleSize.width / 2,
          handleSize.height - 2 * _kSelectionHandleRadius + _kSelectionHandleOverlap,
        );
      // A collapsed handle anchors itself so that it's centered.
      default:
        return Offset(
          handleSize.width / 2,
          textLineHeight + (handleSize.height - textLineHeight) / 2,
        );
    }
  }
}

/// Text selection controls that follows iOS design conventions.
final TextSelectionControls cupertinoTextSelectionControls = _CupertinoTextSelectionControls();