// 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 'package:flutter/cupertino.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/rendering.dart';

import 'colors.dart';
import 'constants.dart';
import 'debug.dart';
import 'material_state.dart';
import 'shadows.dart';
import 'switch_theme.dart';
import 'theme.dart';
import 'theme_data.dart';
import 'toggleable.dart';

const double _kTrackHeight = 14.0;
const double _kTrackWidth = 33.0;
const double _kTrackRadius = _kTrackHeight / 2.0;
const double _kThumbRadius = 10.0;
const double _kSwitchMinSize = kMinInteractiveDimension - 8.0;
const double _kSwitchWidth = _kTrackWidth - 2 * _kTrackRadius + _kSwitchMinSize;
const double _kSwitchHeight = _kSwitchMinSize + 8.0;
const double _kSwitchHeightCollapsed = _kSwitchMinSize;

enum _SwitchType { material, adaptive }

/// A Material Design switch.
///
/// Used to toggle the on/off state of a single setting.
///
/// The switch itself does not maintain any state. Instead, when the state of
/// the switch changes, the widget calls the [onChanged] callback. Most widgets
/// that use a switch will listen for the [onChanged] callback and rebuild the
/// switch with a new [value] to update the visual appearance of the switch.
///
/// If the [onChanged] callback is null, then the switch will be disabled (it
/// will not respond to input). A disabled switch's thumb and track are rendered
/// in shades of grey by default. The default appearance of a disabled switch
/// can be overridden with [inactiveThumbColor] and [inactiveTrackColor].
///
/// Requires one of its ancestors to be a [Material] widget.
///
/// {@tool dartpad}
/// This example shows a toggleable [Switch]. When the thumb slides to the other
/// side of the track, the switch is toggled between on/off.
///
/// ** See code in examples/api/lib/material/switch/switch.0.dart **
/// {@end-tool}
///
/// {@tool dartpad}
/// This example shows how to customize [Switch] using [MaterialStateProperty]
/// switch properties.
///
/// ** See code in examples/api/lib/material/switch/switch.1.dart **
/// {@end-tool}
///
/// See also:
///
///  * [SwitchListTile], which combines this widget with a [ListTile] so that
///    you can give the switch a label.
///  * [Checkbox], another widget with similar semantics.
///  * [Radio], for selecting among a set of explicit values.
///  * [Slider], for selecting a value in a range.
///  * [MaterialStateProperty], an interface for objects that "resolve" to
///    different values depending on a widget's material state.
///  * <https://material.io/design/components/selection-controls.html#switches>
class Switch extends StatelessWidget {
  /// Creates a Material Design switch.
  ///
  /// The switch itself does not maintain any state. Instead, when the state of
  /// the switch changes, the widget calls the [onChanged] callback. Most widgets
  /// that use a switch will listen for the [onChanged] callback and rebuild the
  /// switch with a new [value] to update the visual appearance of the switch.
  ///
  /// The following arguments are required:
  ///
  /// * [value] determines whether this switch is on or off.
  /// * [onChanged] is called when the user toggles the switch on or off.
  const Switch({
    super.key,
    required this.value,
    required this.onChanged,
    this.activeColor,
    this.activeTrackColor,
    this.inactiveThumbColor,
    this.inactiveTrackColor,
    this.activeThumbImage,
    this.onActiveThumbImageError,
    this.inactiveThumbImage,
    this.onInactiveThumbImageError,
    this.thumbColor,
    this.trackColor,
    this.materialTapTargetSize,
    this.dragStartBehavior = DragStartBehavior.start,
    this.mouseCursor,
    this.focusColor,
    this.hoverColor,
    this.overlayColor,
    this.splashRadius,
    this.focusNode,
    this.autofocus = false,
  })  : _switchType = _SwitchType.material,
        assert(dragStartBehavior != null),
        assert(activeThumbImage != null || onActiveThumbImageError == null),
        assert(inactiveThumbImage != null || onInactiveThumbImageError == null);

  /// Creates an adaptive [Switch] based on whether the target platform is iOS
  /// or macOS, following Material design's
  /// [Cross-platform guidelines](https://material.io/design/platform-guidance/cross-platform-adaptation.html).
  ///
  /// On iOS and macOS, this constructor creates a [CupertinoSwitch], which has
  /// matching functionality and presentation as Material switches, and are the
  /// graphics expected on iOS. On other platforms, this creates a Material
  /// design [Switch].
  ///
  /// If a [CupertinoSwitch] is created, the following parameters are ignored:
  /// [activeTrackColor], [inactiveThumbColor], [inactiveTrackColor],
  /// [activeThumbImage], [onActiveThumbImageError], [inactiveThumbImage],
  /// [onInactiveThumbImageError], [materialTapTargetSize].
  ///
  /// The target platform is based on the current [Theme]: [ThemeData.platform].
  const Switch.adaptive({
    super.key,
    required this.value,
    required this.onChanged,
    this.activeColor,
    this.activeTrackColor,
    this.inactiveThumbColor,
    this.inactiveTrackColor,
    this.activeThumbImage,
    this.onActiveThumbImageError,
    this.inactiveThumbImage,
    this.onInactiveThumbImageError,
    this.materialTapTargetSize,
    this.thumbColor,
    this.trackColor,
    this.dragStartBehavior = DragStartBehavior.start,
    this.mouseCursor,
    this.focusColor,
    this.hoverColor,
    this.overlayColor,
    this.splashRadius,
    this.focusNode,
    this.autofocus = false,
  })  : assert(autofocus != null),
        assert(activeThumbImage != null || onActiveThumbImageError == null),
        assert(inactiveThumbImage != null || onInactiveThumbImageError == null),
        _switchType = _SwitchType.adaptive;

  /// Whether this switch is on or off.
  ///
  /// This property must not be null.
  final bool value;

  /// Called when the user toggles the switch on or off.
  ///
  /// The switch passes the new value to the callback but does not actually
  /// change state until the parent widget rebuilds the switch with the new
  /// value.
  ///
  /// If null, the switch will be displayed as disabled.
  ///
  /// The callback provided to [onChanged] should update the state of the parent
  /// [StatefulWidget] using the [State.setState] method, so that the parent
  /// gets rebuilt; for example:
  ///
  /// ```dart
  /// Switch(
  ///   value: _giveVerse,
  ///   onChanged: (bool newValue) {
  ///     setState(() {
  ///       _giveVerse = newValue;
  ///     });
  ///   },
  /// )
  /// ```
  final ValueChanged<bool>? onChanged;

  /// The color to use when this switch is on.
  ///
  /// Defaults to [ColorScheme.secondary].
  ///
  /// If [thumbColor] returns a non-null color in the [MaterialState.selected]
  /// state, it will be used instead of this color.
  final Color? activeColor;

  /// The color to use on the track when this switch is on.
  ///
  /// Defaults to [ColorScheme.secondary] with the opacity set at 50%.
  ///
  /// Ignored if this switch is created with [Switch.adaptive].
  ///
  /// If [trackColor] returns a non-null color in the [MaterialState.selected]
  /// state, it will be used instead of this color.
  final Color? activeTrackColor;

  /// The color to use on the thumb when this switch is off.
  ///
  /// Defaults to the colors described in the Material design specification.
  ///
  /// Ignored if this switch is created with [Switch.adaptive].
  ///
  /// If [thumbColor] returns a non-null color in the default state, it will be
  /// used instead of this color.
  final Color? inactiveThumbColor;

  /// The color to use on the track when this switch is off.
  ///
  /// Defaults to the colors described in the Material design specification.
  ///
  /// Ignored if this switch is created with [Switch.adaptive].
  ///
  /// If [trackColor] returns a non-null color in the default state, it will be
  /// used instead of this color.
  final Color? inactiveTrackColor;

  /// An image to use on the thumb of this switch when the switch is on.
  ///
  /// Ignored if this switch is created with [Switch.adaptive].
  final ImageProvider? activeThumbImage;

  /// An optional error callback for errors emitted when loading
  /// [activeThumbImage].
  final ImageErrorListener? onActiveThumbImageError;

  /// An image to use on the thumb of this switch when the switch is off.
  ///
  /// Ignored if this switch is created with [Switch.adaptive].
  final ImageProvider? inactiveThumbImage;

  /// An optional error callback for errors emitted when loading
  /// [inactiveThumbImage].
  final ImageErrorListener? onInactiveThumbImageError;

  /// {@template flutter.material.switch.thumbColor}
  /// The color of this [Switch]'s thumb.
  ///
  /// Resolved in the following states:
  ///  * [MaterialState.selected].
  ///  * [MaterialState.hovered].
  ///  * [MaterialState.focused].
  ///  * [MaterialState.disabled].
  ///
  /// {@tool snippet}
  /// This example resolves the [thumbColor] based on the current
  /// [MaterialState] of the [Switch], providing a different [Color] when it is
  /// [MaterialState.disabled].
  ///
  /// ```dart
  /// Switch(
  ///   value: true,
  ///   onChanged: (_) => true,
  ///   thumbColor: MaterialStateProperty.resolveWith<Color>((Set<MaterialState> states) {
  ///     if (states.contains(MaterialState.disabled)) {
  ///       return Colors.orange.withOpacity(.48);
  ///     }
  ///     return Colors.orange;
  ///   }),
  /// )
  /// ```
  /// {@end-tool}
  /// {@endtemplate}
  ///
  /// If null, then the value of [activeColor] is used in the selected
  /// state and [inactiveThumbColor] in the default state. If that is also null,
  /// then the value of [SwitchThemeData.thumbColor] is used. If that is also
  /// null, then the following colors are used:
  ///
  /// | State    | Light theme                       | Dark theme                        |
  /// |----------|-----------------------------------|-----------------------------------|
  /// | Default  | `Colors.grey.shade50`             | `Colors.grey.shade400`            |
  /// | Selected | [ColorScheme.secondary] | [ColorScheme.secondary] |
  /// | Disabled | `Colors.grey.shade400`            | `Colors.grey.shade800`            |
  final MaterialStateProperty<Color?>? thumbColor;

  /// {@template flutter.material.switch.trackColor}
  /// The color of this [Switch]'s track.
  ///
  /// Resolved in the following states:
  ///  * [MaterialState.selected].
  ///  * [MaterialState.hovered].
  ///  * [MaterialState.focused].
  ///  * [MaterialState.disabled].
  ///
  /// {@tool snippet}
  /// This example resolves the [trackColor] based on the current
  /// [MaterialState] of the [Switch], providing a different [Color] when it is
  /// [MaterialState.disabled].
  ///
  /// ```dart
  /// Switch(
  ///   value: true,
  ///   onChanged: (_) => true,
  ///   thumbColor: MaterialStateProperty.resolveWith<Color>((Set<MaterialState> states) {
  ///     if (states.contains(MaterialState.disabled)) {
  ///       return Colors.orange.withOpacity(.48);
  ///     }
  ///     return Colors.orange;
  ///   }),
  /// )
  /// ```
  /// {@end-tool}
  /// {@endtemplate}
  ///
  /// If null, then the value of [activeTrackColor] is used in the selected
  /// state and [inactiveTrackColor] in the default state. If that is also null,
  /// then the value of [SwitchThemeData.trackColor] is used. If that is also
  /// null, then the following colors are used:
  ///
  /// | State    | Light theme                     | Dark theme                      |
  /// |----------|---------------------------------|---------------------------------|
  /// | Default  | `Color(0x52000000)`             | `Colors.white30`                |
  /// | Selected | [activeColor] with alpha `0x80` | [activeColor] with alpha `0x80` |
  /// | Disabled | `Colors.black12`                | `Colors.white10`                |
  final MaterialStateProperty<Color?>? trackColor;

  /// {@template flutter.material.switch.materialTapTargetSize}
  /// Configures the minimum size of the tap target.
  /// {@endtemplate}
  ///
  /// If null, then the value of [SwitchThemeData.materialTapTargetSize] is
  /// used. If that is also null, then the value of
  /// [ThemeData.materialTapTargetSize] is used.
  ///
  /// See also:
  ///
  ///  * [MaterialTapTargetSize], for a description of how this affects tap targets.
  final MaterialTapTargetSize? materialTapTargetSize;

  final _SwitchType _switchType;

  /// {@macro flutter.cupertino.CupertinoSwitch.dragStartBehavior}
  final DragStartBehavior dragStartBehavior;

  /// {@template flutter.material.switch.mouseCursor}
  /// The cursor for a mouse pointer when it enters or is hovering over the
  /// widget.
  ///
  /// If [mouseCursor] is a [MaterialStateProperty<MouseCursor>],
  /// [MaterialStateProperty.resolve] is used for the following [MaterialState]s:
  ///
  ///  * [MaterialState.selected].
  ///  * [MaterialState.hovered].
  ///  * [MaterialState.focused].
  ///  * [MaterialState.disabled].
  /// {@endtemplate}
  ///
  /// If null, then the value of [SwitchThemeData.mouseCursor] is used. If that
  /// is also null, then [MaterialStateMouseCursor.clickable] is used.
  ///
  /// See also:
  ///
  ///  * [MaterialStateMouseCursor], a [MouseCursor] that implements
  ///    `MaterialStateProperty` which is used in APIs that need to accept
  ///    either a [MouseCursor] or a [MaterialStateProperty<MouseCursor>].
  final MouseCursor? mouseCursor;

  /// The color for the button's [Material] when it has the input focus.
  ///
  /// If [overlayColor] returns a non-null color in the [MaterialState.focused]
  /// state, it will be used instead.
  ///
  /// If null, then the value of [SwitchThemeData.overlayColor] is used in the
  /// focused state. If that is also null, then the value of
  /// [ThemeData.focusColor] is used.
  final Color? focusColor;

  /// The color for the button's [Material] when a pointer is hovering over it.
  ///
  /// If [overlayColor] returns a non-null color in the [MaterialState.hovered]
  /// state, it will be used instead.
  ///
  /// If null, then the value of [SwitchThemeData.overlayColor] is used in the
  /// hovered state. If that is also null, then the value of
  /// [ThemeData.hoverColor] is used.
  final Color? hoverColor;

  /// {@template flutter.material.switch.overlayColor}
  /// The color for the switch's [Material].
  ///
  /// Resolves in the following states:
  ///  * [MaterialState.pressed].
  ///  * [MaterialState.selected].
  ///  * [MaterialState.hovered].
  ///  * [MaterialState.focused].
  /// {@endtemplate}
  ///
  /// If null, then the value of [activeColor] with alpha
  /// [kRadialReactionAlpha], [focusColor] and [hoverColor] is used in the
  /// pressed, focused and hovered state. If that is also null,
  /// the value of [SwitchThemeData.overlayColor] is used. If that is
  /// also null, then the value of [ColorScheme.secondary] with alpha
  /// [kRadialReactionAlpha], [ThemeData.focusColor] and [ThemeData.hoverColor]
  /// is used in the pressed, focused and hovered state.
  final MaterialStateProperty<Color?>? overlayColor;

  /// {@template flutter.material.switch.splashRadius}
  /// The splash radius of the circular [Material] ink response.
  /// {@endtemplate}
  ///
  /// If null, then the value of [SwitchThemeData.splashRadius] is used. If that
  /// is also null, then [kRadialReactionRadius] is used.
  final double? splashRadius;

  /// {@macro flutter.widgets.Focus.focusNode}
  final FocusNode? focusNode;

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

  Size _getSwitchSize(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final SwitchThemeData switchTheme = SwitchTheme.of(context);

    final MaterialTapTargetSize effectiveMaterialTapTargetSize = materialTapTargetSize
      ?? switchTheme.materialTapTargetSize
      ?? theme.materialTapTargetSize;
    switch (effectiveMaterialTapTargetSize) {
      case MaterialTapTargetSize.padded:
        return const Size(_kSwitchWidth, _kSwitchHeight);
      case MaterialTapTargetSize.shrinkWrap:
        return const Size(_kSwitchWidth, _kSwitchHeightCollapsed);
    }
  }

  Widget _buildCupertinoSwitch(BuildContext context) {
    final Size size = _getSwitchSize(context);
    return Focus(
      focusNode: focusNode,
      autofocus: autofocus,
      child: Container(
        width: size.width, // Same size as the Material switch.
        height: size.height,
        alignment: Alignment.center,
        child: CupertinoSwitch(
            dragStartBehavior: dragStartBehavior,
            value: value,
            onChanged: onChanged,
            activeColor: activeColor,
            trackColor: inactiveTrackColor,
        ),
      ),
    );
  }

  Widget _buildMaterialSwitch(BuildContext context) {
    return _MaterialSwitch(
      value: value,
      onChanged: onChanged,
      size: _getSwitchSize(context),
      activeColor: activeColor,
      activeTrackColor: activeTrackColor,
      inactiveThumbColor: inactiveThumbColor,
      inactiveTrackColor: inactiveTrackColor,
      activeThumbImage: activeThumbImage,
      onActiveThumbImageError: onActiveThumbImageError,
      inactiveThumbImage: inactiveThumbImage,
      onInactiveThumbImageError: onInactiveThumbImageError,
      thumbColor: thumbColor,
      trackColor: trackColor,
      materialTapTargetSize: materialTapTargetSize,
      dragStartBehavior: dragStartBehavior,
      mouseCursor: mouseCursor,
      focusColor: focusColor,
      hoverColor: hoverColor,
      overlayColor: overlayColor,
      splashRadius: splashRadius,
      focusNode: focusNode,
      autofocus: autofocus,
    );
  }

  @override
  Widget build(BuildContext context) {
    switch (_switchType) {
      case _SwitchType.material:
        return _buildMaterialSwitch(context);

      case _SwitchType.adaptive: {
        final ThemeData theme = Theme.of(context);
        assert(theme.platform != null);
        switch (theme.platform) {
          case TargetPlatform.android:
          case TargetPlatform.fuchsia:
          case TargetPlatform.linux:
          case TargetPlatform.windows:
            return _buildMaterialSwitch(context);
          case TargetPlatform.iOS:
          case TargetPlatform.macOS:
            return _buildCupertinoSwitch(context);
        }
      }
    }
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(FlagProperty('value', value: value, ifTrue: 'on', ifFalse: 'off', showName: true));
    properties.add(ObjectFlagProperty<ValueChanged<bool>>('onChanged', onChanged, ifNull: 'disabled'));
  }
}

class _MaterialSwitch extends StatefulWidget {
  const _MaterialSwitch({
    required this.value,
    required this.onChanged,
    required this.size,
    this.activeColor,
    this.activeTrackColor,
    this.inactiveThumbColor,
    this.inactiveTrackColor,
    this.activeThumbImage,
    this.onActiveThumbImageError,
    this.inactiveThumbImage,
    this.onInactiveThumbImageError,
    this.thumbColor,
    this.trackColor,
    this.materialTapTargetSize,
    this.dragStartBehavior = DragStartBehavior.start,
    this.mouseCursor,
    this.focusColor,
    this.hoverColor,
    this.overlayColor,
    this.splashRadius,
    this.focusNode,
    this.autofocus = false,
  })  : assert(dragStartBehavior != null),
        assert(activeThumbImage != null || onActiveThumbImageError == null),
        assert(inactiveThumbImage != null || onInactiveThumbImageError == null);

  final bool value;
  final ValueChanged<bool>? onChanged;
  final Color? activeColor;
  final Color? activeTrackColor;
  final Color? inactiveThumbColor;
  final Color? inactiveTrackColor;
  final ImageProvider? activeThumbImage;
  final ImageErrorListener? onActiveThumbImageError;
  final ImageProvider? inactiveThumbImage;
  final ImageErrorListener? onInactiveThumbImageError;
  final MaterialStateProperty<Color?>? thumbColor;
  final MaterialStateProperty<Color?>? trackColor;
  final MaterialTapTargetSize? materialTapTargetSize;
  final DragStartBehavior dragStartBehavior;
  final MouseCursor? mouseCursor;
  final Color? focusColor;
  final Color? hoverColor;
  final MaterialStateProperty<Color?>? overlayColor;
  final double? splashRadius;
  final FocusNode? focusNode;
  final bool autofocus;
  final Size size;

  @override
  State<StatefulWidget> createState() => _MaterialSwitchState();
}

class _MaterialSwitchState extends State<_MaterialSwitch> with TickerProviderStateMixin, ToggleableStateMixin {
  final _SwitchPainter _painter = _SwitchPainter();

  @override
  void didUpdateWidget(_MaterialSwitch oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.value != widget.value) {
      // During a drag we may have modified the curve, reset it if its possible
      // to do without visual discontinuation.
      if (position.value == 0.0 || position.value == 1.0) {
        position
          ..curve = Curves.easeIn
          ..reverseCurve = Curves.easeOut;
      }
      animateToValue();
    }
  }

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

  @override
  ValueChanged<bool?>? get onChanged => widget.onChanged != null ? _handleChanged : null;

  @override
  bool get tristate => false;

  @override
  bool? get value => widget.value;

  MaterialStateProperty<Color?> get _widgetThumbColor {
    return MaterialStateProperty.resolveWith((Set<MaterialState> states) {
      if (states.contains(MaterialState.disabled)) {
        return widget.inactiveThumbColor;
      }
      if (states.contains(MaterialState.selected)) {
        return widget.activeColor;
      }
      return widget.inactiveThumbColor;
    });
  }

  MaterialStateProperty<Color> get _defaultThumbColor {
    final ThemeData theme = Theme.of(context);
    final bool isDark = theme.brightness == Brightness.dark;

    return MaterialStateProperty.resolveWith((Set<MaterialState> states) {
      if (states.contains(MaterialState.disabled)) {
        return isDark ? Colors.grey.shade800 : Colors.grey.shade400;
      }
      if (states.contains(MaterialState.selected)) {
        return theme.colorScheme.secondary;
      }
      return isDark ? Colors.grey.shade400 : Colors.grey.shade50;
    });
  }

  MaterialStateProperty<Color?> get _widgetTrackColor {
    return MaterialStateProperty.resolveWith((Set<MaterialState> states) {
      if (states.contains(MaterialState.disabled)) {
        return widget.inactiveTrackColor;
      }
      if (states.contains(MaterialState.selected)) {
        return widget.activeTrackColor;
      }
      return widget.inactiveTrackColor;
    });
  }

  MaterialStateProperty<Color> get _defaultTrackColor {
    final ThemeData theme = Theme.of(context);
    final bool isDark = theme.brightness == Brightness.dark;
    const Color black32 = Color(0x52000000); // Black with 32% opacity

    return MaterialStateProperty.resolveWith((Set<MaterialState> states) {
      if (states.contains(MaterialState.disabled)) {
        return isDark ? Colors.white10 : Colors.black12;
      }
      if (states.contains(MaterialState.selected)) {
        final Set<MaterialState> activeState = states..add(MaterialState.selected);
        final Color activeColor = _widgetThumbColor.resolve(activeState) ?? _defaultThumbColor.resolve(activeState);
        return activeColor.withAlpha(0x80);
      }
      return isDark ? Colors.white30 : black32;
    });
  }

  double get _trackInnerLength => widget.size.width - _kSwitchMinSize;

  void _handleDragStart(DragStartDetails details) {
    if (isInteractive) {
      reactionController.forward();
    }
  }

  void _handleDragUpdate(DragUpdateDetails details) {
    if (isInteractive) {
      position
        ..curve = Curves.linear
        ..reverseCurve = null;
      final double delta = details.primaryDelta! / _trackInnerLength;
      switch (Directionality.of(context)) {
        case TextDirection.rtl:
          positionController.value -= delta;
          break;
        case TextDirection.ltr:
          positionController.value += delta;
          break;
      }
    }
  }

  bool _needsPositionAnimation = false;

  void _handleDragEnd(DragEndDetails details) {
    if (position.value >= 0.5 != widget.value) {
      widget.onChanged!(!widget.value);
      // Wait with finishing the animation until widget.value has changed to
      // !widget.value as part of the widget.onChanged call above.
      setState(() {
        _needsPositionAnimation = true;
      });
    } else {
      animateToValue();
    }
    reactionController.reverse();

  }

  void _handleChanged(bool? value) {
    assert(value != null);
    assert(widget.onChanged != null);
    widget.onChanged!(value!);
  }

  @override
  Widget build(BuildContext context) {
    assert(debugCheckHasMaterial(context));

    if (_needsPositionAnimation) {
      _needsPositionAnimation = false;
      animateToValue();
    }

    final ThemeData theme = Theme.of(context);
    final SwitchThemeData switchTheme = SwitchTheme.of(context);

    // Colors need to be resolved in selected and non selected states separately
    // so that they can be lerped between.
    final Set<MaterialState> activeStates = states..add(MaterialState.selected);
    final Set<MaterialState> inactiveStates = states..remove(MaterialState.selected);
    final Color effectiveActiveThumbColor = widget.thumbColor?.resolve(activeStates)
      ?? _widgetThumbColor.resolve(activeStates)
      ?? switchTheme.thumbColor?.resolve(activeStates)
      ?? _defaultThumbColor.resolve(activeStates);
    final Color effectiveInactiveThumbColor = widget.thumbColor?.resolve(inactiveStates)
      ?? _widgetThumbColor.resolve(inactiveStates)
      ?? switchTheme.thumbColor?.resolve(inactiveStates)
      ?? _defaultThumbColor.resolve(inactiveStates);
    final Color effectiveActiveTrackColor = widget.trackColor?.resolve(activeStates)
      ?? _widgetTrackColor.resolve(activeStates)
      ?? switchTheme.trackColor?.resolve(activeStates)
      ?? _defaultTrackColor.resolve(activeStates);
    final Color effectiveInactiveTrackColor = widget.trackColor?.resolve(inactiveStates)
      ?? _widgetTrackColor.resolve(inactiveStates)
      ?? switchTheme.trackColor?.resolve(inactiveStates)
      ?? _defaultTrackColor.resolve(inactiveStates);

    final Set<MaterialState> focusedStates = states..add(MaterialState.focused);
    final Color effectiveFocusOverlayColor = widget.overlayColor?.resolve(focusedStates)
      ?? widget.focusColor
      ?? switchTheme.overlayColor?.resolve(focusedStates)
      ?? theme.focusColor;

    final Set<MaterialState> hoveredStates = states..add(MaterialState.hovered);
    final Color effectiveHoverOverlayColor = widget.overlayColor?.resolve(hoveredStates)
        ?? widget.hoverColor
        ?? switchTheme.overlayColor?.resolve(hoveredStates)
        ?? theme.hoverColor;

    final Set<MaterialState> activePressedStates = activeStates..add(MaterialState.pressed);
    final Color effectiveActivePressedOverlayColor = widget.overlayColor?.resolve(activePressedStates)
        ?? switchTheme.overlayColor?.resolve(activePressedStates)
        ?? effectiveActiveThumbColor.withAlpha(kRadialReactionAlpha);

    final Set<MaterialState> inactivePressedStates = inactiveStates..add(MaterialState.pressed);
    final Color effectiveInactivePressedOverlayColor = widget.overlayColor?.resolve(inactivePressedStates)
        ?? switchTheme.overlayColor?.resolve(inactivePressedStates)
        ?? effectiveInactiveThumbColor.withAlpha(kRadialReactionAlpha);

    final MaterialStateProperty<MouseCursor> effectiveMouseCursor = MaterialStateProperty.resolveWith<MouseCursor>((Set<MaterialState> states) {
      return MaterialStateProperty.resolveAs<MouseCursor?>(widget.mouseCursor, states)
        ?? switchTheme.mouseCursor?.resolve(states)
        ?? MaterialStateProperty.resolveAs<MouseCursor>(MaterialStateMouseCursor.clickable, states);
    });

    return Semantics(
      toggled: widget.value,
      child: GestureDetector(
        excludeFromSemantics: true,
        onHorizontalDragStart: _handleDragStart,
        onHorizontalDragUpdate: _handleDragUpdate,
        onHorizontalDragEnd: _handleDragEnd,
        dragStartBehavior: widget.dragStartBehavior,
        child: buildToggleable(
          mouseCursor: effectiveMouseCursor,
          focusNode: widget.focusNode,
          autofocus: widget.autofocus,
          size: widget.size,
          painter: _painter
            ..position = position
            ..reaction = reaction
            ..reactionFocusFade = reactionFocusFade
            ..reactionHoverFade = reactionHoverFade
            ..inactiveReactionColor = effectiveInactivePressedOverlayColor
            ..reactionColor = effectiveActivePressedOverlayColor
            ..hoverColor = effectiveHoverOverlayColor
            ..focusColor = effectiveFocusOverlayColor
            ..splashRadius = widget.splashRadius ?? switchTheme.splashRadius ?? kRadialReactionRadius
            ..downPosition = downPosition
            ..isFocused = states.contains(MaterialState.focused)
            ..isHovered = states.contains(MaterialState.hovered)
            ..activeColor = effectiveActiveThumbColor
            ..inactiveColor = effectiveInactiveThumbColor
            ..activeThumbImage = widget.activeThumbImage
            ..onActiveThumbImageError = widget.onActiveThumbImageError
            ..inactiveThumbImage = widget.inactiveThumbImage
            ..onInactiveThumbImageError = widget.onInactiveThumbImageError
            ..activeTrackColor = effectiveActiveTrackColor
            ..inactiveTrackColor = effectiveInactiveTrackColor
            ..configuration = createLocalImageConfiguration(context)
            ..isInteractive = isInteractive
            ..trackInnerLength = _trackInnerLength
            ..textDirection = Directionality.of(context)
            ..surfaceColor = theme.colorScheme.surface,
        ),
      ),
    );
  }
}

class _SwitchPainter extends ToggleablePainter {
  ImageProvider? get activeThumbImage => _activeThumbImage;
  ImageProvider? _activeThumbImage;
  set activeThumbImage(ImageProvider? value) {
    if (value == _activeThumbImage) {
      return;
    }
    _activeThumbImage = value;
    notifyListeners();
  }

  ImageErrorListener? get onActiveThumbImageError => _onActiveThumbImageError;
  ImageErrorListener? _onActiveThumbImageError;
  set onActiveThumbImageError(ImageErrorListener? value) {
    if (value == _onActiveThumbImageError) {
      return;
    }
    _onActiveThumbImageError = value;
    notifyListeners();
  }

  ImageProvider? get inactiveThumbImage => _inactiveThumbImage;
  ImageProvider? _inactiveThumbImage;
  set inactiveThumbImage(ImageProvider? value) {
    if (value == _inactiveThumbImage) {
      return;
    }
    _inactiveThumbImage = value;
    notifyListeners();
  }

  ImageErrorListener? get onInactiveThumbImageError => _onInactiveThumbImageError;
  ImageErrorListener? _onInactiveThumbImageError;
  set onInactiveThumbImageError(ImageErrorListener? value) {
    if (value == _onInactiveThumbImageError) {
      return;
    }
    _onInactiveThumbImageError = value;
    notifyListeners();
  }

  Color get activeTrackColor => _activeTrackColor!;
  Color? _activeTrackColor;
  set activeTrackColor(Color value) {
    assert(value != null);
    if (value == _activeTrackColor) {
      return;
    }
    _activeTrackColor = value;
    notifyListeners();
  }

  Color get inactiveTrackColor => _inactiveTrackColor!;
  Color? _inactiveTrackColor;
  set inactiveTrackColor(Color value) {
    assert(value != null);
    if (value == _inactiveTrackColor) {
      return;
    }
    _inactiveTrackColor = value;
    notifyListeners();
  }

  ImageConfiguration get configuration => _configuration!;
  ImageConfiguration? _configuration;
  set configuration(ImageConfiguration value) {
    assert(value != null);
    if (value == _configuration) {
      return;
    }
    _configuration = value;
    notifyListeners();
  }

  TextDirection get textDirection => _textDirection!;
  TextDirection? _textDirection;
  set textDirection(TextDirection value) {
    assert(value != null);
    if (_textDirection == value) {
      return;
    }
    _textDirection = value;
    notifyListeners();
  }

  Color get surfaceColor => _surfaceColor!;
  Color? _surfaceColor;
  set surfaceColor(Color value) {
    assert(value != null);
    if (value == _surfaceColor) {
      return;
    }
    _surfaceColor = value;
    notifyListeners();
  }

  bool get isInteractive => _isInteractive!;
  bool? _isInteractive;
  set isInteractive(bool value) {
    if (value == _isInteractive) {
      return;
    }
    _isInteractive = value;
    notifyListeners();
  }

  double get trackInnerLength => _trackInnerLength!;
  double? _trackInnerLength;
  set trackInnerLength(double value) {
    if (value == _trackInnerLength) {
      return;
    }
    _trackInnerLength = value;
    notifyListeners();
  }

  Color? _cachedThumbColor;
  ImageProvider? _cachedThumbImage;
  ImageErrorListener? _cachedThumbErrorListener;
  BoxPainter? _cachedThumbPainter;

  BoxDecoration _createDefaultThumbDecoration(Color color, ImageProvider? image, ImageErrorListener? errorListener) {
    return BoxDecoration(
      color: color,
      image: image == null ? null : DecorationImage(image: image, onError: errorListener),
      shape: BoxShape.circle,
      boxShadow: kElevationToShadow[1],
    );
  }

  bool _isPainting = false;

  void _handleDecorationChanged() {
    // If the image decoration is available synchronously, we'll get called here
    // during paint. There's no reason to mark ourselves as needing paint if we
    // are already in the middle of painting. (In fact, doing so would trigger
    // an assert).
    if (!_isPainting) {
      notifyListeners();
    }
  }

  @override
  void paint(Canvas canvas, Size size) {
    final bool isEnabled = isInteractive;
    final double currentValue = position.value;

    final double visualPosition;
    switch (textDirection) {
      case TextDirection.rtl:
        visualPosition = 1.0 - currentValue;
        break;
      case TextDirection.ltr:
        visualPosition = currentValue;
        break;
    }

    final Color trackColor = Color.lerp(inactiveTrackColor, activeTrackColor, currentValue)!;
    final Color lerpedThumbColor = Color.lerp(inactiveColor, activeColor, currentValue)!;
    // Blend the thumb color against a `surfaceColor` background in case the
    // thumbColor is not opaque. This way we do not see through the thumb to the
    // track underneath.
    final Color thumbColor = Color.alphaBlend(lerpedThumbColor, surfaceColor);

    final ImageProvider? thumbImage = isEnabled
      ? (currentValue < 0.5 ? inactiveThumbImage : activeThumbImage)
      : inactiveThumbImage;

    final ImageErrorListener? thumbErrorListener = isEnabled
      ? (currentValue < 0.5 ? onInactiveThumbImageError : onActiveThumbImageError)
      : onInactiveThumbImageError;

    final Paint paint = Paint()
      ..color = trackColor;

    final Offset trackPaintOffset = _computeTrackPaintOffset(size, _kTrackWidth, _kTrackHeight);
    final Offset thumbPaintOffset = _computeThumbPaintOffset(trackPaintOffset, visualPosition);
    final Offset radialReactionOrigin = Offset(thumbPaintOffset.dx + _kThumbRadius, size.height / 2);

    _paintTrackWith(canvas, paint, trackPaintOffset);
    paintRadialReaction(canvas: canvas, origin: radialReactionOrigin);
    _paintThumbWith(
      thumbPaintOffset,
      canvas,
      currentValue,
      thumbColor,
      thumbImage,
      thumbErrorListener,
    );
  }

  /// Computes canvas offset for track's upper left corner
  Offset _computeTrackPaintOffset(Size canvasSize, double trackWidth, double trackHeight) {
    final double horizontalOffset = (canvasSize.width - _kTrackWidth) / 2.0;
    final double verticalOffset = (canvasSize.height - _kTrackHeight) / 2.0;

    return Offset(horizontalOffset, verticalOffset);
  }

  /// Computes canvas offset for thumb's upper left corner as if it were a
  /// square
  Offset _computeThumbPaintOffset(Offset trackPaintOffset, double visualPosition) {
    // How much thumb radius extends beyond the track
    const double additionalThumbRadius = _kThumbRadius - _kTrackRadius;

    final double horizontalProgress = visualPosition * trackInnerLength;
    final double thumbHorizontalOffset = trackPaintOffset.dx - additionalThumbRadius + horizontalProgress;
    final double thumbVerticalOffset = trackPaintOffset.dy - additionalThumbRadius;

    return Offset(thumbHorizontalOffset, thumbVerticalOffset);
  }

  void _paintTrackWith(Canvas canvas, Paint paint, Offset trackPaintOffset) {
    final Rect trackRect = Rect.fromLTWH(
      trackPaintOffset.dx,
      trackPaintOffset.dy,
      _kTrackWidth,
      _kTrackHeight,
    );
    final RRect trackRRect = RRect.fromRectAndRadius(
      trackRect,
      const Radius.circular(_kTrackRadius),
    );

    canvas.drawRRect(trackRRect, paint);
  }

  void _paintThumbWith(
    Offset thumbPaintOffset,
    Canvas canvas,
    double currentValue,
    Color thumbColor,
    ImageProvider? thumbImage,
    ImageErrorListener? thumbErrorListener,
  ) {
    try {
      _isPainting = true;
      if (_cachedThumbPainter == null || thumbColor != _cachedThumbColor || thumbImage != _cachedThumbImage || thumbErrorListener != _cachedThumbErrorListener) {
        _cachedThumbColor = thumbColor;
        _cachedThumbImage = thumbImage;
        _cachedThumbErrorListener = thumbErrorListener;
        _cachedThumbPainter?.dispose();
        _cachedThumbPainter = _createDefaultThumbDecoration(thumbColor, thumbImage, thumbErrorListener).createBoxPainter(_handleDecorationChanged);
      }
      final BoxPainter thumbPainter = _cachedThumbPainter!;

      // The thumb contracts slightly during the animation
      final double inset = 1.0 - (currentValue - 0.5).abs() * 2.0;
      final double radius = _kThumbRadius - inset;

      thumbPainter.paint(
        canvas,
        thumbPaintOffset + Offset(0, inset),
        configuration.copyWith(size: Size.fromRadius(radius)),
      );
    } finally {
      _isPainting = false;
    }
  }

  @override
  void dispose() {
    _cachedThumbPainter?.dispose();
    _cachedThumbPainter = null;
    _cachedThumbColor = null;
    _cachedThumbImage = null;
    _cachedThumbErrorListener = null;
    super.dispose();
  }
}
