packages/flutter/lib/src/material/scrollbar_theme.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:ui' show lerpDouble;

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

import 'material_state.dart';
import 'theme.dart';

/// Defines default property values for descendant [Scrollbar] widgets.
///
/// Descendant widgets obtain the current [ScrollbarThemeData] object with
/// `ScrollbarTheme.of(context)`. Instances of [ScrollbarThemeData] can be customized
/// with [ScrollbarThemeData.copyWith].
///
/// Typically the [ScrollbarThemeData] of a [ScrollbarTheme] is specified as part of the overall
/// [Theme] with [ThemeData.scrollbarTheme].
///
/// All [ScrollbarThemeData] properties are `null` by default. When null, the [Scrollbar]
/// computes its own default values, typically based on the overall theme's
/// [ThemeData.colorScheme].
///
/// See also:
///
///  * [ThemeData], which describes the overall theme information for the
///    application.
@immutable
class ScrollbarThemeData with Diagnosticable {
  /// Creates a theme that can be used for [ThemeData.scrollbarTheme].
  const ScrollbarThemeData({
    this.thickness,
    this.showTrackOnHover,
    this.isAlwaysShown,
    this.radius,
    this.thumbColor,
    this.trackColor,
    this.trackBorderColor,
    this.crossAxisMargin,
    this.mainAxisMargin,
    this.minThumbLength,
    this.interactive,
  });

  /// Overrides the default value of [Scrollbar.thickness] in all
  /// descendant [Scrollbar] widgets.
  ///
  /// Resolves in the following states:
  ///  * [MaterialState.hovered] on web and desktop platforms.
  final MaterialStateProperty<double?>? thickness;

  /// Overrides the default value of [Scrollbar.showTrackOnHover] in all
  /// descendant [Scrollbar] widgets.
  final bool? showTrackOnHover;

  /// Overrides the default value of [Scrollbar.isAlwaysShown] in all
  /// descendant [Scrollbar] widgets.
  final bool? isAlwaysShown;

  /// Overrides the default value of [Scrollbar.interactive] in all
  /// descendant [Scrollbar] widgets.
  final bool? interactive;

  /// Overrides the default value of [Scrollbar.radius] in all
  /// descendant widgets.
  final Radius? radius;

  /// Overrides the default [Color] of the [Scrollbar] thumb in all descendant
  /// [Scrollbar] widgets.
  ///
  /// Resolves in the following states:
  ///  * [MaterialState.dragged].
  ///  * [MaterialState.hovered] on web and desktop platforms.
  final MaterialStateProperty<Color?>? thumbColor;

  /// Overrides the default [Color] of the [Scrollbar] track when
  /// [showTrackOnHover] is true in all descendant [Scrollbar] widgets.
  ///
  /// Resolves in the following states:
  ///  * [MaterialState.hovered] on web and desktop platforms.
  final MaterialStateProperty<Color?>? trackColor;

  /// Overrides the default [Color] of the [Scrollbar] track border when
  /// [showTrackOnHover] is true in all descendant [Scrollbar] widgets.
  ///
  /// Resolves in the following states:
  ///  * [MaterialState.hovered] on web and desktop platforms.
  final MaterialStateProperty<Color?>? trackBorderColor;

  /// Overrides the default value of the [ScrollbarPainter.crossAxisMargin]
  /// property in all descendant [Scrollbar] widgets.
  ///
  /// See also:
  ///
  ///  * [ScrollbarPainter.crossAxisMargin], which sets the distance from the
  ///    scrollbar's side to the nearest edge in logical pixels.
  final double? crossAxisMargin;

  /// Overrides the default value of the [ScrollbarPainter.mainAxisMargin]
  /// property in all descendant [Scrollbar] widgets.
  ///
  /// See also:
  ///
  ///  * [ScrollbarPainter.mainAxisMargin], which sets the distance from the
  ///    scrollbar's start and end to the edge of the viewport in logical pixels.
  final double? mainAxisMargin;

  /// Overrides the default value of the [ScrollbarPainter.minLength]
  /// property in all descendant [Scrollbar] widgets.
  ///
  /// See also:
  ///
  ///  * [ScrollbarPainter.minLength], which sets the preferred smallest size
  ///    the scrollbar can shrink to when the total scrollable extent is large,
  ///    the current visible viewport is small, and the viewport is not
  ///    overscrolled.
  final double? minThumbLength;

  /// Creates a copy of this object with the given fields replaced with the
  /// new values.
  ScrollbarThemeData copyWith({
    MaterialStateProperty<double?>? thickness,
    bool? showTrackOnHover,
    bool? isAlwaysShown,
    bool? interactive,
    Radius? radius,
    MaterialStateProperty<Color?>? thumbColor,
    MaterialStateProperty<Color?>? trackColor,
    MaterialStateProperty<Color?>? trackBorderColor,
    double? crossAxisMargin,
    double? mainAxisMargin,
    double? minThumbLength,
  }) {
    return ScrollbarThemeData(
      thickness: thickness ?? this.thickness,
      showTrackOnHover: showTrackOnHover ?? this.showTrackOnHover,
      isAlwaysShown: isAlwaysShown ?? this.isAlwaysShown,
      interactive: interactive ?? this.interactive,
      radius: radius ?? this.radius,
      thumbColor: thumbColor ?? this.thumbColor,
      trackColor: trackColor ?? this.trackColor,
      trackBorderColor: trackBorderColor ?? this.trackBorderColor,
      crossAxisMargin: crossAxisMargin ?? this.crossAxisMargin,
      mainAxisMargin: mainAxisMargin ?? this.mainAxisMargin,
      minThumbLength: minThumbLength ?? this.minThumbLength,
    );
  }

  /// Linearly interpolate between two Scrollbar themes.
  ///
  /// The argument `t` must not be null.
  ///
  /// {@macro dart.ui.shadow.lerp}
  static ScrollbarThemeData lerp(ScrollbarThemeData? a, ScrollbarThemeData? b, double t) {
    assert(t != null);
    return ScrollbarThemeData(
      thickness: _lerpProperties<double?>(a?.thickness, b?.thickness, t, lerpDouble),
      showTrackOnHover: t < 0.5 ? a?.showTrackOnHover : b?.showTrackOnHover,
      isAlwaysShown: t < 0.5 ? a?.isAlwaysShown : b?.isAlwaysShown,
      interactive: t < 0.5 ? a?.interactive : b?.interactive,
      radius: Radius.lerp(a?.radius, b?.radius, t),
      thumbColor: _lerpProperties<Color?>(a?.thumbColor, b?.thumbColor, t, Color.lerp),
      trackColor: _lerpProperties<Color?>(a?.trackColor, b?.trackColor, t, Color.lerp),
      trackBorderColor: _lerpProperties<Color?>(a?.trackBorderColor, b?.trackBorderColor, t, Color.lerp),
      crossAxisMargin: lerpDouble(a?.crossAxisMargin, b?.crossAxisMargin, t),
      mainAxisMargin: lerpDouble(a?.mainAxisMargin, b?.mainAxisMargin, t),
      minThumbLength: lerpDouble(a?.minThumbLength, b?.minThumbLength, t),
    );
  }

  @override
  int get hashCode {
    return hashValues(
      thickness,
      showTrackOnHover,
      isAlwaysShown,
      interactive,
      radius,
      thumbColor,
      trackColor,
      trackBorderColor,
      crossAxisMargin,
      mainAxisMargin,
      minThumbLength,
    );
  }

  @override
  bool operator ==(Object other) {
    if (identical(this, other))
      return true;
    if (other.runtimeType != runtimeType)
      return false;
    return other is ScrollbarThemeData
      && other.thickness == thickness
      && other.showTrackOnHover == showTrackOnHover
      && other.isAlwaysShown == isAlwaysShown
      && other.interactive == interactive
      && other.radius == radius
      && other.thumbColor == thumbColor
      && other.trackColor == trackColor
      && other.trackBorderColor == trackBorderColor
      && other.crossAxisMargin == crossAxisMargin
      && other.mainAxisMargin == mainAxisMargin
      && other.minThumbLength == minThumbLength;
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<MaterialStateProperty<double?>>('thickness', thickness, defaultValue: null));
    properties.add(DiagnosticsProperty<bool>('showTrackOnHover', showTrackOnHover, defaultValue: null));
    properties.add(DiagnosticsProperty<bool>('isAlwaysShown', isAlwaysShown, defaultValue: null));
    properties.add(DiagnosticsProperty<bool>('interactive', interactive, defaultValue: null));
    properties.add(DiagnosticsProperty<Radius>('radius', radius, defaultValue: null));
    properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('thumbColor', thumbColor, defaultValue: null));
    properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('trackColor', trackColor, defaultValue: null));
    properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('trackBorderColor', trackBorderColor, defaultValue: null));
    properties.add(DiagnosticsProperty<double>('crossAxisMargin', crossAxisMargin, defaultValue: null));
    properties.add(DiagnosticsProperty<double>('mainAxisMargin', mainAxisMargin, defaultValue: null));
    properties.add(DiagnosticsProperty<double>('minThumbLength', minThumbLength, defaultValue: null));
  }

  static MaterialStateProperty<T>? _lerpProperties<T>(
    MaterialStateProperty<T>? a,
    MaterialStateProperty<T>? b,
    double t,
    T Function(T?, T?, double) lerpFunction,
  ) {
    // Avoid creating a _LerpProperties object for a common case.
    if (a == null && b == null)
      return null;
    return _LerpProperties<T>(a, b, t, lerpFunction);
  }
}

class _LerpProperties<T> implements MaterialStateProperty<T> {
  const _LerpProperties(this.a, this.b, this.t, this.lerpFunction);

  final MaterialStateProperty<T>? a;
  final MaterialStateProperty<T>? b;
  final double t;
  final T Function(T?, T?, double) lerpFunction;

  @override
  T resolve(Set<MaterialState> states) {
    final T? resolvedA = a?.resolve(states);
    final T? resolvedB = b?.resolve(states);
    return lerpFunction(resolvedA, resolvedB, t);
  }
}

/// Applies a scrollbar theme to descendant [Scrollbar] widgets.
///
/// Descendant widgets obtain the current theme's [ScrollbarThemeData] using
/// [ScrollbarTheme.of]. When a widget uses [ScrollbarTheme.of], it is
/// automatically rebuilt if the theme later changes.
///
/// A scrollbar theme can be specified as part of the overall Material theme
/// using [ThemeData.scrollbarTheme].
///
/// See also:
///
///  * [ScrollbarThemeData], which describes the configuration of a
///    scrollbar theme.
class ScrollbarTheme extends InheritedWidget {
  /// Constructs a scrollbar theme that configures all descendant [Scrollbar]
  /// widgets.
  const ScrollbarTheme({
    Key? key,
    required this.data,
    required Widget child,
  }) : super(key: key, child: child);

  /// The properties used for all descendant [Scrollbar] widgets.
  final ScrollbarThemeData data;

  /// Returns the configuration [data] from the closest [ScrollbarTheme]
  /// ancestor. If there is no ancestor, it returns [ThemeData.scrollbarTheme].
  ///
  /// Typical usage is as follows:
  ///
  /// ```dart
  /// ScrollbarThemeData theme = ScrollbarTheme.of(context);
  /// ```
  static ScrollbarThemeData of(BuildContext context) {
    final ScrollbarTheme? scrollbarTheme = context.dependOnInheritedWidgetOfExactType<ScrollbarTheme>();
    return scrollbarTheme?.data ?? Theme.of(context).scrollbarTheme;
  }

  @override
  bool updateShouldNotify(ScrollbarTheme oldWidget) => data != oldWidget.data;
}