packages/flutter/lib/src/material/app_bar_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 'text_theme.dart';
import 'theme.dart';

/// Defines default property values for descendant [AppBar] widgets.
///
/// Descendant widgets obtain the current [AppBarTheme] object using
/// `AppBarTheme.of(context)`. Instances of [AppBarTheme] can be customized
/// with [AppBarTheme.copyWith].
///
/// Typically an [AppBarTheme] is specified as part of the overall [Theme] with
/// [ThemeData.appBarTheme].
///
/// All [AppBarTheme] properties are `null` by default. When null, the [AppBar]
/// will use the values from [ThemeData] if they exist, otherwise it will
/// provide its own defaults.
///
/// See also:
///
///  * [ThemeData], which describes the overall theme information for the
///    application.
@immutable
class AppBarTheme with Diagnosticable {
  /// Creates a theme that can be used for [ThemeData.appBarTheme].
  const AppBarTheme({
    this.brightness,
    this.color,
    this.foregroundColor,
    this.elevation,
    this.shadowColor,
    this.iconTheme,
    this.actionsIconTheme,
    this.textTheme,
    this.centerTitle,
    this.titleSpacing,
  });

  /// AppBar uses this value to determine the default (background) [color] and
  /// [foregroundColor] as well as the app bar's [SystemUiOverlayStyle].
  ///
  /// For [Brightness.dark], [SystemUiOverlayStyle.light] is used and for
  /// [Brightness.light], [SystemUiOverlayStyle.dark] is used.
  ///
  /// See also:
  ///
  ///  * [AppBar.brightness], which overrides the this value and the overall
  ///    theme's [ColorScheme.brightness].
  ///  * [Theme.of], which returns the current overall Material theme as
  ///    a [ThemeData].
  ///  * [ThemeData.colorScheme], the thirteen colors that most Material widget
  ///    default colors are based on.
  ///  * [ColorScheme.brightness], which indicates if the overall [Theme]
  ///    is light or dark.
  final Brightness? brightness;

  /// The app bar's background color.
  ///
  /// If null, [AppBar] uses the overall theme's [ColorScheme.primary] if the
  /// overall theme's brightness is [Brightness.light], and [ColorScheme.surface]
  /// if the overall theme's [brightness] is [Brightness.dark].
  ///
  /// See also:
  ///
  ///  * [AppBar.backgroundColor], which specifies the AppBar's background color
  ///    and overrides the background color defined by this theme.
  ///  * [foregroundColor], which specifies the color for icons and text within
  ///    the app bar.
  ///  * [Theme.of], which returns the current overall Material theme as
  ///    a [ThemeData].
  ///  * [ThemeData.colorScheme], the thirteen colors that most Material widget
  ///    default colors are based on.
  ///  * [ColorScheme.brightness], which indicates if the overall [Theme]
  ///    is light or dark.
  final Color? color;

  /// The default color for [Text] and [Icon]s within the app bar.
  ///
  /// If null, [AppBar] uses the overall theme's [ColorScheme.onPrimary] if the
  /// overall theme's brightness is [Brightness.light], and [ColorScheme.onSurface]
  /// if the overall theme's [brightness] is [Brightness.dark].
  ///
  /// This color is used to configure [DefaultTextStyle] and [IconTheme]
  /// widgets.
  ///
  /// See also:
  ///
  ///  * [AppBar.foregroundColor], which specifies the app bar's text and icon
  ///    colors and overrides the foreground color defined by this theme.
  ///  * [color], which specifies the app bar's background color.
  ///  * [Theme.of], which returns the current overall Material theme as
  ///    a [ThemeData].
  ///  * [ThemeData.colorScheme], the thirteen colors that most Material widget
  ///    default colors are based on.
  ///  * [ColorScheme.brightness], which indicates if the overall [Theme]
  ///    is light or dark.
  final Color? foregroundColor;

  /// Default value for [AppBar.elevation].
  ///
  /// If null, [AppBar] uses a default value of 4.0.
  final double? elevation;

  /// Default value for [AppBar.shadowColor].
  ///
  /// If null, [AppBar] uses a default value of fully opaque black.
  final Color? shadowColor;

  /// Default value for [AppBar.iconTheme].
  ///
  /// If null, [AppBar] uses [ThemeData.primaryIconTheme].
  final IconThemeData? iconTheme;

  /// Default value for [AppBar.actionsIconTheme].
  ///
  /// If null, [AppBar] uses [ThemeData.primaryIconTheme].
  final IconThemeData? actionsIconTheme;

  /// Default value for [AppBar.textTheme].
  ///
  /// If null, [AppBar] uses [ThemeData.primaryTextTheme].
  final TextTheme? textTheme;

  /// Default value for [AppBar.centerTitle].
  ///
  /// If null, the value is adapted to current [TargetPlatform].
  final bool? centerTitle;

  /// Default value for [AppBar.titleSpacing].
  ///
  /// If null, [AppBar] uses default value of [NavigationToolbar.kMiddleSpacing].
  final double? titleSpacing;

  /// Creates a copy of this object with the given fields replaced with the
  /// new values.
  AppBarTheme copyWith({
    IconThemeData? actionsIconTheme,
    Brightness? brightness,
    Color? color,
    Color? foregroundColor,
    double? elevation,
    Color? shadowColor,
    IconThemeData? iconTheme,
    TextTheme? textTheme,
    bool? centerTitle,
    double? titleSpacing,
  }) {
    return AppBarTheme(
      brightness: brightness ?? this.brightness,
      color: color ?? this.color,
      foregroundColor: foregroundColor ?? this.foregroundColor,
      elevation: elevation ?? this.elevation,
      shadowColor: shadowColor ?? this.shadowColor,
      iconTheme: iconTheme ?? this.iconTheme,
      actionsIconTheme: actionsIconTheme ?? this.actionsIconTheme,
      textTheme: textTheme ?? this.textTheme,
      centerTitle: centerTitle ?? this.centerTitle,
      titleSpacing: titleSpacing ?? this.titleSpacing,
    );
  }

  /// The [ThemeData.appBarTheme] property of the ambient [Theme].
  static AppBarTheme of(BuildContext context) {
    return Theme.of(context).appBarTheme;
  }

  /// Linearly interpolate between two AppBar themes.
  ///
  /// The argument `t` must not be null.
  ///
  /// {@macro dart.ui.shadow.lerp}
  static AppBarTheme lerp(AppBarTheme? a, AppBarTheme? b, double t) {
    assert(t != null);
    return AppBarTheme(
      brightness: t < 0.5 ? a?.brightness : b?.brightness,
      color: Color.lerp(a?.color, b?.color, t),
      foregroundColor: Color.lerp(a?.foregroundColor, b?.foregroundColor, t),
      elevation: lerpDouble(a?.elevation, b?.elevation, t),
      shadowColor: Color.lerp(a?.shadowColor, b?.shadowColor, t),
      iconTheme: IconThemeData.lerp(a?.iconTheme, b?.iconTheme, t),
      actionsIconTheme: IconThemeData.lerp(a?.actionsIconTheme, b?.actionsIconTheme, t),
      textTheme: TextTheme.lerp(a?.textTheme, b?.textTheme, t),
      centerTitle: t < 0.5 ? a?.centerTitle : b?.centerTitle,
      titleSpacing: lerpDouble(a?.titleSpacing, b?.titleSpacing, t),
    );
  }

  @override
  int get hashCode {
    return hashValues(
      brightness,
      color,
      foregroundColor,
      elevation,
      shadowColor,
      iconTheme,
      actionsIconTheme,
      textTheme,
      centerTitle,
      titleSpacing,
    );
  }

  @override
  bool operator ==(Object other) {
    if (identical(this, other))
      return true;
    if (other.runtimeType != runtimeType)
      return false;
    return other is AppBarTheme
        && other.brightness == brightness
        && other.color == color
        && other.foregroundColor == foregroundColor
        && other.elevation == elevation
        && other.shadowColor == shadowColor
        && other.iconTheme == iconTheme
        && other.actionsIconTheme == actionsIconTheme
        && other.textTheme == textTheme
        && other.centerTitle == centerTitle
        && other.titleSpacing == titleSpacing;
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<Brightness>('brightness', brightness, defaultValue: null));
    properties.add(ColorProperty('color', color, defaultValue: null));
    properties.add(ColorProperty('foregroundColor', foregroundColor, defaultValue: null));
    properties.add(DiagnosticsProperty<double>('elevation', elevation, defaultValue: null));
    properties.add(ColorProperty('shadowColor', shadowColor, defaultValue: null));
    properties.add(DiagnosticsProperty<IconThemeData>('iconTheme', iconTheme, defaultValue: null));
    properties.add(DiagnosticsProperty<IconThemeData>('actionsIconTheme', actionsIconTheme, defaultValue: null));
    properties.add(DiagnosticsProperty<TextTheme>('textTheme', textTheme, defaultValue: null));
    properties.add(DiagnosticsProperty<bool>('centerTitle', centerTitle, defaultValue: null));
    properties.add(DiagnosticsProperty<double>('titleSpacing', titleSpacing, defaultValue: null));
  }
}