packages/flutter/lib/src/services/system_chrome.dart

// Copyright 2016 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:async';

import 'system_channels.dart';

/// Specifies a particular device orientation.
///
/// To determine which values correspond to which orientations, first position
/// the device in its default orientation (this is the orientation that the
/// system first uses for its boot logo, or the orientation in which the
/// hardware logos or markings are upright, or the orientation in which the
/// cameras are at the top). If this is a portrait orientation, then this is
/// [portraitUp]. Otherwise, it's [landscapeLeft]. As you rotate the device by
/// 90 degrees in a counter-clockwise direction around the axis that pierces the
/// screen, you step through each value in this enum in the order given.
///
/// For a device with a landscape default orientation, the orientation obtained
/// by rotating the device 90 degrees clockwise from its default orientation is
/// [portraitUp].
///
/// Used by [SystemChrome.setPreferredOrientations].
enum DeviceOrientation {
  /// If the device shows its boot logo in portrait, then the boot logo is shown
  /// in [portraitUp]. Otherwise, the device shows its boot logo in landscape
  /// and this orientation is obtained by rotating the device 90 degrees
  /// clockwise from its boot orientation.
  portraitUp,

  /// The orientation that is 90 degrees clockwise from [portraitUp].
  ///
  /// If the device shows its boot logo in landscape, then the boot logo is
  /// shown in [landscapeLeft].
  landscapeLeft,

  /// The orientation that is 180 degrees from [portraitUp].
  portraitDown,

  /// The orientation that is 90 degrees counterclockwise from [portraitUp].
  landscapeRight,
}

/// Specifies a description of the application that is pertinent to the
/// embedder's application switcher (also known as "recent tasks") user
/// interface.
///
/// Used by [SystemChrome.setApplicationSwitcherDescription].
class ApplicationSwitcherDescription {
  /// Creates an ApplicationSwitcherDescription.
  const ApplicationSwitcherDescription({ this.label, this.primaryColor });

  /// A label and description of the current state of the application.
  final String label;

  /// The application's primary color.
  ///
  /// This may influence the color that the operating system uses to represent
  /// the application.
  final int primaryColor;
}

/// Specifies a system overlay at a particular location.
///
/// Used by [SystemChrome.setEnabledSystemUIOverlays].
enum SystemUiOverlay {
  /// The status bar provided by the embedder on the top of the application
  /// surface, if any.
  top,

  /// The status bar provided by the embedder on the bottom of the application
  /// surface, if any.
  bottom,
}

/// Specifies a preference for the style of the system overlays.
///
/// Used by [SystemChrome.setSystemUIOverlayStyle].
enum SystemUiOverlayStyle {
  /// System overlays should be drawn with a light color. Intended for
  /// applications with a dark background.
  light,

  /// System overlays should be drawn with a dark color. Intended for
  /// applications with a light background.
  dark,
}

List<String> _stringify(List<dynamic> list) {
  final List<String> result = <String>[];
  for (dynamic item in list)
    result.add(item.toString());
  return result;
}

/// Controls specific aspects of the operating system's graphical interface and
/// how it interacts with the application.
class SystemChrome {
  SystemChrome._();

  /// Specifies the set of orientations the application interface can
  /// be displayed in.
  ///
  /// The `orientation` argument is a list of [DeviceOrientation] enum values.
  /// The empty list is synonymous with having all options enabled.
  static Future<Null> setPreferredOrientations(List<DeviceOrientation> orientations) async {
    await SystemChannels.platform.invokeMethod(
      'SystemChrome.setPreferredOrientations',
      _stringify(orientations),
    );
  }

  /// Specifies the description of the current state of the application as it
  /// pertains to the application switcher (also known as "recent tasks").
  ///
  /// Any part of the description that is unsupported on the current platform
  /// will be ignored.
  static Future<Null> setApplicationSwitcherDescription(ApplicationSwitcherDescription description) async {
    await SystemChannels.platform.invokeMethod(
      'SystemChrome.setApplicationSwitcherDescription',
      <String, dynamic>{
        'label': description.label,
        'primaryColor': description.primaryColor,
      },
    );
  }

  /// Specifies the set of system overlays to have visible when the application
  /// is running.
  ///
  /// The `overlays` argument is a list of [SystemUiOverlay] enum values
  /// denoting the overlays to show.
  ///
  /// If a particular overlay is unsupported on the platform, enabling or
  /// disabling that overlay will be ignored.
  static Future<Null> setEnabledSystemUIOverlays(List<SystemUiOverlay> overlays) async {
    await SystemChannels.platform.invokeMethod(
      'SystemChrome.setEnabledSystemUIOverlays',
      _stringify(overlays),
    );
 }

  /// Specifies the style to use for the system overlays that are visible (if
  /// any).
  ///
  /// This method will schedule the embedder update to be run in a microtask.
  /// Any subsequent calls to this method during the current event loop will
  /// overwrite the pending value, such that only the last specified value takes
  /// effect.
  ///
  /// If a particular style is not supported on the platform, selecting it will
  /// have no effect.
  static void setSystemUIOverlayStyle(SystemUiOverlayStyle style) {
    assert(style != null);

    if (_pendingStyle != null) {
      // The microtask has already been queued; just update the pending value.
      _pendingStyle = style;
      return;
    }

    if (style == _latestStyle) {
      // Trivial success: no microtask has been queued and the given style is
      // already in effect, so no need to queue a microtask.
      return;
    }

    _pendingStyle = style;
    scheduleMicrotask(() {
      assert(_pendingStyle != null);
      if (_pendingStyle != _latestStyle) {
        SystemChannels.platform.invokeMethod(
          'SystemChrome.setSystemUIOverlayStyle',
          _pendingStyle.toString(),
        );
        _latestStyle = _pendingStyle;
      }
      _pendingStyle = null;
    });
  }

  static SystemUiOverlayStyle _pendingStyle;
  static SystemUiOverlayStyle _latestStyle;
}