// Copyright 2015 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 'dart:ui' as ui show Image, Codec, FrameInfo;
import 'dart:ui' show hashValues;

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

/// A [dart:ui.Image] object with its corresponding scale.
///
/// ImageInfo objects are used by [ImageStream] objects to represent the
/// actual data of the image once it has been obtained.
@immutable
class ImageInfo {
  /// Creates an [ImageInfo] object for the given image and scale.
  ///
  /// Both the image and the scale must not be null.
  const ImageInfo({ @required this.image, this.scale: 1.0 })
      : assert(image != null),
        assert(scale != null);

  /// The raw image pixels.
  ///
  /// This is the object to pass to the [Canvas.drawImage],
  /// [Canvas.drawImageRect], or [Canvas.drawImageNine] methods when painting
  /// the image.
  final ui.Image image;

  /// The linear scale factor for drawing this image at its intended size.
  ///
  /// The scale factor applies to the width and the height.
  ///
  /// For example, if this is 2.0 it means that there are four image pixels for
  /// every one logical pixel, and the image's actual width and height (as given
  /// by the [dart:ui.Image.width] and [dart:ui.Image.height] properties) are double the
  /// height and width that should be used when painting the image (e.g. in the
  /// arguments given to [Canvas.drawImage]).
  final double scale;

  @override
  String toString() => '$image @ ${scale}x';

  @override
  int get hashCode => hashValues(image, scale);

  @override
  bool operator ==(Object other) {
    if (other.runtimeType != runtimeType)
      return false;
    final ImageInfo typedOther = other;
    return typedOther.image == image
        && typedOther.scale == scale;
  }
}

/// Signature for callbacks reporting that an image is available.
///
/// Used by [ImageStream].
///
/// The `synchronousCall` argument is true if the listener is being invoked
/// during the call to addListener. This can be useful if, for example,
/// [ImageStream.addListener] is invoked during a frame, so that a new rendering
/// frame is requested if the call was asynchronous (after the current frame)
/// and no rendering frame is requested if the call was synchronous (within the
/// same stack frame as the call to [ImageStream.addListener]).
typedef void ImageListener(ImageInfo image, bool synchronousCall);

/// A handle to an image resource.
///
/// ImageStream represents a handle to a [dart:ui.Image] object and its scale
/// (together represented by an [ImageInfo] object). The underlying image object
/// might change over time, either because the image is animating or because the
/// underlying image resource was mutated.
///
/// ImageStream objects can also represent an image that hasn't finished
/// loading.
///
/// ImageStream objects are backed by [ImageStreamCompleter] objects.
///
/// See also:
///
///  * [ImageProvider], which has an example that includes the use of an
///    [ImageStream] in a [Widget].
class ImageStream extends Diagnosticable {
  /// Create an initially unbound image stream.
  ///
  /// Once an [ImageStreamCompleter] is available, call [setCompleter].
  ImageStream();

  /// The completer that has been assigned to this image stream.
  ///
  /// Generally there is no need to deal with the completer directly.
  ImageStreamCompleter get completer => _completer;
  ImageStreamCompleter _completer;

  List<ImageListener> _listeners;

  /// Assigns a particular [ImageStreamCompleter] to this [ImageStream].
  ///
  /// This is usually done automatically by the [ImageProvider] that created the
  /// [ImageStream].
  ///
  /// This method can only be called once per stream. To have an [ImageStream]
  /// represent multiple images over time, assign it a completer that
  /// completes several images in succession.
  void setCompleter(ImageStreamCompleter value) {
    assert(_completer == null);
    _completer = value;
    if (_listeners != null) {
      final List<ImageListener> initialListeners = _listeners;
      _listeners = null;
      initialListeners.forEach(_completer.addListener);
    }
  }

  /// Adds a listener callback that is called whenever a new concrete [ImageInfo]
  /// object is available. If a concrete image is already available, this object
  /// will call the listener synchronously.
  ///
  /// If the assigned [completer] completes multiple images over its lifetime,
  /// this listener will fire multiple times.
  ///
  /// The listener will be passed a flag indicating whether a synchronous call
  /// occurred. If the listener is added within a render object paint function,
  /// then use this flag to avoid calling [RenderObject.markNeedsPaint] during
  /// a paint.
  void addListener(ImageListener listener) {
    if (_completer != null)
      return _completer.addListener(listener);
    _listeners ??= <ImageListener>[];
    _listeners.add(listener);
  }

  /// Stop listening for new concrete [ImageInfo] objects.
  void removeListener(ImageListener listener) {
    if (_completer != null)
      return _completer.removeListener(listener);
    assert(_listeners != null);
    _listeners.remove(listener);
  }

  /// Returns an object which can be used with `==` to determine if this
  /// [ImageStream] shares the same listeners list as another [ImageStream].
  ///
  /// This can be used to avoid unregistering and reregistering listeners after
  /// calling [ImageProvider.resolve] on a new, but possibly equivalent,
  /// [ImageProvider].
  ///
  /// The key may change once in the lifetime of the object. When it changes, it
  /// will go from being different than other [ImageStream]'s keys to
  /// potentially being the same as others'. No notification is sent when this
  /// happens.
  Object get key => _completer != null ? _completer : this;

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(new ObjectFlagProperty<ImageStreamCompleter>(
      'completer',
      _completer,
      ifPresent: _completer?.toStringShort(),
      ifNull: 'unresolved',
    ));
    properties.add(new ObjectFlagProperty<List<ImageListener>>(
      'listeners',
      _listeners,
      ifPresent: '${_listeners?.length} listener${_listeners?.length == 1 ? "" : "s" }',
      ifNull: 'no listeners',
      level: _completer != null ? DiagnosticLevel.hidden : DiagnosticLevel.info,
    ));
    _completer?.debugFillProperties(properties);
  }
}

/// Base class for those that manage the loading of [dart:ui.Image] objects for
/// [ImageStream]s.
///
/// [ImageStreamListener] objects are rarely constructed directly. Generally, an
/// [ImageProvider] subclass will return an [ImageStream] and automatically
/// configure it with the right [ImageStreamCompleter] when possible.
abstract class ImageStreamCompleter extends Diagnosticable {
  final List<ImageListener> _listeners = <ImageListener>[];
  ImageInfo _current;

  /// Adds a listener callback that is called whenever a new concrete [ImageInfo]
  /// object is available. If a concrete image is already available, this object
  /// will call the listener synchronously.
  ///
  /// If the [ImageStreamCompleter] completes multiple images over its lifetime,
  /// this listener will fire multiple times.
  ///
  /// The listener will be passed a flag indicating whether a synchronous call
  /// occurred. If the listener is added within a render object paint function,
  /// then use this flag to avoid calling [RenderObject.markNeedsPaint] during
  /// a paint.
  void addListener(ImageListener listener) {
    _listeners.add(listener);
    if (_current != null) {
      try {
        listener(_current, true);
      } catch (exception, stack) {
        _handleImageError('by a synchronously-called image listener', exception, stack);
      }
    }
  }

  /// Stop listening for new concrete [ImageInfo] objects.
  void removeListener(ImageListener listener) {
    _listeners.remove(listener);
  }

  /// Calls all the registered listeners to notify them of a new image.
  @protected
  void setImage(ImageInfo image) {
    _current = image;
    if (_listeners.isEmpty)
      return;
    final List<ImageListener> localListeners = new List<ImageListener>.from(_listeners);
    for (ImageListener listener in localListeners) {
      try {
        listener(image, false);
      } catch (exception, stack) {
        _handleImageError('by an image listener', exception, stack);
      }
    }
  }

  void _handleImageError(String context, dynamic exception, dynamic stack) {
    FlutterError.reportError(new FlutterErrorDetails(
      exception: exception,
      stack: stack,
      library: 'image resource service',
      context: context
    ));
  }

  /// Accumulates a list of strings describing the object's state. Subclasses
  /// should override this to have their information included in [toString].
  @override
  void debugFillProperties(DiagnosticPropertiesBuilder description) {
    super.debugFillProperties(description);
    description.add(new DiagnosticsProperty<ImageInfo>('current', _current, ifNull: 'unresolved', showName: false));
    description.add(new ObjectFlagProperty<List<ImageListener>>(
      'listeners',
      _listeners,
      ifPresent: '${_listeners?.length} listener${_listeners?.length == 1 ? "" : "s" }',
    ));
  }
}

/// Manages the loading of [dart:ui.Image] objects for static [ImageStream]s (those
/// with only one frame).
class OneFrameImageStreamCompleter extends ImageStreamCompleter {
  /// Creates a manager for one-frame [ImageStream]s.
  ///
  /// The image resource awaits the given [Future]. When the future resolves,
  /// it notifies the [ImageListener]s that have been registered with
  /// [addListener].
  ///
  /// The [InformationCollector], if provided, is invoked if the given [Future]
  /// resolves with an error, and can be used to supplement the reported error
  /// message (for example, giving the image's URL).
  ///
  /// Errors are reported using [FlutterError.reportError] with the `silent`
  /// argument on [FlutterErrorDetails] set to true, meaning that by default the
  /// message is only dumped to the console in debug mode (see [new
  /// FlutterErrorDetails]).
  OneFrameImageStreamCompleter(Future<ImageInfo> image, { InformationCollector informationCollector })
    : assert(image != null) {
    image.then<void>(setImage, onError: (dynamic error, StackTrace stack) {
      FlutterError.reportError(new FlutterErrorDetails(
        exception: error,
        stack: stack,
        library: 'services',
        context: 'resolving a single-frame image stream',
        informationCollector: informationCollector,
        silent: true,
      ));
    });
  }
}

/// Manages the decoding and scheduling of image frames.
///
/// New frames will only be emitted while there are registered listeners to the
/// stream (registered with [addListener]).
///
/// This class deals with 2 types of frames:
///
///  * image frames - image frames of an animated image.
///  * app frames - frames that the flutter engine is drawing to the screen to
///    show the app GUI.
///
/// For single frame images the stream will only complete once.
///
/// For animated images, this class eagerly decodes the next image frame,
/// and notifies the listeners that a new frame is ready on the first app frame
/// that is scheduled after the image frame duration has passed.
///
/// Scheduling new timers only from scheduled app frames, makes sure we pause
/// the animation when the app is not visible (as new app frames will not be
/// scheduled).
///
/// See the following timeline example:
///
///     | Time | Event                                      | Comment                   |
///     |------|--------------------------------------------|---------------------------|
///     | t1   | App frame scheduled (image frame A posted) |                           |
///     | t2   | App frame scheduled                        |                           |
///     | t3   | App frame scheduled                        |                           |
///     | t4   | Image frame B decoded                      |                           |
///     | t5   | App frame scheduled                        | t5 - t1 < frameB_duration |
///     | t6   | App frame scheduled (image frame B posted) | t6 - t1 > frameB_duration |
///
class MultiFrameImageStreamCompleter extends ImageStreamCompleter {
  /// Creates a image stream completer.
  ///
  /// Immediately starts decoding the first image frame when the codec is ready.
  ///
  /// [codec] is a future for an initialized [ui.Codec] that will be used to
  /// decode the image.
  /// [scale] is the linear scale factor for drawing this frames of this image
  /// at their intended size.
  MultiFrameImageStreamCompleter({
    @required Future<ui.Codec> codec,
    @required double scale,
    InformationCollector informationCollector
  }) : assert(codec != null),
       _informationCollector = informationCollector,
       _scale = scale,
       _framesEmitted = 0,
       _timer = null {
    codec.then<void>(_handleCodecReady, onError: (dynamic error, StackTrace stack) {
      FlutterError.reportError(new FlutterErrorDetails(
        exception: error,
        stack: stack,
        library: 'services',
        context: 'resolving an image codec',
        informationCollector: informationCollector,
        silent: true,
      ));
    });
  }

  ui.Codec _codec;
  final double _scale;
  final InformationCollector _informationCollector;
  ui.FrameInfo _nextFrame;
  // When the current was first shown.
  Duration _shownTimestamp;
  // The requested duration for the current frame;
  Duration _frameDuration;
  // How many frames have been emitted so far.
  int _framesEmitted;
  Timer _timer;

  void _handleCodecReady(ui.Codec codec) {
    _codec = codec;
    assert(_codec != null);

    _decodeNextFrameAndSchedule();
  }

  void _handleAppFrame(Duration timestamp) {
    if (!_hasActiveListeners)
      return;
    if (_isFirstFrame() || _hasFrameDurationPassed(timestamp)) {
      _emitFrame(new ImageInfo(image: _nextFrame.image, scale: _scale));
      _shownTimestamp = timestamp;
      _frameDuration = _nextFrame.duration;
      _nextFrame = null;
      final int completedCycles = _framesEmitted ~/ _codec.frameCount;
      if (_codec.repetitionCount == -1 || completedCycles <= _codec.repetitionCount) {
        _decodeNextFrameAndSchedule();
      }
      return;
    }
    final Duration delay = _frameDuration - (timestamp - _shownTimestamp);
    _timer = new Timer(delay * timeDilation, () {
      SchedulerBinding.instance.scheduleFrameCallback(_handleAppFrame);
    });
  }

  bool _isFirstFrame() {
    return _frameDuration == null;
  }

  bool _hasFrameDurationPassed(Duration timestamp) {
    assert(_shownTimestamp != null);
    return timestamp - _shownTimestamp >= _frameDuration;
  }

  Future<Null> _decodeNextFrameAndSchedule() async {
    try {
      _nextFrame = await _codec.getNextFrame();
    } catch (exception, stack) {
      FlutterError.reportError(new FlutterErrorDetails(
          exception: exception,
          stack: stack,
          library: 'services',
          context: 'resolving an image frame',
          informationCollector: _informationCollector,
          silent: true,
      ));
      return;
    }
    if (_codec.frameCount == 1) {
      // This is not an animated image, just return it and don't schedule more
      // frames.
      _emitFrame(new ImageInfo(image: _nextFrame.image, scale: _scale));
      return;
    }
    SchedulerBinding.instance.scheduleFrameCallback(_handleAppFrame);
  }

  void _emitFrame(ImageInfo imageInfo) {
    setImage(imageInfo);
    _framesEmitted += 1;
  }

  bool get _hasActiveListeners => _listeners.isNotEmpty;

  @override
  void addListener(ImageListener listener) {
    if (!_hasActiveListeners && _codec != null) {
      _decodeNextFrameAndSchedule();
    }
    super.addListener(listener);
  }

  @override
  void removeListener(ImageListener listener) {
    super.removeListener(listener);
    if (!_hasActiveListeners) {
      _timer?.cancel();
      _timer = null;
    }
  }
}
