// Copyright 2013 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 "FLTVideoPlayerPlugin.h"
#import <AVFoundation/AVFoundation.h>
#import <GLKit/GLKit.h>
#import "messages.h"

#if !__has_feature(objc_arc)
#error Code Requires ARC.
#endif

@interface FLTFrameUpdater : NSObject
@property(nonatomic) int64_t textureId;
@property(nonatomic, weak, readonly) NSObject<FlutterTextureRegistry>* registry;
- (void)onDisplayLink:(CADisplayLink*)link;
@end

@implementation FLTFrameUpdater
- (FLTFrameUpdater*)initWithRegistry:(NSObject<FlutterTextureRegistry>*)registry {
  NSAssert(self, @"super init cannot be nil");
  if (self == nil) return nil;
  _registry = registry;
  return self;
}

- (void)onDisplayLink:(CADisplayLink*)link {
  [_registry textureFrameAvailable:_textureId];
}
@end

@interface FLTVideoPlayer : NSObject <FlutterTexture, FlutterStreamHandler>
@property(readonly, nonatomic) AVPlayer* player;
@property(readonly, nonatomic) AVPlayerItemVideoOutput* videoOutput;
@property(readonly, nonatomic) CADisplayLink* displayLink;
@property(nonatomic) FlutterEventChannel* eventChannel;
@property(nonatomic) FlutterEventSink eventSink;
@property(nonatomic) CGAffineTransform preferredTransform;
@property(nonatomic, readonly) bool disposed;
@property(nonatomic, readonly) bool isPlaying;
@property(nonatomic) bool isLooping;
@property(nonatomic, readonly) bool isInitialized;
- (instancetype)initWithURL:(NSURL*)url
               frameUpdater:(FLTFrameUpdater*)frameUpdater
                httpHeaders:(NSDictionary<NSString*, NSString*>*)headers;
- (void)play;
- (void)pause;
- (void)setIsLooping:(bool)isLooping;
- (void)updatePlayingState;
@end

static void* timeRangeContext = &timeRangeContext;
static void* statusContext = &statusContext;
static void* playbackLikelyToKeepUpContext = &playbackLikelyToKeepUpContext;
static void* playbackBufferEmptyContext = &playbackBufferEmptyContext;
static void* playbackBufferFullContext = &playbackBufferFullContext;

@implementation FLTVideoPlayer
- (instancetype)initWithAsset:(NSString*)asset frameUpdater:(FLTFrameUpdater*)frameUpdater {
  NSString* path = [[NSBundle mainBundle] pathForResource:asset ofType:nil];
  return [self initWithURL:[NSURL fileURLWithPath:path] frameUpdater:frameUpdater httpHeaders:nil];
}

- (void)addObservers:(AVPlayerItem*)item {
  [item addObserver:self
         forKeyPath:@"loadedTimeRanges"
            options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
            context:timeRangeContext];
  [item addObserver:self
         forKeyPath:@"status"
            options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
            context:statusContext];
  [item addObserver:self
         forKeyPath:@"playbackLikelyToKeepUp"
            options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
            context:playbackLikelyToKeepUpContext];
  [item addObserver:self
         forKeyPath:@"playbackBufferEmpty"
            options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
            context:playbackBufferEmptyContext];
  [item addObserver:self
         forKeyPath:@"playbackBufferFull"
            options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
            context:playbackBufferFullContext];

  // Add an observer that will respond to itemDidPlayToEndTime
  [[NSNotificationCenter defaultCenter] addObserver:self
                                           selector:@selector(itemDidPlayToEndTime:)
                                               name:AVPlayerItemDidPlayToEndTimeNotification
                                             object:item];
}

- (void)itemDidPlayToEndTime:(NSNotification*)notification {
  if (_isLooping) {
    AVPlayerItem* p = [notification object];
    [p seekToTime:kCMTimeZero completionHandler:nil];
  } else {
    if (_eventSink) {
      _eventSink(@{@"event" : @"completed"});
    }
  }
}

const int64_t TIME_UNSET = -9223372036854775807;

static inline int64_t FLTCMTimeToMillis(CMTime time) {
  // When CMTIME_IS_INDEFINITE return a value that matches TIME_UNSET from ExoPlayer2 on Android.
  // Fixes https://github.com/flutter/flutter/issues/48670
  if (CMTIME_IS_INDEFINITE(time)) return TIME_UNSET;
  if (time.timescale == 0) return 0;
  return time.value * 1000 / time.timescale;
}

static inline CGFloat radiansToDegrees(CGFloat radians) {
  // Input range [-pi, pi] or [-180, 180]
  CGFloat degrees = GLKMathRadiansToDegrees((float)radians);
  if (degrees < 0) {
    // Convert -90 to 270 and -180 to 180
    return degrees + 360;
  }
  // Output degrees in between [0, 360[
  return degrees;
};

- (AVMutableVideoComposition*)getVideoCompositionWithTransform:(CGAffineTransform)transform
                                                     withAsset:(AVAsset*)asset
                                                withVideoTrack:(AVAssetTrack*)videoTrack {
  AVMutableVideoCompositionInstruction* instruction =
      [AVMutableVideoCompositionInstruction videoCompositionInstruction];
  instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [asset duration]);
  AVMutableVideoCompositionLayerInstruction* layerInstruction =
      [AVMutableVideoCompositionLayerInstruction
          videoCompositionLayerInstructionWithAssetTrack:videoTrack];
  [layerInstruction setTransform:_preferredTransform atTime:kCMTimeZero];

  AVMutableVideoComposition* videoComposition = [AVMutableVideoComposition videoComposition];
  instruction.layerInstructions = @[ layerInstruction ];
  videoComposition.instructions = @[ instruction ];

  // If in portrait mode, switch the width and height of the video
  CGFloat width = videoTrack.naturalSize.width;
  CGFloat height = videoTrack.naturalSize.height;
  NSInteger rotationDegrees =
      (NSInteger)round(radiansToDegrees(atan2(_preferredTransform.b, _preferredTransform.a)));
  if (rotationDegrees == 90 || rotationDegrees == 270) {
    width = videoTrack.naturalSize.height;
    height = videoTrack.naturalSize.width;
  }
  videoComposition.renderSize = CGSizeMake(width, height);

  // TODO(@recastrodiaz): should we use videoTrack.nominalFrameRate ?
  // Currently set at a constant 30 FPS
  videoComposition.frameDuration = CMTimeMake(1, 30);

  return videoComposition;
}

- (void)createVideoOutputAndDisplayLink:(FLTFrameUpdater*)frameUpdater {
  NSDictionary* pixBuffAttributes = @{
    (id)kCVPixelBufferPixelFormatTypeKey : @(kCVPixelFormatType_32BGRA),
    (id)kCVPixelBufferIOSurfacePropertiesKey : @{}
  };
  _videoOutput = [[AVPlayerItemVideoOutput alloc] initWithPixelBufferAttributes:pixBuffAttributes];

  _displayLink = [CADisplayLink displayLinkWithTarget:frameUpdater
                                             selector:@selector(onDisplayLink:)];
  [_displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
  _displayLink.paused = YES;
}

- (instancetype)initWithURL:(NSURL*)url
               frameUpdater:(FLTFrameUpdater*)frameUpdater
                httpHeaders:(NSDictionary<NSString*, NSString*>*)headers {
  NSDictionary<NSString*, id>* options = nil;
  if (headers != nil && [headers count] != 0) {
    options = @{@"AVURLAssetHTTPHeaderFieldsKey" : headers};
  }
  AVURLAsset* urlAsset = [AVURLAsset URLAssetWithURL:url options:options];
  AVPlayerItem* item = [AVPlayerItem playerItemWithAsset:urlAsset];
  return [self initWithPlayerItem:item frameUpdater:frameUpdater];
}

- (CGAffineTransform)fixTransform:(AVAssetTrack*)videoTrack {
  CGAffineTransform transform = videoTrack.preferredTransform;
  // TODO(@recastrodiaz): why do we need to do this? Why is the preferredTransform incorrect?
  // At least 2 user videos show a black screen when in portrait mode if we directly use the
  // videoTrack.preferredTransform Setting tx to the height of the video instead of 0, properly
  // displays the video https://github.com/flutter/flutter/issues/17606#issuecomment-413473181
  if (transform.tx == 0 && transform.ty == 0) {
    NSInteger rotationDegrees = (NSInteger)round(radiansToDegrees(atan2(transform.b, transform.a)));
    NSLog(@"TX and TY are 0. Rotation: %ld. Natural width,height: %f, %f", (long)rotationDegrees,
          videoTrack.naturalSize.width, videoTrack.naturalSize.height);
    if (rotationDegrees == 90) {
      NSLog(@"Setting transform tx");
      transform.tx = videoTrack.naturalSize.height;
      transform.ty = 0;
    } else if (rotationDegrees == 270) {
      NSLog(@"Setting transform ty");
      transform.tx = 0;
      transform.ty = videoTrack.naturalSize.width;
    }
  }
  return transform;
}

- (instancetype)initWithPlayerItem:(AVPlayerItem*)item frameUpdater:(FLTFrameUpdater*)frameUpdater {
  self = [super init];
  NSAssert(self, @"super init cannot be nil");
  _isInitialized = false;
  _isPlaying = false;
  _disposed = false;

  AVAsset* asset = [item asset];
  void (^assetCompletionHandler)(void) = ^{
    if ([asset statusOfValueForKey:@"tracks" error:nil] == AVKeyValueStatusLoaded) {
      NSArray* tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
      if ([tracks count] > 0) {
        AVAssetTrack* videoTrack = tracks[0];
        void (^trackCompletionHandler)(void) = ^{
          if (self->_disposed) return;
          if ([videoTrack statusOfValueForKey:@"preferredTransform"
                                        error:nil] == AVKeyValueStatusLoaded) {
            // Rotate the video by using a videoComposition and the preferredTransform
            self->_preferredTransform = [self fixTransform:videoTrack];
            // Note:
            // https://developer.apple.com/documentation/avfoundation/avplayeritem/1388818-videocomposition
            // Video composition can only be used with file-based media and is not supported for
            // use with media served using HTTP Live Streaming.
            AVMutableVideoComposition* videoComposition =
                [self getVideoCompositionWithTransform:self->_preferredTransform
                                             withAsset:asset
                                        withVideoTrack:videoTrack];
            item.videoComposition = videoComposition;
          }
        };
        [videoTrack loadValuesAsynchronouslyForKeys:@[ @"preferredTransform" ]
                                  completionHandler:trackCompletionHandler];
      }
    }
  };

  _player = [AVPlayer playerWithPlayerItem:item];
  _player.actionAtItemEnd = AVPlayerActionAtItemEndNone;

  [self createVideoOutputAndDisplayLink:frameUpdater];

  [self addObservers:item];

  [asset loadValuesAsynchronouslyForKeys:@[ @"tracks" ] completionHandler:assetCompletionHandler];

  return self;
}

- (void)observeValueForKeyPath:(NSString*)path
                      ofObject:(id)object
                        change:(NSDictionary*)change
                       context:(void*)context {
  if (context == timeRangeContext) {
    if (_eventSink != nil) {
      NSMutableArray<NSArray<NSNumber*>*>* values = [[NSMutableArray alloc] init];
      for (NSValue* rangeValue in [object loadedTimeRanges]) {
        CMTimeRange range = [rangeValue CMTimeRangeValue];
        int64_t start = FLTCMTimeToMillis(range.start);
        [values addObject:@[ @(start), @(start + FLTCMTimeToMillis(range.duration)) ]];
      }
      _eventSink(@{@"event" : @"bufferingUpdate", @"values" : values});
    }
  } else if (context == statusContext) {
    AVPlayerItem* item = (AVPlayerItem*)object;
    switch (item.status) {
      case AVPlayerItemStatusFailed:
        if (_eventSink != nil) {
          _eventSink([FlutterError
              errorWithCode:@"VideoError"
                    message:[@"Failed to load video: "
                                stringByAppendingString:[item.error localizedDescription]]
                    details:nil]);
        }
        break;
      case AVPlayerItemStatusUnknown:
        break;
      case AVPlayerItemStatusReadyToPlay:
        [item addOutput:_videoOutput];
        [self sendInitialized];
        [self updatePlayingState];
        break;
    }
  } else if (context == playbackLikelyToKeepUpContext) {
    if ([[_player currentItem] isPlaybackLikelyToKeepUp]) {
      [self updatePlayingState];
      if (_eventSink != nil) {
        _eventSink(@{@"event" : @"bufferingEnd"});
      }
    }
  } else if (context == playbackBufferEmptyContext) {
    if (_eventSink != nil) {
      _eventSink(@{@"event" : @"bufferingStart"});
    }
  } else if (context == playbackBufferFullContext) {
    if (_eventSink != nil) {
      _eventSink(@{@"event" : @"bufferingEnd"});
    }
  }
}

- (void)updatePlayingState {
  if (!_isInitialized) {
    return;
  }
  if (_isPlaying) {
    [_player play];
  } else {
    [_player pause];
  }
  _displayLink.paused = !_isPlaying;
}

- (void)sendInitialized {
  if (_eventSink && !_isInitialized) {
    CGSize size = [self.player currentItem].presentationSize;
    CGFloat width = size.width;
    CGFloat height = size.height;

    // The player has not yet initialized.
    if (height == CGSizeZero.height && width == CGSizeZero.width) {
      return;
    }
    // The player may be initialized but still needs to determine the duration.
    if ([self duration] == 0) {
      return;
    }

    _isInitialized = true;
    _eventSink(@{
      @"event" : @"initialized",
      @"duration" : @([self duration]),
      @"width" : @(width),
      @"height" : @(height)
    });
  }
}

- (void)play {
  _isPlaying = true;
  [self updatePlayingState];
}

- (void)pause {
  _isPlaying = false;
  [self updatePlayingState];
}

- (int64_t)position {
  return FLTCMTimeToMillis([_player currentTime]);
}

- (int64_t)duration {
  return FLTCMTimeToMillis([[_player currentItem] duration]);
}

- (void)seekTo:(int)location {
  [_player seekToTime:CMTimeMake(location, 1000)
      toleranceBefore:kCMTimeZero
       toleranceAfter:kCMTimeZero];
}

- (void)setIsLooping:(bool)isLooping {
  _isLooping = isLooping;
}

- (void)setVolume:(double)volume {
  _player.volume = (float)((volume < 0.0) ? 0.0 : ((volume > 1.0) ? 1.0 : volume));
}

- (void)setPlaybackSpeed:(double)speed {
  // See https://developer.apple.com/library/archive/qa/qa1772/_index.html for an explanation of
  // these checks.
  if (speed > 2.0 && !_player.currentItem.canPlayFastForward) {
    if (_eventSink != nil) {
      _eventSink([FlutterError errorWithCode:@"VideoError"
                                     message:@"Video cannot be fast-forwarded beyond 2.0x"
                                     details:nil]);
    }
    return;
  }

  if (speed < 1.0 && !_player.currentItem.canPlaySlowForward) {
    if (_eventSink != nil) {
      _eventSink([FlutterError errorWithCode:@"VideoError"
                                     message:@"Video cannot be slow-forwarded"
                                     details:nil]);
    }
    return;
  }

  _player.rate = speed;
}

- (CVPixelBufferRef)copyPixelBuffer {
  CMTime outputItemTime = [_videoOutput itemTimeForHostTime:CACurrentMediaTime()];
  if ([_videoOutput hasNewPixelBufferForItemTime:outputItemTime]) {
    return [_videoOutput copyPixelBufferForItemTime:outputItemTime itemTimeForDisplay:NULL];
  } else {
    return NULL;
  }
}

- (void)onTextureUnregistered:(NSObject<FlutterTexture>*)texture {
  dispatch_async(dispatch_get_main_queue(), ^{
    [self dispose];
  });
}

- (FlutterError* _Nullable)onCancelWithArguments:(id _Nullable)arguments {
  _eventSink = nil;
  return nil;
}

- (FlutterError* _Nullable)onListenWithArguments:(id _Nullable)arguments
                                       eventSink:(nonnull FlutterEventSink)events {
  _eventSink = events;
  // TODO(@recastrodiaz): remove the line below when the race condition is resolved:
  // https://github.com/flutter/flutter/issues/21483
  // This line ensures the 'initialized' event is sent when the event
  // 'AVPlayerItemStatusReadyToPlay' fires before _eventSink is set (this function
  // onListenWithArguments is called)
  [self sendInitialized];
  return nil;
}

/// This method allows you to dispose without touching the event channel.  This
/// is useful for the case where the Engine is in the process of deconstruction
/// so the channel is going to die or is already dead.
- (void)disposeSansEventChannel {
  _disposed = true;
  [_displayLink invalidate];
  [[_player currentItem] removeObserver:self forKeyPath:@"status" context:statusContext];
  [[_player currentItem] removeObserver:self
                             forKeyPath:@"loadedTimeRanges"
                                context:timeRangeContext];
  [[_player currentItem] removeObserver:self
                             forKeyPath:@"playbackLikelyToKeepUp"
                                context:playbackLikelyToKeepUpContext];
  [[_player currentItem] removeObserver:self
                             forKeyPath:@"playbackBufferEmpty"
                                context:playbackBufferEmptyContext];
  [[_player currentItem] removeObserver:self
                             forKeyPath:@"playbackBufferFull"
                                context:playbackBufferFullContext];
  [_player replaceCurrentItemWithPlayerItem:nil];
  [[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)dispose {
  [self disposeSansEventChannel];
  [_eventChannel setStreamHandler:nil];
}

@end

@interface FLTVideoPlayerPlugin () <FLTVideoPlayerApi>
@property(readonly, weak, nonatomic) NSObject<FlutterTextureRegistry>* registry;
@property(readonly, weak, nonatomic) NSObject<FlutterBinaryMessenger>* messenger;
@property(readonly, strong, nonatomic) NSMutableDictionary* players;
@property(readonly, strong, nonatomic) NSObject<FlutterPluginRegistrar>* registrar;
@end

@implementation FLTVideoPlayerPlugin
+ (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
  FLTVideoPlayerPlugin* instance = [[FLTVideoPlayerPlugin alloc] initWithRegistrar:registrar];
  [registrar publish:instance];
  FLTVideoPlayerApiSetup(registrar.messenger, instance);
}

- (instancetype)initWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
  self = [super init];
  NSAssert(self, @"super init cannot be nil");
  _registry = [registrar textures];
  _messenger = [registrar messenger];
  _registrar = registrar;
  _players = [NSMutableDictionary dictionaryWithCapacity:1];
  return self;
}

- (void)detachFromEngineForRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
  for (NSNumber* textureId in _players.allKeys) {
    FLTVideoPlayer* player = _players[textureId];
    [player disposeSansEventChannel];
  }
  [_players removeAllObjects];
  // TODO(57151): This should be commented out when 57151's fix lands on stable.
  // This is the correct behavior we never did it in the past and the engine
  // doesn't currently support it.
  // FLTVideoPlayerApiSetup(registrar.messenger, nil);
}

- (FLTTextureMessage*)onPlayerSetup:(FLTVideoPlayer*)player
                       frameUpdater:(FLTFrameUpdater*)frameUpdater {
  int64_t textureId = [_registry registerTexture:player];
  frameUpdater.textureId = textureId;
  FlutterEventChannel* eventChannel = [FlutterEventChannel
      eventChannelWithName:[NSString stringWithFormat:@"flutter.io/videoPlayer/videoEvents%lld",
                                                      textureId]
           binaryMessenger:_messenger];
  [eventChannel setStreamHandler:player];
  player.eventChannel = eventChannel;
  _players[@(textureId)] = player;
  FLTTextureMessage* result = [[FLTTextureMessage alloc] init];
  result.textureId = @(textureId);
  return result;
}

- (void)initialize:(FlutterError* __autoreleasing*)error {
  // Allow audio playback when the Ring/Silent switch is set to silent
  [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];

  for (NSNumber* textureId in _players) {
    [_registry unregisterTexture:[textureId unsignedIntegerValue]];
    [_players[textureId] dispose];
  }
  [_players removeAllObjects];
}

- (FLTTextureMessage*)create:(FLTCreateMessage*)input error:(FlutterError**)error {
  FLTFrameUpdater* frameUpdater = [[FLTFrameUpdater alloc] initWithRegistry:_registry];
  FLTVideoPlayer* player;
  if (input.asset) {
    NSString* assetPath;
    if (input.packageName) {
      assetPath = [_registrar lookupKeyForAsset:input.asset fromPackage:input.packageName];
    } else {
      assetPath = [_registrar lookupKeyForAsset:input.asset];
    }
    player = [[FLTVideoPlayer alloc] initWithAsset:assetPath frameUpdater:frameUpdater];
    return [self onPlayerSetup:player frameUpdater:frameUpdater];
  } else if (input.uri) {
    player = [[FLTVideoPlayer alloc] initWithURL:[NSURL URLWithString:input.uri]
                                    frameUpdater:frameUpdater
                                     httpHeaders:input.httpHeaders];
    return [self onPlayerSetup:player frameUpdater:frameUpdater];
  } else {
    *error = [FlutterError errorWithCode:@"video_player" message:@"not implemented" details:nil];
    return nil;
  }
}

- (void)dispose:(FLTTextureMessage*)input error:(FlutterError**)error {
  FLTVideoPlayer* player = _players[input.textureId];
  [_registry unregisterTexture:input.textureId.intValue];
  [_players removeObjectForKey:input.textureId];
  // If the Flutter contains https://github.com/flutter/engine/pull/12695,
  // the `player` is disposed via `onTextureUnregistered` at the right time.
  // Without https://github.com/flutter/engine/pull/12695, there is no guarantee that the
  // texture has completed the un-reregistration. It may leads a crash if we dispose the
  // `player` before the texture is unregistered. We add a dispatch_after hack to make sure the
  // texture is unregistered before we dispose the `player`.
  //
  // TODO(cyanglaz): Remove this dispatch block when
  // https://github.com/flutter/flutter/commit/8159a9906095efc9af8b223f5e232cb63542ad0b is in
  // stable And update the min flutter version of the plugin to the stable version.
  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)),
                 dispatch_get_main_queue(), ^{
                   if (!player.disposed) {
                     [player dispose];
                   }
                 });
}

- (void)setLooping:(FLTLoopingMessage*)input error:(FlutterError**)error {
  FLTVideoPlayer* player = _players[input.textureId];
  [player setIsLooping:[input.isLooping boolValue]];
}

- (void)setVolume:(FLTVolumeMessage*)input error:(FlutterError**)error {
  FLTVideoPlayer* player = _players[input.textureId];
  [player setVolume:[input.volume doubleValue]];
}

- (void)setPlaybackSpeed:(FLTPlaybackSpeedMessage*)input error:(FlutterError**)error {
  FLTVideoPlayer* player = _players[input.textureId];
  [player setPlaybackSpeed:[input.speed doubleValue]];
}

- (void)play:(FLTTextureMessage*)input error:(FlutterError**)error {
  FLTVideoPlayer* player = _players[input.textureId];
  [player play];
}

- (FLTPositionMessage*)position:(FLTTextureMessage*)input error:(FlutterError**)error {
  FLTVideoPlayer* player = _players[input.textureId];
  FLTPositionMessage* result = [[FLTPositionMessage alloc] init];
  result.position = @([player position]);
  return result;
}

- (void)seekTo:(FLTPositionMessage*)input error:(FlutterError**)error {
  FLTVideoPlayer* player = _players[input.textureId];
  [player seekTo:[input.position intValue]];
}

- (void)pause:(FLTTextureMessage*)input error:(FlutterError**)error {
  FLTVideoPlayer* player = _players[input.textureId];
  [player pause];
}

- (void)setMixWithOthers:(FLTMixWithOthersMessage*)input
                   error:(FlutterError* _Nullable __autoreleasing*)error {
  if ([input.mixWithOthers boolValue]) {
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback
                                     withOptions:AVAudioSessionCategoryOptionMixWithOthers
                                           error:nil];
  } else {
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];
  }
}

@end