// 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 "flutter/shell/platform/darwin/macos/framework/Headers/FlutterEngine.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h"

#include <algorithm>
#include <vector>

#import "flutter/shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMacDelegate.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterDartProject_Internal.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterExternalTextureGL.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterGLCompositor.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalRenderer.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterOpenGLRenderer.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterRenderingBackend.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewController_Internal.h"
#include "flutter/shell/platform/embedder/embedder.h"

/**
 * Constructs and returns a FlutterLocale struct corresponding to |locale|, which must outlive
 * the returned struct.
 */
static FlutterLocale FlutterLocaleFromNSLocale(NSLocale* locale) {
  FlutterLocale flutterLocale = {};
  flutterLocale.struct_size = sizeof(FlutterLocale);
  flutterLocale.language_code = [[locale objectForKey:NSLocaleLanguageCode] UTF8String];
  flutterLocale.country_code = [[locale objectForKey:NSLocaleCountryCode] UTF8String];
  flutterLocale.script_code = [[locale objectForKey:NSLocaleScriptCode] UTF8String];
  flutterLocale.variant_code = [[locale objectForKey:NSLocaleVariantCode] UTF8String];
  return flutterLocale;
}

/**
 * Private interface declaration for FlutterEngine.
 */
@interface FlutterEngine () <FlutterBinaryMessenger>

/**
 * Sends the list of user-preferred locales to the Flutter engine.
 */
- (void)sendUserLocales;

/**
 * Handles a platform message from the engine.
 */
- (void)engineCallbackOnPlatformMessage:(const FlutterPlatformMessage*)message;

/**
 * Requests that the task be posted back the to the Flutter engine at the target time. The target
 * time is in the clock used by the Flutter engine.
 */
- (void)postMainThreadTask:(FlutterTask)task targetTimeInNanoseconds:(uint64_t)targetTime;

/**
 * Loads the AOT snapshots and instructions from the elf bundle (app_elf_snapshot.so) into _aotData,
 * if it is present in the assets directory.
 */
- (void)loadAOTData:(NSString*)assetsDir;

@end

#pragma mark -

/**
 * `FlutterPluginRegistrar` implementation handling a single plugin.
 */
@interface FlutterEngineRegistrar : NSObject <FlutterPluginRegistrar>
- (instancetype)initWithPlugin:(nonnull NSString*)pluginKey
                 flutterEngine:(nonnull FlutterEngine*)flutterEngine;
@end

@implementation FlutterEngineRegistrar {
  NSString* _pluginKey;
  FlutterEngine* _flutterEngine;
}

- (instancetype)initWithPlugin:(NSString*)pluginKey flutterEngine:(FlutterEngine*)flutterEngine {
  self = [super init];
  if (self) {
    _pluginKey = [pluginKey copy];
    _flutterEngine = flutterEngine;
  }
  return self;
}

#pragma mark - FlutterPluginRegistrar

- (id<FlutterBinaryMessenger>)messenger {
  return _flutterEngine.binaryMessenger;
}

- (id<FlutterTextureRegistry>)textures {
  return _flutterEngine.renderer;
}

- (NSView*)view {
  return _flutterEngine.viewController.view;
}

- (void)addMethodCallDelegate:(nonnull id<FlutterPlugin>)delegate
                      channel:(nonnull FlutterMethodChannel*)channel {
  [channel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
    [delegate handleMethodCall:call result:result];
  }];
}

@end

// Callbacks provided to the engine. See the called methods for documentation.
#pragma mark - Static methods provided to engine configuration

static void OnPlatformMessage(const FlutterPlatformMessage* message, FlutterEngine* engine) {
  [engine engineCallbackOnPlatformMessage:message];
}

#pragma mark -

@implementation FlutterEngine {
  // The embedding-API-level engine object.
  FLUTTER_API_SYMBOL(FlutterEngine) _engine;

  // The private member for accessibility.
  std::shared_ptr<flutter::AccessibilityBridge> _bridge;

  // The project being run by this engine.
  FlutterDartProject* _project;

  // A mapping of channel names to the registered handlers for those channels.
  NSMutableDictionary<NSString*, FlutterBinaryMessageHandler>* _messageHandlers;

  // Whether the engine can continue running after the view controller is removed.
  BOOL _allowHeadlessExecution;

  // Pointer to the Dart AOT snapshot and instruction data.
  _FlutterEngineAOTData* _aotData;

  // _macOSGLCompositor is created when the engine is created and
  // it's destruction is handled by ARC when the engine is destroyed.
  std::unique_ptr<flutter::FlutterGLCompositor> _macOSGLCompositor;

  // FlutterCompositor is copied and used in embedder.cc.
  FlutterCompositor _compositor;
}

- (instancetype)initWithName:(NSString*)labelPrefix project:(FlutterDartProject*)project {
  return [self initWithName:labelPrefix project:project allowHeadlessExecution:YES];
}

- (instancetype)initWithName:(NSString*)labelPrefix
                     project:(FlutterDartProject*)project
      allowHeadlessExecution:(BOOL)allowHeadlessExecution {
  self = [super init];
  NSAssert(self, @"Super init cannot be nil");

  _project = project ?: [[FlutterDartProject alloc] init];
  _messageHandlers = [[NSMutableDictionary alloc] init];
  _allowHeadlessExecution = allowHeadlessExecution;
  _semanticsEnabled = NO;

  _embedderAPI.struct_size = sizeof(FlutterEngineProcTable);
  FlutterEngineGetProcAddresses(&_embedderAPI);

  if ([FlutterRenderingBackend renderUsingMetal]) {
    _renderer = [[FlutterMetalRenderer alloc] initWithFlutterEngine:self];
  } else {
    _renderer = [[FlutterOpenGLRenderer alloc] initWithFlutterEngine:self];
  }

  NSNotificationCenter* notificationCenter = [NSNotificationCenter defaultCenter];
  [notificationCenter addObserver:self
                         selector:@selector(sendUserLocales)
                             name:NSCurrentLocaleDidChangeNotification
                           object:nil];

  return self;
}

- (void)dealloc {
  [self shutDownEngine];
  if (_aotData) {
    _embedderAPI.CollectAOTData(_aotData);
  }
}

- (BOOL)runWithEntrypoint:(NSString*)entrypoint {
  if (self.running) {
    return NO;
  }

  if (!_allowHeadlessExecution && !_viewController) {
    NSLog(@"Attempted to run an engine with no view controller without headless mode enabled.");
    return NO;
  }

  // TODO(stuartmorgan): Move internal channel registration from FlutterViewController to here.

  // FlutterProjectArgs is expecting a full argv, so when processing it for
  // flags the first item is treated as the executable and ignored. Add a dummy
  // value so that all provided arguments are used.
  std::vector<std::string> switches = _project.switches;
  std::vector<const char*> argv = {"placeholder"};
  std::transform(switches.begin(), switches.end(), std::back_inserter(argv),
                 [](const std::string& arg) -> const char* { return arg.c_str(); });

  std::vector<const char*> dartEntrypointArgs;
  for (NSString* argument in [_project dartEntrypointArguments]) {
    dartEntrypointArgs.push_back([argument UTF8String]);
  }

  FlutterProjectArgs flutterArguments = {};
  flutterArguments.struct_size = sizeof(FlutterProjectArgs);
  flutterArguments.assets_path = _project.assetsPath.UTF8String;
  flutterArguments.icu_data_path = _project.ICUDataPath.UTF8String;
  flutterArguments.command_line_argc = static_cast<int>(argv.size());
  flutterArguments.command_line_argv = argv.size() > 0 ? argv.data() : nullptr;
  flutterArguments.platform_message_callback = (FlutterPlatformMessageCallback)OnPlatformMessage;
  flutterArguments.update_semantics_node_callback = [](const FlutterSemanticsNode* node,
                                                       void* user_data) {
    FlutterEngine* engine = (__bridge FlutterEngine*)user_data;
    [engine updateSemanticsNode:node];
  };
  flutterArguments.update_semantics_custom_action_callback =
      [](const FlutterSemanticsCustomAction* action, void* user_data) {
        FlutterEngine* engine = (__bridge FlutterEngine*)user_data;
        [engine updateSemanticsCustomActions:action];
      };
  flutterArguments.custom_dart_entrypoint = entrypoint.UTF8String;
  flutterArguments.shutdown_dart_vm_when_done = true;
  flutterArguments.dart_entrypoint_argc = dartEntrypointArgs.size();
  flutterArguments.dart_entrypoint_argv = dartEntrypointArgs.data();

  static size_t sTaskRunnerIdentifiers = 0;
  const FlutterTaskRunnerDescription cocoa_task_runner_description = {
      .struct_size = sizeof(FlutterTaskRunnerDescription),
      .user_data = (void*)CFBridgingRetain(self),
      .runs_task_on_current_thread_callback = [](void* user_data) -> bool {
        return [[NSThread currentThread] isMainThread];
      },
      .post_task_callback = [](FlutterTask task, uint64_t target_time_nanos,
                               void* user_data) -> void {
        [((__bridge FlutterEngine*)(user_data)) postMainThreadTask:task
                                           targetTimeInNanoseconds:target_time_nanos];
      },
      .identifier = ++sTaskRunnerIdentifiers,
  };
  const FlutterCustomTaskRunners custom_task_runners = {
      .struct_size = sizeof(FlutterCustomTaskRunners),
      .platform_task_runner = &cocoa_task_runner_description,
  };
  flutterArguments.custom_task_runners = &custom_task_runners;

  [self loadAOTData:_project.assetsPath];
  if (_aotData) {
    flutterArguments.aot_data = _aotData;
  }

  flutterArguments.compositor = [self createFlutterCompositor];

  FlutterRendererConfig rendererConfig = [_renderer createRendererConfig];
  FlutterEngineResult result = _embedderAPI.Initialize(
      FLUTTER_ENGINE_VERSION, &rendererConfig, &flutterArguments, (__bridge void*)(self), &_engine);
  if (result != kSuccess) {
    NSLog(@"Failed to initialize Flutter engine: error %d", result);
    return NO;
  }

  result = _embedderAPI.RunInitialized(_engine);
  if (result != kSuccess) {
    NSLog(@"Failed to run an initialized engine: error %d", result);
    return NO;
  }

  [self sendUserLocales];
  [self updateWindowMetrics];
  [self updateDisplayConfig];
  return YES;
}

- (void)loadAOTData:(NSString*)assetsDir {
  if (!_embedderAPI.RunsAOTCompiledDartCode()) {
    return;
  }

  BOOL isDirOut = false;  // required for NSFileManager fileExistsAtPath.
  NSFileManager* fileManager = [NSFileManager defaultManager];

  // This is the location where the test fixture places the snapshot file.
  // For applications built by Flutter tool, this is in "App.framework".
  NSString* elfPath = [NSString pathWithComponents:@[ assetsDir, @"app_elf_snapshot.so" ]];

  if (![fileManager fileExistsAtPath:elfPath isDirectory:&isDirOut]) {
    return;
  }

  FlutterEngineAOTDataSource source = {};
  source.type = kFlutterEngineAOTDataSourceTypeElfPath;
  source.elf_path = [elfPath cStringUsingEncoding:NSUTF8StringEncoding];

  auto result = _embedderAPI.CreateAOTData(&source, &_aotData);
  if (result != kSuccess) {
    NSLog(@"Failed to load AOT data from: %@", elfPath);
  }
}

- (void)setViewController:(FlutterViewController*)controller {
  _viewController = controller;
  [_renderer setFlutterView:controller.flutterView];

  if (!controller && !_allowHeadlessExecution) {
    [self shutDownEngine];
  }
}

- (FlutterCompositor*)createFlutterCompositor {
  // When rendering with metal do not support platform views.
  if ([FlutterRenderingBackend renderUsingMetal]) {
    return nil;
  }

  // TODO(richardjcai): Add support for creating a FlutterGLCompositor
  // with a nil _viewController for headless engines.
  // https://github.com/flutter/flutter/issues/71606
  if (!_viewController) {
    return nil;
  }

  FlutterOpenGLRenderer* openGLRenderer = reinterpret_cast<FlutterOpenGLRenderer*>(_renderer);
  [openGLRenderer.openGLContext makeCurrentContext];

  _macOSGLCompositor =
      std::make_unique<flutter::FlutterGLCompositor>(_viewController, openGLRenderer.openGLContext);

  _compositor = {};
  _compositor.struct_size = sizeof(FlutterCompositor);
  _compositor.user_data = _macOSGLCompositor.get();

  _compositor.create_backing_store_callback = [](const FlutterBackingStoreConfig* config,  //
                                                 FlutterBackingStore* backing_store_out,   //
                                                 void* user_data                           //
                                              ) {
    return reinterpret_cast<flutter::FlutterGLCompositor*>(user_data)->CreateBackingStore(
        config, backing_store_out);
  };

  _compositor.collect_backing_store_callback = [](const FlutterBackingStore* backing_store,  //
                                                  void* user_data                            //
                                               ) {
    return reinterpret_cast<flutter::FlutterGLCompositor*>(user_data)->CollectBackingStore(
        backing_store);
  };

  _compositor.present_layers_callback = [](const FlutterLayer** layers,  //
                                           size_t layers_count,          //
                                           void* user_data               //
                                        ) {
    return reinterpret_cast<flutter::FlutterGLCompositor*>(user_data)->Present(layers,
                                                                               layers_count);
  };

  __weak FlutterEngine* weakSelf = self;
  _macOSGLCompositor->SetPresentCallback([weakSelf]() {
    FlutterOpenGLRenderer* openGLRenderer =
        reinterpret_cast<FlutterOpenGLRenderer*>(weakSelf.renderer);
    return [openGLRenderer glPresent];
  });

  _compositor.avoid_backing_store_cache = true;

  return &_compositor;
}

- (id<FlutterBinaryMessenger>)binaryMessenger {
  // TODO(stuartmorgan): Switch to FlutterBinaryMessengerRelay to avoid plugins
  // keeping the engine alive.
  return self;
}

#pragma mark - Framework-internal methods

- (BOOL)running {
  return _engine != nullptr;
}

- (void)updateDisplayConfig {
  if (!_engine) {
    return;
  }

  CVDisplayLinkRef displayLinkRef;
  CGDirectDisplayID mainDisplayID = CGMainDisplayID();
  CVDisplayLinkCreateWithCGDisplay(mainDisplayID, &displayLinkRef);
  CVTime nominal = CVDisplayLinkGetNominalOutputVideoRefreshPeriod(displayLinkRef);
  if (!(nominal.flags & kCVTimeIsIndefinite)) {
    double refreshRate = static_cast<double>(nominal.timeScale) / nominal.timeValue;

    FlutterEngineDisplay display;
    display.struct_size = sizeof(display);
    display.display_id = mainDisplayID;
    display.refresh_rate = round(refreshRate);

    std::vector<FlutterEngineDisplay> displays = {display};
    _embedderAPI.NotifyDisplayUpdate(_engine, kFlutterEngineDisplaysUpdateTypeStartup,
                                     displays.data(), displays.size());
  }

  CVDisplayLinkRelease(displayLinkRef);
}

- (FlutterEngineProcTable&)embedderAPI {
  return _embedderAPI;
}

- (std::weak_ptr<flutter::AccessibilityBridge>)accessibilityBridge {
  return _bridge;
}

- (void)updateWindowMetrics {
  if (!_engine) {
    return;
  }
  NSView* view = _viewController.view;
  CGRect scaledBounds = [view convertRectToBacking:view.bounds];
  CGSize scaledSize = scaledBounds.size;
  double pixelRatio = view.bounds.size.width == 0 ? 1 : scaledSize.width / view.bounds.size.width;

  const FlutterWindowMetricsEvent windowMetricsEvent = {
      .struct_size = sizeof(windowMetricsEvent),
      .width = static_cast<size_t>(scaledSize.width),
      .height = static_cast<size_t>(scaledSize.height),
      .pixel_ratio = pixelRatio,
      .left = static_cast<size_t>(scaledBounds.origin.x),
      .top = static_cast<size_t>(scaledBounds.origin.y),
  };
  _embedderAPI.SendWindowMetricsEvent(_engine, &windowMetricsEvent);
}

- (void)sendPointerEvent:(const FlutterPointerEvent&)event {
  _embedderAPI.SendPointerEvent(_engine, &event, 1);
}

- (void)sendKeyEvent:(const FlutterKeyEvent&)event
            callback:(FlutterKeyEventCallback)callback
            userData:(void*)userData {
  _embedderAPI.SendKeyEvent(_engine, &event, callback, userData);
}

- (void)setSemanticsEnabled:(BOOL)enabled {
  if (_semanticsEnabled == enabled) {
    return;
  }
  _semanticsEnabled = enabled;
  if (!_semanticsEnabled && _bridge) {
    _bridge.reset();
  } else if (_semanticsEnabled && !_bridge) {
    _bridge = std::make_shared<flutter::AccessibilityBridge>(
        std::make_unique<flutter::AccessibilityBridgeMacDelegate>(self));
  }
  if (!_semanticsEnabled) {
    self.viewController.view.accessibilityChildren = nil;
  }
  _embedderAPI.UpdateSemanticsEnabled(_engine, _semanticsEnabled);
}

- (void)dispatchSemanticsAction:(FlutterSemanticsAction)action
                       toTarget:(uint16_t)target
                       withData:(const std::vector<uint8_t>&)data {
  _embedderAPI.DispatchSemanticsAction(_engine, target, action, data.data(), data.size());
}

#pragma mark - Private methods

- (void)sendUserLocales {
  if (!self.running) {
    return;
  }

  // Create a list of FlutterLocales corresponding to the preferred languages.
  NSMutableArray<NSLocale*>* locales = [NSMutableArray array];
  std::vector<FlutterLocale> flutterLocales;
  flutterLocales.reserve(locales.count);
  for (NSString* localeID in [NSLocale preferredLanguages]) {
    NSLocale* locale = [[NSLocale alloc] initWithLocaleIdentifier:localeID];
    [locales addObject:locale];
    flutterLocales.push_back(FlutterLocaleFromNSLocale(locale));
  }
  // Convert to a list of pointers, and send to the engine.
  std::vector<const FlutterLocale*> flutterLocaleList;
  flutterLocaleList.reserve(flutterLocales.size());
  std::transform(
      flutterLocales.begin(), flutterLocales.end(), std::back_inserter(flutterLocaleList),
      [](const auto& arg) -> const auto* { return &arg; });
  _embedderAPI.UpdateLocales(_engine, flutterLocaleList.data(), flutterLocaleList.size());
}

- (void)engineCallbackOnPlatformMessage:(const FlutterPlatformMessage*)message {
  NSData* messageData = nil;
  if (message->message_size > 0) {
    messageData = [NSData dataWithBytesNoCopy:(void*)message->message
                                       length:message->message_size
                                 freeWhenDone:NO];
  }
  NSString* channel = @(message->channel);
  __block const FlutterPlatformMessageResponseHandle* responseHandle = message->response_handle;

  FlutterBinaryReply binaryResponseHandler = ^(NSData* response) {
    if (responseHandle) {
      _embedderAPI.SendPlatformMessageResponse(self->_engine, responseHandle,
                                               static_cast<const uint8_t*>(response.bytes),
                                               response.length);
      responseHandle = NULL;
    } else {
      NSLog(@"Error: Message responses can be sent only once. Ignoring duplicate response "
             "on channel '%@'.",
            channel);
    }
  };

  FlutterBinaryMessageHandler channelHandler = _messageHandlers[channel];
  if (channelHandler) {
    channelHandler(messageData, binaryResponseHandler);
  } else {
    binaryResponseHandler(nil);
  }
}

/**
 * Note: Called from dealloc. Should not use accessors or other methods.
 */
- (void)shutDownEngine {
  if (_engine == nullptr) {
    return;
  }

  if (_viewController && _viewController.flutterView) {
    [_viewController.flutterView shutdown];
  }

  FlutterEngineResult result = _embedderAPI.Deinitialize(_engine);
  if (result != kSuccess) {
    NSLog(@"Could not de-initialize the Flutter engine: error %d", result);
  }

  // Balancing release for the retain in the task runner dispatch table.
  CFRelease((CFTypeRef)self);

  result = _embedderAPI.Shutdown(_engine);
  if (result != kSuccess) {
    NSLog(@"Failed to shut down Flutter engine: error %d", result);
  }
  _engine = nullptr;
}

#pragma mark - FlutterBinaryMessenger

- (void)sendOnChannel:(nonnull NSString*)channel message:(nullable NSData*)message {
  [self sendOnChannel:channel message:message binaryReply:nil];
}

- (void)sendOnChannel:(NSString*)channel
              message:(NSData* _Nullable)message
          binaryReply:(FlutterBinaryReply _Nullable)callback {
  FlutterPlatformMessageResponseHandle* response_handle = nullptr;
  if (callback) {
    struct Captures {
      FlutterBinaryReply reply;
    };
    auto captures = std::make_unique<Captures>();
    captures->reply = callback;
    auto message_reply = [](const uint8_t* data, size_t data_size, void* user_data) {
      auto captures = reinterpret_cast<Captures*>(user_data);
      NSData* reply_data = nil;
      if (data != nullptr && data_size > 0) {
        reply_data = [NSData dataWithBytes:static_cast<const void*>(data) length:data_size];
      }
      captures->reply(reply_data);
      delete captures;
    };

    FlutterEngineResult create_result = _embedderAPI.PlatformMessageCreateResponseHandle(
        _engine, message_reply, captures.get(), &response_handle);
    if (create_result != kSuccess) {
      NSLog(@"Failed to create a FlutterPlatformMessageResponseHandle (%d)", create_result);
      return;
    }
    captures.release();
  }

  FlutterPlatformMessage platformMessage = {
      .struct_size = sizeof(FlutterPlatformMessage),
      .channel = [channel UTF8String],
      .message = static_cast<const uint8_t*>(message.bytes),
      .message_size = message.length,
      .response_handle = response_handle,
  };

  FlutterEngineResult message_result = _embedderAPI.SendPlatformMessage(_engine, &platformMessage);
  if (message_result != kSuccess) {
    NSLog(@"Failed to send message to Flutter engine on channel '%@' (%d).", channel,
          message_result);
  }

  if (response_handle != nullptr) {
    FlutterEngineResult release_result =
        _embedderAPI.PlatformMessageReleaseResponseHandle(_engine, response_handle);
    if (release_result != kSuccess) {
      NSLog(@"Failed to release the response handle (%d).", release_result);
    };
  }
}

- (FlutterBinaryMessengerConnection)setMessageHandlerOnChannel:(nonnull NSString*)channel
                                          binaryMessageHandler:
                                              (nullable FlutterBinaryMessageHandler)handler {
  _messageHandlers[channel] = [handler copy];
  return 0;
}

- (void)cleanupConnection:(FlutterBinaryMessengerConnection)connection {
  // There hasn't been a need to implement this yet for macOS.
}

#pragma mark - FlutterPluginRegistry

- (id<FlutterPluginRegistrar>)registrarForPlugin:(NSString*)pluginName {
  return [[FlutterEngineRegistrar alloc] initWithPlugin:pluginName flutterEngine:self];
}

#pragma mark - FlutterTextureRegistrar

- (int64_t)registerTexture:(id<FlutterTexture>)texture {
  return [_renderer registerTexture:texture];
}

- (BOOL)registerTextureWithID:(int64_t)textureId {
  return _embedderAPI.RegisterExternalTexture(_engine, textureId) == kSuccess;
}

- (void)textureFrameAvailable:(int64_t)textureID {
  [_renderer textureFrameAvailable:textureID];
}

- (BOOL)markTextureFrameAvailable:(int64_t)textureID {
  return _embedderAPI.MarkExternalTextureFrameAvailable(_engine, textureID) == kSuccess;
}

- (void)unregisterTexture:(int64_t)textureID {
  [_renderer unregisterTexture:textureID];
}

- (BOOL)unregisterTextureWithID:(int64_t)textureID {
  return _embedderAPI.UnregisterExternalTexture(_engine, textureID) == kSuccess;
}

- (void)updateSemanticsNode:(const FlutterSemanticsNode*)node {
  NSAssert(_bridge, @"The accessibility bridge must be initialized.");
  if (node->id == kFlutterSemanticsNodeIdBatchEnd) {
    return;
  }
  _bridge->AddFlutterSemanticsNodeUpdate(node);
}

- (void)updateSemanticsCustomActions:(const FlutterSemanticsCustomAction*)action {
  NSAssert(_bridge, @"The accessibility bridge must be initialized.");
  if (action->id == kFlutterSemanticsNodeIdBatchEnd) {
    // Custom action with id = kFlutterSemanticsNodeIdBatchEnd indicates this is
    // the end of the update batch.
    _bridge->CommitUpdates();
    // Attaches the accessibility root to the flutter view.
    auto root = _bridge->GetFlutterPlatformNodeDelegateFromID(0).lock();
    if (root) {
      if ([self.viewController.view.accessibilityChildren count] == 0) {
        NSAccessibilityElement* native_root = root->GetNativeViewAccessible();
        self.viewController.view.accessibilityChildren = @[ native_root ];
      }
    } else {
      self.viewController.view.accessibilityChildren = nil;
    }
    return;
  }
  _bridge->AddFlutterSemanticsCustomActionUpdate(action);
}

#pragma mark - Task runner integration

- (void)postMainThreadTask:(FlutterTask)task targetTimeInNanoseconds:(uint64_t)targetTime {
  const auto engine_time = _embedderAPI.GetCurrentTime();

  __weak FlutterEngine* weak_self = self;
  auto worker = ^{
    FlutterEngine* strong_self = weak_self;
    if (strong_self && strong_self->_engine) {
      auto result = _embedderAPI.RunTask(strong_self->_engine, &task);
      if (result != kSuccess) {
        NSLog(@"Could not post a task to the Flutter engine.");
      }
    }
  };

  if (targetTime <= engine_time) {
    dispatch_async(dispatch_get_main_queue(), worker);

  } else {
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, targetTime - engine_time),
                   dispatch_get_main_queue(), worker);
  }
}

@end