FlutterEngine.mm

// 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 <iostream>
#include <vector>

#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterCompositor.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterDartProject_Internal.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterMenuPlugin.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterMouseCursorPlugin.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterPlatformViewController.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterRenderer.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewController_Internal.h"
#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProvider.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;
}

/// The private notification for voice over.
static NSString* const kEnhancedUserInterfaceNotification =
    @"NSApplicationDidChangeAccessibilityEnhancedUserInterfaceNotification";
static NSString* const kEnhancedUserInterfaceKey = @"AXEnhancedUserInterface";

/// Clipboard plain text format.
constexpr char kTextPlainFormat[] = "text/plain";

#pragma mark -

// Records an active handler of the messenger (FlutterEngine) that listens to
// platform messages on a given channel.
@interface FlutterEngineHandlerInfo : NSObject

- (instancetype)initWithConnection:(NSNumber*)connection
                           handler:(FlutterBinaryMessageHandler)handler;

@property(nonatomic, readonly) FlutterBinaryMessageHandler handler;
@property(nonatomic, readonly) NSNumber* connection;

@end

@implementation FlutterEngineHandlerInfo
- (instancetype)initWithConnection:(NSNumber*)connection
                           handler:(FlutterBinaryMessageHandler)handler {
  self = [super init];
  NSAssert(self, @"Super init cannot be nil");
  _connection = connection;
  _handler = handler;
  return self;
}
@end

#pragma mark -

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

/**
 * A mutable array that holds one bool value that determines if responses to platform messages are
 * clear to execute. This value should be read or written only inside of a synchronized block and
 * will return `NO` after the FlutterEngine has been dealloc'd.
 */
@property(nonatomic, strong) NSMutableArray<NSNumber*>* isResponseValid;

- (nullable FlutterViewController*)viewControllerForId:(uint64_t)viewId;

/**
 * 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;

/**
 * Invoked right before the engine is restarted.
 *
 * This should reset states to as if the application has just started.  It
 * usually indicates a hot restart (Shift-R in Flutter CLI.)
 */
- (void)engineCallbackOnPreEngineRestart;

/**
 * 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;

/**
 * Creates a platform view channel and sets up the method handler.
 */
- (void)setUpPlatformViewChannel;

/**
 * Handles messages received from the Flutter engine on the _*Channel channels.
 */
- (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result;

@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 {
  if (!_flutterEngine.viewController.viewLoaded) {
    [_flutterEngine.viewController loadView];
  }
  return _flutterEngine.viewController.flutterView;
}

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

- (void)registerViewFactory:(nonnull NSObject<FlutterPlatformViewFactory>*)factory
                     withId:(nonnull NSString*)factoryId {
  [[_flutterEngine platformViewController] registerViewFactory:factory withId:factoryId];
}

@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::AccessibilityBridgeMac> _bridge;

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

  // A mapping of channel names to the registered information for those channels.
  NSMutableDictionary<NSString*, FlutterEngineHandlerInfo*>* _messengerHandlers;

  // A self-incremental integer to assign to newly assigned channels as
  // identification.
  FlutterBinaryMessengerConnection _currentMessengerConnection;

  // 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;

  // _macOSCompositor is created when the engine is created and its destruction is handled by ARC
  // when the engine is destroyed.
  std::unique_ptr<flutter::FlutterCompositor> _macOSCompositor;

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

  // Method channel for platform view functions. These functions include creating, disposing and
  // mutating a platform view.
  FlutterMethodChannel* _platformViewsChannel;

  // Used to support creation and deletion of platform views and registering platform view
  // factories. Lifecycle is tied to the engine.
  FlutterPlatformViewController* _platformViewController;

  // A message channel for sending user settings to the flutter engine.
  FlutterBasicMessageChannel* _settingsChannel;

  // A method channel for miscellaneous platform functionality.
  FlutterMethodChannel* _platformChannel;
}

- (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];
  _messengerHandlers = [[NSMutableDictionary alloc] init];
  _currentMessengerConnection = 1;
  _allowHeadlessExecution = allowHeadlessExecution;
  _semanticsEnabled = NO;
  _isResponseValid = [[NSMutableArray alloc] initWithCapacity:1];
  [_isResponseValid addObject:@YES];

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

  _renderer = [[FlutterRenderer alloc] initWithFlutterEngine:self];

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

  _platformViewController = [[FlutterPlatformViewController alloc] init];
  [self setUpPlatformViewChannel];
  [self setUpNotificationCenterListeners];

  return self;
}

- (void)dealloc {
  @synchronized(_isResponseValid) {
    [_isResponseValid removeAllObjects];
    [_isResponseValid addObject:@NO];
  }
  [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;
  }

  [self addInternalPlugins];

  // The first argument of argv is required to be the executable name.
  std::vector<const char*> argv = {[self.executableName UTF8String]};
  std::vector<std::string> switches = _project.switches;
  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.empty() ? nullptr : argv.data();
  flutterArguments.platform_message_callback = (FlutterPlatformMessageCallback)OnPlatformMessage;
  flutterArguments.update_semantics_callback = [](const FlutterSemanticsUpdate* update,
                                                  void* user_data) {
    FlutterEngine* engine = (__bridge FlutterEngine*)user_data;
    [engine updateSemantics:update];
  };
  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();
  flutterArguments.root_isolate_create_callback = _project.rootIsolateCreateCallback;
  flutterArguments.log_message_callback = [](const char* tag, const char* message,
                                             void* user_data) {
    if (tag && tag[0]) {
      std::cout << tag << ": ";
    }
    std::cout << message << std::endl;
  };

  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];

  flutterArguments.on_pre_engine_restart_callback = [](void* user_data) {
    FlutterEngine* engine = (__bridge FlutterEngine*)user_data;
    [engine engineCallbackOnPreEngineRestart];
  };

  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];
  // Send the initial user settings such as brightness and text scale factor
  // to the engine.
  [self sendInitialSettings];
  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 {
  if (_viewController == controller) {
    // From nil to nil, or from non-nil to the same controller.
    return;
  }
  if (_viewController == nil && controller != nil) {
    _viewController = controller;
    [_viewController attachToEngine:self withId:kFlutterDefaultViewId];
  } else if (_viewController != nil && controller == nil) {
    [_viewController detachFromEngine];
    _viewController = nil;
    if (!_allowHeadlessExecution) {
      [self shutDownEngine];
    }
  } else {
    NSLog(@"Failed to set view controller to the engine: "
          @"Replacing the view controller of the engine is not supported.");
  }
}

- (FlutterCompositor*)createFlutterCompositor {
  _macOSCompositor = std::make_unique<flutter::FlutterCompositor>(
      [[FlutterViewEngineProvider alloc] initWithEngine:self], _platformViewController);

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

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

  _compositor.collect_backing_store_callback = [](const FlutterBackingStore* backing_store,  //
                                                  void* user_data                            //
                                               ) { return true; };

  _compositor.present_layers_callback = [](const FlutterLayer** layers,  //
                                           size_t layers_count,          //
                                           void* user_data               //
                                        ) {
    // TODO(dkwingsmt): This callback only supports single-view, therefore it
    // only operates on the default view. To support multi-view, we need a new
    // callback that also receives a view ID.
    return reinterpret_cast<flutter::FlutterCompositor*>(user_data)->Present(kFlutterDefaultViewId,
                                                                             layers, layers_count);
  };

  _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);
}

- (void)onSettingsChanged:(NSNotification*)notification {
  // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/32015.
  NSString* brightness =
      [[NSUserDefaults standardUserDefaults] stringForKey:@"AppleInterfaceStyle"];
  [_settingsChannel sendMessage:@{
    @"platformBrightness" : [brightness isEqualToString:@"Dark"] ? @"dark" : @"light",
    // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/32006.
    @"textScaleFactor" : @1.0,
    @"alwaysUse24HourFormat" : @false
  }];
}

- (void)sendInitialSettings {
  // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/32015.
  [[NSDistributedNotificationCenter defaultCenter]
      addObserver:self
         selector:@selector(onSettingsChanged:)
             name:@"AppleInterfaceThemeChangedNotification"
           object:nil];
  [self onSettingsChanged:nil];
}

- (FlutterEngineProcTable&)embedderAPI {
  return _embedderAPI;
}

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

- (nonnull NSString*)executableName {
  return [[[NSProcessInfo processInfo] arguments] firstObject] ?: @"Flutter";
}

- (void)updateWindowMetrics {
  if (!_engine || !self.viewController.viewLoaded) {
    return;
  }
  NSView* view = self.viewController.flutterView;
  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;
  // Remove the accessibility children from flutter view before reseting the bridge.
  if (!_semanticsEnabled && self.viewController.viewLoaded) {
    self.viewController.flutterView.accessibilityChildren = nil;
  }
  if (!_semanticsEnabled && _bridge) {
    _bridge.reset();
  } else if (_semanticsEnabled && !_bridge) {
    _bridge = [self createAccessibilityBridge:self viewController:self.viewController];
  }
  _embedderAPI.UpdateSemanticsEnabled(_engine, _semanticsEnabled);
}

- (std::shared_ptr<flutter::AccessibilityBridgeMac>)
    createAccessibilityBridge:(nonnull FlutterEngine*)engine
               viewController:(nonnull FlutterViewController*)viewController {
  return std::make_shared<flutter::AccessibilityBridgeMac>(engine, _viewController);
}

- (void)dispatchSemanticsAction:(FlutterSemanticsAction)action
                       toTarget:(uint16_t)target
                       withData:(fml::MallocMapping)data {
  _embedderAPI.DispatchSemanticsAction(_engine, target, action, data.GetMapping(), data.GetSize());
}

- (FlutterPlatformViewController*)platformViewController {
  return _platformViewController;
}

#pragma mark - Private methods

- (FlutterViewController*)viewControllerForId:(uint64_t)viewId {
  // TODO(dkwingsmt): The engine only supports single-view, therefore it
  // only processes the default ID. After the engine supports multiple views,
  // this method should be able to return the view for any IDs.
  NSAssert(viewId == kFlutterDefaultViewId, @"Unexpected view ID %llu", viewId);
  if (viewId == kFlutterDefaultViewId) {
    return _viewController;
  }
  return nil;
}

- (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;
  __block FlutterEngine* weakSelf = self;
  NSMutableArray* isResponseValid = self.isResponseValid;
  FlutterEngineSendPlatformMessageResponseFnPtr sendPlatformMessageResponse =
      _embedderAPI.SendPlatformMessageResponse;
  FlutterBinaryReply binaryResponseHandler = ^(NSData* response) {
    @synchronized(isResponseValid) {
      if (![isResponseValid[0] boolValue]) {
        // Ignore, engine was killed.
        return;
      }
      if (responseHandle) {
        sendPlatformMessageResponse(weakSelf->_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);
      }
    }
  };

  FlutterEngineHandlerInfo* handlerInfo = _messengerHandlers[channel];
  if (handlerInfo) {
    handlerInfo.handler(messageData, binaryResponseHandler);
  } else {
    binaryResponseHandler(nil);
  }
}

- (void)engineCallbackOnPreEngineRestart {
  if (_viewController) {
    [_viewController onPreEngineRestart];
  }
}

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

  [self.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;
}

- (void)setUpPlatformViewChannel {
  _platformViewsChannel =
      [FlutterMethodChannel methodChannelWithName:@"flutter/platform_views"
                                  binaryMessenger:self.binaryMessenger
                                            codec:[FlutterStandardMethodCodec sharedInstance]];

  __weak FlutterEngine* weakSelf = self;
  [_platformViewsChannel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
    [[weakSelf platformViewController] handleMethodCall:call result:result];
  }];
}

- (void)setUpNotificationCenterListeners {
  NSNotificationCenter* center = [NSNotificationCenter defaultCenter];
  // macOS fires this private message when VoiceOver turns on or off.
  [center addObserver:self
             selector:@selector(onAccessibilityStatusChanged:)
                 name:kEnhancedUserInterfaceNotification
               object:nil];
  [center addObserver:self
             selector:@selector(applicationWillTerminate:)
                 name:NSApplicationWillTerminateNotification
               object:nil];
}

- (void)addInternalPlugins {
  __weak FlutterEngine* weakSelf = self;
  [FlutterMouseCursorPlugin registerWithRegistrar:[self registrarForPlugin:@"mousecursor"]];
  [FlutterMenuPlugin registerWithRegistrar:[self registrarForPlugin:@"menu"]];
  _settingsChannel =
      [FlutterBasicMessageChannel messageChannelWithName:@"flutter/settings"
                                         binaryMessenger:self.binaryMessenger
                                                   codec:[FlutterJSONMessageCodec sharedInstance]];
  _platformChannel =
      [FlutterMethodChannel methodChannelWithName:@"flutter/platform"
                                  binaryMessenger:self.binaryMessenger
                                            codec:[FlutterJSONMethodCodec sharedInstance]];
  [_platformChannel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
    [weakSelf handleMethodCall:call result:result];
  }];
}

- (void)applicationWillTerminate:(NSNotification*)notification {
  [self shutDownEngine];
}

- (void)onAccessibilityStatusChanged:(NSNotification*)notification {
  BOOL enabled = [notification.userInfo[kEnhancedUserInterfaceKey] boolValue];
  [self.viewController onAccessibilityStatusChanged:enabled];
  self.semanticsEnabled = enabled;
}

- (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
  if ([call.method isEqualToString:@"SystemNavigator.pop"]) {
    [NSApp terminate:self];
    result(nil);
  } else if ([call.method isEqualToString:@"SystemSound.play"]) {
    [self playSystemSound:call.arguments];
    result(nil);
  } else if ([call.method isEqualToString:@"Clipboard.getData"]) {
    result([self getClipboardData:call.arguments]);
  } else if ([call.method isEqualToString:@"Clipboard.setData"]) {
    [self setClipboardData:call.arguments];
    result(nil);
  } else if ([call.method isEqualToString:@"Clipboard.hasStrings"]) {
    result(@{@"value" : @([self clipboardHasStrings])});
  } else {
    result(FlutterMethodNotImplemented);
  }
}

- (void)playSystemSound:(NSString*)soundType {
  if ([soundType isEqualToString:@"SystemSoundType.alert"]) {
    NSBeep();
  }
}

- (NSDictionary*)getClipboardData:(NSString*)format {
  NSPasteboard* pasteboard = self.pasteboard;
  if ([format isEqualToString:@(kTextPlainFormat)]) {
    NSString* stringInPasteboard = [pasteboard stringForType:NSPasteboardTypeString];
    return stringInPasteboard == nil ? nil : @{@"text" : stringInPasteboard};
  }
  return nil;
}

- (void)setClipboardData:(NSDictionary*)data {
  NSPasteboard* pasteboard = self.pasteboard;
  NSString* text = data[@"text"];
  [pasteboard clearContents];
  if (text && ![text isEqual:[NSNull null]]) {
    [pasteboard setString:text forType:NSPasteboardTypeString];
  }
}

- (BOOL)clipboardHasStrings {
  return [self.pasteboard stringForType:NSPasteboardTypeString].length > 0;
}

- (NSPasteboard*)pasteboard {
  return [NSPasteboard generalPasteboard];
}

#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 {
  _currentMessengerConnection += 1;
  _messengerHandlers[channel] =
      [[FlutterEngineHandlerInfo alloc] initWithConnection:@(_currentMessengerConnection)
                                                   handler:[handler copy]];
  return _currentMessengerConnection;
}

- (void)cleanUpConnection:(FlutterBinaryMessengerConnection)connection {
  // Find the _messengerHandlers that has the required connection, and record its
  // channel.
  NSString* foundChannel = nil;
  for (NSString* key in [_messengerHandlers allKeys]) {
    FlutterEngineHandlerInfo* handlerInfo = [_messengerHandlers objectForKey:key];
    if ([handlerInfo.connection isEqual:@(connection)]) {
      foundChannel = key;
      break;
    }
  }
  if (foundChannel) {
    [_messengerHandlers removeObjectForKey:foundChannel];
  }
}

#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)updateSemantics:(const FlutterSemanticsUpdate*)update {
  NSAssert(_bridge, @"The accessibility bridge must be initialized.");
  for (size_t i = 0; i < update->nodes_count; i++) {
    const FlutterSemanticsNode* node = &update->nodes[i];
    _bridge->AddFlutterSemanticsNodeUpdate(node);
  }

  for (size_t i = 0; i < update->custom_actions_count; i++) {
    const FlutterSemanticsCustomAction* action = &update->custom_actions[i];
    _bridge->AddFlutterSemanticsCustomActionUpdate(action);
  }

  _bridge->CommitUpdates();

  // Accessibility tree can only be used when the view is loaded.
  if (!self.viewController.viewLoaded) {
    return;
  }
  // Attaches the accessibility root to the flutter view.
  auto root = _bridge->GetFlutterPlatformNodeDelegateFromID(0).lock();
  if (root) {
    if ([self.viewController.flutterView.accessibilityChildren count] == 0) {
      NSAccessibilityElement* native_root = root->GetNativeViewAccessible();
      self.viewController.flutterView.accessibilityChildren = @[ native_root ];
    }
  } else {
    self.viewController.flutterView.accessibilityChildren = nil;
  }
}

#pragma mark - Task runner integration

- (void)runTaskOnEmbedder:(FlutterTask)task {
  if (_engine) {
    auto result = _embedderAPI.RunTask(_engine, &task);
    if (result != kSuccess) {
      NSLog(@"Could not post a task to the Flutter engine.");
    }
  }
}

- (void)postMainThreadTask:(FlutterTask)task targetTimeInNanoseconds:(uint64_t)targetTime {
  __weak FlutterEngine* weakSelf = self;
  auto worker = ^{
    [weakSelf runTaskOnEmbedder:task];
  };

  const auto engine_time = _embedderAPI.GetCurrentTime();
  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);
  }
}

// Getter used by test harness, only exposed through the FlutterEngine(Test) category
- (flutter::FlutterCompositor*)macOSCompositor {
  return _macOSCompositor.get();
}

@end