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diff --git a/dom/media/mediacontrol/MediaControlService.h b/dom/media/mediacontrol/MediaControlService.h
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DOM_MEDIA_MEDIACONTROL_MEDIACONTROLSERVICE_H_
+#define DOM_MEDIA_MEDIACONTROL_MEDIACONTROLSERVICE_H_
+
+#include "mozilla/AlreadyAddRefed.h"
+
+#include "AudioFocusManager.h"
+#include "MediaController.h"
+#include "MediaControlKeyManager.h"
+#include "mozilla/dom/MediaControllerBinding.h"
+#include "nsIObserver.h"
+#include "nsTArray.h"
+
+namespace mozilla::dom {
+
+/**
+ * MediaControlService is an interface to access controllers by providing
+ * controller Id. Everytime when controller becomes active, which means there is
+ * one or more media started in the corresponding browsing context, so now the
+ * controller is actually controlling something in the content process, so it
+ * would be added into the list of the MediaControlService. The controller would
+ * be removed from the list of the MediaControlService when it becomes inactive,
+ * which means no media is playing in the corresponding browsing context. Note
+ * that, a controller can't be added to or remove from the list twice. It should
+ * should have a responsibility to add and remove itself in the proper time.
+ */
+class MediaControlService final : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  static RefPtr<MediaControlService> GetService();
+
+  // Currently these following static methods are only being used in testing.
+  static void GenerateMediaControlKey(const GlobalObject& global,
+                                      MediaControlKey aKey);
+  static void GetCurrentActiveMediaMetadata(const GlobalObject& aGlobal,
+                                            MediaMetadataInit& aMetadata);
+  static MediaSessionPlaybackState GetCurrentMediaSessionPlaybackState(
+      GlobalObject& aGlobal);
+
+  AudioFocusManager& GetAudioFocusManager() { return mAudioFocusManager; }
+  MediaControlKeySource* GetMediaControlKeySource() {
+    return mMediaControlKeyManager;
+  }
+
+  // Use these functions to register/unresgister controller to/from the active
+  // controller list in the service. Return true if the controller is registered
+  // or unregistered sucessfully.
+  bool RegisterActiveMediaController(MediaController* aController);
+  bool UnregisterActiveMediaController(MediaController* aController);
+  uint64_t GetActiveControllersNum() const;
+
+  // This method would be called when the controller changes its playback state.
+  void NotifyControllerPlaybackStateChanged(MediaController* aController);
+
+  // This method is used to help a media controller become a main controller, if
+  // it fits the requirement.
+  void RequestUpdateMainController(MediaController* aController);
+
+  // The main controller is the controller which can receive the media control
+  // key events and would show its metadata to virtual controller interface.
+  MediaController* GetMainController() const;
+
+  /**
+   * These following functions are used for testing only. We use them to
+   * generate fake media control key events, get the media metadata and playback
+   * state from the main controller.
+   */
+  void GenerateTestMediaControlKey(MediaControlKey aKey);
+  MediaMetadataBase GetMainControllerMediaMetadata() const;
+  MediaSessionPlaybackState GetMainControllerPlaybackState() const;
+
+  // Media title that should be used as a fallback. This commonly used
+  // when playing media in private browsing mode and we are trying to avoid
+  // exposing potentially sensitive titles.
+  nsString GetFallbackTitle() const;
+
+  // These functions are used to update the variable which would be used for
+  // telemetry probe.
+  void NotifyMediaControlHasEverBeenUsed();
+  void NotifyMediaControlHasEverBeenEnabled();
+
+ private:
+  MediaControlService();
+  ~MediaControlService();
+
+  /**
+   * When there are multiple media controllers existing, we would only choose
+   * one media controller as the main controller which can be controlled by
+   * media control keys event. The latest controller which is added into the
+   * service would become the main controller.
+   *
+   * However, as the main controller would be changed from time to time, so we
+   * create this wrapper to hold a real main controller if it exists. This class
+   * would also observe the playback state of controller in order to update the
+   * playback state of the event source.
+   *
+   * In addition, after finishing bug1592037, we would get the media metadata
+   * from the main controller, and update them to the event source in order to
+   * show those information on the virtual media controller interface on each
+   * platform.
+   */
+  class ControllerManager final {
+   public:
+    explicit ControllerManager(MediaControlService* aService);
+    ~ControllerManager() = default;
+
+    using MediaKeysArray = nsTArray<MediaControlKey>;
+    using LinkedListControllerPtr = LinkedListElement<RefPtr<MediaController>>*;
+    using ConstLinkedListControllerPtr =
+        const LinkedListElement<RefPtr<MediaController>>*;
+
+    bool AddController(MediaController* aController);
+    bool RemoveController(MediaController* aController);
+    void UpdateMainControllerIfNeeded(MediaController* aController);
+
+    void Shutdown();
+
+    MediaController* GetMainController() const;
+    bool Contains(MediaController* aController) const;
+    uint64_t GetControllersNum() const;
+
+    // These functions are used for monitoring main controller's status change.
+    void MainControllerPlaybackStateChanged(MediaSessionPlaybackState aState);
+    void MainControllerMetadataChanged(const MediaMetadataBase& aMetadata);
+
+   private:
+    // When applying `eInsertAsMainController`, we would always insert the
+    // element to the tail of the list. Eg. Insert C , [A, B] -> [A, B, C]
+    // When applying `eInsertAsNormalController`, we would insert the element
+    // prior to the element with a higher priority controller. Eg. Insert E and
+    // C and D have higher priority. [A, B, C, D] -> [A, B, E, C, D]
+    enum class InsertOptions {
+      eInsertAsMainController,
+      eInsertAsNormalController,
+    };
+
+    // Adjust the given controller's order by the insert option.
+    void ReorderGivenController(MediaController* aController,
+                                InsertOptions aOption);
+
+    void UpdateMainControllerInternal(MediaController* aController);
+    void ConnectMainControllerEvents();
+    void DisconnectMainControllerEvents();
+
+    LinkedList<RefPtr<MediaController>> mControllers;
+    RefPtr<MediaController> mMainController;
+
+    // These member are use to listen main controller's play state changes and
+    // update the playback state to the event source.
+    RefPtr<MediaControlKeySource> mSource;
+    MediaEventListener mMetadataChangedListener;
+    MediaEventListener mSupportedKeysChangedListener;
+    MediaEventListener mFullScreenChangedListener;
+    MediaEventListener mPictureInPictureModeChangedListener;
+    MediaEventListener mPositionChangedListener;
+  };
+
+  void Init();
+  void Shutdown();
+
+  AudioFocusManager mAudioFocusManager;
+  RefPtr<MediaControlKeyManager> mMediaControlKeyManager;
+  RefPtr<MediaControlKeyListener> mMediaKeysHandler;
+  MediaEventProducer<uint64_t> mMediaControllerAmountChangedEvent;
+  UniquePtr<ControllerManager> mControllerManager;
+  nsString mFallbackTitle;
+
+  // Used for telemetry probe.
+  void UpdateTelemetryUsageProbe();
+  bool mHasEverUsedMediaControl = false;
+  bool mHasEverEnabledMediaControl = false;
+};
+
+}  // namespace mozilla::dom
+
+#endif