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diff --git a/dom/audiochannel/AudioChannelService.h b/dom/audiochannel/AudioChannelService.h
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+++ b/dom/audiochannel/AudioChannelService.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 mozilla_dom_audiochannelservice_h__
+#define mozilla_dom_audiochannelservice_h__
+
+#include "nsIObserver.h"
+#include "nsTObserverArray.h"
+#include "nsTArray.h"
+
+#include "AudioChannelAgent.h"
+#include "nsAttrValue.h"
+#include "mozilla/Logging.h"
+#include "mozilla/UniquePtr.h"
+
+#include <functional>
+
+class nsPIDOMWindowOuter;
+struct PRLogModuleInfo;
+
+namespace mozilla::dom {
+
+class AudioPlaybackConfig {
+ public:
+  AudioPlaybackConfig()
+      : mVolume(1.0),
+        mMuted(false),
+        mSuspend(nsISuspendedTypes::NONE_SUSPENDED),
+        mNumberOfAgents(0) {}
+
+  AudioPlaybackConfig(float aVolume, bool aMuted, uint32_t aSuspended)
+      : mVolume(aVolume),
+        mMuted(aMuted),
+        mSuspend(aSuspended),
+        mNumberOfAgents(0) {}
+
+  float mVolume;
+  bool mMuted;
+  uint32_t mSuspend;
+  bool mCapturedAudio = false;
+  uint32_t mNumberOfAgents;
+};
+
+class AudioChannelService final : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  /**
+   * We use `AudibleState` to represent the audible state of an owner of audio
+   * channel agent. Those information in AudioChannelWindow could help us to
+   * determine if a tab is being audible or not, in order to tell Chrome JS to
+   * show the sound indicator or delayed autoplay icon on the tab bar.
+   *
+   * - Sound indicator
+   * When a tab is playing sound, we would show the sound indicator on tab bar
+   * to tell users that this tab is producing sound now. In addition, the sound
+   * indicator also give users an ablility to mute or unmute tab.
+   *
+   * When an AudioChannelWindow first contains an agent with state `eAudible`,
+   * or an AudioChannelWindow losts its last agent with state `eAudible`, we
+   * would notify Chrome JS about those changes, to tell them that a tab has
+   * been being audible or not, in order to display or remove the indicator for
+   * a corresponding tab.
+   *
+   * - Delayed autoplay icon (Play Tab icon)
+   * When we enable delaying autoplay, which is to postpone the autoplay media
+   * for unvisited tab until it first goes to foreground, or user click the
+   * play tab icon to resume the delayed media.
+   *
+   * When an AudioChannelWindow first contains an agent with state `eAudible` or
+   * `eMaybeAudible`, we would notify Chrome JS about this change, in order to
+   * show the delayed autoplay tab icon to user, which is used to notice user
+   * there is a media being delayed starting, and then user can click the play
+   * tab icon to resume the start of media, or visit that tab to resume delayed
+   * media automatically.
+   *
+   * According to our UX design, we don't show this icon for inaudible media.
+   * The reason of showing the icon for a tab, where the agent starts with state
+   * `eMaybeAudible`, is because some video might be silent in the beginning
+   * but would soon become audible later.
+   *
+   * ---------------------------------------------------------------------------
+   *
+   * eNotAudible : agent is not audible
+   * eMaybeAudible : agent is not audible now, but it might be audible later
+   * eAudible : agent is audible now
+   */
+  enum AudibleState : uint8_t {
+    eNotAudible = 0,
+    eMaybeAudible = 1,
+    eAudible = 2
+  };
+
+  enum AudioCaptureState : bool { eCapturing = true, eNotCapturing = false };
+
+  enum AudibleChangedReasons : uint32_t {
+    eVolumeChanged = 0,
+    eDataAudibleChanged = 1,
+    ePauseStateChanged = 2
+  };
+
+  /**
+   * Returns the AudioChannelServce singleton.
+   * If AudioChannelService doesn't exist, create and return new one.
+   * Only to be called from main thread.
+   */
+  static already_AddRefed<AudioChannelService> GetOrCreate();
+
+  /**
+   * Returns the AudioChannelService singleton if one exists.
+   * If AudioChannelService doesn't exist, returns null.
+   */
+  static already_AddRefed<AudioChannelService> Get();
+
+  static LogModule* GetAudioChannelLog();
+
+  static bool IsEnableAudioCompeting();
+
+  /**
+   * Any audio channel agent that starts playing should register itself to
+   * this service, sharing the AudioChannel.
+   */
+  void RegisterAudioChannelAgent(AudioChannelAgent* aAgent,
+                                 AudibleState aAudible);
+
+  /**
+   * Any audio channel agent that stops playing should unregister itself to
+   * this service.
+   */
+  void UnregisterAudioChannelAgent(AudioChannelAgent* aAgent);
+
+  /**
+   * Return the state to indicate this audioChannel for his window should keep
+   * playing/muted/suspended.
+   */
+  AudioPlaybackConfig GetMediaConfig(nsPIDOMWindowOuter* aWindow) const;
+
+  /**
+   * Called this method when the audible state of the audio playback changed,
+   * it would dispatch the playback event to observers which want to know the
+   * actual audible state of the window.
+   */
+  void AudioAudibleChanged(AudioChannelAgent* aAgent, AudibleState aAudible,
+                           AudibleChangedReasons aReason);
+
+  bool IsWindowActive(nsPIDOMWindowOuter* aWindow);
+
+  void RefreshAgentsVolume(nsPIDOMWindowOuter* aWindow, float aVolume,
+                           bool aMuted);
+
+  // This method needs to know the inner window that wants to capture audio. We
+  // group agents per top outer window, but we can have multiple innerWindow per
+  // top outerWindow (subiframes, etc.) and we have to identify all the agents
+  // just for a particular innerWindow.
+  void SetWindowAudioCaptured(nsPIDOMWindowOuter* aWindow,
+                              uint64_t aInnerWindowID, bool aCapture);
+
+  void NotifyResumingDelayedMedia(nsPIDOMWindowOuter* aWindow);
+
+ private:
+  AudioChannelService();
+  ~AudioChannelService();
+
+  void RefreshAgents(nsPIDOMWindowOuter* aWindow,
+                     const std::function<void(AudioChannelAgent*)>& aFunc);
+
+  void RefreshAgentsSuspend(nsPIDOMWindowOuter* aWindow,
+                            nsSuspendedTypes aSuspend);
+
+  static void CreateServiceIfNeeded();
+
+  /**
+   * Shutdown the singleton.
+   */
+  static void Shutdown();
+
+  void RefreshAgentsAudioFocusChanged(AudioChannelAgent* aAgent);
+
+  class AudioChannelWindow final {
+   public:
+    explicit AudioChannelWindow(uint64_t aWindowID)
+        : mWindowID(aWindowID),
+          mIsAudioCaptured(false),
+          mShouldSendActiveMediaBlockStopEvent(false) {}
+
+    void AudioAudibleChanged(AudioChannelAgent* aAgent, AudibleState aAudible,
+                             AudibleChangedReasons aReason);
+
+    void AppendAgent(AudioChannelAgent* aAgent, AudibleState aAudible);
+    void RemoveAgent(AudioChannelAgent* aAgent);
+
+    void NotifyMediaBlockStop(nsPIDOMWindowOuter* aWindow);
+
+    uint64_t mWindowID;
+    bool mIsAudioCaptured;
+    AudioPlaybackConfig mConfig;
+
+    // Raw pointer because the AudioChannelAgent must unregister itself.
+    nsTObserverArray<AudioChannelAgent*> mAgents;
+    nsTObserverArray<AudioChannelAgent*> mAudibleAgents;
+
+    // If we've dispatched "activeMediaBlockStart" event, we must dispatch
+    // another event "activeMediablockStop" when the window is resumed from
+    // suspend-block.
+    bool mShouldSendActiveMediaBlockStopEvent;
+
+   private:
+    void AppendAudibleAgentIfNotContained(AudioChannelAgent* aAgent,
+                                          AudibleChangedReasons aReason);
+    void RemoveAudibleAgentIfContained(AudioChannelAgent* aAgent,
+                                       AudibleChangedReasons aReason);
+
+    void AppendAgentAndIncreaseAgentsNum(AudioChannelAgent* aAgent);
+    void RemoveAgentAndReduceAgentsNum(AudioChannelAgent* aAgent);
+
+    bool IsFirstAudibleAgent() const;
+    bool IsLastAudibleAgent() const;
+
+    void NotifyAudioAudibleChanged(nsPIDOMWindowOuter* aWindow,
+                                   AudibleState aAudible,
+                                   AudibleChangedReasons aReason);
+
+    void MaybeNotifyMediaBlockStart(AudioChannelAgent* aAgent);
+  };
+
+  AudioChannelWindow* GetOrCreateWindowData(nsPIDOMWindowOuter* aWindow);
+
+  AudioChannelWindow* GetWindowData(uint64_t aWindowID) const;
+
+  nsTObserverArray<UniquePtr<AudioChannelWindow>> mWindows;
+};
+
+const char* SuspendTypeToStr(const nsSuspendedTypes& aSuspend);
+const char* AudibleStateToStr(
+    const AudioChannelService::AudibleState& aAudible);
+const char* AudibleChangedReasonToStr(
+    const AudioChannelService::AudibleChangedReasons& aReason);
+
+}  // namespace mozilla::dom
+
+#endif