// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Low-latency audio capturing class utilizing audio input stream provided
// by a server (browser) process by use of an IPC interface.
//
// Relationship of classes:
//
//  AudioInputController                 AudioInputDevice
//           ^                                  ^
//           |                                  |
//           v                  IPC             v
// AudioInputRendererHost  <----------->  AudioInputIPC
//           ^                            (AudioInputMessageFilter)
//           |
//           v
// AudioInputDeviceManager
//
// Transportation of audio samples from the browser to the render process
// is done by using shared memory in combination with a SyncSocket.
// The AudioInputDevice user registers an AudioInputDevice::CaptureCallback by
// calling Initialize().  The callback will be called with recorded audio from
// the underlying audio layers.
// The session ID is used by the AudioInputRendererHost to start the device
// referenced by this ID.
//
// State sequences:
//
// Start -> InitializeOnIOThread -> CreateStream ->
//       <- OnStreamCreated <-
//       -> StartOnIOThread -> PlayStream ->
//
//
// AudioInputDevice::Capture => low latency audio transport on audio thread =>
//                               |
// Stop --> ShutDownOnIOThread ------>  CloseStream -> Close
//
// This class depends on two threads to function:
//
// 1. An IO thread.
//    This thread is used to asynchronously process Start/Stop etc operations
//    that are available via the public interface.  The public methods are
//    asynchronous and simply post a task to the IO thread to actually perform
//    the work.
// 2. Audio transport thread.
//    Responsible for calling the CaptureCallback and feed audio samples from
//    the server side audio layer using a socket and shared memory.
//
// Implementation notes:
// - The user must call Stop() before deleting the class instance.

#ifndef MEDIA_AUDIO_AUDIO_INPUT_DEVICE_H_
#define MEDIA_AUDIO_AUDIO_INPUT_DEVICE_H_

#include <memory>
#include <string>

#include "base/compiler_specific.h"
#include "base/macros.h"
#include "base/memory/shared_memory.h"
#include "media/audio/audio_device_thread.h"
#include "media/audio/audio_input_ipc.h"
#include "media/audio/scoped_task_runner_observer.h"
#include "media/base/audio_capturer_source.h"
#include "media/base/audio_parameters.h"
#include "media/base/media_export.h"

namespace media {

// TODO(henrika): This class is based on the AudioOutputDevice class and it has
// many components in common. Investigate potential for re-factoring.
// See http://crbug.com/179597.
// TODO(henrika): Add support for event handling (e.g. OnStateChanged,
// OnCaptureStopped etc.) and ensure that we can deliver these notifications
// to any clients using this class.
class MEDIA_EXPORT AudioInputDevice
    : NON_EXPORTED_BASE(public AudioCapturerSource),
      NON_EXPORTED_BASE(public AudioInputIPCDelegate),
      NON_EXPORTED_BASE(public ScopedTaskRunnerObserver) {
 public:
  // NOTE: Clients must call Initialize() before using.
  AudioInputDevice(
      std::unique_ptr<AudioInputIPC> ipc,
      const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner);

  // AudioCapturerSource implementation.
  void Initialize(const AudioParameters& params,
                  CaptureCallback* callback,
                  int session_id) override;
  void Start() override;
  void Stop() override;
  void SetVolume(double volume) override;
  void SetAutomaticGainControl(bool enabled) override;

 protected:
  friend class base::RefCountedThreadSafe<AudioInputDevice>;
  ~AudioInputDevice() override;

  // Methods called on IO thread ----------------------------------------------
  // AudioInputIPCDelegate implementation.
  void OnStreamCreated(base::SharedMemoryHandle handle,
                       base::SyncSocket::Handle socket_handle,
                       int length,
                       int total_segments) override;
  void OnVolume(double volume) override;
  void OnStateChanged(AudioInputIPCDelegateState state) override;
  void OnIPCClosed() override;

 private:
  // Note: The ordering of members in this enum is critical to correct behavior!
  enum State {
    IPC_CLOSED,  // No more IPCs can take place.
    IDLE,  // Not started.
    CREATING_STREAM,  // Waiting for OnStreamCreated() to be called back.
    RECORDING,  // Receiving audio data.
  };

  // Methods called on IO thread ----------------------------------------------
  // The following methods are tasks posted on the IO thread that needs to
  // be executed on that thread. They interact with AudioInputMessageFilter and
  // sends IPC messages on that thread.
  void StartUpOnIOThread();
  void ShutDownOnIOThread();
  void SetVolumeOnIOThread(double volume);
  void SetAutomaticGainControlOnIOThread(bool enabled);

  // base::MessageLoop::DestructionObserver implementation for the IO loop.
  // If the IO loop dies before we do, we shut down the audio thread from here.
  void WillDestroyCurrentMessageLoop() override;

  AudioParameters audio_parameters_;

  CaptureCallback* callback_;

  // A pointer to the IPC layer that takes care of sending requests over to
  // the AudioInputRendererHost.  Only valid when state_ != IPC_CLOSED and must
  // only be accessed on the IO thread.
  std::unique_ptr<AudioInputIPC> ipc_;

  // Current state (must only be accessed from the IO thread).  See comments for
  // State enum above.
  State state_;

  // The media session ID used to identify which input device to be started.
  // Only modified in Initialize() and ShutDownOnIOThread().
  int session_id_;

  // Stores the Automatic Gain Control state. Default is false.
  // Only modified on the IO thread.
  bool agc_is_enabled_;

  // Our audio thread callback class.  See source file for details.
  class AudioThreadCallback;

  // In order to avoid a race between OnStreamCreated and Stop(), we use this
  // guard to control stopping and starting the audio thread.
  base::Lock audio_thread_lock_;
  AudioDeviceThread audio_thread_;
  std::unique_ptr<AudioInputDevice::AudioThreadCallback> audio_callback_;

  // Temporary hack to ignore OnStreamCreated() due to the user calling Stop()
  // so we don't start the audio thread pointing to a potentially freed
  // |callback_|.
  //
  // TODO(miu): Replace this by changing AudioCapturerSource to accept the
  // callback via Start(). See http://crbug.com/151051 for details.
  bool stopping_hack_;

  DISALLOW_IMPLICIT_CONSTRUCTORS(AudioInputDevice);
};

}  // namespace media

#endif  // MEDIA_AUDIO_AUDIO_INPUT_DEVICE_H_