// Copyright 2016 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.

#ifndef CHROMECAST_MEDIA_BASE_MEDIA_RESOURCE_TRACKER_H_
#define CHROMECAST_MEDIA_BASE_MEDIA_RESOURCE_TRACKER_H_

#include "base/callback.h"
#include "base/memory/ref_counted.h"
#include "base/sequenced_task_runner_helpers.h"

namespace base {
class SingleThreadTaskRunner;
}

namespace chromecast {
namespace media {

// Keeps track of internal usage of resources that need access to underlying
// media playback hardware.  Some example users are the CMA pipeline, and the
// CDMs.  When it's time to release media resources, this class can be used
// to be wait and receive notification when all such users have stopped.
//
// Application should have one MediaResourceTracker instance and perform all
// CastMediaShlib::Initialize/Finalize through this interface.
// Threading model and lifetime:
// * This class interacts on both UI and media threads (task runners required
//   by ctor to perform thread hopping and checks). See function-level comments
//   on which thread to use for which operations.
// * All interaction with delegate is performed on UI thread.
// * The application should instantiate a single MediaResourceTracker instance.
//   Destruction should be performed by calling FinalizeAndDestroy from the UI
//   thread.
class MediaResourceTracker {
 public:
  class Delegate {
   public:
    // Called on UI thread when media usage starts (i.e. count steps 0->1).
    // Does not mean Initialize has happened.
    virtual void OnStartUsingMedia() = 0;

    // Called on UI thread when media usage stops (i.e. count steps 1->0).
    // Does not mean Finalize has happened.
    virtual void OnStopUsingMedia() = 0;

   protected:
    virtual ~Delegate() {}
  };

  MediaResourceTracker(
      const scoped_refptr<base::SingleThreadTaskRunner>& ui_task_runner,
      const scoped_refptr<base::SingleThreadTaskRunner>& media_task_runner);

  // Sets the delegate to receive start/stop media usage notifications.  Must
  // call on UI thread.  Set to nullptr to clear existing delegate.
  void SetDelegate(Delegate* delegate);

  // Media resource acquire implementation. Must call on ui thread; runs
  // CastMediaShlib::Initialize on media thread.  Safe to call even if media lib
  // already initialized.
  void InitializeMediaLib();

  // Media resource release implementation:
  // (1) Waits for usage count to drop to zero
  // (2) Calls CastMediaShlib::Finalize on media thread
  // (3) Calls completion_cb
  // Must be called on UI thread.  Only one Finalize request may be in flight
  // at a time. |completion_cb| must not be null.
  void FinalizeMediaLib(const base::Closure& completion_cb);

  // Shutdown process:
  // (1) Waits for usage count to drop to zero
  // (2) Calls CastMediaShlib::Finalize on media thread
  // (3) Deletes this object
  // Must be called on UI thread. No further calls should be made on UI thread
  // after this. Delegate is implicitly cleared.
  void FinalizeAndDestroy();

  // Users of media resource (e.g. CMA pipeline) should call these when they
  // start and stop using media calls (must be called on media thread).
  void IncrementUsageCount();
  void DecrementUsageCount();

 private:
  friend class base::DeleteHelper<MediaResourceTracker>;
  ~MediaResourceTracker();

  // Tasks posted to UI thread
  void CallDelegateStartOnUiThread();
  void CallDelegateStopOnUiThread();

  // Tasks posted to media thread
  void CallInitializeOnMediaThread();
  void MaybeCallFinalizeOnMediaThread(const base::Closure& completion_cb);
  void MaybeCallFinalizeOnMediaThreadAndDeleteSelf();
  void CallFinalizeOnMediaThread();

  // Accessed on UI thread
  Delegate* delegate_;

  // Accessed on media thread + ctor
  size_t media_use_count_;
  bool media_lib_initialized_;
  base::Closure finalize_completion_cb_;
  bool delete_on_finalize_;

  scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
  scoped_refptr<base::SingleThreadTaskRunner> media_task_runner_;

  DISALLOW_COPY_AND_ASSIGN(MediaResourceTracker);
};

}  // namespace media
}  // namespace chromecast

#endif  // CHROMECAST_MEDIA_BASE_MEDIA_RESOURCE_TRACKER_H_