// Copyright 2014 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 MEDIA_BASE_CDM_CONTEXT_H_
#define MEDIA_BASE_CDM_CONTEXT_H_

#include "base/callback.h"
#include "base/macros.h"
#include "build/build_config.h"
#include "media/base/media_export.h"
#include "media/media_buildflags.h"

namespace media {

class CallbackRegistration;
class CdmProxyContext;
class Decryptor;
class MediaCryptoContext;

// An interface representing the context that a media player needs from a
// content decryption module (CDM) to decrypt (and decode) encrypted buffers.
// Typically this will be passed to the media player (e.g. using SetCdm()).
//
// Lifetime: The returned raw pointers are only guaranteed to be valid when the
// CdmContext is alive, which is usually guaranteed by holding a CdmContextRef
// (see below).
//
// Thread Model: Since this interface is used in many different contexts (e.g.
// different processes or platforms), the thread model is not defined as part
// of this interface. Subclasses must ensure thread safety.
class MEDIA_EXPORT CdmContext {
 public:
  // Indicates an invalid CDM ID. See GetCdmId() for details.
  enum { kInvalidCdmId = 0 };

  // Events happening in a CDM that a media player should be aware of.
  enum class Event {
    // A key is newly usable, e.g. new key available, or previously expired key
    // has been renewed, etc.
    kHasAdditionalUsableKey,

    // A hardware reset happened. Some hardware context, e.g. hardware decoder
    // context may be lost.
    kHardwareContextLost,
  };

  // Callback to notify the occurrence of an Event.
  using EventCB = base::RepeatingCallback<void(Event)>;

  virtual ~CdmContext();

  // Registers a callback which will be called when an event happens in the CDM.
  // Returns null if the registration fails, otherwise the caller should hold
  // the returned CallbackRegistration (see "Lifetime" notes below). Can be
  // called multiple times to register multiple callbacks, all of which will be
  // called when an event happens.
  // Notes:
  // - Lifetime: The caller should keep the returned CallbackRegistration object
  // to keep the callback registered. The callback will be unregistered upon the
  // destruction of the returned CallbackRegistration object. The returned
  // CallbackRegistration object can be destructed on any thread.
  // - Thread Model: Can be called on any thread. The registered callback will
  // always be called on the thread where RegisterEventCB() is called.
  // - TODO(xhwang): Not using base::CallbackList because it is not thread-
  // safe. Consider refactoring base::CallbackList to avoid code duplication.
  virtual std::unique_ptr<CallbackRegistration> RegisterEventCB(
      EventCB event_cb);

  // Gets the Decryptor object associated with the CDM. Returns nullptr if the
  // CDM does not support a Decryptor (i.e. platform-based CDMs where decryption
  // occurs implicitly along with decoding).
  virtual Decryptor* GetDecryptor();

  // Returns an ID that can be used to find a remote CDM, in which case this CDM
  // serves as a proxy to the remote one. Returns kInvalidCdmId when remote CDM
  // is not supported (e.g. this CDM is a local CDM).
  // TODO(crbug.com/804397): Use base::UnguessableToken for CDM ID.
  virtual int GetCdmId() const;

#if BUILDFLAG(ENABLE_LIBRARY_CDMS)
  // Returns a CdmProxyContext that can be used by hardware decoders/decryptors.
  // Returns nullptr if CdmProxyContext is not supported, e.g. |this| is not
  // hosted by a CdmProxy.
  virtual CdmProxyContext* GetCdmProxyContext();
#endif  // BUILDFLAG(ENABLE_LIBRARY_CDMS)

#if defined(OS_ANDROID)
  // Returns a MediaCryptoContext that can be used by MediaCodec based decoders.
  virtual MediaCryptoContext* GetMediaCryptoContext();
#endif

 protected:
  CdmContext();

 private:
  DISALLOW_COPY_AND_ASSIGN(CdmContext);
};

// Callback to notify that the CdmContext has been completely attached to
// the media pipeline. Parameter indicates whether the operation succeeded.
typedef base::Callback<void(bool)> CdmAttachedCB;

// A dummy implementation of CdmAttachedCB.
MEDIA_EXPORT void IgnoreCdmAttached(bool success);

// A reference holder to make sure the CdmContext is always valid as long as
// |this| is alive. Typically |this| will hold a reference (directly or
// indirectly) to the host, e.g. a ContentDecryptionModule or a CdmProxy.
// This class must be held on the same thread where the host lives. The raw
// CdmContext pointer returned by GetCdmContext() may be used on other threads
// if it's supported by the CdmContext implementation.
class MEDIA_EXPORT CdmContextRef {
 public:
  virtual ~CdmContextRef() {}

  // Returns the CdmContext which is guaranteed to be alive as long as |this| is
  // alive. This function should never return nullptr.
  virtual CdmContext* GetCdmContext() = 0;
};

}  // namespace media

#endif  // MEDIA_BASE_CDM_CONTEXT_H_