// 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.

#ifndef MEDIA_CRYPTO_AES_DECRYPTOR_H_
#define MEDIA_CRYPTO_AES_DECRYPTOR_H_

#include <string>

#include "base/basictypes.h"
#include "base/hash_tables.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/string_piece.h"
#include "base/synchronization/lock.h"
#include "media/base/decryptor.h"
#include "media/base/media_export.h"

namespace crypto {
class SymmetricKey;
}

namespace media {

class DecryptorClient;

// Decrypts an AES encrypted buffer into an unencrypted buffer. The AES
// encryption must be CTR with a key size of 128bits. Optionally checks the
// integrity of the encrypted data.
class MEDIA_EXPORT AesDecryptor : public Decryptor {
 public:
  // The AesDecryptor does not take ownership of the |client|. The |client|
  // must be valid throughout the lifetime of the AesDecryptor.
  explicit AesDecryptor(DecryptorClient* client);
  virtual ~AesDecryptor();

  // Decryptor implementation.
  virtual void GenerateKeyRequest(const std::string& key_system,
                                  const uint8* init_data,
                                  int init_data_length) OVERRIDE;
  virtual void AddKey(const std::string& key_system,
                      const uint8* key,
                      int key_length,
                      const uint8* init_data,
                      int init_data_length,
                      const std::string& session_id) OVERRIDE;
  virtual void CancelKeyRequest(const std::string& key_system,
                                const std::string& session_id) OVERRIDE;
  // Decrypts |encrypted| buffer. |encrypted| should not be NULL. |encrypted|
  // will signal if an integrity check must be performed before decryption.
  // Returns a DecoderBuffer with the decrypted data if the decryption
  // succeeded through |decrypt_cb|.
  virtual void Decrypt(const scoped_refptr<DecoderBuffer>& encrypted,
                       const DecryptCB& decrypt_cb) OVERRIDE;
  virtual void Stop() OVERRIDE;

 private:
  // Helper class that manages the decryption key and HMAC key. The HMAC key
  // may be NULL.
  class DecryptionKey {
   public:
    explicit DecryptionKey(const std::string& secret);
    ~DecryptionKey();

    // Creates the encryption key, and derives the WebM decryption key and HMAC.
    bool Init();

    crypto::SymmetricKey* decryption_key() { return decryption_key_.get(); }
    crypto::SymmetricKey* webm_decryption_key()
      { return webm_decryption_key_.get(); }
    base::StringPiece hmac_key() { return base::StringPiece(hmac_key_); }

   private:
    // The base secret that is used to derive the decryption key and optionally
    // the HMAC key.
    const std::string secret_;

    // The key used to decrypt the data.
    scoped_ptr<crypto::SymmetricKey> decryption_key_;

    // The key used for decryption of WebM media, derived from the secret.
    scoped_ptr<crypto::SymmetricKey> webm_decryption_key_;

    // The key used to perform the integrity check.  Currently the HMAC key is
    // defined by the WebM encrypted specification. Current encrypted WebM
    // request for comments specification is here
    // http://wiki.webmproject.org/encryption/webm-encryption-rfc
    std::string hmac_key_;

    DISALLOW_COPY_AND_ASSIGN(DecryptionKey);
  };

  // Sets |key| for |key_id|. The AesDecryptor takes the ownership of the |key|.
  void SetKey(const std::string& key_id, scoped_ptr<DecryptionKey> key);

  // Gets a DecryptionKey associated with |key_id|. The AesDecryptor still owns
  // the key. Returns NULL if no key is associated with |key_id|.
  DecryptionKey* GetKey(const std::string& key_id) const;

  // KeyMap owns the DecryptionKey* and must delete them when they are
  // not needed any more.
  typedef base::hash_map<std::string, DecryptionKey*> KeyMap;

  // Since only Decrypt() is called off the renderer thread, we only need to
  // protect |key_map_|, the only member variable that is shared between
  // Decrypt() and other methods.
  KeyMap key_map_;  // Protected by the |key_map_lock_|.
  mutable base::Lock key_map_lock_;  // Protects the |key_map_|.

  // Make session ID unique per renderer by making it static.
  // TODO(xhwang): Make session ID more strictly defined if needed:
  // https://www.w3.org/Bugs/Public/show_bug.cgi?id=16739#c0
  static uint32 next_session_id_;

  DecryptorClient* const client_;

  DISALLOW_COPY_AND_ASSIGN(AesDecryptor);
};

}  // namespace media

#endif  // MEDIA_CRYPTO_AES_DECRYPTOR_H_