// Copyright 2019 Google LLC. All Rights Reserved. This file and proprietary
// source code may only be used and distributed under the Widevine
// License Agreement.

#ifndef CDM_OEC_DECRYPT_FALLBACK_CHAIN_H_
#define CDM_OEC_DECRYPT_FALLBACK_CHAIN_H_

#include "OEMCryptoCENC.h"
#include "disallow_copy_and_assign.h"
#include "oemcrypto_fuzz_structs.h"

namespace wvoec {

// This class groups static methods relating to providing proper fallback
// behavior when calling DecryptCENC in OEMCrypto v16. Outside code can leverage
// this behavior by passing the samples to be decrypted to Decrypt(), which will
// set off the chain of fallback functions as needed.
//
// The behavior of this class is pathological. For each block of data, it will
// greedily try every possible way of passing data to OEMCrypto until one works.
// In the order tried, the ways to send data are:
//   1) Multiple Samples at once
//   2) Individual Samples one at a time
//   3) Individual Subsamples one at a time
//   4) Individual Half-Subsamples one at a time
// On a device that only accepts half-subsamples, the way OEMCrypto v15 did,
// this results in many needless roundtrips to OEMCrypto. This would be
// inefficient behavior for a real CDM, but for the sake of testing, we want to
// use the maximal way the OEMCrypto implementation will accept the data. And,
// for implementations that do not accept multiple samples or subsamples per
// call, we want to test that they correctly reject larger calls.
class DecryptFallbackChain {
 public:
  static OEMCryptoResult Decrypt(
      const uint8_t* key_handle, size_t key_handle_length,
      const OEMCrypto_SampleDescription* samples, size_t samples_length,
      OEMCryptoCipherMode cipher_mode,
      const OEMCrypto_CENCEncryptPatternDesc* pattern);

 private:
  static OEMCryptoResult DecryptSample(
      const uint8_t* key_handle, size_t key_handle_length,
      const OEMCrypto_SampleDescription& sample,
      OEMCryptoCipherMode cipher_mode,
      const OEMCrypto_CENCEncryptPatternDesc* pattern);

  static OEMCryptoResult DecryptSubsample(
      const uint8_t* key_handle, size_t key_handle_length,
      const OEMCrypto_SampleDescription& sample,
      const OEMCrypto_CENCEncryptPatternDesc* pattern,
      OEMCryptoCipherMode cipher_mode);

  static OEMCryptoResult DecryptSubsampleHalf(
      const uint8_t* key_handle, size_t key_handle_length,
      const OEMCrypto_SampleDescription& sample,
      const OEMCrypto_CENCEncryptPatternDesc* pattern,
      OEMCryptoCipherMode cipher_mode);

  // There is no reason to have an instance of this class.
  DecryptFallbackChain() = delete;
  CORE_DISALLOW_COPY_AND_ASSIGN(DecryptFallbackChain);
};

void WriteDecryptCencCorpus(OEMCryptoCipherMode cipher_mode,
                            const OEMCrypto_SampleDescription* samples,
                            const OEMCrypto_CENCEncryptPatternDesc* pattern,
                            size_t samples_length);

}  // namespace wvoec

#endif  // CDM_OEC_DECRYPT_FALLBACK_CHAIN_H_