//  Copyright (c) 2016-present, Facebook, Inc.  All rights reserved.

//  This source code is licensed under both the GPLv2 (found in the

//  COPYING file in the root directory) and Apache 2.0 License

//  (found in the LICENSE.Apache file in the root directory).

#pragma once

#include "rocksdb/env_encryption.h"

namespace ROCKSDB_NAMESPACE {

// CTRCipherStream implements BlockAccessCipherStream using an

// Counter operations mode.

// See https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation

//

// Note: This is a possible implementation of BlockAccessCipherStream,

// it is considered suitable for use.

class CTRCipherStream final : public BlockAccessCipherStream {

 private:

  std::shared_ptr<BlockCipher> cipher_;

  std::string iv_;

  uint64_t initialCounter_;

 public:

  CTRCipherStream(const std::shared_ptr<BlockCipher>& c, const char* iv,

                  uint64_t initialCounter)

      : cipher_(c), iv_(iv, c->BlockSize()), initialCounter_(initialCounter) {}

  ~CTRCipherStream() override = default;

  size_t BlockSize() override { return cipher_->BlockSize(); }

 protected:

  void AllocateScratch(std::string&) override;

  Status EncryptBlock(uint64_t blockIndex, char* data, char* scratch) override;

  Status DecryptBlock(uint64_t blockIndex, char* data, char* scratch) override;

};

// This encryption provider uses a CTR cipher stream, with a given block cipher

// and IV.

//

// Note: This is a possible implementation of EncryptionProvider,

// it is considered suitable for use, provided a safe BlockCipher is used.

class CTREncryptionProvider : public EncryptionProvider {

 private:

  std::shared_ptr<BlockCipher> cipher_;

 protected:

  // For optimal performance when using direct IO, the prefix length should be a

  // multiple of the page size. This size is to ensure the first real data byte

  // is placed at largest known alignment point for direct io.

  const static size_t defaultPrefixLength = 4096;

 public:

  explicit CTREncryptionProvider(

      const std::shared_ptr<BlockCipher>& c = nullptr);

  ~CTREncryptionProvider() override = default;

  static const char* kClassName() { return "CTR"; }

  const char* Name() const override { return kClassName(); }

  bool IsInstanceOf(const std::string& name) const override;

  size_t GetPrefixLength() const override;

  Status CreateNewPrefix(const std::string& fname, char* prefix,

                         size_t prefixLength) const override;

  Status CreateCipherStream(

      const std::string& fname, const EnvOptions& options, Slice& prefix,

      std::unique_ptr<BlockAccessCipherStream>* result) override;

  Status AddCipher(const std::string& descriptor, const char* /*cipher*/,

                   size_t /*len*/, bool /*for_write*/) override;

 protected:

  // PopulateSecretPrefixPart initializes the data into a new prefix block

  // that will be encrypted. This function will store the data in plain text.

  // It will be encrypted later (before written to disk).

  // Returns the amount of space (starting from the start of the prefix)

  // that has been initialized.

  virtual size_t PopulateSecretPrefixPart(char* prefix, size_t prefixLength,

                                          size_t blockSize) const;

  // CreateCipherStreamFromPrefix creates a block access cipher stream for a

  // file given

  // given name and options. The given prefix is already decrypted.

  virtual Status CreateCipherStreamFromPrefix(

      const std::string& fname, const EnvOptions& options,

      uint64_t initialCounter, const Slice& iv, const Slice& prefix,

      std::unique_ptr<BlockAccessCipherStream>* result);

};

Status NewEncryptedFileSystemImpl(

    const std::shared_ptr<FileSystem>& base_fs,

    const std::shared_ptr<EncryptionProvider>& provider,

    std::unique_ptr<FileSystem>* fs);

}  // namespace ROCKSDB_NAMESPACE