text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2020 The Bitcoin Core developers
  // Copyright (c) 2021 The Danecoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef DANECOIN_FLATFILE_H
  #define DANECOIN_FLATFILE_H
  
  #include <string>
  
  #include <fs.h>
  #include <serialize.h>
  
  struct FlatFilePos
  {
      int nFile;
      unsigned int nPos;
  
      SERIALIZE_METHODS(FlatFilePos, obj) { READWRITE(VARINT_MODE(obj.nFile, VarIntMode::NONNEGATIVE_SIGNED), VARINT(obj.nPos)); }
  
      FlatFilePos() : nFile(-1), nPos(0) {}
  
      FlatFilePos(int nFileIn, unsigned int nPosIn) :
          nFile(nFileIn),
          nPos(nPosIn)
      {}
  
      friend bool operator==(const FlatFilePos &a, const FlatFilePos &b) {
          return (a.nFile == b.nFile && a.nPos == b.nPos);
      }
  
      friend bool operator!=(const FlatFilePos &a, const FlatFilePos &b) {
          return !(a == b);
      }
  
      void SetNull() { nFile = -1; nPos = 0; }
      bool IsNull() const { return (nFile == -1); }
  
      std::string ToString() const;
  };
  
  /**
   * FlatFileSeq represents a sequence of numbered files storing raw data. This class facilitates
   * access to and efficient management of these files.
   */
  class FlatFileSeq
  {
  private:
      const fs::path m_dir;
      const char* const m_prefix;
      const size_t m_chunk_size;
  
  public:
      /**
       * Constructor
       *
       * @param dir The base directory that all files live in.
       * @param prefix A short prefix given to all file names.
       * @param chunk_size Disk space is pre-allocated in multiples of this amount.
       */
      FlatFileSeq(fs::path dir, const char* prefix, size_t chunk_size);
  
      /** Get the name of the file at the given position. */
      fs::path FileName(const FlatFilePos& pos) const;
  
      /** Open a handle to the file at the given position. */
      FILE* Open(const FlatFilePos& pos, bool read_only = false);
  
      /**
       * Allocate additional space in a file after the given starting position. The amount allocated
       * will be the minimum multiple of the sequence chunk size greater than add_size.
       *
       * @param[in] pos The starting position that bytes will be allocated after.
       * @param[in] add_size The minimum number of bytes to be allocated.
       * @param[out] out_of_space Whether the allocation failed due to insufficient disk space.
       * @return The number of bytes successfully allocated.
       */
      size_t Allocate(const FlatFilePos& pos, size_t add_size, bool& out_of_space);
  
      /**
       * Commit a file to disk, and optionally truncate off extra pre-allocated bytes if final.
       *
       * @param[in] pos The first unwritten position in the file to be flushed.
       * @param[in] finalize True if no more data will be written to this file.
       * @return true on success, false on failure.
       */
      bool Flush(const FlatFilePos& pos, bool finalize = false);
  };
  
  #endif // DANECOIN_FLATFILE_H
  