text: /*
  
  Copyright (c) 2012-2016, Arvid Norberg
  All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:
  
      * Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.
      * Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in
        the documentation and/or other materials provided with the distribution.
      * Neither the name of the author nor the names of its
        contributors may be used to endorse or promote products derived
        from this software without specific prior written permission.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE.
  
  */
  
  #include <string>
  #include <vector>
  #include <mutex>
  #include <unordered_map>
  #include <cstdint>
  
  #include "libtorrent/config.hpp"
  #include "libtorrent/file.hpp"
  #include "libtorrent/error_code.hpp"
  
  namespace libtorrent
  {
  	struct TORRENT_EXTRA_EXPORT part_file
  	{
  		// create a part file at 'path', that can hold 'num_pieces' pieces.
  		// each piece being 'piece_size' number of bytes
  		part_file(std::string const& path, std::string const& name, int num_pieces, int piece_size);
  		~part_file();
  
  		int writev(file::iovec_t const* bufs, int num_bufs, int piece, int offset, error_code& ec);
  		int readv(file::iovec_t const* bufs, int num_bufs, int piece, int offset, error_code& ec);
  
  		// free the slot the given piece is stored in. We no longer need to store this
  		// piece in the part file
  		void free_piece(int piece);
  
  		void move_partfile(std::string const& path, error_code& ec);
  
  		void import_file(file& f, std::int64_t offset, std::int64_t size, error_code& ec);
  		void export_file(file& f, std::int64_t offset, std::int64_t size, error_code& ec);
  
  		// flush the metadata
  		void flush_metadata(error_code& ec);
  
  	private:
  
  		void open_file(int mode, error_code& ec);
  		void flush_metadata_impl(error_code& ec);
  
  		std::string m_path;
  		std::string m_name;
  
  		// allocate a slot and return the slot index
  		int allocate_slot(int piece);
  
  		// this mutex must be held while accessing the data
  		// structure. Not while reading or writing from the file though!
  		// it's important to support multithreading
  		std::mutex m_mutex;
  
  		// this is a list of unallocated slots in the part file
  		// within the m_num_allocated range
  		std::vector<int> m_free_slots;
  
  		// this is the number of slots allocated
  		int m_num_allocated;
  
  		// the max number of pieces in the torrent this part file is
  		// backing
  		int m_max_pieces;
  
  		// number of bytes each piece contains
  		int m_piece_size;
  
  		// this is the size of the part_file header, it is added
  		// to offsets when calculating the offset to read and write
  		// payload data from
  		int m_header_size;
  
  		// if this is true, the metadata in memory has changed since
  		// we last saved or read it from disk. It means that we
  		// need to flush the metadata before closing the file
  		bool m_dirty_metadata;
  
  		// maps a piece index to the part-file slot it is stored in
  		std::unordered_map<int, int> m_piece_map;
  
  		// this is the file handle to the part file
  		file m_file;
  	};
  }
  
  