/*

Copyright (c) 2003-2018, Arvid Norberg
All rights reserved.

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modification, are permitted provided that the following conditions
are met:

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    * 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.
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      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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*/

#ifndef TORRENT_STORAGE_HPP_INCLUDE
#define TORRENT_STORAGE_HPP_INCLUDE

#include "libtorrent/config.hpp"

#include <mutex>
#include <atomic>
#include <memory>

#include "libtorrent/fwd.hpp"
#include "libtorrent/aux_/disk_job_fence.hpp"
#include "libtorrent/aux_/storage_piece_set.hpp"
#include "libtorrent/storage_defs.hpp"
#include "libtorrent/part_file.hpp"
#include "libtorrent/stat_cache.hpp"
#include "libtorrent/bitfield.hpp"
#include "libtorrent/span.hpp"
#include "libtorrent/aux_/vector.hpp"

// OVERVIEW
//
// libtorrent provides a customization point for storage of data. By default,
// (``default_storage``) downloaded files are saved to disk according with the
// general conventions of bittorrent clients, mimicking the original file layout
// when the torrent was created. The libtorrent user may define a custom
// storage to store piece data in a different way.
//
// A custom storage implementation must derive from and implement the
// storage_interface. You must also provide a function that constructs the
// custom storage object and provide this function to the add_torrent() call
// via add_torrent_params. Either passed in to the constructor or by setting
// the add_torrent_params::storage field.
//
// This is an example storage implementation that stores all pieces in a
// ``std::map``, i.e. in RAM. It's not necessarily very useful in practice, but
// illustrates the basics of implementing a custom storage.
//
// .. include:: ../examples/custom_storage.cpp
//	:code: c++
//	:tab-width: 2
//	:start-after: -- example begin
//	:end-before: // -- example end
namespace libtorrent {

	namespace aux { struct session_settings; }

	// The storage interface is a pure virtual class that can be implemented to
	// customize how and where data for a torrent is stored. The default storage
	// implementation uses regular files in the filesystem, mapping the files in
	// the torrent in the way one would assume a torrent is saved to disk.
	// Implementing your own storage interface makes it possible to store all
	// data in RAM, or in some optimized order on disk (the order the pieces are
	// received for instance), or saving multi file torrents in a single file in
	// order to be able to take advantage of optimized disk-I/O.
	//
	// It is also possible to write a thin class that uses the default storage
	// but modifies some particular behavior, for instance encrypting the data
	// before it's written to disk, and decrypting it when it's read again.
	//
	// The storage interface is based on pieces. Every read and write operation
	// happens in the piece-space. Each piece fits ``piece_size`` number
	// of bytes. All access is done by writing and reading whole or partial
	// pieces.
	//
	// libtorrent comes with two built-in storage implementations;
	// ``default_storage`` and ``disabled_storage``. Their constructor functions
	// are called default_storage_constructor() and
	// ``disabled_storage_constructor`` respectively. The disabled storage does
	// just what it sounds like. It throws away data that's written, and it
	// reads garbage. It's useful mostly for benchmarking and profiling purpose.
	//
	struct TORRENT_EXPORT storage_interface
		: std::enable_shared_from_this<storage_interface>
		, aux::disk_job_fence
		, aux::storage_piece_set
	{
		explicit storage_interface(file_storage const& fs) : m_files(fs) {}

		storage_interface(storage_interface const&) = delete;
		storage_interface& operator=(storage_interface const&) = delete;

		// This function is called when the *storage* on disk is to be
		// initialized. The default storage will create directories and empty
		// files at this point. If ``allocate_files`` is true, it will also
		// ``ftruncate`` all files to their target size.
		//
		// This function may be called multiple time on a single instance. When a
		// torrent is force-rechecked, the storage is re-initialized to trigger
		// the re-check from scratch.
		//
		// The function is not necessarily called before other member functions.
		// For instance has_any_files() and verify_resume_data() are
		// called early to determine whether we may have to check all files or
		// not. If we're doing a full check of the files every piece will be
		// hashed, causing readv() to be called as well.
		//
		// Any required internals that need initialization should be done in the
		// constructor. This function is called before the torrent starts to
		// download.
		//
		// If an error occurs, ``storage_error`` should be set to reflect it.
		virtual void initialize(storage_error& ec) = 0;

		// These functions should read and write the data in or to the given
		// ``piece`` at the given ``offset``. It should read or write
		// ``num_bufs`` buffers sequentially, where the size of each buffer is
		// specified in the buffer array ``bufs``. The iovec_t type has the
		// following members::
		//
		//	struct iovec_t { void* iov_base; size_t iov_len; };
		//
		// These functions may be called simultaneously from multiple threads.
		// Make sure they are thread safe. The ``file`` in libtorrent is thread
		// safe when it can fall back to ``pread``, ``preadv`` or the windows
		// equivalents. On targets where read operations cannot be thread safe
		// (i.e one has to seek first and then read), only one disk thread is
		// used.
		//
		// The ``offset`` is aligned to 16 kiB boundaries  *most of the time*, but
		// there are rare exceptions when it's not. Specifically if the read
		// cache is disabled/or full and a peer requests unaligned data. Most
		// clients request aligned data.
		//
		// The number of bytes read or written should be returned, or -1 on
		// error. If there's an error, the ``storage_error`` must be filled out
		// to represent the error that occurred.
		//
		// For possible values of ``flags``, see open_mode_t.
		virtual int readv(span<iovec_t const> bufs
			, piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) = 0;
		virtual int writev(span<iovec_t const> bufs
			, piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) = 0;

		// This function is called when first checking (or re-checking) the
		// storage for a torrent. It should return true if any of the files that
		// is used in this storage exists on disk. If so, the storage will be
		// checked for existing pieces before starting the download.
		//
		// If an error occurs, ``storage_error`` should be set to reflect it.
		virtual bool has_any_file(storage_error& ec) = 0;

		// change the priorities of files. This is a fenced job and is
		// guaranteed to be the only running function on this storage
		// when called
		virtual void set_file_priority(aux::vector<download_priority_t, file_index_t>& prio
			, storage_error& ec) = 0;

		// This function should move all the files belonging to the storage to
		// the new save_path. The default storage moves the single file or the
		// directory of the torrent.
		//
		// Before moving the files, any open file handles may have to be closed,
		// like ``release_files()``.
		//
		//If an error occurs, ``storage_error`` should be set to reflect it.
		virtual status_t move_storage(std::string const& save_path
			, move_flags_t flags, storage_error& ec) = 0;

		// This function should verify the resume data ``rd`` with the files
		// on disk. If the resume data seems to be up-to-date, return true. If
		// not, set ``error`` to a description of what mismatched and return false.
		//
		// The default storage may compare file sizes and time stamps of the files.
		//
		// If an error occurs, ``storage_error`` should be set to reflect it.
		//
		// This function should verify the resume data ``rd`` with the files
		// on disk. If the resume data seems to be up-to-date, return true. If
		// not, set ``error`` to a description of what mismatched and return false.
		//
		// If the ``links`` pointer is non-empty, it has the same number
		// of elements as there are files. Each element is either empty or contains
		// the absolute path to a file identical to the corresponding file in this
		// torrent. The storage must create hard links (or copy) those files. If
		// any file does not exist or is inaccessible, the disk job must fail.
		virtual bool verify_resume_data(add_torrent_params const& rd
			, aux::vector<std::string, file_index_t> const& links
			, storage_error& ec) = 0;

		// This function should release all the file handles that it keeps open
		// to files belonging to this storage. The default implementation just
		// calls file_pool::release_files().
		//
		// If an error occurs, ``storage_error`` should be set to reflect it.
		//
		virtual void release_files(storage_error& ec) = 0;

		// Rename the file with index ``file`` to name ``new_name``.
		//
		// If an error occurs, ``storage_error`` should be set to reflect it.
		//
		virtual void rename_file(file_index_t index, std::string const& new_filename
			, storage_error& ec) = 0;

		// This function should delete some or all of the storage for this torrent.
		// The ``options`` parameter specifies whether to delete all files or just
		// the partfile. ``options`` are set to the same value as the options
		// passed to session::remove_torrent().
		//
		// If an error occurs, ``storage_error`` should be set to reflect it.
		//
		// The ``disk_buffer_pool`` is used to allocate and free disk buffers. It
		// has the following members:
		//
		// .. code:: c++
		//
		//		struct disk_buffer_pool
		//		{
		//			char* allocate_buffer(char const* category);
		//			void free_buffer(char* buf);
		//
		//			char* allocate_buffers(int blocks, char const* category);
		//			void free_buffers(char* buf, int blocks);
		//
		//			int block_size() const { return m_block_size; }
		//
		//		};
		virtual void delete_files(remove_flags_t options, storage_error& ec) = 0;

		// called periodically (useful for deferred flushing). When returning
		// false, it means no more ticks are necessary. Any disk job submitted
		// will re-enable ticking. The default will always turn ticking back
		// off again.
		virtual bool tick() { return false; }

		file_storage const& files() const { return m_files; }

		bool set_need_tick()
		{
			bool const prev = m_need_tick;
			m_need_tick = true;
			return prev;
		}

		void do_tick()
		{
			m_need_tick = false;
			tick();
		}

		void set_owner(std::shared_ptr<void> const& tor) { m_torrent = tor; }

		// access global session_settings
		aux::session_settings const& settings() const { return *m_settings; }

		// hidden
		virtual ~storage_interface() {}

		// initialized in disk_io_thread::perform_async_job
		std::atomic<aux::session_settings const*> m_settings{nullptr};

		storage_index_t storage_index() const { return m_storage_index; }
		void set_storage_index(storage_index_t st) { m_storage_index = st; }

		int dec_refcount()
		{
			TORRENT_ASSERT(m_references > 0);
			return --m_references;
		}
		void inc_refcount() { ++m_references; }
	private:

		bool m_need_tick = false;
		file_storage const& m_files;

		// the reason for this to be a void pointer
		// is to avoid creating a dependency on the
		// torrent. This shared_ptr is here only
		// to keep the torrent object alive until
		// the storage_interface destructs. This is because
		// the file_storage object is owned by the torrent.
		std::shared_ptr<void> m_torrent;

		storage_index_t m_storage_index{0};

		// the number of block_cache_reference objects referencing this storage
		std::atomic<int> m_references{1};
	};

	// The default implementation of storage_interface. Behaves as a normal
	// bittorrent client. It is possible to derive from this class in order to
	// override some of its behavior, when implementing a custom storage.
	class TORRENT_EXPORT default_storage : public storage_interface
	{
	public:
		// constructs the default_storage based on the give file_storage (fs).
		// ``mapped`` is an optional argument (it may be nullptr). If non-nullptr it
		// represents the file mapping that have been made to the torrent before
		// adding it. That's where files are supposed to be saved and looked for
		// on disk. ``save_path`` is the root save folder for this torrent.
		// ``file_pool`` is the cache of file handles that the storage will use.
		// All files it opens will ask the file_pool to open them. ``file_prio``
		// is a vector indicating the priority of files on startup. It may be
		// an empty vector. Any file whose index is not represented by the vector
		// (because the vector is too short) are assumed to have priority 1.
		// this is used to treat files with priority 0 slightly differently.
		explicit default_storage(storage_params const& params, file_pool&);

		// hidden
		~default_storage() override;

		bool has_any_file(storage_error& ec) override;
		void set_file_priority(aux::vector<download_priority_t, file_index_t>& prio
			, storage_error& ec) override;
		void rename_file(file_index_t index, std::string const& new_filename
			, storage_error& ec) override;
		void release_files(storage_error& ec) override;
		void delete_files(remove_flags_t options, storage_error& ec) override;
		void initialize(storage_error& ec) override;
		status_t move_storage(std::string const& save_path
			, move_flags_t flags, storage_error& ec) override;
		bool verify_resume_data(add_torrent_params const& rd
			, aux::vector<std::string, file_index_t> const& links
			, storage_error& error) override;
		bool tick() override;

		int readv(span<iovec_t const> bufs
			, piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) override;
		int writev(span<iovec_t const> bufs
			, piece_index_t piece, int offset, open_mode_t flags, storage_error& ec) override;

		// if the files in this storage are mapped, returns the mapped
		// file_storage, otherwise returns the original file_storage object.
		file_storage const& files() const
		{
			return m_mapped_files ? *m_mapped_files : storage_interface::files();
		}

	private:

		void need_partfile();

		std::unique_ptr<file_storage> m_mapped_files;

		// in order to avoid calling stat() on each file multiple times
		// during startup, cache the results in here, and clear it all
		// out once the torrent starts (to avoid getting stale results)
		// each entry represents the size and timestamp of the file
		mutable stat_cache m_stat_cache;

		// helper function to open a file in the file pool with the right mode
		file_handle open_file(file_index_t file, open_mode_t mode, storage_error& ec) const;
		file_handle open_file_impl(file_index_t file, open_mode_t mode, error_code& ec) const;

		bool use_partfile(file_index_t index) const;
		void use_partfile(file_index_t index, bool b);

		aux::vector<download_priority_t, file_index_t> m_file_priority;
		std::string m_save_path;
		std::string m_part_file_name;

		// this this is an array indexed by file-index. Each slot represents
		// whether this file has the part-file enabled for it. This is used for
		// backwards compatibility with pre-partfile versions of libtorrent. If
		// this vector is empty, the default is that files *do* use the partfile.
		// on startup, any 0-priority file that's found in it's original location
		// is expected to be an old-style (pre-partfile) torrent storage, and
		// those files have their slot set to false in this vector.
		// note that the vector is *sparse*, it's only allocated if a file has its
		// entry set to false, and only indices up to that entry.
		aux::vector<bool, file_index_t> m_use_partfile;

		// the file pool is a member of the disk_io_thread
		// to make all storage instances share the pool
		file_pool& m_pool;

		// used for skipped files
		std::unique_ptr<part_file> m_part_file;

		// this is a bitfield with one bit per file. A bit being set means
		// we've written to that file previously. If we do write to a file
		// whose bit is 0, we set the file size, to make the file allocated
		// on disk (in full allocation mode) and just sparsely allocated in
		// case of sparse allocation mode
		mutable std::mutex m_file_created_mutex;
		mutable typed_bitfield<file_index_t> m_file_created;

		bool m_allocate_files;
	};

}

#endif // TORRENT_STORAGE_HPP_INCLUDED
