/*

Copyright (c) 2016, 2019-2021, Arvid Norberg
Copyright (c) 2019, Steven Siloti
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 "libtorrent/config.hpp"

#if TORRENT_HAVE_MMAP || TORRENT_HAVE_MAP_VIEW_OF_FILE

#define TRACE_FILE_VIEW_POOL 0

#include "libtorrent/assert.hpp"
#include "libtorrent/aux_/file_view_pool.hpp"
#include "libtorrent/error_code.hpp"
#include "libtorrent/file_storage.hpp"
#include "libtorrent/units.hpp"
#include "libtorrent/disk_interface.hpp"
#include "libtorrent/aux_/path.hpp"
#include "libtorrent/aux_/throw.hpp"
#ifdef TORRENT_WINDOWS
#include "libtorrent/aux_/win_util.hpp"
#endif

#include <limits>

#if TRACE_FILE_VIEW_POOL
#include <iostream>
#include <thread>
#endif


using namespace libtorrent::flags;

namespace libtorrent { namespace aux {

	file_view_pool::file_view_pool(int size) : m_size(size) {}
	file_view_pool::~file_view_pool() = default;

	std::shared_ptr<file_mapping>
	file_view_pool::open_file(storage_index_t st, std::string const& p
		, file_index_t const file_index, file_storage const& fs
		, open_mode_t const m
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
		, std::shared_ptr<std::mutex> open_unmap_lock
#endif
		)
	{
		// potentially used to hold a reference to a file object that's
		// about to be destructed. If we have such object we assign it to
		// this member to be destructed after we release the std::mutex. On some
		// operating systems (such as OSX) closing a file may take a long
		// time. We don't want to hold the std::mutex for that.
		std::shared_ptr<file_mapping> defer_destruction1;
		std::shared_ptr<file_mapping> defer_destruction2;

		std::unique_lock<std::mutex> l(m_mutex);

		TORRENT_ASSERT(is_complete(p));
		auto& key_view = m_files.get<0>();
		file_id const file_key{st, file_index};
		auto i = key_view.find(file_key);

		if (i == key_view.end())
		{
			auto opening = std::find_if(m_opening_files.begin(), m_opening_files.end()
				, [&file_key, m](opening_file_entry const& oe) {
					return oe.file_key == file_key
						&& (!(m & open_mode::write) || (oe.mode & open_mode::write));
				});
			if (opening != m_opening_files.end())
			{
				wait_open_entry woe;
				opening->waiters.push_back(woe);

#if TRACE_FILE_VIEW_POOL
				std::cout << std::this_thread::get_id() << " waiting for: ("
					<< file_key.first << ", " << file_key.second << ")\n";
#endif
				do {
					woe.cond.wait(l);
				} while (!woe.mapping && !woe.error);
				if (woe.error)
				{
#if TRACE_FILE_VIEW_POOL
					std::cout << std::this_thread::get_id() << " open failed: ("
						<< file_key.first << ", " << file_key.second
						<< "): " << woe.error.ec << std::endl;
#endif
					throw_ex<storage_error>(woe.error);
				}

#if TRACE_FILE_VIEW_POOL
				std::cout << std::this_thread::get_id() << " file opened: ("
					<< file_key.first << ", " << file_key.second << ")\n";
#endif
				return woe.mapping;
			}
		}

		// make sure the write bit is set if we asked for it
		// it's OK to use a read-write file if we just asked for read. But if
		// we asked for write, the file we serve back must be opened in write
		// mode
		if (i != key_view.end()
			&& (!(m & open_mode::write) || (i->mode & open_mode::write)))
		{
			key_view.modify(i, [&](file_entry& e)
			{
				e.last_use = aux::time_now();
			});

			auto& lru_view = m_files.get<1>();
			lru_view.relocate(lru_view.end(), m_files.project<1>(i));

#if TORRENT_USE_ASSERTS
			// ensure the LRU index is maintained as we would expect it to be
			TORRENT_ASSERT(lru_view.back().key == i->key);
#endif
			return i->mapping;
		}

		if (int(m_files.size()) >= m_size - 1)
		{
			// the file cache is at its maximum size, close
			// the least recently used file
			defer_destruction1 = remove_oldest(l);
		}

		opening_file_entry ofe;
		ofe.file_key = file_key;
		ofe.mode = m;
		m_opening_files.push_back(ofe);

#if TRACE_FILE_VIEW_POOL
		std::cout << std::this_thread::get_id() << " opening file: ("
			<< file_key.first << ", " << file_key.second << ")\n";
#endif

		l.unlock();

		try
		{
			file_entry e = open_file_impl(p, file_index, fs, m, file_key
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
				, std::move(open_unmap_lock)
#endif
				);

			l.lock();

			// there's an edge case where two threads are racing to insert a newly
			// opened file, one thread is opening a file for writing and the other
			// for reading. If the reading thread wins, it's important that the
			// thread opening for writing still overwrites the file in the pool,
			// since a file opened for reading and writing can be used for both.
			// So, we can't move e in here, because we may need it again of the
			// insertion failed.
			// if the insertion failed, check to see if we can use the existing
			// entry. If not, overwrite it with the newly opened file ``e``.
			bool added;
			std::tie(i, added) = key_view.insert(e);
			if (added == false)
			{
				// this is the case where this file was already in the pool. Make
				// sure we can use it. If we asked for write mode, it must have been
				// opened in write mode too.
				TORRENT_ASSERT(i != key_view.end());

				if ((m & open_mode::write) && !(i->mode & open_mode::write))
				{
					key_view.modify(i, [&](file_entry& fe)
					{
						defer_destruction2 = std::move(fe.mapping);
						fe = std::move(e);
					});
				}

				auto& lru_view = m_files.get<1>();
				lru_view.relocate(lru_view.end(), m_files.project<1>(i));
			}
#if TORRENT_USE_ASSERTS
			// ensure the LRU index is maintained as we would expect it to be
			auto& lru_view = m_files.get<1>();
			TORRENT_ASSERT(lru_view.back().key == e.key);
#endif
			notify_file_open(ofe, i->mapping, storage_error());
			return i->mapping;
		}
		catch (storage_error const& se)
		{
			if (!l.owns_lock()) l.lock();
			notify_file_open(ofe, {}, se);
			throw;
		}
		catch (std::bad_alloc const&)
		{
			if (!l.owns_lock()) l.lock();
			notify_file_open(ofe, {}, storage_error(
				errors::no_memory, file_index, operation_t::file_open));
			throw;
		}
		catch (boost::system::system_error const& se)
		{
			if (!l.owns_lock()) l.lock();
			notify_file_open(ofe, {}, storage_error(
				se.code(), file_index, operation_t::file_open));
			throw;
		}
		catch (...)
		{
			if (!l.owns_lock()) l.lock();
			notify_file_open(ofe, {}, storage_error(
				errors::no_memory, file_index, operation_t::file_open));
			throw;
		}
	}

	void file_view_pool::notify_file_open(opening_file_entry& ofe
		, std::shared_ptr<file_mapping> mapping
		, lt::storage_error const& se = lt::storage_error())
	{
#if TRACE_FILE_VIEW_POOL
		if (!ofe.waiters.empty())
		{
			std::cout << std::this_thread::get_id() << " notify_file_open: ("
				<< ofe.file_key.first << ", " << ofe.file_key.second << ")\n";
		}
#endif

		m_opening_files.erase(m_opening_files.s_iterator_to(ofe));
		for (auto& woe : ofe.waiters)
		{
			woe.mapping = mapping;
			woe.error = se;
			woe.cond.notify_all();
		}
	}

	file_view_pool::file_entry file_view_pool::open_file_impl(std::string const& p
		, file_index_t const file_index, file_storage const& fs
		, open_mode_t const m, file_id const file_key
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
		, std::shared_ptr<std::mutex> open_unmap_lock
#endif
		)
	{
		std::string const file_path = fs.file_path(file_index, p);
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
		std::unique_lock<std::mutex> lou(*open_unmap_lock);
#endif
		try
		{
			return file_entry(file_key, file_path, m, fs.file_size(file_index)
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
				, open_unmap_lock
#endif
				);
		}
		catch (storage_error& se)
		{
			// opening the file failed. If it was because the directory was
			// missing, create it and try again. Otherwise, propagate the
			// error
			if (!(m & open_mode::write)
				|| (se.ec != boost::system::errc::no_such_file_or_directory
#ifdef TORRENT_WINDOWS
					// this is a workaround for improper handling of files on windows shared drives.
					// if the directory on a shared drive does not exist,
					// windows returns ERROR_IO_DEVICE instead of ERROR_FILE_NOT_FOUND
					&& se.ec != error_code(ERROR_IO_DEVICE, system_category())
#endif
				   ))
			{
				throw;
			}

			// create directory and try again
			// this means the directory the file is in doesn't exist.
			// so create it
			se.ec.clear();
			create_directories(parent_path(fs.file_path(file_index, p)), se.ec);

			if (se.ec)
			{
				// if the directory creation failed, don't try to open the file again
				// but actually just fail
				throw_ex<storage_error>(se);
			}

			return file_entry(file_key, file_path, m, fs.file_size(file_index)
#if TORRENT_HAVE_MAP_VIEW_OF_FILE
				, open_unmap_lock
#endif
				);
		}
	}

	file_open_mode_t to_file_open_mode(open_mode_t const mode, bool const has_mapping)
	{
		return ((mode & open_mode::write)
				? file_open_mode::read_write : file_open_mode::read_only)
			| ((mode & open_mode::no_atime)
				? file_open_mode::no_atime : file_open_mode::read_only)
			| (has_mapping ? file_open_mode::mmapped : file_open_mode_t{})
			;
	}

	std::vector<open_file_state> file_view_pool::get_status(storage_index_t const st) const
	{
		std::vector<open_file_state> ret;
		{
			std::unique_lock<std::mutex> l(m_mutex);

			auto& key_view = m_files.get<0>();
			auto const start = key_view.lower_bound(file_id{st, file_index_t(0)});
			auto const end = key_view.upper_bound(file_id{st, std::numeric_limits<file_index_t>::max()});

			for (auto i = start; i != end; ++i)
			{
				ret.push_back({i->key.second
					, to_file_open_mode(i->mode, i->mapping->has_memory_map())
					, i->last_use});
			}
		}
		return ret;
	}

	std::shared_ptr<file_mapping> file_view_pool::remove_oldest(std::unique_lock<std::mutex>&)
	{
		auto& lru_view = m_files.get<1>();
		if (lru_view.size() == 0) return {};

#if TRACE_FILE_VIEW_POOL
		std::cout << std::this_thread::get_id() << " removing: ("
			<< lru_view.front().key.first << ", " << lru_view.front().key.second << ")\n";
#endif

		auto mapping = std::move(lru_view.front().mapping);
		lru_view.pop_front();

		// closing a file may be long running operation (mac os x)
		// let the caller destruct it once it has released the mutex
		return mapping;
	}

	void file_view_pool::release(storage_index_t const st, file_index_t file_index)
	{
		std::unique_lock<std::mutex> l(m_mutex);

		auto& key_view = m_files.get<0>();
		auto const i = key_view.find(file_id{st, file_index});
		if (i == key_view.end()) return;

		auto mapping = std::move(i->mapping);
		key_view.erase(i);

		// closing a file may take a long time (mac os x), so make sure
		// we're not holding the mutex
		l.unlock();
	}

	// closes files belonging to the specified
	// storage, or all if none is specified.
	void file_view_pool::release()
	{
		std::unique_lock<std::mutex> l(m_mutex);
		std::unique_lock<std::mutex> l2(m_destruction_mutex);
		m_deferred_destruction = std::move(m_files);
		l.unlock();

		// the files and mappings will be destructed here, not holding the main
		// mutex
		m_deferred_destruction.clear();
	}

	void file_view_pool::release(storage_index_t const st)
	{
		std::vector<std::shared_ptr<file_mapping>> defer_destruction;

		std::unique_lock<std::mutex> l(m_mutex);

		auto& key_view = m_files.get<0>();
		auto const begin = key_view.lower_bound(file_id{st, file_index_t(0)});
		auto const end = key_view.upper_bound(file_id{st, std::numeric_limits<file_index_t>::max()});

		for (auto it = begin; it != end; ++it)
			defer_destruction.emplace_back(std::move(it->mapping));

		if (begin != end) key_view.erase(begin, end);
		l.unlock();
		// the files are closed here while the lock is not held
	}

	void file_view_pool::resize(int const size)
	{
		// these are destructed _after_ the mutex is released
		std::vector<std::shared_ptr<file_mapping>> defer_destruction;

		std::unique_lock<std::mutex> l(m_mutex);

		TORRENT_ASSERT(size > 0);

		if (size == m_size) return;
		m_size = size;
		if (int(m_files.size()) <= m_size) return;

		// close the least recently used files
		while (int(m_files.size()) > m_size)
			defer_destruction.emplace_back(remove_oldest(l));
	}

	void file_view_pool::close_oldest()
	{
		// closing a file may be long running operation (mac os x)
		// destruct it after the mutex is released
		std::shared_ptr<file_mapping> deferred_destruction;

		std::unique_lock<std::mutex> l(m_mutex);
		deferred_destruction = remove_oldest(l);
	}

#if TORRENT_HAVE_MAP_VIEW_OF_FILE
	void file_view_pool::flush_next_file()
	{
		std::shared_ptr<file_mapping> mapping;
		{
			std::unique_lock<std::mutex> l(m_mutex);
			auto& flush_view = m_files.get<2>();
			if (flush_view.size() == 0) return;

			auto it = std::prev(flush_view.end());
			if (it->dirty_bytes == 0) return;
			mapping = it->mapping;
			flush_view.modify(it, [](file_entry& e) { e.dirty_bytes = 0; });
		}

		// we invoke flush after we release the mutex
		mapping->flush();
	}

	void file_view_pool::record_file_write(storage_index_t const st
		, file_index_t const file_index, uint64_t const bytes)
	{
		std::unique_lock<std::mutex> l(m_mutex);
		auto& key_view = m_files.get<0>();
		auto i = key_view.find(file_id{st, file_index});
		if (i == key_view.end()) return;
		key_view.modify(i, [bytes](file_entry& e) { e.dirty_bytes += bytes; });
	}
#endif
}
}

#endif // HAVE_MMAP || HAVE_MAP_VIEW_OF_FILE

