/*

Copyright (c) 2020, 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 <iostream>
#include <thread>
#include <chrono>
#include <fstream>
#include <csignal>

#include <libtorrent/session.hpp>
#include <libtorrent/session_params.hpp>
#include <libtorrent/add_torrent_params.hpp>
#include <libtorrent/torrent_handle.hpp>
#include <libtorrent/alert_types.hpp>
#include <libtorrent/bencode.hpp>
#include <libtorrent/torrent_status.hpp>
#include <libtorrent/read_resume_data.hpp>
#include <libtorrent/write_resume_data.hpp>
#include <libtorrent/error_code.hpp>
#include <libtorrent/magnet_uri.hpp>

namespace {

using clk = std::chrono::steady_clock;

// return the name of a torrent status enum
char const* state(lt::torrent_status::state_t s)
{
#ifdef __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wcovered-switch-default"
#endif
	switch(s) {
		case lt::torrent_status::checking_files: return "checking";
		case lt::torrent_status::downloading_metadata: return "dl metadata";
		case lt::torrent_status::downloading: return "downloading";
		case lt::torrent_status::finished: return "finished";
		case lt::torrent_status::seeding: return "seeding";
		case lt::torrent_status::checking_resume_data: return "checking resume";
		default: return "<>";
	}
#ifdef __clang__
#pragma clang diagnostic pop
#endif
}

std::vector<char> load_file(char const* filename)
{
	std::ifstream ifs(filename, std::ios_base::binary);
	ifs.unsetf(std::ios_base::skipws);
	return {std::istream_iterator<char>(ifs), std::istream_iterator<char>()};
}

// set when we're exiting
std::atomic<bool> shut_down{false};

void sighandler(int) { shut_down = true; }

} // anonymous namespace

int main(int argc, char const* argv[]) try
{
	if (argc != 2) {
		std::cerr << "usage: " << argv[0] << " <magnet-url>" << std::endl;
		return 1;
	}

	// load session parameters
	auto session_params = load_file(".session");
	lt::session_params params = session_params.empty()
		? lt::session_params() : lt::read_session_params(session_params);
	params.settings.set_int(lt::settings_pack::alert_mask
		, lt::alert_category::error
		| lt::alert_category::storage
		| lt::alert_category::status);

	lt::session ses(params);
	clk::time_point last_save_resume = clk::now();

	// load resume data from disk and pass it in as we add the magnet link
	auto buf = load_file(".resume_file");

	lt::add_torrent_params magnet = lt::parse_magnet_uri(argv[1]);
	if (buf.size()) {
		lt::add_torrent_params atp = lt::read_resume_data(buf);
		if (atp.info_hashes == magnet.info_hashes) magnet = std::move(atp);
	}
	magnet.save_path = "."; // save in current dir
	ses.async_add_torrent(std::move(magnet));

	// this is the handle we'll set once we get the notification of it being
	// added
	lt::torrent_handle h;

	std::signal(SIGINT, &sighandler);

	// set when we're exiting
	bool done = false;
	for (;;) {
		std::vector<lt::alert*> alerts;
		ses.pop_alerts(&alerts);

		if (shut_down) {
			shut_down = false;
			auto const handles = ses.get_torrents();
			if (handles.size() == 1) {
				handles[0].save_resume_data(lt::torrent_handle::only_if_modified
					| lt::torrent_handle::save_info_dict);
				done = true;
			}
		}

		for (lt::alert const* a : alerts) {
			if (auto at = lt::alert_cast<lt::add_torrent_alert>(a)) {
				h = at->handle;
			}
			// if we receive the finished alert or an error, we're done
			if (lt::alert_cast<lt::torrent_finished_alert>(a)) {
				h.save_resume_data(lt::torrent_handle::only_if_modified
					| lt::torrent_handle::save_info_dict);
				done = true;
			}
			if (lt::alert_cast<lt::torrent_error_alert>(a)) {
				std::cout << a->message() << std::endl;
				done = true;
				h.save_resume_data(lt::torrent_handle::only_if_modified
					| lt::torrent_handle::save_info_dict);
			}

			// when resume data is ready, save it
			if (auto rd = lt::alert_cast<lt::save_resume_data_alert>(a)) {
				std::ofstream of(".resume_file", std::ios_base::binary);
				of.unsetf(std::ios_base::skipws);
				auto const b = write_resume_data_buf(rd->params);
				of.write(b.data(), int(b.size()));
				if (done) goto done;
			}

			if (lt::alert_cast<lt::save_resume_data_failed_alert>(a)) {
				if (done) goto done;
			}

			if (auto st = lt::alert_cast<lt::state_update_alert>(a)) {
				if (st->status.empty()) continue;

				// we only have a single torrent, so we know which one
				// the status is for
				lt::torrent_status const& s = st->status[0];
				std::cout << '\r' << state(s.state) << ' '
					<< (s.download_payload_rate / 1000) << " kB/s "
					<< (s.total_done / 1000) << " kB ("
					<< (s.progress_ppm / 10000) << "%) downloaded ("
					<< s.num_peers << " peers)\x1b[K";
				std::cout.flush();
			}
		}
		std::this_thread::sleep_for(std::chrono::milliseconds(200));

		// ask the session to post a state_update_alert, to update our
		// state output for the torrent
		ses.post_torrent_updates();

		// save resume data once every 30 seconds
		if (clk::now() - last_save_resume > std::chrono::seconds(30)) {
			h.save_resume_data(lt::torrent_handle::only_if_modified
				| lt::torrent_handle::save_info_dict);
			last_save_resume = clk::now();
		}
	}

done:
	std::cout << "\nsaving session state" << std::endl;
	{
		std::ofstream of(".session", std::ios_base::binary);
		of.unsetf(std::ios_base::skipws);
		auto const b = write_session_params_buf(ses.session_state()
			, lt::save_state_flags_t::all());
		of.write(b.data(), int(b.size()));
	}

	std::cout << "\ndone, shutting down" << std::endl;
}
catch (std::exception& e)
{
	std::cerr << "Error: " << e.what() << std::endl;
}