/*

Copyright (c) 2016-2020, Arvid Norberg
All rights reserved.

You may use, distribute and modify this code under the terms of the BSD license,
see LICENSE file.
*/

#include <iostream>
#include <thread>
#include <chrono>
#include <fstream>

#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
}

} // anonymous namespace

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

	lt::settings_pack pack;
	pack.set_int(lt::settings_pack::alert_mask
		, lt::alert_category::error
		| lt::alert_category::storage
		| lt::alert_category::status);

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

	// load resume data from disk and pass it in as we add the magnet link
	std::ifstream ifs(".resume_file", std::ios_base::binary);
	ifs.unsetf(std::ios_base::skipws);
	std::vector<char> buf{std::istream_iterator<char>(ifs)
		, std::istream_iterator<char>()};

	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;

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

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