/*

Copyright (c) 2019-2020, 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 "libtorrent/session.hpp"
#include "libtorrent/alert_types.hpp"
#include "libtorrent/session_params.hpp"
#include "libtorrent/random.hpp"

#include <fstream>
#include <chrono>
#include <atomic>
#include <csignal>
#include <iostream>
#include <iterator>
#include <vector>

using namespace lt;
using namespace lt::dht;
using namespace std::placeholders;

using namespace std::literals::chrono_literals;

lt::clock_type::duration const min_request_interval = 5min;

#ifdef TORRENT_DISABLE_DHT

int main(int, char*[])
{
	std::cerr << "not built with DHT support\n";
	return 1;
}

#else

namespace {

std::atomic_bool quit(false);

void stop(int) { quit = true; }

[[noreturn]] void usage()
{
	std::cerr << "USAGE: dht-sample\n";
	exit(1);
}

lt::session_params load_dht_state()
{
	std::fstream f(".dht", std::ios_base::in | std::ios_base::binary);
	f.unsetf(std::ios_base::skipws);
	std::cout << "load dht state from .dht\n";
	std::vector<char> const state(std::istream_iterator<char>{f}
		, std::istream_iterator<char>{});

	if (f.bad())
	{
		std::cerr << "failed to read .dht\n";
		return {};
	}
	return read_session_params(state);
}

struct node_entry
{
	lt::time_point next_request = lt::min_time();
	lt::time_point last_seen = lt::clock_type::now();
};

} // anonymous namespace

int main(int argc, char*[])
{
	if (argc != 1) usage();

	signal(SIGINT, &stop);
	signal(SIGTERM, &stop);

	session_params sp = load_dht_state();
	sp.settings.set_bool(settings_pack::enable_dht, true);
	sp.settings.set_int(settings_pack::alert_mask, 0x7fffffff);
	lt::session s(sp);

	lt::time_point next_send = lt::clock_type::now() + 5s;
	lt::time_point next_prune = lt::clock_type::now() + 30min;
	std::map<udp::endpoint, node_entry> nodes;
	std::set<lt::sha1_hash> info_hashes;

	while (!quit)
	{
		s.wait_for_alert(5s);

		std::vector<alert*> alerts;
		s.pop_alerts(&alerts);
		auto const now = lt::clock_type::now();
		for (alert* a : alerts)
		{
			if (auto* sa = lt::alert_cast<dht_sample_infohashes_alert>(a))
			{

				for (auto const& ih : sa->samples())
				{
					if (info_hashes.insert(ih).second)
						std::cout << ih << '\n';
				}
				for (auto const& n : sa->nodes())
				{
					auto it = nodes.find(n.second);
					if (it == nodes.end())
						it = nodes.insert({n.second, {}}).first;
					else
						it->second.last_seen = now;
					it->second.next_request = now + std::max(sa->interval
						, min_request_interval);
				}
				std::cout.flush();
			}
			else if (auto* dp = alert_cast<dht_pkt_alert>(a))
			{
				auto it = nodes.find(dp->node);
				if (it == nodes.end())
					nodes.insert({dp->node, {}});
				else
					it->second.last_seen = now;
			}
			else if (auto* aa = alert_cast<dht_announce_alert>(a))
			{
				if (info_hashes.insert(aa->info_hash).second)
					std::cout << aa->info_hash << std::endl;
			}
		}

		if (now > next_send)
		{
			next_send = now + 1s;
			auto const it = std::find_if(nodes.begin(), nodes.end()
				, [now](std::pair<udp::endpoint const, node_entry> const& n)
				{ return n.second.next_request < now; });
			if (it != nodes.end())
			{
				// just push this forward. If we get a response, this will be
				// updated with the interval announced by the node
				it->second.next_request = now + 1h;
				sha1_hash target;
				for (auto& b : target) b = std::uint8_t(std::rand());
				s.dht_sample_infohashes(it->first, target);
			}
		}

		if (now > next_prune)
		{
			next_prune = now + 30min;

			// remove any node that we haven't seen in 6 hours
			for (auto it = nodes.begin(); it != nodes.end();)
			{
				if (it->second.last_seen + 6h < now)
					it = nodes.erase(it);
				else
					++it;
			}
		}
	}

	std::vector<char> const state = write_session_params_buf(s.session_state(session::save_dht_state));
	std::fstream f(".dht", std::ios_base::out | std::ios_base::binary | std::ios_base::trunc);
	f.write(state.data(), static_cast<std::streamsize>(state.size()));

	return 0;
}

#endif