// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#include "s_fetch.h"

ircd::mapi::header
IRCD_MODULE
{
    "Event Fetch Unit", ircd::m::fetch::init, ircd::m::fetch::fini
};

//
// init
//

void
ircd::m::fetch::init()
{
	context = ctx::context
	{
		"fetcher",
		128_KiB,
		std::bind(&ircd::m::fetch::worker),
		ctx::context::POST
	};

	log::debug
	{
		vm::log, "Fetch unit ready."
	};
}

void
ircd::m::fetch::fini()
{
	log::debug
	{
		vm::log, "Shutting down fetch unit..."
	};

	context.terminate();
	context.join();

	log::debug
	{
		vm::log, "Fetch unit complete."
	};
}

//
// fetch_phase
//

decltype(ircd::m::fetch::hook)
ircd::m::fetch::hook
{
	enter,
	{
		{ "_site",  "vm.fetch" }
	}
};

void
ircd::m::fetch::enter(const event &event,
                      vm::eval &eval)
{
	assert(eval.opts);
	const auto &opts{*eval.opts};
	const m::room::id &room_id{at<"room_id"_>(event)};

	int64_t top;
	id::event::buf head;
	std::tie(head, top, std::ignore) = m::top(std::nothrow, room_id);
	if(top < 0 && (opts.head_must_exist || opts.history))
	{
		const auto &type{at<"type"_>(event)};
		if(type == "m.room.member" && membership(event) == "invite")
		{
			const auto &user_id{at<"state_key"_>(event)};
			//m::join(m::room{room_id}, user_id);
		}
		else if(type != "m.room.create")
			throw vm::error
			{
				vm::fault::STATE, "Found nothing for room %s",
				string_view{room_id}
			};
	}

	const event::prev prev
	{
		*eval.event_
	};

	const auto &prev_events
	{
		json::get<"prev_events"_>(prev)
	};

	const size_t &prev_count
	{
		size(prev_events)
	};

	for(size_t i(0); i < prev_count; ++i)
	{
		const auto &prev_id(prev.prev_event(i));
		if(!exists(prev_id))
			log::warning
			{
				log, "Missing prev %s in %s in %s",
				string_view{prev_id},
				json::get<"event_id"_>(*eval.event_),
				json::get<"room_id"_>(*eval.event_)
			};

		if(!eval.opts->prev_check_exists || exists(prev_id))
			continue;

		auto &request
		{
			fetch(json::get<"room_id"_>(*eval.event_), prev_id)
		};

		++request.refcnt;
		request.dock.wait([&request]
		{
			return request.eval;
		});

		const unwind uw{[&request]
		{
			if(!--request.refcnt)
				fetching.erase(request);
		}};

		if(request.eptr)
			throw vm::error
			{
				vm::fault::EVENT, "Missing prev event %s (%s)",
				prev_id,
				what(request.eptr)
			};
	}
}

//
// API interface
//

ircd::m::fetch::request &
ircd::m::fetch::fetch(const m::room::id &room_id,
                      const m::event::id &event_id)
{
	auto it
	{
		fetching.lower_bound(event_id)
	};

	if(it == end(fetching) || it->event_id != event_id)
		it = fetching.emplace_hint(it, room_id, event_id);
	else
		return const_cast<struct request &>(*it);

	auto &request
	{
		const_cast<struct request &>(*it)
	};

	request.start();
	dock.notify_all();
	return request;
}

//
// fetcher
//

decltype(ircd::m::fetch::dock)
ircd::m::fetch::dock;

decltype(ircd::m::fetch::fetching)
ircd::m::fetch::fetching;

decltype(ircd::m::fetch::completed)
ircd::m::fetch::completed;

/// The fetch context is an internal worker which drives the fetch process
/// and then indicates completion to anybody waiting on a fetch. This involves
/// handling errors/timeouts from a fetch attempt and retrying with another
/// server etc.
///
decltype(ircd::m::fetch::context)
ircd::m::fetch::context;

void
ircd::m::fetch::worker()
try
{
	while(1)
	{
		dock.wait(requesting);
		if(!handle())
			continue;

		while(!completed.empty())
		{
			auto *const &request
			{
				completed.front()
			};

			completed.pop_front();
			request->eval = true;
			std::cout << "evals " << request->event_id << " ref " << request->refcnt << std::endl;
			request->dock.notify_all();
		}
	}
}
catch(const std::exception &e)
{
	log::critical
	{
		"Fetch worker :%s", e.what()
	};
}

bool
ircd::m::fetch::handle()
try
{
	auto next
	{
		ctx::when_any(begin(fetching), end(fetching))
	};

	if(!next.wait(seconds(2), std::nothrow))
		return false;

	const auto it
	{
		next.get()
	};

	if(it == end(fetching))
		return false;

	auto &request
	{
		const_cast<struct request &>(*it)
	};

	if(!request.finished && !request.eptr)
		if(!request.handle())
			return false;

	assert(request.finished || request.eptr);
	if(!request.completed)
	{
		completed.emplace_back(&request);
		request.completed = true;
		return true;
	}

	return false;
}
catch(const std::exception &e)
{
	log::error
	{
		"Fetch worker :%s", e.what()
	};

	return false;
}

bool
ircd::m::fetch::requesting()
{
	return std::any_of(begin(fetching), end(fetching), []
	(const request &request)
	{
		return !request.finished;
	});
}

//
// fetch::request
//

ircd::m::fetch::request::request(const m::room::id &room_id,
                                 const m::event::id &event_id,
                                 const mutable_buffer &buf)
:room_id{room_id}
,event_id{event_id}
,_buf
{
	!buf?
		unique_buffer<mutable_buffer>{96_KiB}:
		unique_buffer<mutable_buffer>{}
}
,buf
{
	empty(buf)? _buf: buf
}
{
	// Ensure buffer has enough room for a worst-case event, request
	// headers and response headers.
	assert(size(this->buf) >= 64_KiB + 8_KiB + 8_KiB);
}

void
ircd::m::fetch::request::start()
{
	m::v1::event::opts opts;
	opts.dynamic = false;
	opts.remote = origin?: select_random_origin();
	start(std::move(opts));
}

void
ircd::m::fetch::request::start(m::v1::event::opts &&opts)
{
	if(!started)
		started = ircd::time();

	last = ircd::time();
	static_cast<m::v1::event &>(*this) =
	{
		this->event_id, this->buf, std::move(opts)
	};
}

ircd::string_view
ircd::m::fetch::request::select_random_origin()
{
	const m::room::origins origins
	{
		room_id
	};

	// copies randomly selected origin into the attempted set.
	const auto closure{[this]
	(const string_view &origin)
	{
		this->select_origin(origin);
	}};

	// Tests if origin is potentially viable
	const auto proffer{[this]
	(const string_view &origin)
	{
		// Don't want to request from myself.
		if(my_host(origin))
			return false;

		// Don't want to use a peer we already tried and failed with.
		if(attempted.count(origin))
			return false;

		// Don't want to use a peer marked with an error by ircd::server
		if(ircd::server::errmsg(origin))
			return false;

		return true;
	}};

	if(!origins.random(closure, proffer))
		throw m::NOT_FOUND
		{
			"Cannot find any server to fetch %s in %s",
			string_view{event_id},
			string_view{room_id},
		};

	return this->origin;
}

ircd::string_view
ircd::m::fetch::request::select_origin(const string_view &origin)
{
	const auto iit
	{
		attempted.emplace(std::string{origin})
	};

	this->origin = *iit.first;
	return this->origin;
}

bool
ircd::m::fetch::request::handle()
{
	auto &future
	{
		static_cast<m::v1::event &>(*this)
	};

	future.wait(); try
	{
		future.get();
	}
	catch(...)
	{
		eptr = std::current_exception();
	}

	if(!eptr)
		finish();
	else
		retry();

	return finished;
}

void
ircd::m::fetch::request::retry()
try
{
	eptr = std::exception_ptr{};
	origin = {};
	start();
}
catch(...)
{
	eptr = std::current_exception();
	finish();
}

void
ircd::m::fetch::request::finish()
{
	finished = ircd::time();
}

bool
ircd::m::fetch::request::operator()(const request &a,
                                    const request &b)
const
{
	return a.event_id < b.event_id;
}

bool
ircd::m::fetch::request::operator()(const request &a,
                                    const string_view &b)
const
{
	return a.event_id < b;
}

bool
ircd::m::fetch::request::operator()(const string_view &a,
                                    const request &b)
const
{
	return a < b.event_id;
}

namespace ircd::m::fetch
{
	extern "C" void auth_chain_fetch(const m::room::id &room_id,
	                                 const m::event::id &event_id,
	                                 const net::hostport &remote,
	                                 const milliseconds &timeout,
	                                 const std::function<bool (const m::event &)> &closure);

	extern "C" void auth_chain_eval(const m::room::id &room_id,
	                                const m::event::id &event_id,
	                                const net::hostport &remote);
}

extern "C" void
ircd::m::fetch::auth_chain_fetch(const m::room::id &room_id,
                                 const m::event::id &event_id,
                                 const net::hostport &remote,
                                 const milliseconds &timeout,
                                 const std::function<bool (const m::event &)> &closure)
{
	m::v1::event_auth::opts opts;
	opts.remote = remote;
	opts.dynamic = true;
	const unique_buffer<mutable_buffer> buf
	{
		16_KiB
	};

	m::v1::event_auth request
	{
		room_id, event_id, buf, std::move(opts)
	};

	request.wait(timeout);
	request.get();

    const json::array &auth_chain
    {
        request
    };

	std::vector<m::event> events{auth_chain.count()};
	std::transform(begin(auth_chain), end(auth_chain), begin(events), []
	(const json::object &pdu)
	{
		return m::event{pdu};
	});

	std::sort(begin(events), end(events));
	for(const auto &event : events)
		if(!closure(event))
			return;
}

extern "C" void
ircd::m::fetch::auth_chain_eval(const m::room::id &room_id,
                                const m::event::id &event_id,
                                const net::hostport &remote)
{
	m::vm::opts opts;
	opts.non_conform.set(m::event::conforms::MISSING_PREV_STATE);
	opts.non_conform.set(m::event::conforms::MISSING_MEMBERSHIP);
	opts.infolog_accept = true;
	opts.warnlog |= m::vm::fault::STATE;
	opts.warnlog &= ~m::vm::fault::EXISTS;
	opts.errorlog &= ~m::vm::fault::STATE;

	auth_chain_fetch(room_id, event_id, remote, seconds(30), [&opts]
	(const auto &event)
	{
		m::vm::eval
		{
			event, opts
		};

		return true;
	});
}