use errors;
use io;
use net;
use net::ip;
use rt;
use unix::signal;

export type op = enum u64 {
	NONE     = 0,
	READV    = 1 << 0,
	WRITEV   = 1 << 1,

	READABLE     = 1 << 16,
	WRITABLE     = 2 << 16,
	ACCEPT       = 3 << 16,
	CONNECT_TCP  = 4 << 16,
	CONNECT_UNIX = 5 << 16,
	SIGNAL       = 6 << 16,
	TIMER        = 7 << 16,
	SENDTO       = 8 << 16,
	RECVFROM     = 9 << 16,
	SEND         = 10 << 16,
	RECV         = 11 << 16,
};

export type fflags = enum uint {
	NONE = 0,
	BLOCKING = 1 << 31,
};

export type file = struct {
	fd: io::file,
	ev: *loop,

	flags: fflags,
	op: op,
	cb: nullable *opaque,
	cb2: nullable *opaque,
	user: nullable *opaque,

	// Operation-specific data
	union {
		struct {
			rvbuf: io::vector,
			rvec: []io::vector,
			wvbuf: io::vector,
			wvec: []io::vector,
		},
		sockflag: net::sockflag,
		sigmask: signal::sigset,
		sendrecv: struct {
			sbuf: []u8,
			rbuf: []u8,
			dest: ip::addr,
			port: u16,
		},
	},
};

// Registers a file descriptor with an event loop.
export fn register(
	loop: *loop,
	fd: io::file,

	user: nullable *opaque = null,

) (*file | errors::error) = {
	const file = alloc(file {
		flags = fflags::NONE,
		fd = fd,
		ev = loop,
		op = op::NONE,

		user = user,

		...
	});

	let ev = rt::epoll_event {
		events = 0,
		data = rt::epoll_data {
			fd = 0,
		}
	};
	ev.data.ptr = file;
	match (rt::epoll_ctl(loop.fd, rt::EPOLL_CTL_ADD, fd, &ev)) {
	case void =>
		yield;
	case let err: rt::errno =>
		if (err == rt::EPERM) {
			// epoll(2) does not support regular files, use blocking
			// I/O instead
			file.flags = fflags::BLOCKING;
			return file;
		};
		return errors::errno(err);
	};

	return file;
};

// Unregisters a file object with an event loop and frees resources associated
// with it. Does not close the underlying file descriptor.
export fn unregister(file: *file) void = {
	const loop = file.ev;
	if (file.flags & fflags::BLOCKING == 0) {
		// The only way that this could fail is in the event of a
		// use-after-free or if the user fucks around and constructs a
		// custom [[file]] which was never registered, so assert on
		// error.
		rt::epoll_ctl(loop.fd, rt::EPOLL_CTL_DEL, file.fd, null)!;
	};
	if (file.op == op::SIGNAL) {
		signal_restore(file);
	};
	free(file);
};

// Unregisters a file object with an event loop, frees resources associated with
// it, and closes the underlying file descriptor.
export fn close(file: *file) void = {
	const fd = file.fd;
	unregister(file);
	io::close(fd)!;
};

// Sets the user data field on this file object to the provided object.
export fn setuser(file: *file, user: nullable *opaque) void = {
	file.user = user;
};

// Returns the user data field from this file object. If the field was null, an
// assertion is raised.
export fn getuser(file: *file) *opaque = {
	return file.user as *opaque;
};

// Returns the file descriptor for a given file. Note that ev assumes that it
// will be responsible for all I/O on the file and any user modifications may
// cause the event loop to enter an invalid state.
export fn getfd(file: *file) io::file = {
	return file.fd;
};

// Returns the event loop for a given file.
export fn getloop(file: *file) *loop = {
	return file.ev;
};

// Updates epoll events for a given file. For internal use.
fn file_epoll_ctl(file: *file) void = {
	let events = rt::EPOLLONESHOT;
	if (file.op & op::READV != 0 || file.op == op::READABLE) {
		events |= rt::EPOLLIN | rt::EPOLLHUP;
	};
	if (file.op & op::WRITEV != 0 || file.op == op::WRITABLE) {
		events |= rt::EPOLLOUT | rt::EPOLLHUP;
	};
	switch (file.op) {
	case op::ACCEPT =>
		events |= rt::EPOLLIN;
	case op::CONNECT_TCP, op::CONNECT_UNIX =>
		events |= rt::EPOLLOUT;
	case op::SIGNAL =>
		events |= rt::EPOLLIN;
	case op::TIMER =>
		events &= ~rt::EPOLLONESHOT;
		events |= rt::EPOLLIN;
	case op::SEND, op::SENDTO =>
		events |= rt::EPOLLOUT;
	case op::RECV, op::RECVFROM =>
		events |= rt::EPOLLIN;
	case =>
		yield;
	};

	let ev = rt::epoll_event {
		events = events,
		data = rt::epoll_data {
			fd = 0,
		},
	};
	ev.data.ptr = file;
	// This can only fail under conditions associated with EPOLLEXCLUSIVE,
	// which we do not support.
	rt::epoll_ctl(file.ev.fd, rt::EPOLL_CTL_MOD, file.fd, &ev)!;
};

use errors;
use io;
use rt;
use time;
use types;
use unix::signal;

// Dispatch callback. See [[ondispatch]].
export type dispatchcb = fn(loop: *loop, user: nullable *opaque) void;

export type ondispatch = struct {
	cb: *dispatchcb,
	user: nullable *opaque,
	loop: *loop,
};

export type loop = struct {
	fd: io::file,
	events: []rt::epoll_event,
	dispatch: []*ondispatch,
	stop: bool,
};

// Creates a new event loop. The user must pass the return value to [[finish]]
// to free associated resources when done using the loop.
export fn newloop() (loop | errors::error) = {
	const fd = match (rt::epoll_create1(rt::EPOLL_CLOEXEC)) {
	case let fd: int =>
		yield fd: io::file;
	case let err: rt::errno =>
		return errors::errno(err);
	};

	return loop {
		fd = fd,
		// XXX: Should the number of events be customizable?
		events = alloc([rt::epoll_event {
			events = 0,
			data = rt::epoll_data {
				fd = 0,
			}
		}...], 256),
		dispatch = [],
		stop = false,
	};
};

// Frees resources associated with an event loop. Must only be called once per
// event loop object. Calling finish invalidates all I/O objects associated with
// the event loop.
export fn finish(loop: *loop) void = {
	free(loop.events);
	io::close(loop.fd)!;
};

// Returns an [[io::file]] for this event loop which can be polled on when
// events are available for processing, for chaining together different event
// loops. The exact semantics of this function are platform-specific, and it may
// not be available for all implementations.
export fn loop_file(loop: *loop) io::file = {
	return loop.fd;
};

// Registers a callback to be invoked before the event loop dispatches pending
// I/O requests. The callback may schedule additional I/O requests to be
// processed in this batch.
export fn do(
	loop: *loop,
	cb: *dispatchcb,

	user: nullable *opaque,

	user: nullable *opaque = null,

) req = {
	const dispatch = alloc(ondispatch {
		cb = cb,
		user = user,
		loop = loop,
	});
	append(loop.dispatch, dispatch);
	return mkreq(&do_cancel, dispatch);
};

fn do_cancel(req: *req) void = {
	const dispatch = req.user: *ondispatch;
	const loop = dispatch.loop;
	for (let i = 0z; i < len(loop.dispatch); i += 1) {
		if (loop.dispatch[i] == dispatch) {
			delete(loop.dispatch[i]);
			break;
		};
	};
	free(dispatch);
};

// Dispatches the event loop, waiting for new events and calling their callbacks
// as appropriate.
//
// A timeout of -1 will block indefinitely until the next event occurs. A
// timeout of 0 will cause dispatch to return immediately if no events are
// available to process. Portable use of the timeout argument supports only
// millisecond granularity of up to 24 days ([[types::INT_MAX]] milliseconds).
// Negative values other than -1 will cause the program to abort.
//
// Returns false if the loop has been stopped via [[stop]], or true otherwise.
export fn dispatch(
	loop: *loop,
	timeout: time::duration,
) (bool | errors::error) = {
	const millis: int = if (timeout == -1) {
		yield -1;
	} else if (timeout < 0) {
		abort("ev::dispatch: invalid timeout");
	} else {
		yield (timeout / time::MILLISECOND): int;
	};
	if (loop.stop) {
		return false;
	};

	let todo = loop.dispatch;
	loop.dispatch = [];
	for (let dispatch .. todo) {
		dispatch.cb(loop, dispatch.user);
		free(dispatch);
	};
	free(todo);

	if (len(loop.events) == 0) {
		return true;
	};

	// TODO: Deal with signals
	const maxev = len(loop.events);
	assert(maxev <= types::INT_MAX: size, "ev::dispatch: too many events");
	const nevent = match(rt::epoll_pwait(
		loop.fd, &loop.events[0],
		maxev: int, millis, null)) {
	case let nevent: int =>
		yield nevent;
	case let err: rt::errno =>
		switch (err) {
		case rt::EINTR =>
			// We shallow system suspension error code
			return true;
		case =>
			abort("ev::dispatch: epoll_pwait failure");
		};
	};

	for (let ev &.. loop.events) {
		const file = ev.data.ptr: *file;
		if (ev.events == 0) {
			continue;
		};
		const pending = file.op;
		if (ev.events & (rt::EPOLLIN | rt::EPOLLHUP) != 0
				&& file.op & op::READV != 0) {
			readv_ready(file, ev);
		};
		if (ev.events & (rt::EPOLLOUT | rt::EPOLLHUP) != 0
				&& file.op & op::WRITEV != 0) {
			writev_ready(file, ev);
		};
		switch (pending) {
		case op::NONE =>
			abort("No operation pending for ready object");
		case op::READABLE =>
			readable_ready(file, ev);
		case op::WRITABLE =>
			writable_ready(file, ev);
		case op::ACCEPT =>
			accept_ready(file, ev);
		case op::CONNECT_TCP =>
			connect_tcp_ready(file, ev);
		case op::CONNECT_UNIX =>
			connect_unix_ready(file, ev);
		case op::SIGNAL =>
			signal_ready(file, ev);
		case op::TIMER =>
			timer_ready(file, ev);
		case op::SENDTO =>
			sendto_ready(file, ev);
		case op::RECVFROM =>
			recvfrom_ready(file, ev);
		case op::SEND =>
			send_ready(file, ev);
		case op::RECV =>
			recv_ready(file, ev);
		case =>
			assert(pending & ~(op::READV | op::WRITEV) == 0);
		};
	};

	return !loop.stop;
};

// Signals the loop to stop processing events. If called during a callback, it
// will cause that invocation of [[dispatch]] to return false. Otherwise, false
// will be returned only upon the next call to [[dispatch]].
export fn stop(loop: *loop) void = {
	loop.stop = true;
};

export type req = struct {
	cancel: nullable *cancelfn,
	user: nullable *opaque,
};

// Makes a new request object.

export fn mkreq(cancel: *cancelfn, user: nullable *opaque) req = {

export fn mkreq(cancel: *cancelfn, user: nullable *opaque = null) req = {

	return req {
		cancel = cancel,
		user = user,
	};
};

// A function which cancels an in-flight request.
export type cancelfn = fn(req: *req) void;

// Cancels an in-flight request. The user can safely cancel a request more than
// once. A request cannot be cancelled once it has completed.
export fn cancel(req: *req) void = {
	match (req.cancel) {
	case let cancel: *cancelfn =>
		cancel(req);
	case null => yield;
	};
	req.cancel = null;
};

use ev;
use fmt;
use net;
use net::dial;
use net::ip;
use net::uri;

// Callback for a [[dial]] operation.
export type dialcb = fn(user: nullable *opaque, r: (*ev::file | error)) void;

// Dials a remote address, establishing a connection and returning the resulting
// [[net::socket]] to the callback. The proto parameter should be the transport
// protocol (e.g. "tcp"), the address parameter should be the remote address,
// and the service should be the name of the service, or the default port to
// use.
//
// See also [[net::dial::dial]].
export fn dial(
	loop: *ev::loop,
	proto: str,
	address: str,
	service: str,
	cb: *dialcb,

	user: nullable *opaque,

	user: nullable *opaque = null,

) (ev::req | error) = {
	for (const p .. default_protocols) {
		if (p.name == proto) {
			return p.dial(loop, address, service, cb, user);
		};
	};
	for (const p .. protocols) {
		if (p.name == proto) {
			return p.dial(loop, address, service, cb, user);
		};
	};
	return net::unknownproto: net::error;
};

def HOST_MAX: size = 255;

// Performs a [[dial]] operation for a given URI, taking the service name from
// the URI scheme and forming an address from the URI host and port.
//
// See also [[net::dial::uri]].
export fn dial_uri(
	loop: *ev::loop,
	proto: str,
	uri: *uri::uri,
	cb: *dialcb,

	user: nullable *opaque,

	user: nullable *opaque = null,

) (ev::req | error) = {
	if (uri.host is str && len(uri.host as str) > HOST_MAX) {
		return invalid_address;
	};
	static let addr: [HOST_MAX + len("[]:65535")]u8 = [0...];

	const colon = if (uri.port != 0) ":" else "";
	const port: fmt::formattable = if (uri.port != 0) uri.port else "";

	let addr = match (uri.host) {
	case let host: str =>
		yield fmt::bsprintf(addr, "{}{}{}", host, colon, port);
	case let ip: ip::addr4 =>
		const host = ip::string(ip);
		yield fmt::bsprintf(addr, "{}{}{}", host, colon, port);
	case let ip: ip::addr6 =>
		const host = ip::string(ip);
		yield fmt::bsprintf(addr, "[{}]{}{}", host, colon, port);
	};

	return dial(loop, proto, addr, uri.scheme, cb, user);
};

use crypto::random;
use errors;
use ev;
use edns = ev::dns;
use net;
use net::ip;
use net::dial;
use net::dns;
use unix::hosts;

// Callback from a [[resolve]] operation.
export type resolvecb = fn(
	user: nullable *opaque,
	r: (([]ip::addr, u16) | error),
) void;

type resolve_state = struct {
	user: nullable *opaque,
	cb: *resolvecb,
	r4: ev::req,
	r6: ev::req,
	nq: uint,
	ip: []ip::addr,
	port: u16,
};

// Performs DNS resolution on a given address string for a given service,
// including /etc/hosts lookup and SRV resolution, and returns a list of
// candidate IP addresses and the appropriate port, or an error, to the
// callback.
//
// The caller must free the [[net::ip::addr]] slice.
export fn resolve(
	loop: *ev::loop,
	proto: str,
	addr: str,
	service: str,
	cb: *resolvecb,

	user: nullable *opaque

	user: nullable *opaque = null

) (ev::req | error) = {
	// TODO: Reduce duplication with net::dial
	let state = alloc(resolve_state {
		cb = cb,
		user = user,
		...
	});

	const (addr, port) = match (dial::splitaddr(addr, service)) {
	case let svc: (str, u16) =>
		yield svc;
	case dial::invalid_address =>
		resolve_finish(state, invalid_address);
		return ev::req { ... };
	};

	if (service == "unknown" && port == 0) {
		resolve_finish(state, unknown_service);
		return ev::req { ... };
	};

	if (port == 0) {
		match (lookup_service(proto, service)) {
		case let p: u16 =>
			port = p;
		case void => yield;
		};
	};

	// TODO:
	// - Consult /etc/services
	// - Fetch the SRV record

	if (port == 0) {
		resolve_finish(state, unknown_service);
		return ev::req { ... };
	};

	match (ip::parse(addr)) {
	case let addr: ip::addr =>
		const addrs = alloc([addr]);
		resolve_finish(state, (addrs, port));
		return ev::req { ... };
	case ip::invalid => yield;
	};

	const addrs = hosts::lookup(addr)?;
	if (len(addrs) != 0) {
		resolve_finish(state, (addrs, port));
		return ev::req { ... };
	};

	state.port = port;
	return resolve_dns(state, loop, addr);
};

fn resolve_dns(
	state: *resolve_state,
	loop: *ev::loop,
	addr: str,
) (ev::req | error) = {
	const domain = dns::parse_domain(addr);
	defer free(domain);

	let rand: []u8 = [0, 0];
	random::buffer(rand);
	let id = *(&rand[0]: *u16);

	const query6 = dns::message {
		header = dns::header {
			id = id,
			op = dns::op {
				qr = dns::qr::QUERY,
				opcode = dns::opcode::QUERY,
				rd = true,
				...
			},
			qdcount = 1,
			...
		},
		questions = [
			dns::question {
				qname = domain,
				qtype = dns::qtype::AAAA,
				qclass = dns::qclass::IN,
			},
		],
		...
	};
	const query4 = dns::message {
		header = dns::header {
			id = id + 1,
			op = dns::op {
				qr = dns::qr::QUERY,
				opcode = dns::opcode::QUERY,
				rd = true,
				...
			},
			qdcount = 1,
			...
		},
		questions = [
			dns::question {
				qname = domain,
				qtype = dns::qtype::A,
				qclass = dns::qclass::IN,
			},
		],
		...
	};

	state.r6 = edns::query(loop, &query6, &query_cb_v6, state)?;
	state.r4 = edns::query(loop, &query4, &query_cb_v4, state)?;
	return ev::mkreq(&resolve_cancel, state);
};

fn resolve_finish(st: *resolve_state, r: (([]ip::addr, u16) | error)) void = {
	const user = st.user;
	const cb = st.cb;
	if (r is error) {
		free(st.ip);
	};
	free(st);
	cb(user, r);
};

fn resolve_cancel(req: *ev::req) void = {
	const state = req.user: *resolve_state;
	ev::cancel(&state.r4);
	ev::cancel(&state.r6);
	free(state.ip);
	free(state);
};

fn query_cb_v4(user: nullable *opaque, r: (*dns::message | dns::error)) void = {
	let state = user: *resolve_state;
	state.r4 = ev::req { ... };

	match (r) {
	case let err: dns::error =>
		ev::cancel(&state.r6);
		resolve_finish(state, err);
		return;
	case let msg: *dns::message =>
		collect_answers(&state.ip, &msg.answers);
		state.nq += 1;
	};

	if (state.nq < 2) {
		return;
	};
	resolve_finish(state, (state.ip, state.port));
};

fn query_cb_v6(user: nullable *opaque, r: (*dns::message | dns::error)) void = {
	let state = user: *resolve_state;
	state.r6 = ev::req { ... };

	match (r) {
	case let err: dns::error =>
		ev::cancel(&state.r4);
		resolve_finish(state, err);
		return;
	case let msg: *dns::message =>
		collect_answers(&state.ip, &msg.answers);
		state.nq += 1;
	};

	if (state.nq < 2) {
		return;
	};
	resolve_finish(state, (state.ip, state.port));
};

fn collect_answers(addrs: *[]ip::addr, answers: *[]dns::rrecord) void = {
	for (let answer &.. answers) {
		match (answer.rdata) {
		case let addr: dns::aaaa =>
			append(addrs, addr: ip::addr);
		case let addr: dns::a =>
			append(addrs, addr: ip::addr);
		case => void;
		};
	};
};