use errors;
use io;
use net;
use rt;

export type op = enum {
	NONE,
	READV,
	WRITEV,
	ACCEPT,

	CONNECT,

};

export type fflags = enum uint {
	BLOCKING = 1 << 31,
};

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

	flags: fflags,
	op: op,
	cb: nullable *void,
	user: nullable *void,

	// Operation-specific data
	union {
		struct {
			vbuf: rt::iovec,
			vec: []rt::iovec,
		},
		sockflags: net::sockflags,
	},
};

// Registers a file descriptor with an event loop.
export fn register(
	loop: *loop,
	fd: io::file,
) (*file | errors::error) = {
	const file = alloc(file {
		fd = fd,
		ev = loop,
		op = op::NONE,
		...
	});

	let ev = rt::epoll_event {
		events = 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: int == 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)!;
	};
	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 *void) 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) *void = {
	return file.user as *void;
};

// 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;
};

// Modifies the epoll events for a given file. For internal use.
fn filemod(file: *file, events: u32) void = {
	let ev = rt::epoll_event {
		events = events | rt::EPOLLONESHOT,
		...
	};
	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;

export type loop = struct {
	fd: io::file,
	events: []rt::epoll_event,
	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 { ... }...], 256),
		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;
};

// 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;
	};
	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 = rt::epoll_pwait(
		loop.fd, &loop.events[0],
		maxev: int, millis, null)!;

	for (let i = 0; i < nevent; i += 1) {
		const ev = &loop.events[i];
		const file = ev.data.ptr: *file;
		if (ev.events == 0) {
			continue;
		};
		switch (file.op) {
		case op::NONE =>
			abort("Invalid pending operation");
		case op::READV =>
			readv_ready(file, ev);
		case op::WRITEV =>
			writev_ready(file, ev);
		case op::ACCEPT =>
			accept_ready(file, ev);

		case op::CONNECT =>
			connect_ready(file, ev);

		};
	};

	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;
};

use errors;
use net;
use net::ip;
use net::tcp;
use rt;

// Creates a socket which listens for incoming TCP connections on the given
// IP address and port.
export fn listen_tcp(
	loop: *loop,
	addr: ip::addr,
	port: u16,
	opts: tcp::listen_option...
) (*file | net::error | errors::error) = {
	const sock = tcp::listen(addr, port, opts...)?;
	return register(loop, sock)?;
};

export type connectcb = fn(result: (*file | net::error), user: nullable *void) void;

// Creates a socket and connects to a given IP address and port over TCP.
//
// The variadic arguments accept [[net::sockflags]] and/or no more than one user
// data pointer. If the user data pointer is provided, it will be passed to the
// callback. This allows the user to pass a state object through the connection
// process:
//
//	let user: state = // ...
// 	ev::connect_tcp(&loop, &connected, addr, port, &user);
//
// 	fn connected(result: (*ev::file | net::error), user: nullable *void) void = {
// 		let user = user: *state;
// 	};
//
// If you don't need a user data object you can just omit it:
//
// 	ev::connect_tcp(&loop, &connected, addr, port, &user);
export fn connect_tcp(
	loop: *loop,
	cb: *connectcb,
	addr: ip::addr,
	port: u16,
	opts: (net::sockflags | *void)...
) (void | net::error | errors::error) = {
	// XXX: This doesn't let us set keepalive
	let opt: net::sockflags = 0;
	let user: nullable *void = null;
	for (let i = 0z; i < len(opts); i += 1) {
		match (opts[i]) {
		case let o: net::sockflags =>
			opt |= o;
		case let u: *void =>
			assert(user == null);
			user = u;
		};
	};
	const sock = tcp::connect(addr, port, opt | net::sockflags::NONBLOCK)?;
	let file = register(loop, sock)?;
	file.user = user;
	file.cb = cb;
	file.op = op::CONNECT;
	filemod(file, rt::EPOLLOUT);
};

fn connect_ready(
	sock: *file,
	ev: *rt::epoll_event,
) void = {
	assert(sock.op == op::CONNECT);
	assert(ev.events & rt::EPOLLOUT != 0);
	assert(sock.cb != null);
	const cb = sock.cb: *connectcb;
	sock.op = op::NONE;
	filemod(sock, 0);

	let errno = 0i, optsz = size(int): u32;
	rt::getsockopt(sock.fd, rt::SOL_SOCKET, rt::SO_ERROR, &errno, &optsz)!;
	if (errno != 0) {
		cb(errors::errno(errno), sock.user);
		close(sock);
	} else {
		// XXX: If the user puts NONBLOCK into the opts provided at
		// [[connect_tcp]] we could try to preserve that here
		const fl = rt::fcntl(sock.fd, rt::F_GETFL, void)!;
		rt::fcntl(sock.fd, rt::F_SETFL, fl & ~rt::O_NONBLOCK)!;
		cb(sock, sock.user);
	};
};

// A callback for an [[accept]] operation.
export type acceptcb = fn(file: *file, result: (*file | net::error)) void;

// Schedules an accept operation on a socket.
export fn accept(
	sock: *file,
	cb: *acceptcb,
	flags: net::sockflags...
) req = {
	assert(sock.op == op::NONE);
	let fl: net::sockflags = 0;
	for (let i = 0z; i < len(flags); i += 1) {
		fl |= flags[i];
	};
	sock.op = op::ACCEPT;
	sock.cb = cb;
	sock.sockflags = fl;
	filemod(sock, rt::EPOLLIN);
	return req { ... };
};

fn accept_ready(
	sock: *file,
	ev: *rt::epoll_event,
) void = {
	assert(sock.op == op::ACCEPT);
	assert(ev.events & rt::EPOLLIN != 0);
	assert(sock.cb != null);
	const cb = sock.cb: *acceptcb;
	sock.op = op::NONE;
	filemod(sock, 0);

	const r = tcp::accept(sock.fd, sock.sockflags);
	match (r) {
	case let fd: net::socket =>
		// TODO: Bubble up errors from here?
		const file = register(sock.ev, fd)!;
		cb(sock, file);
	case let err: net::error =>
		cb(sock, err);
	};
};