use io;
use rt;

// A callback for a [[read]] or [[readv]] operation.
export type readcb = fn(file: *file, result: (size | io::EOF | io::error)) void;

// Schedules a read operation on a file object.
export fn read(
	file: *file,
	cb: *readcb,
	buf: []u8,
) req = {
	file.vbuf = io::mkvector(buf);
	// XXX: Bit of a hack to avoid allocating a slice
	const vec = (&file.vbuf: *[*]io::vector)[..1];
	return readv(file, cb, vec...);
};

// Schedules a vectored read operation on a file object.
export fn readv(
	file: *file,
	cb: *readcb,
	vec: io::vector...
) req = {
	assert(file.op == op::NONE);
	if (file.flags & fflags::BLOCKING != 0) {
		const r = io::readv(file.fd, vec...);
		cb(file, r);
		return req { ... };
	};

	file.op = op::READV;
	file.cb = cb;
	file.vec = vec;
	filemod(file, rt::EPOLLIN | rt::EPOLLHUP);
	return req { ... };
};

fn readv_finish(file: *file, ev: *rt::epoll_event) void = {

fn readv_ready(file: *file, ev: *rt::epoll_event) void = {

	assert(file.op == op::READV);
	assert(ev.events & (rt::EPOLLIN | rt::EPOLLHUP) != 0);
	assert(file.cb != null);
	const cb = file.cb: *readcb;
	file.op = op::NONE;

	if (ev.events & rt::EPOLLHUP != 0) {
		cb(file, io::EOF);
	} else {
		const r = io::readv(file.fd, file.vec...);
		cb(file, r);
	};
};

// A callback for a [[write]] or [[writev]] operation.
export type writecb = fn(file: *file, result: (size | io::error)) void;

// Schedules a write operation on a file object.
export fn write(
	file: *file,
	cb: *writecb,
	buf: []u8,
) req = {
	file.vbuf = io::mkvector(buf);
	// XXX: Bit of a hack to avoid allocating a slice
	const vec = (&file.vbuf: *[*]io::vector)[..1];
	return writev(file, cb, vec...);
};

// Schedules a vectored read operation on a file object.
export fn writev(
	file: *file,
	cb: *writecb,
	vec: io::vector...
) req = {
	// XXX: Should we support both pending reads and writes at the same
	// time? (yes)
	assert(file.op == op::NONE);
	if (file.flags & fflags::BLOCKING != 0) {
		const r = io::writev(file.fd, vec...);
		cb(file, r);
		return req { ... };
	};

	file.op = op::WRITEV;
	file.cb = cb;
	file.vec = vec;
	filemod(file, rt::EPOLLOUT | rt::EPOLLHUP);
	return req { ... };
};

fn writev_finish(file: *file, ev: *rt::epoll_event) void = {

fn writev_ready(file: *file, ev: *rt::epoll_event) void = {

	assert(file.op == op::WRITEV && ev.events & rt::EPOLLOUT != 0);
	assert(file.cb != null);
	const r = io::writev(file.fd, file.vec...);
	const cb = file.cb: *writecb;
	file.op = op::NONE;
	cb(file, r);
};

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 (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_finish(file, ev);

			readv_ready(file, ev);

		case op::WRITEV =>

			writev_finish(file, ev);

			writev_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;
};