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

export type op = enum u64 {

	NONE    = 0,
	READV   = 1 << 0,
	WRITEV  = 1 << 1,
	ACCEPT  = 1 << 2,
	CONNECT = 1 << 3,

	NONE     = 0,
	READV    = 1 << 0,
	WRITEV   = 1 << 1,

	READABLE = 1 << 16,
	WRITABLE = 2 << 16,
	ACCEPT   = 3 << 16,
	CONNECT  = 4 << 16,

};

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

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

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

	// Operation-specific data
	union {
		struct {
			rvbuf: rt::iovec,
			rvec: []rt::iovec,
			wvbuf: rt::iovec,
			wvec: []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;
};

// 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) {

	if (file.op & op::READV != 0 || file.op & op::READABLE != 0) {

		events |= rt::EPOLLIN | rt::EPOLLHUP;
	};

	if (file.op & op::WRITEV != 0) {

	if (file.op & op::WRITEV != 0 || file.op & op::WRITABLE != 0) {

		events |= rt::EPOLLOUT | rt::EPOLLHUP;
	};
	if (file.op & op::ACCEPT != 0) {
		events |= rt::EPOLLIN;
	};
	if (file.op & op::CONNECT != 0) {
		events |= rt::EPOLLOUT;
	};

	let ev = rt::epoll_event {
		events = events,
		...
	};
	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 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.rvbuf = io::mkvector(buf);
	// XXX: Bit of a hack to avoid allocating a slice
	const vec = (&file.rvbuf: *[*]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::READV == 0);
	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.rvec = vec;
	file_epoll_ctl(file);
	return req { ... };
};

fn readv_ready(file: *file, ev: *rt::epoll_event) void = {
	assert(file.op & op::READV != 0);
	assert(file.cb != null);
	const cb = file.cb: *readcb;
	file.op &= ~op::READV;
	file_epoll_ctl(file);

	if (ev.events & rt::EPOLLHUP != 0) {
		cb(file, io::EOF);
	} else {
		const r = io::readv(file.fd, file.rvec...);
		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.wvbuf = io::mkvector(buf);
	// XXX: Bit of a hack to avoid allocating a slice
	const vec = (&file.wvbuf: *[*]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::WRITEV == 0);
	if (file.flags & fflags::BLOCKING != 0) {
		const r = io::writev(file.fd, vec...);
		cb(file, r);
		return req { ... };
	};

	file.op |= op::WRITEV;
	file.cb2 = cb;
	file.wvec = vec;
	file_epoll_ctl(file);
	return req { ... };
};

fn writev_ready(file: *file, ev: *rt::epoll_event) void = {
	assert(file.op & op::WRITEV != 0);
	assert(file.cb != null);
	const r = io::writev(file.fd, file.wvec...);
	const cb = file.cb2: *writecb;
	file.op &= ~op::WRITEV;
	file_epoll_ctl(file);
	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 ([[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;
		};

		if (file.op == op::NONE) {
			abort("Invalid pending operation");
		};

		const pending = file.op;

		if (ev.events & (rt::EPOLLIN | rt::EPOLLHUP) != 0

				&& file.op & op::READV != 0) {

				&& pending & op::READV != 0) {

			readv_ready(file, ev);
		};
		if (ev.events & (rt::EPOLLOUT | rt::EPOLLHUP) != 0

				&& file.op & op::WRITEV != 0) {

				&& pending & op::WRITEV != 0) {

			writev_ready(file, ev);
		};

		if (file.op & op::ACCEPT != 0) {

		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);

		};
		if (file.op & op::CONNECT != 0) {

		case op::CONNECT =>

			connect_ready(file, ev);

		case =>
			yield;

		};
	};

	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 rt;

// A callback for a [[readable]] operation.
export type readablecb = fn(file: *file) void;

// Executes the callback when a given file is readable. Cannot be combined with
// [[read]] or [[readv]].
export fn readable(
	file: *file,
	cb: *readablecb,
) req = {
	assert(file.op & op::READABLE == 0 && file.op & op::READV == 0);
	if (file.flags & fflags::BLOCKING != 0) {
		cb(file);
		return req { ... };
	};

	file.op |= op::READABLE;
	file.cb = cb;
	file_epoll_ctl(file);
	return req { ... };
};

fn readable_ready(file: *file, ev: *rt::epoll_event) void = {
	assert(file.op & op::READABLE != 0);
	assert(file.cb != null);
	const cb = file.cb: *readablecb;
	file.op &= ~op::READABLE;
	file_epoll_ctl(file);
	cb(file);
};

// A callback for a [[writable]] operation.
export type writablecb = fn(file: *file) void;

// Executes the callback when a given file is writable. Cannot be combined with
// [[write]] or [[writev]].
export fn writable(
	file: *file,
	cb: *writablecb,
) req = {
	assert(file.op & op::WRITABLE == 0 && file.op & op::WRITEV == 0);
	if (file.flags & fflags::BLOCKING != 0) {
		cb(file);
		return req { ... };
	};

	file.op |= op::WRITABLE;
	file.cb = cb;
	file_epoll_ctl(file);
	return req { ... };
};

fn writable_ready(file: *file, ev: *rt::epoll_event) void = {
	assert(file.op & op::WRITABLE != 0);
	assert(file.cb != null);
	const cb = file.cb: *writablecb;
	file.op &= ~op::WRITABLE;
	file_epoll_ctl(file);
	cb(file);
};