#define LINUX       1
#define NUM_SOCKETS 1
#define NUM_WORKERS 8

#define _GNU_SOURCE
#include <aio.h>        /* for struct aiocb, aio_read(), aio_write(), aio_error(), aio_return(), SIGEV_SIGNAL */
#include <arpa/inet.h>  /* for htons() */
#include <errno.h>      /* for errno, EAGAIN, EWOULDBLOCK, EINPROGRESS, EINVAL */
#include <error.h>      /* for error() */
#include <netinet/in.h> /* for struct sockaddr_in */
#include <signal.h>     /* for siginfo_t, struct sigaction, sigaction(), SIGRTMIN, SIGRTMAX, SA_SIGINFO */
#include <stdlib.h>     /* for shutdown(), SHUT_RD, SHUT_WR, SHUT_RDWR */
#include <string.h>     /* for memset() */
#include <sys/socket.h> /* for struct sockaddr, socket(), SOCK_* flags, setsockopt(), SOL_SOCKET, SO_REUSEADDR, bind(), listen(), accept() */
#if LINUX
#  include <fcntl.h>    /* for fcntl(), F_SETFL, O_ASYNC, F_SETSIG */
#endif

#include "netio.h"
#include "coroutine.h"

/* I found the following post to be very helpful when writing this:
 * http://davmac.org/davpage/linux/async-io.html */

static int sigs_allocated = 0;
static int sig_io = 0;
#if LINUX
static int sig_accept = 0;
#endif

struct netio_socket {
	int   fd;
#if LINUX
	cid_t accept_waiters[NUM_WORKERS];
#endif
};

static struct netio_socket socket_table[NUM_SOCKETS] = {0};

static void handle_sig_io(int sig __attribute__ ((unused)), siginfo_t *info, void *ucontext __attribute__ ((unused))) {
	cr_unpause((cid_t)info->si_value.sival_int);
}

#if LINUX
static void handle_sig_accept(int sig __attribute__ ((unused)), siginfo_t *info, void *ucontext __attribute__ ((unused))) {
	struct netio_socket *sock = NULL;
	for (int i = 0; sock == NULL && i < NUM_SOCKETS; i++)
		if (info->si_fd  == socket_table[i].fd)
			sock = &socket_table[i];
	if (!sock)
		return;
	for (int i = 0; i < NUM_WORKERS; i++)
		if (sock->accept_waiters[i] > 0) {
			cr_unpause(sock->accept_waiters[i]);
			sock->accept_waiters[i] = 0;
			return;
		}
}
#endif

static void _netio_init(void) {
	struct sigaction action;

	if (sig_io)
		return;
	
	sig_io = SIGRTMIN + (sigs_allocated++);
	if (sig_io > SIGRTMAX)
		error(1, 0, "SIGRTMAX exceeded");
	memset(&action, 0, sizeof(action));
	action.sa_flags = SA_SIGINFO;
	action.sa_sigaction = handle_sig_io;
	if (sigaction(sig_io, &action, NULL) < 0)
		error(1, errno, "sigaction");

#if LINUX
	sig_accept = SIGRTMIN + (sigs_allocated++);
	if (sig_accept > SIGRTMAX)
		error(1, 0, "SIGRTMAX exceeded");
	memset(&action, 0, sizeof(action));
	action.sa_flags = SA_SIGINFO;
	action.sa_sigaction = handle_sig_accept;
	if (sigaction(sig_accept, &action, NULL) < 0)
		error(1, errno, "sigaction");
#endif
}

int netio_listen(uint16_t port) {
	int handle;
	struct netio_socket *sock;
	union {
		struct sockaddr_in in;
		struct sockaddr gen;
	} addr;

	_netio_init();

	/* Allocate a handle out of socket_table.  */
	handle = -1;
	for (int i = 0; handle < 0 && i < NUM_SOCKETS; i++)
		if (socket_table[i].fd == 0)
			handle = i;
	if (handle < 0)
		error(1, 0, "NUM_SOCKETS exceeded");
	sock = &socket_table[handle];

	/* Bind the socket.  */
	memset(&addr, 0, sizeof addr);
	addr.in.sin_family = AF_INET;
	addr.in.sin_port = htons(port);
	sock->fd = socket(AF_INET, SOCK_STREAM | (LINUX ? 0 : SOCK_NONBLOCK), 0);
	if (sock->fd < 0)
		error(1, errno, "socket");
	if (setsockopt(sock->fd, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) < 0)
		error(1, errno, "setsockopt");
#if LINUX
	if (fcntl(sock->fd, F_SETFL, O_ASYNC) < 0)
		error(1, errno, "fcntl(F_SETFL)");
	if (fcntl(sock->fd, F_SETSIG, sig_accept) < 0)
		error(1, errno, "fcntl(F_SETSIG)");
#endif
	if (bind(sock->fd, &addr.gen, sizeof addr) < 0)
		error(1, errno, "bind");
	if (listen(sock->fd, NUM_WORKERS) < 0)
		error(1, errno, "listen");

	/* Return.  */
	return handle;
}

int netio_accept(int sock) {
#if LINUX
	int conn;
	for (int i = 0; i < NUM_WORKERS; i++)
		if (socket_table[sock].accept_waiters[i] == 0) {
			socket_table[sock].accept_waiters[i] = cr_getcid();
			break;
		}
	cr_pause_and_yield();
	conn = accept(socket_table[sock].fd, NULL, NULL);
	return conn < 0 ? -errno : conn;
#else
	/* AFAICT in pure POSIX there's no good way to do this that
	 * isn't just busy-polling.  */
	for (;;) {
		int conn = accept(socket_table[sock].fd, NULL, NULL);
		if (conn < 0) {
			if (errno == EAGAIN || errno == EWOULDBLOCK) {
				cr_yield();
				continue;
			}
			return -errno;
		}
		return conn;
	}
#endif
}

size_t netio_read(int conn, void *buf, size_t count) {
	int r;
	struct aiocb ctl_block = {
		.aio_fildes = conn,
		.aio_buf = buf,
		.aio_nbytes = count,
		.aio_sigevent = {
			.sigev_notify = SIGEV_SIGNAL,
			.sigev_signo = sig_io,
			.sigev_value = {
				.sival_int = (int)cr_getcid(),
			},
		},
	};

	if (aio_read(&ctl_block) < 0)
		return -errno;

	while ((r = aio_error(&ctl_block)) == EINPROGRESS)
		cr_pause_and_yield();
	return r ? -abs(r) : aio_return(&ctl_block);
}

size_t netio_write(int conn, void *buf, size_t count) {
	int r;
	struct aiocb ctl_block = {
		.aio_fildes = conn,
		.aio_buf = buf,
		.aio_nbytes = count,
		.aio_sigevent = {
			.sigev_notify = SIGEV_SIGNAL,
			.sigev_signo = sig_io,
			.sigev_value = {
				.sival_int = (int)cr_getcid(),
			},
		},
	};

	if (aio_write(&ctl_block) < 0)
		return -errno;

	while ((r = aio_error(&ctl_block)) == EINPROGRESS)
		cr_pause_and_yield();
	return r ? -abs(r) : aio_return(&ctl_block);
}

int netio_close(int conn, bool rd, bool wr) {
	int how;
	if (rd && wr)
		how = SHUT_RDWR;
	else if (rd && !wr)
		how = SHUT_RD;
	else if (!rd && wr)
		how = SHUT_WR;
	else
		return -EINVAL;
	return shutdown(conn, how) ? -errno : 0;
}