#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() */
#include <unistd.h>     /* for getpid() */

#define USE_CONFIG_NETIO_POSIX
#include "config.h"

#if CONFIG_NETIO_ISLINUX
#  include <fcntl.h>    /* for fcntl(), F_SETFL, O_ASYNC, F_SETSIG */
#endif

#include <libnetio/netio.h>
#include <libcr/coroutine.h>
#include <libcr_ipc/sema.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 CONFIG_NETIO_ISLINUX
static int sig_accept = 0;
#endif

struct netio_socket {
	int             fd;
#if CONFIG_NETIO_ISLINUX
	cr_sema_t       accept_waiters;
#endif
};

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

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

#if CONFIG_NETIO_ISLINUX
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 < CONFIG_NETIO_NUM_PORTS; i++)
		if (info->si_fd  == socket_table[i].fd)
			sock = &socket_table[i];
	if (!sock)
		return;
	cr_sema_signal_from_intrhandler(&sock->accept_waiters);
}
#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 CONFIG_NETIO_ISLINUX
	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 = { 0 };

	_netio_init();

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

	/* Bind the socket.  */
	addr.in.sin_family = AF_INET;
	addr.in.sin_port = htons(port);
	sock->fd = socket(AF_INET, SOCK_STREAM | 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 CONFIG_NETIO_ISLINUX
	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)");
	if (fcntl(sock->fd, F_SETOWN, getpid()) < 0)
		error(1, errno, "fcntl(F_SETOWN)");
#endif
	if (bind(sock->fd, &addr.gen, sizeof addr) < 0)
		error(1, errno, "bind");
	if (listen(sock->fd, CONFIG_NETIO_NUM_CONNS) < 0)
		error(1, errno, "listen");

	/* Return.  */
	return handle;
}

int netio_accept(int sock) {
	/* AFAICT in pure POSIX there's no good way to do this that
	 * isn't just busy-polling.
	 *
	 * On Linux where we can get a signal to notify us when
	 * there's something to accept, we still do this non-blocking
	 * and check EAGAIN/EWOULDBLOCK in case the client timed out
	 * while waiting for us to accept().  */
	for (;;) {
#if CONFIG_NETIO_ISLINUX
		cr_sema_wait(&socket_table[sock].accept_waiters);
#endif
		int conn = accept(socket_table[sock].fd, NULL, NULL);
		if (conn < 0) {
			if (errno == EAGAIN || errno == EWOULDBLOCK) {
#if !CONFIG_NETIO_ISLINUX
				cr_yield();
#endif
				continue;
			}
			return -errno;
		}
		return conn;
	}
}

ssize_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);
}

ssize_t netio_write(int conn, void *buf, size_t goal) {
	size_t done = 0;
	while (done < goal) {
		int r;
		struct aiocb ctl_block = {
			.aio_fildes = conn,
			.aio_buf = &(((uint8_t *)buf)[done]),
			.aio_nbytes = goal-done,
			.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();
		if (r < 0)
			return -abs(r);
		done += aio_return(&ctl_block);
	}
	return done;
}

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;
}