/* netio_posix.c - netio implementation for POSIX-ish systems
 *                 (actually uses a few GNU extensions)
 *
 * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
 * SPDX-Licence-Identifier: AGPL-3.0-or-later
 */

#define _GNU_SOURCE     /* for pthread_sigqueue(3gnu) */
/* misc */
#include <assert.h>     /* for assert() */
#include <errno.h>      /* for errno, EAGAIN, EINVAL */
#include <error.h>      /* for error(3gnu) */
#include <stdlib.h>     /* for abs(), shutdown(), SHUT_RD, SHUT_WR, SHUT_RDWR */
#include <unistd.h>     /* for read(), write() */
/* net */
#include <arpa/inet.h>  /* for htons(3p) */
#include <netinet/in.h> /* for struct sockaddr_in */
#include <sys/socket.h> /* for struct sockaddr, socket(), SOCK_* flags, setsockopt(), SOL_SOCKET, SO_REUSEADDR, bind(), listen(), accept() */
/* async */
#include <pthread.h>    /* for pthread_* */
#include <signal.h>     /* for siginfo_t, struct sigaction, enum sigval, sigaction(), SIGRTMIN, SIGRTMAX, SA_SIGINFO */

#include <libcr/coroutine.h>

#include <libnetio/netio.h>

/* configuration **************************************************************/

#include "config.h"

#ifndef CONFIG_NETIO_NUM_CONNS
#	error config.h must define CONFIG_NETIO_NUM_CONNS
#endif

/* common *********************************************************************/

#define UNUSED(name) /* name __attribute__ ((unused)) */

static int sig_io = 0;

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

static void _netio_init(void) {
	struct sigaction action = {0};

	if (sig_io)
		return;

	sig_io = SIGRTMIN;
	if (sig_io > SIGRTMAX)
		error(1, 0, "SIGRTMAX exceeded");

	action.sa_flags = SA_SIGINFO;
	action.sa_sigaction = handle_sig_io;
	if (sigaction(sig_io, &action, NULL) < 0)
		error(1, errno, "sigaction");
}

#define WAKE_COROUTINE(args) do {                                             \
		int r;                                                        \
		union sigval val = {0};                                       \
		val.sival_int = (int)((args)->cr_coroutine);                  \
		do {                                                          \
			r = pthread_sigqueue((args)->cr_thread, sig_io, val); \
			assert(r == 0 || r == EAGAIN);                        \
		} while (r == EAGAIN);                                        \
	} while (0)

#define RUN_PTHREAD(fn, args) do {                           \
		pthread_t thread;                            \
		int r;                                       \
		r = pthread_create(&thread, NULL, fn, args); \
		if (r)                                       \
			return -abs(r);                      \
		cr_pause_and_yield();                        \
		r = pthread_join(thread, NULL);              \
		if (r)                                       \
			return -abs(r);                      \
	} while (0)

/* listen() *******************************************************************/

int netio_listen(uint16_t port) {
	int sockfd;
	union {
		struct sockaddr_in in;
		struct sockaddr gen;
	} addr = { 0 };

	_netio_init();

	addr.in.sin_family = AF_INET;
	addr.in.sin_port = htons(port);
	sockfd = socket(AF_INET, SOCK_STREAM, 0);
	if (sockfd < 0)
		error(1, errno, "socket");
	if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) < 0)
		error(1, errno, "setsockopt");
	if (bind(sockfd, &addr.gen, sizeof addr) < 0)
		error(1, errno, "bind");
	if (listen(sockfd, CONFIG_NETIO_NUM_CONNS) < 0)
		error(1, errno, "listen");

	return sockfd;
}

/* accept() *******************************************************************/

struct _pthread_accept_args {
	pthread_t        cr_thread;
	cid_t            cr_coroutine;

	int              sockfd;

	int             *ret;
};

void *_pthread_accept(void *_args) {
	struct _pthread_accept_args *args = _args;
	*(args->ret) = accept(args->sockfd, NULL, NULL);
	if (*(args->ret) < 0)
		*(args->ret) = -errno;
	WAKE_COROUTINE(args);
	return NULL;
};

int netio_accept(int sock) {
	int ret;
	struct _pthread_accept_args args = {
		.cr_thread    = pthread_self(),
		.cr_coroutine = cr_getcid(),
		.sockfd       = sock,
		.ret          = &ret,
	};
	RUN_PTHREAD(_pthread_accept, &args);
	return ret;
}

/* read() *********************************************************************/

struct _pthread_read_args {
	pthread_t        cr_thread;
	cid_t            cr_coroutine;

	int              connfd;
	void            *buf;
	size_t           count;

	ssize_t         *ret;
};

void *_pthread_read(void *_args) {
	struct _pthread_read_args *args = _args;
	*(args->ret) = read(args->connfd, args->buf, args->count);
	if (*(args->ret) < 0)
		*(args->ret) = -errno;
	WAKE_COROUTINE(args);
	return NULL;
};

ssize_t netio_read(int conn, void *buf, size_t count) {
	ssize_t ret;
	struct _pthread_read_args args = {
		.cr_thread    = pthread_self(),
		.cr_coroutine = cr_getcid(),

		.connfd       = conn,
		.buf          = buf,
		.count        = count,

		.ret          = &ret,
	};
	RUN_PTHREAD(_pthread_read, &args);
	return ret;
}

/* write() ********************************************************************/

struct _pthread_write_args {
	pthread_t        cr_thread;
	cid_t            cr_coroutine;

	int              connfd;
	void            *buf;
	size_t           count;

	ssize_t         *ret;
};

void *_pthread_write(void *_args) {
	struct _pthread_read_args *args = _args;
	size_t done = 0;
	while (done < args->count) {
		ssize_t r = write(args->connfd, args->buf, args->count);
		if (r < 0) {
			*(args->ret) = -errno;
			break;
		}
		done += r;
	}
	if (done == args->count)
		*(args->ret) = done;
	WAKE_COROUTINE(args);
	return NULL;
};

ssize_t netio_write(int conn, void *buf, size_t count) {
	ssize_t ret;
	struct _pthread_write_args args = {
		.cr_thread    = pthread_self(),
		.cr_coroutine = cr_getcid(),

		.connfd       = conn,
		.buf          = buf,
		.count        = count,

		.ret          = &ret,
	};
	RUN_PTHREAD(_pthread_write, &args);
	return ret;
}

/* close() ********************************************************************/

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;
}