/*! \file osmo_io_poll.c
 * New osmocom async I/O API.
 *
 * (C) 2022 by Harald Welte <laforge@osmocom.org>
 * (C) 2022-2023 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
 * Author: Daniel Willmann <dwillmann@sysmocom.de>
 *
 * All Rights Reserved.
 *
 * SPDX-License-Identifier: GPL-2.0+
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 */

#include "../config.h"
#if defined(__linux__)

#include <errno.h>
#include <stdio.h>
#include <talloc.h>
#include <unistd.h>
#include <stdbool.h>
#include <sys/socket.h>

#include <osmocom/core/osmo_io.h>
#include <osmocom/core/linuxlist.h>
#include <osmocom/core/logging.h>
#include <osmocom/core/msgb.h>
#include <osmocom/core/select.h>
#include <osmocom/core/socket.h>
#include <osmocom/core/talloc.h>
#include <osmocom/core/utils.h>

#include "osmo_io_internal.h"

static void iofd_poll_ofd_cb_recvmsg_sendmsg(struct osmo_fd *ofd, unsigned int what)
{
	struct osmo_io_fd *iofd = ofd->data;
	struct msgb *msg;
	int rc, flags = 0;

	if (what & OSMO_FD_READ) {
		struct iofd_msghdr hdr;

		msg = iofd_msgb_pending_or_alloc(iofd);
		if (!msg) {
			LOGPIO(iofd, LOGL_ERROR, "Could not allocate msgb for reading\n");
			OSMO_ASSERT(0);
		}

		hdr.msg = msg;
		hdr.iov[0].iov_base = msg->tail;
		hdr.iov[0].iov_len = msgb_tailroom(msg);
		hdr.hdr = (struct msghdr) {
			.msg_iov = &hdr.iov[0],
			.msg_iovlen = 1,
			.msg_name = &hdr.osa.u.sa,
			.msg_namelen = sizeof(struct osmo_sockaddr),
		};
		if (iofd->mode == OSMO_IO_FD_MODE_RECVMSG_SENDMSG) {
			hdr.hdr.msg_control = alloca(iofd->cmsg_size);
			hdr.hdr.msg_controllen = iofd->cmsg_size;
		}

		rc = recvmsg(ofd->fd, &hdr.hdr, flags);
		if (rc > 0)
			msgb_put(msg, rc);

		iofd_handle_recv(iofd, msg, (rc < 0 && errno > 0) ? -errno : rc, &hdr);
	}

	if (IOFD_FLAG_ISSET(iofd, IOFD_FLAG_CLOSED))
		return;

	if (what & OSMO_FD_WRITE) {
		struct iofd_msghdr *msghdr = iofd_txqueue_dequeue(iofd);
		if (msghdr) {
			rc = sendmsg(ofd->fd, &msghdr->hdr, msghdr->flags);
			iofd_handle_send_completion(iofd, rc, msghdr);
		} else {
			/* Socket is writable, but we have no data to send. A non-blocking/async
			   connect() is signalled this way. */
			switch (iofd->mode) {
			case OSMO_IO_FD_MODE_READ_WRITE:
				iofd->io_ops.write_cb(iofd, 0, NULL);
				break;
			case OSMO_IO_FD_MODE_RECVFROM_SENDTO:
				iofd->io_ops.sendto_cb(iofd, 0, NULL, NULL);
				break;
			case OSMO_IO_FD_MODE_RECVMSG_SENDMSG:
				iofd->io_ops.sendmsg_cb(iofd, 0, NULL);
				break;
			default:
				break;
			}
			if (osmo_iofd_txqueue_len(iofd) == 0)
				iofd_poll_ops.write_disable(iofd);
		}
	}
}

static int iofd_poll_ofd_cb_dispatch(struct osmo_fd *ofd, unsigned int what)
{
	struct osmo_io_fd *iofd = ofd->data;

	IOFD_FLAG_SET(iofd, IOFD_FLAG_IN_CALLBACK);
	iofd_poll_ofd_cb_recvmsg_sendmsg(ofd, what);
	IOFD_FLAG_UNSET(iofd, IOFD_FLAG_IN_CALLBACK);

	if (IOFD_FLAG_ISSET(iofd, IOFD_FLAG_TO_FREE)) {
		talloc_free(iofd);
		return 0;
	}

	return 0;
}

static int iofd_poll_register(struct osmo_io_fd *iofd)
{
	struct osmo_fd *ofd = &iofd->u.poll.ofd;
	int rc;

	if (IOFD_FLAG_ISSET(iofd, IOFD_FLAG_FD_REGISTERED))
		return 0;
	osmo_fd_setup(ofd, iofd->fd, 0, &iofd_poll_ofd_cb_dispatch, iofd, 0);
	rc = osmo_fd_register(ofd);
	if (!rc)
		IOFD_FLAG_SET(iofd, IOFD_FLAG_FD_REGISTERED);
	return rc;
}

static int iofd_poll_unregister(struct osmo_io_fd *iofd)
{
	struct osmo_fd *ofd = &iofd->u.poll.ofd;

	if (!IOFD_FLAG_ISSET(iofd, IOFD_FLAG_FD_REGISTERED))
		return 0;
	osmo_fd_unregister(ofd);
	IOFD_FLAG_UNSET(iofd, IOFD_FLAG_FD_REGISTERED);

	return 0;
}

static int iofd_poll_close(struct osmo_io_fd *iofd)
{
	iofd_poll_unregister(iofd);
	osmo_fd_close(&iofd->u.poll.ofd);

	return 0;
}

static void iofd_poll_read_enable(struct osmo_io_fd *iofd)
{
	osmo_fd_read_enable(&iofd->u.poll.ofd);
}

static void iofd_poll_read_disable(struct osmo_io_fd *iofd)
{
	osmo_fd_read_disable(&iofd->u.poll.ofd);
}

static void iofd_poll_write_enable(struct osmo_io_fd *iofd)
{
	osmo_fd_write_enable(&iofd->u.poll.ofd);
}

static void iofd_poll_write_disable(struct osmo_io_fd *iofd)
{
	osmo_fd_write_disable(&iofd->u.poll.ofd);
}

static void iofd_poll_notify_connected(struct osmo_io_fd *iofd)
{
	int rc;

	rc = iofd_poll_register(iofd);
	if (rc < 0)
		return;
	osmo_fd_write_enable(&iofd->u.poll.ofd);
}

const struct iofd_backend_ops iofd_poll_ops = {
	.register_fd = iofd_poll_register,
	.unregister_fd = iofd_poll_unregister,
	.close = iofd_poll_close,
	.write_enable = iofd_poll_write_enable,
	.write_disable = iofd_poll_write_disable,
	.read_enable = iofd_poll_read_enable,
	.read_disable = iofd_poll_read_disable,
	.notify_connected = iofd_poll_notify_connected,
};

#endif /* defined(__linux__) */