/*
** Copyright (C) 2001-2025 Zabbix SIA
**
** This program is free software: you can redistribute it and/or modify it under the terms of
** the GNU Affero General Public License as published by the Free Software Foundation, version 3.
**
** 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 Affero General Public License for more details.
**
** You should have received a copy of the GNU Affero General Public License along with this program.
** If not, see <https://www.gnu.org/licenses/>.
**/

#include "zbxalgo.h"
#include "zbxasyncpoller.h"
#include "zbxcommon.h"
#include "zbxcomms.h"
#include "zbxtime.h"

#ifdef HAVE_LIBEVENT
#include "zbxip.h"
#include <event2/dns.h>
#include <event2/event.h>
#include <event2/util.h>

ZBX_VECTOR_IMPL(address, zbx_address_t)

typedef struct
{
	void					*data;
	zbx_async_task_process_task_cb_t	async_task_process_task_cb;
	zbx_async_task_process_result_cb_t	async_task_process_result_cb;
	struct event				*tx_event;
	struct event				*rx_event;
	struct event				*timeout_event;
	int					timeout;
	char					*error;
	struct evdns_base			*dnsbase;
	struct evutil_addrinfo			*ai;
	zbx_vector_address_t			addresses;
	char					*reverse_dns;
}
zbx_async_task_t;

static void	async_reverse_dns_event(int err, char type, int count, int ttl, void *addresses, void *arg);

static void	async_task_process_result_and_remove(zbx_async_task_t *task)
{
	task->async_task_process_result_cb(task->data);

	if (NULL != task->rx_event)
		event_free(task->rx_event);

	if (NULL != task->tx_event)
		event_free(task->tx_event);

	if (NULL != task->timeout_event)
		event_free(task->timeout_event);

	if (NULL != task->ai)
		evutil_freeaddrinfo(task->ai);

	zbx_vector_address_destroy(&task->addresses);
	zbx_free(task->reverse_dns);
	zbx_free(task->error);
	zbx_free(task);
}

const char	*zbx_task_state_to_str(zbx_async_task_state_t task_state)
{
	switch (task_state)
	{
		case ZBX_ASYNC_TASK_WRITE:
			return "write";
		case ZBX_ASYNC_TASK_READ:
			return "read";
		case ZBX_ASYNC_TASK_STOP:
			return "stop";
		case ZBX_ASYNC_TASK_RESOLVE_REVERSE:
			return "resolve reverse";
		default:
			return "unknown";
	}
}

static void	async_event(evutil_socket_t fd, short what, void *arg)
{
	zbx_async_task_t	*task = (zbx_async_task_t *)arg;
	int			ret, fd_in = fd;
	struct event_base	*ev;

	zabbix_log(LOG_LEVEL_DEBUG, "In %s()", __func__);

	ret = task->async_task_process_task_cb(what, task->data, &fd, &task->addresses, task->reverse_dns, task->error,
			task->timeout_event);

	switch (ret)
	{
		case ZBX_ASYNC_TASK_STOP:
			async_task_process_result_and_remove(task);
			break;
		case ZBX_ASYNC_TASK_RESOLVE_REVERSE:
			event_free(task->timeout_event);
			task->timeout_event = NULL;

			if (AF_INET == task->ai->ai_addr->sa_family)
			{
				const struct sockaddr_in	*sin = (const struct sockaddr_in *) (void *)task->ai->ai_addr;

				evdns_base_resolve_reverse(task->dnsbase, &sin->sin_addr, 0, async_reverse_dns_event,
						task);
			}
			else if (AF_INET6 == task->ai->ai_addr->sa_family)
			{
				const struct sockaddr_in6	*sin6 = (const struct sockaddr_in6 *) (void *)task->ai->ai_addr;

				evdns_base_resolve_reverse_ipv6(task->dnsbase, &sin6->sin6_addr, 0,
						async_reverse_dns_event, task);
			}
			break;
		case ZBX_ASYNC_TASK_READ:
			if (fd_in != fd && NULL != task->tx_event)
			{
				event_free(task->tx_event);
				task->tx_event = NULL;
			}

			if (fd_in != fd || NULL == task->rx_event)
			{
				ev = event_get_base(task->timeout_event);

				if (NULL != task->rx_event)
					event_free(task->rx_event);

				task->rx_event = event_new(ev, fd, EV_READ, async_event, (void *)task);
			}
			event_add(task->rx_event, NULL);
			break;
		case ZBX_ASYNC_TASK_WRITE:
			if (fd_in != fd && NULL != task->rx_event)
			{
				event_free(task->rx_event);
				task->rx_event = NULL;
			}

			if (fd_in != fd || NULL == task->tx_event)
			{
				ev = event_get_base(task->timeout_event);

				if (NULL != task->tx_event)
					event_free(task->tx_event);

				task->tx_event = event_new(ev, fd, EV_WRITE, async_event, (void *)task);
			}
			event_add(task->tx_event, NULL);
			break;

	}

	zabbix_log(LOG_LEVEL_DEBUG, "End of %s():%s", __func__, zbx_task_state_to_str(ret));
}

static void	async_reverse_dns_event(int err, char type, int count, int ttl, void *addresses, void *arg)
{
	zbx_async_task_t	*task = (zbx_async_task_t *)arg;

	zabbix_log(LOG_LEVEL_DEBUG, "In %s() result:%d type:%d count:%d ttl:%d", __func__, err, type, count, ttl);

	if (DNS_ERR_NONE != err)
	{
		zabbix_log(LOG_LEVEL_DEBUG, "cannot reverse DNS name: %s", evdns_err_to_string(err));
		task->error = zbx_strdup(task->error, evdns_err_to_string(err));
		zbx_free(task->reverse_dns);
	}
	else
	{
		if (0 != count)
		{
			task->reverse_dns = zbx_strdup(task->reverse_dns, *(char **)addresses);
			zabbix_log(LOG_LEVEL_DEBUG, "resolved reverse DNS name: %s", task->reverse_dns);
		}
		else
			zbx_free(task->reverse_dns);
	}

	async_event(-1, 0, task);

	zabbix_log(LOG_LEVEL_DEBUG, "End of %s()", __func__);
}
#ifdef HAVE_ARES
static void	ares_addrinfo_cb(void *arg, int err, int timeouts, struct ares_addrinfo *ai)
{
	zbx_async_task_t	*task = (zbx_async_task_t *)arg;

	zabbix_log(LOG_LEVEL_DEBUG, "In %s() result:%d timeouts:%d", __func__, err, timeouts);

	if (ARES_SUCCESS != err)
	{
		zabbix_log(LOG_LEVEL_DEBUG, "cannot resolve DNS name: %s", ares_strerror(err));
		task->error = zbx_strdup(task->error, ares_strerror(err));
		async_event(-1, EV_TIMEOUT, task);
	}
	else
	{
		for (struct ares_addrinfo_node	*nodes = ai->nodes; NULL != nodes; nodes = nodes->ai_next)
		{
			zbx_address_t	address;

			if (FAIL == zbx_inet_ntop(nodes->ai_addr, address.ip, (socklen_t)sizeof(address.ip)))
				address.ip[0] = '\0';

			zabbix_log(LOG_LEVEL_DEBUG, "resolved address '%s'", address.ip);

			zbx_vector_address_append(&task->addresses, address);
		}

		ares_freeaddrinfo(ai);

		struct timeval	tv = {task->timeout, 0};

		evtimer_add(task->timeout_event, &tv);
		async_event(-1, 0, task);
	}

	zabbix_log(LOG_LEVEL_DEBUG, "End of %s()", __func__);
}
#endif
static void	async_dns_event(int err, struct evutil_addrinfo *ai, void *arg)
{
	zbx_async_task_t	*task = (zbx_async_task_t *)arg;

	zabbix_log(LOG_LEVEL_DEBUG, "In %s() result:%d", __func__, err);

	if (0 != err)
	{
		zabbix_log(LOG_LEVEL_DEBUG, "cannot resolve DNS name: %s", evutil_gai_strerror(err));
		task->error = zbx_strdup(task->error, evutil_gai_strerror(err));
		async_event(-1, EV_TIMEOUT, task);
	}
	else
	{
		for (struct evutil_addrinfo *current_ai = ai; NULL != current_ai; current_ai = current_ai->ai_next)
		{
			zbx_address_t	address;

			if (FAIL == zbx_inet_ntop(current_ai->ai_addr, address.ip, (socklen_t)sizeof(address.ip)))
				address.ip[0] = '\0';

			zabbix_log(LOG_LEVEL_DEBUG, "resolved address '%s'", address.ip);

			zbx_vector_address_append(&task->addresses, address);
		}

		struct timeval	tv = {task->timeout, 0};

		task->ai = ai;
		evtimer_add(task->timeout_event, &tv);
		async_event(-1, 0, task);
	}

	zabbix_log(LOG_LEVEL_DEBUG, "End of %s()", __func__);
}

void	zbx_async_dns_update_host_addresses(struct evdns_base *dnsbase, zbx_channel_t *channel)
{
	static time_t	time_r = 0, time_h = 0;
	static double	mtime = 0;
	zbx_stat_t	buf_r, buf_h;

	if (60 < zbx_time() - mtime)
	{
		int	ret_h = zbx_stat("/etc/hosts", &buf_h), ret_r = zbx_stat("/etc/resolv.conf", &buf_r);

		if ((0 == ret_r && time_r != buf_r.st_mtime && 0 != time_r) ||
			(0 == ret_h && time_h != buf_h.st_mtime && 0 != time_h))
		{
			int	ret;

			zabbix_log(LOG_LEVEL_DEBUG, "%s() update host addresses", __func__);

			if (NULL != channel)
			{
#if defined(HAVE_ARES) && defined(HAVE_ARES_REINIT)
				if (ARES_SUCCESS != (ret = ares_reinit(channel)))
					zabbix_log(LOG_LEVEL_ERR, "cannot reinitialise ares: %s", ares_strerror(ret));
#endif
			}
			else
			{
				evdns_base_clear_nameservers_and_suspend(dnsbase);

				if (0 != (ret = evdns_base_resolv_conf_parse(dnsbase, DNS_OPTIONS_ALL,
						ZBX_RES_CONF_FILE)))
				{
					zabbix_log(LOG_LEVEL_ERR, "cannot parse resolv.conf result: %s",
						zbx_resolv_conf_errstr(ret));
				}

				evdns_base_resume(dnsbase);
			}
		}
		time_r = buf_r.st_mtime;
		time_h = buf_h.st_mtime;
		mtime = zbx_time();
	}
}

void	zbx_async_poller_add_task(struct event_base *ev, zbx_channel_t *channel, struct evdns_base *dnsbase,
	const char *addr, void *data, int timeout, zbx_async_task_process_task_cb_t async_task_process_task_func,
	zbx_async_task_process_result_cb_t async_task_process_result_func)
{
	zbx_async_task_t	*task;

	task = (zbx_async_task_t *)zbx_malloc(NULL, sizeof(zbx_async_task_t));
	task->data = data;
	task->async_task_process_task_cb = async_task_process_task_func;
	task->async_task_process_result_cb = async_task_process_result_func;
	task->timeout_event = evtimer_new(ev, async_event, (void *)task);
	task->timeout = timeout;

	task->rx_event = NULL;
	task->tx_event = NULL;
	task->error = NULL;
	task->dnsbase = dnsbase;
	task->ai = NULL;
	task->reverse_dns = NULL;

	zbx_vector_address_create(&task->addresses);

	if (NULL != channel)
	{
#ifdef HAVE_ARES
		struct ares_addrinfo_hints	hints = {.ai_family = PF_UNSPEC, .ai_socktype = SOCK_STREAM};

		if (SUCCEED == zbx_is_ip4(addr))
		{
			hints.ai_flags = ARES_AI_NUMERICHOST;
			hints.ai_family = AF_INET;
		}
#ifdef HAVE_IPV6
		else if (SUCCEED == zbx_is_ip6(addr))
		{
			hints.ai_flags = ARES_AI_NUMERICHOST;
			hints.ai_family = AF_INET6;
		}
#endif
		ares_getaddrinfo(channel, addr, NULL, &hints, ares_addrinfo_cb, task);
		return;
#endif
	}

	struct evutil_addrinfo	evutil_hints;

	memset(&evutil_hints, 0, sizeof(evutil_hints));

	if (SUCCEED == zbx_is_ip4(addr))
		evutil_hints.ai_flags = AI_NUMERICHOST;
#ifdef HAVE_IPV6
	else if (SUCCEED == zbx_is_ip6(addr))
		evutil_hints.ai_flags = AI_NUMERICHOST;
#endif
	else
		evutil_hints.ai_flags = 0;

	evutil_hints.ai_family = PF_UNSPEC;
	evutil_hints.ai_socktype = SOCK_STREAM;

	evdns_getaddrinfo(dnsbase, addr, NULL, &evutil_hints, async_dns_event, task);
}

zbx_async_task_state_t	zbx_async_poller_get_task_state_for_event(short event)
{
	if (POLLIN & event)
		return ZBX_ASYNC_TASK_READ;

	if (POLLOUT & event)
		return ZBX_ASYNC_TASK_WRITE;

	return ZBX_ASYNC_TASK_STOP;
}

const char	*zbx_resolv_conf_errstr(const int error)
{
	switch (error)
	{
		case 1:
			return "failed to open file";
		case 2:
			return "failed to stat file";
		case 3:
			return "file too large";
		case 4:
			return "out of memory";
		case 5:
			return "short read from file";
		case 6:
			return "no nameservers listed in the file";
		default:
			return "unknown";
	}
}

const char	*zbx_get_event_string(short event)
{

	if (EV_TIMEOUT & event)
		return "timeout";

	if (EV_READ & event)
		return "read";

	if (EV_WRITE & event)
		return "write";

	if (0 == event)
		return "init";

	return "unknown";
}

#endif