/*
 * Alertik: a tiny 'syslog' server & notification tool for Mikrotik routers.
 * This is free and unencumbered software released into the public domain.
 */

#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "log.h"
#include "events.h"
#include "env_events.h"
#include "alertik.h"
#include "notifiers.h"

/* Regex params. */
#define MAX_MATCHES 32

/* Event match types. */
#define MATCH_TYPES_LEN 2
static const char *const match_types[] = {"substr", "regex"};

/* Environment events list. */
static int num_env_events;
struct env_event env_events[MAX_ENV_EVENTS] = {0};

/**
 * Safe string-to-int routine that takes into account:
 * - Overflow and Underflow
 * - No undefined behavior
 *
 * Taken from https://stackoverflow.com/a/12923949/3594716
 * and slightly adapted: no error classification, because
 * I don't need to know, error is error.
 *
 * @param out Pointer to integer.
 * @param s String to be converted.
 *
 * @return Returns 0 if success and a negative number otherwise.
 */
static int str2int(int *out, const char *s)
{
	char *end;
	if (s[0] == '\0' || isspace(s[0]))
		return -1;
	errno = 0;

	long l = strtol(s, &end, 10);

	/* Both checks are needed because INT_MAX == LONG_MAX is possible. */
	if (l > INT_MAX || (errno == ERANGE && l == LONG_MAX))
		return -1;
	if (l < INT_MIN || (errno == ERANGE && l == LONG_MIN))
		return -1;
	if (*end != '\0')
		return -1;

	*out = l;
	return 0;
}

/**/
static char *get_event_str(int ev_num, char *str)
{
	char *env;
	char ev[64] = {0};
	snprintf(ev, sizeof ev - 1, "EVENT%d_%s", ev_num, str);
	if (!(env = getenv(ev)))
		panic("Unable to find event for %s\n", ev);
	return env;
}

/**/
static int
get_event_idx(int ev_num, char *str, const char *const *str_list, int size)
{
	char *env = get_event_str(ev_num, str);
	for (int i = 0; i < size; i++) {
		if (!strcmp(env, str_list[i]))
			return i;
	}
	panic("String parameter (%s) invalid for %s\n", env, str);
}


static int append_dst(char **dst, const char *dst_end, char c) {
	char *d = *dst;
	if (d < dst_end) {
		*d   = c;
		*dst = ++d;
		return 1;
	}
	return 0;
}

/**/
static int handle_match_replacement(
	char       **dst,   char       *dst_e,
	const char **c_msk, const char *e_msk,
	regmatch_t *pmatch,
	struct env_event *env,
	struct log_event *log_ev)
{
	const char *c = *c_msk;
	const char *e =  e_msk;
	size_t match  = *c - '0';
	regoff_t off;
	regoff_t len;

	/* Check if there is a second digit. */
	if (c < e) {
		if (c[1] >= '0' && c[1] <= '9') {
			match = (match * 10) + (c[1] - '0');
			c++;
		}
	}

	/* Validate if read number is within the match range
	 * i.e., between 1-nsub.
	 */
	if (!match || match > env->regex.re_nsub)
		return 0;

	*c_msk = c;

	/* Append c_msk into our dst, according to the informed
	 * match.
	 */
	off = pmatch[match].rm_so;
	len = pmatch[match].rm_eo - off;

	for (regoff_t i = 0; i < len; i++) {
		if ( !append_dst(dst, dst_e, log_ev->msg[off + i]) )
			return 0;
	}

	return 1;
}

/**/
static char*
create_masked_message(struct env_event *env, regmatch_t *pmatch,
	struct log_event *log_ev, char *buf, size_t buf_size)
{
	char        *dst,   *dst_e;
	const char  *c_msk, *e_msk;

	c_msk = env->ev_mask_msg;
	e_msk = c_msk + strlen(c_msk);
	dst   = buf;
	dst_e = dst + buf_size;

	for (; *c_msk != '\0'; c_msk++)
	{
		if (*c_msk != '@') {
			if (!append_dst(&dst, dst_e, *c_msk))
				break;
			continue;
		}

		/* Abort if there is no next char to look ahead. */
		else if (c_msk + 1 >= e_msk)
			break;

		/* Look next char, in order to escape it if needed.
		 * If next is also '@',escape it.
		 */
		if (c_msk[1] == '@') {
			if (!append_dst(&dst, dst_e, *c_msk))
				break;
			else {
				c_msk++;
				continue; /* skip next char (since we already read it). */
			}
		}

		/* If not a number, abort. */
		else if (!(c_msk[1] >= '0' && c_msk[1] <= '9')) {
			log_msg("Warning: expected number at input, but found (%c), "
				    "the resulting message will be incomplete!\n",
				    c_msk[1]);
			break;
		}

		/* Its a number, proceed the replacement. */
		else
		{
			c_msk++;
			if (!handle_match_replacement(&dst, dst_e, &c_msk, e_msk,
				pmatch, env, log_ev))
			{
				break;
			}
		}
	}
	return dst;
}

/**/
static int handle_regex(struct log_event *ev, int idx_env)
{
	char time_str[32]               = {0};
	regmatch_t pmatch[MAX_MATCHES]  = {0};
	char notification_message[2048] = {0};

	int notif_idx;
	char *notif_p;
	struct env_event *env_ev;

	env_ev    = &env_events[idx_env];
	notif_idx = env_ev->ev_notifier_idx;

	if (regexec(&env_ev->regex, ev->msg, MAX_MATCHES, pmatch, 0) == REG_NOMATCH)
		return 0;

	log_msg("> Environment event detected!\n");
	log_msg(">   type         : regex\n");
	log_msg(">   expr         : %s\n",  env_ev->ev_match_str);
	log_msg(">   amnt sub expr: %zu\n", env_ev->regex.re_nsub);
	log_msg(">   notifier     : %s\n",  notifiers_str[notif_idx]);

	notif_p = notification_message;

	/* Check if there are any subexpressions, if not, just format
	 * the message.
	 */
	if (env_ev->regex.re_nsub) {
		notif_p = create_masked_message(env_ev, pmatch, ev,
			notification_message, sizeof(notification_message) - 1);

		snprintf(
			notif_p,
			(notification_message + sizeof(notification_message)) - notif_p,
			", at: %s",
			get_formatted_time(ev->timestamp, time_str)
		);
	}

	else {
		snprintf(
			notification_message,
			sizeof(notification_message) - 1,
			"%s, at: %s",
			env_ev->ev_mask_msg,
			get_formatted_time(ev->timestamp, time_str)
		);
	}

	if (notifiers[notif_idx].send_notification(notification_message) < 0) {
		log_msg("unable to send the notification through %s\n",
			notifiers_str[notif_idx]);
	}

	return 1;
}

/**/
static int handle_substr(struct log_event *ev, int idx_env)
{
	int notif_idx;
	char time_str[32] = {0};
	struct env_event *env_ev;
	char notification_message[2048] = {0};

	env_ev = &env_events[idx_env];
	notif_idx = env_ev->ev_notifier_idx;

	if (!strstr(ev->msg, env_ev->ev_match_str))
		return 0;

	log_msg("> Environment event detected!\n");
	log_msg(">   type: substr, match: (%s), notifier: %s\n",
		env_ev->ev_match_str, notifiers_str[notif_idx]);

	/* Format the message. */
	snprintf(
		notification_message,
		sizeof notification_message - 1,
		"%s, at: %s",
		env_ev->ev_mask_msg,
		get_formatted_time(ev->timestamp, time_str)
	);

	if (notifiers[notif_idx].send_notification(notification_message) < 0) {
		log_msg("unable to send the notification through %s\n",
			notifiers_str[notif_idx]);
	}

	return 1;
}

/**
 * @brief Given an environment-variable event, checks if it
 * belongs to one of the registered events and then, handle
 * it.
 *
 * @param ev Event to be processed.
 *
 * @return Returns the amount of matches, 0 if none (not handled).
 */
int process_environment_event(struct log_event *ev)
{
	int i;
	int handled;

	for (i = 0, handled = 0; i < num_env_events; i++) {
		if (env_events[i].ev_match_type == EVNT_SUBSTR)
			handled += handle_substr(ev, i);
		else
			handled += handle_regex(ev, i);
	}
	return handled;
}

/**
 * @brief Initialize environment variables events.
 *
 * @return Returns 0 if there is no environment event,
 * 1 if there is at least one _and_ is successfully
 * configured.
*/
int init_environment_events(void)
{
	char *tmp;
	tmp = getenv("ENV_EVENTS");

	if (!tmp || (str2int(&num_env_events, tmp) < 0) || num_env_events <= 0)  {
		log_msg("Environment events not detected, disabling...\n");
		return (0);
	}

	if (num_env_events >= MAX_ENV_EVENTS)
		panic("Environment ENV_EVENTS exceeds the maximum supported (%d/%d)\n",
			num_env_events, MAX_ENV_EVENTS);

	log_msg("%d environment event(s) found, registering...\n", num_env_events);
	for (int i = 0; i < num_env_events; i++) {
		/* EVENTn_MATCH_TYPE. */
		env_events[i].ev_match_type   = get_event_idx(i, "MATCH_TYPE",
			match_types, MATCH_TYPES_LEN);
		/* EVENTn_NOTIFIER. */
		env_events[i].ev_notifier_idx = get_event_idx(i, "NOTIFIER",
			notifiers_str, NUM_NOTIFIERS);
		/* EVENTn_MATCH_STR. */
		env_events[i].ev_match_str    = get_event_str(i, "MATCH_STR");
		/* EVENTn_MASK_MSG. */
		env_events[i].ev_mask_msg     = get_event_str(i, "MASK_MSG");
	}

	log_msg("Environment events summary:\n");
	for (int i = 0; i < num_env_events; i++) {
		printf(
			"EVENT%d_MATCH_TYPE: %s\n"
			"EVENT%d_MATCH_STR:  %s\n"
			"EVENT%d_NOTIFIER:   %s\n"
			"EVENT%d_MASK_MSG:   %s\n\n",
			i, match_types[env_events[i].ev_match_type],
			i, env_events[i].ev_match_str,
			i, notifiers_str[env_events[i].ev_notifier_idx],
			i, env_events[i].ev_mask_msg
		);

		/* Try to setup notifier if not yet. */
		notifiers[env_events[i].ev_notifier_idx].setup();

		/* If regex, compile it first. */
		if (env_events[i].ev_match_type == EVNT_REGEX) {
			if (regcomp(
			    &env_events[i].regex,
			    env_events[i].ev_match_str,
			    REG_EXTENDED))
			{
				panic("Unable to compile regex (%s) for EVENT%d!!!",
					env_events[i].ev_match_str, i);
			}
		}
	}
	return 1;
}