/*
 * Anti mixed UTF8 - a filter written by Bram Matthys ("Syzop").
 * Reported by Mr_Smoke in https://bugs.unrealircd.org/view.php?id=5163
 * Tested by PeGaSuS (The_Myth) with some of the most used spam lines.
 * Help with testing and fixing Cyrillic from 'i' <info@servx.org>
 *
 * ==[ ABOUT ]==
 * This module will detect and stop spam containing of characters of
 * mixed "scripts", where some characters are in Latin script and other
 * characters are in Cyrillic.
 * This unusual behavior can be detected easily and action can be taken.
 *
 * ==[ MODULE LOADING AND CONFIGURATION ]==
 * loadmodule "antimixedutf8";
 * set {
 *         antimixedutf8 {
 *                 score 10;
 *                 ban-action block;
 *                 ban-reason "Possible mixed character spam";
 *                 ban-time 4h; // For other types
 *         };
 * };
 *
 * ==[ LICENSE AND PORTING ]==
 * Feel free to copy/move the idea or code to other IRCds.
 * The license is GPLv1 (or later, at your option):
 *
 * 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 1, 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include "unrealircd.h"

ModuleHeader MOD_HEADER(antimixedutf8)
= {
	"antimixedutf8",
	"1.0",
	"Mixed UTF8 character filter (look-alike character spam) - by Syzop",
	"3.2-b8-1",
	NULL 
};

struct {
	int score;
	int ban_action;
	char *ban_reason;
	long ban_time;
} cfg;

static void free_config(void);
static void init_config(void);
DLLFUNC int antimixedutf8_config_test(ConfigFile *, ConfigEntry *, int, int *);
DLLFUNC int antimixedutf8_config_run(ConfigFile *, ConfigEntry *, int);

#define SCRIPT_UNDEFINED	0
#define SCRIPT_LATIN		1
#define SCRIPT_CYRILLIC		2

/**** the detection algorithm follows first, the module/config code is at the end ****/

/** Detect which script the current character is,
 * such as latin script or cyrillic script.
 * @retval See SCRIPT_*
 */
int detect_script(const char *t)
{
	/* Safety: as long as *t is never \0 then at worst
	 * the character after this will be \0 and since we
	 * only look at 2 characters (at most) at a time
	 * this will be safe.
	 */

	/* Currently we only detect cyrillic and call all the
	 * rest latin (which is not true). This can always
	 * be enhanced later.
	 */

	if ((t[0] == 0xd0) && (t[1] >= 0x80) && (t[1] <= 0xbf))
		return SCRIPT_CYRILLIC;
	else if ((t[0] == 0xd1) && (t[1] >= 0x80) && (t[1] <= 0xbf))
		return SCRIPT_CYRILLIC;
	else if ((t[0] == 0xd2) && (t[1] >= 0x80) && (t[1] <= 0xbf))
		return SCRIPT_CYRILLIC;
	else if ((t[0] == 0xd3) && (t[1] >= 0x80) && (t[1] <= 0xbf))
		return SCRIPT_CYRILLIC;

	if ((t[0] >= 'a') && (t[0] <= 'z'))
		return SCRIPT_LATIN;
	if ((t[0] >= 'A') && (t[0] <= 'Z'))
		return SCRIPT_LATIN;

	return SCRIPT_UNDEFINED;
}

/** Returns length of an (UTF8) character. May return <1 for error conditions.
 * Made by i <info@servx.org>
 */
static int utf8_charlen(const char *str)
{
	struct { char mask; char val; } t[4] =
	{ { 0x80, 0x00 }, { 0xE0, 0xC0 }, { 0xF0, 0xE0 }, { 0xF8, 0xF0 } };
	unsigned k, j;

	for (k = 0; k < 4; k++)
	{
		if ((*str & t[k].mask) == t[k].val)
		{
			if (4 < k + 1)
				return -1;
			for (j = 0; j < k; j++)
			{
				if ((*(++str) & 0xC0) != 0x80)
					return -1;
			}
			return k + 1;
		}
	}
	return 1;
}

int lookalikespam_score(const char *text)
{
	const char *p;
	int last_script = SCRIPT_UNDEFINED;
	int current_script;
	int points = 0;
	int last_character_was_word_separator = 0;
	int skip = 0;

	for (p = text; *p; p++)
	{
		current_script = detect_script(p);

		if (current_script != SCRIPT_UNDEFINED)
		{
			if ((current_script != last_script) && (last_script != SCRIPT_UNDEFINED))
			{
				/* A script change = 1 point */
				points++;

				/* Give an additional point if the script change happened
				 * within the same word, as that would be rather unusual
				 * in normal cases.
				 */
				if (!last_character_was_word_separator)
					points++;
			}
			last_script = current_script;
		}

		if (strchr("., ", *p))
			last_character_was_word_separator = 1;
		else
			last_character_was_word_separator = 0;

		skip = utf8_charlen(p);
		if (skip > 1)
			p += skip - 1;
	}

	return points;
}

static int override_msg(Cmdoverride *ovr, aClient *cptr, aClient *sptr, int parc, char *parv[])
{
	int score, ret;
	
	if (!MyClient(sptr) || (parc < 3) || BadPtr(parv[2]))
	{
		/* Short circuit for: remote clients or insufficient parameters */
		return CallCmdoverride(ovr, cptr, sptr, parc, parv);
	}

	score = lookalikespam_score(StripControlCodes(parv[2]));
	if (score >= cfg.score)
	{
		if (cfg.ban_action == BAN_ACT_KILL)
		{
			sendto_realops("[antimixedutf8] Killed connection from %s (score %d)",
				GetIP(sptr), score);
		} /* no else here!! */

		if ((cfg.ban_action == BAN_ACT_BLOCK)
#ifdef BAN_ACT_SOFT_BLOCK
		    || ((cfg.ban_action == BAN_ACT_SOFT_BLOCK) && !IsLoggedIn(sptr))
#endif
		    )
		{
			sendnotice(sptr, "%s", cfg.ban_reason);
			return 0;
		} else {
			ret = place_host_ban(sptr, cfg.ban_action, cfg.ban_reason, cfg.ban_time);
			if (ret != 0)
				return ret;
			/* a return value of 0 means the user is exempted, so fallthrough.. */
		}
	}

	return CallCmdoverride(ovr, cptr, sptr, parc, parv);
}

/*** rest is module and config stuff ****/

MOD_TEST(antimixedutf8)
{
	HookAdd(modinfo->handle, HOOKTYPE_CONFIGTEST, 0, antimixedutf8_config_test);
	return MOD_SUCCESS;
}

MOD_INIT(antimixedutf8)
{
	MARK_AS_OFFICIAL_MODULE(modinfo);
	
	init_config();
	HookAdd(modinfo->handle, HOOKTYPE_CONFIGRUN, 0, antimixedutf8_config_run);
	return MOD_SUCCESS;
}

MOD_LOAD(antimixedutf8)
{
	if (!CmdoverrideAdd(modinfo->handle, "PRIVMSG", override_msg))
		return MOD_FAILED;

	if (!CmdoverrideAdd(modinfo->handle, "NOTICE", override_msg))
		return MOD_FAILED;

	return MOD_SUCCESS;
}

MOD_UNLOAD(antimixedutf8)
{
	free_config();
	return MOD_SUCCESS;
}

static void init_config(void)
{
	memset(&cfg, 0, sizeof(cfg));
	/* Default values */
	cfg.score = 10;
	cfg.ban_reason = strdup("Possible mixed character spam");
	cfg.ban_action = BAN_ACT_BLOCK;
	cfg.ban_time = 60 * 60 * 4; /* irrelevant for block, but some default for others */
}

static void free_config(void)
{
	safefree(cfg.ban_reason);
	memset(&cfg, 0, sizeof(cfg)); /* needed! */
}

DLLFUNC int antimixedutf8_config_test(ConfigFile *cf, ConfigEntry *ce, int type, int *errs)
{
	int errors = 0;
	ConfigEntry *cep;

	if (type != CONFIG_SET)
		return 0;
	
	/* We are only interrested in set::antimixedutf8... */
	if (!ce || !ce->ce_varname || strcmp(ce->ce_varname, "antimixedutf8"))
		return 0;
	
	for (cep = ce->ce_entries; cep; cep = cep->ce_next)
	{
		if (!cep->ce_varname)
		{
			config_error("%s:%i: blank set::antimixedutf8 item",
				cep->ce_fileptr->cf_filename, cep->ce_varlinenum);
			errors++;
		} else
		if (!cep->ce_vardata)
		{
			config_error("%s:%i: set::antimixedutf8::%s with no value",
				cep->ce_fileptr->cf_filename, cep->ce_varlinenum, cep->ce_varname);
			errors++;
		} else
		if (!strcmp(cep->ce_varname, "score"))
		{
			int v = atoi(cep->ce_vardata);
			if ((v < 1) || (v > 99))
			{
				config_error("%s:%i: set::antimixedutf8::score: must be between 1 - 99 (got: %d)",
					cep->ce_fileptr->cf_filename, cep->ce_varlinenum, v);
				errors++;
			}
		} else
		if (!strcmp(cep->ce_varname, "ban-action"))
		{
			if (!banact_stringtoval(cep->ce_vardata))
			{
				config_error("%s:%i: set::antimixedutf8::ban-action: unknown action '%s'",
					cep->ce_fileptr->cf_filename, cep->ce_varlinenum, cep->ce_vardata);
				errors++;
			}
		} else
		if (!strcmp(cep->ce_varname, "ban-reason"))
		{
		} else
		if (!strcmp(cep->ce_varname, "ban-time"))
		{
		} else
		{
			config_error("%s:%i: unknown directive set::antimixedutf8::%s",
				cep->ce_fileptr->cf_filename, cep->ce_varlinenum, cep->ce_varname);
			errors++;
		}
	}
	*errs = errors;
	return errors ? -1 : 1;
}

DLLFUNC int antimixedutf8_config_run(ConfigFile *cf, ConfigEntry *ce, int type)
{
	ConfigEntry *cep;

	if (type != CONFIG_SET)
		return 0;
	
	/* We are only interrested in set::antimixedutf8... */
	if (!ce || !ce->ce_varname || strcmp(ce->ce_varname, "antimixedutf8"))
		return 0;
	
	for (cep = ce->ce_entries; cep; cep = cep->ce_next)
	{
		if (!strcmp(cep->ce_varname, "score"))
		{
			cfg.score = atoi(cep->ce_vardata);
		} else
		if (!strcmp(cep->ce_varname, "ban-action"))
		{
			cfg.ban_action = banact_stringtoval(cep->ce_vardata);
		} else
		if (!strcmp(cep->ce_varname, "ban-reason"))
		{
			if (cfg.ban_reason)
				MyFree(cfg.ban_reason);
			cfg.ban_reason = strdup(cep->ce_vardata);
		} else
		if (!strcmp(cep->ce_varname, "ban-time"))
		{
			cfg.ban_time = config_checkval(cep->ce_vardata, CFG_TIME);
		}
	}
	return 1;
}