<?php
/*
**	Copyright (C) 1995-2021 by the ITools Authors.
**	This file is part of ITools - the Internet Tools Library
**
**	ITools 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 3 of the License, or
**	(at your option) any later version.
**
**	ITools 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, see <http://www.gnu.org/licenses/>.
*/

/* Default values */
define('_IT_SESSION_COOKIE', 'SESSION');
define('_IT_SESSION_COOKIE_EXPIRY', 0);
define('_IT_SESSION_LIFETIME', 3600);

class it_session
{
	/* PRIVATE */
	var $cookiename;	/* Cookie to store session */
	var $cookie;		/* Session identifier of this session */
	var $uid;		/* Session user id */
	var $domain = '';	/* Session domain (e.g. ".relog.ch") */
	var $address = '';	/* Guessed IP address of client */
	var $ssl;		/* Session using SSL? */
	var $lifetime;		/* Session life-time in seconds */
	var $secret;		/* Session secret to generate session ids */
	var $now;		/* This session start time slot */
	var $prev;		/* Previous session start time slot */
	var $hascookies;	/* Do cookies work? Used by has_cookies() */

/* Constructor */
function __construct()
{
	$this->cookiename = _IT_SESSION_COOKIE;
	$this->lifetime = _IT_SESSION_LIFETIME;
/*
 * NOTE: Does not work with dynamic IPs (dialup with low timeout,
 * load balanced Proxies and maybe more weird stuff).
 *	$this->address = $_SERVER['REMOTE_ADDR'] . '/' . $_SERVER['HTTP_X_FORWARDED_FOR'];
 */
	$this->ssl = !empty($_SERVER['HTTPS']) && !$GLOBALS['ULTRATRUSTED'];	# No SSL cookies for trusted IPs because Chrome does not overwrite SSL cookies with non-SSL ones and thus prevents login to devel after live, reported by David
}


function set_cookiename($cookiename)
{
	if ($cookiename)
		$this->cookiename = $cookiename;
}


function get_uid()
{
	return $this->uid;
}


function set_uid($uid)
{
	$this->uid = $uid;
}


function set_domain($domain)
{
	$this->domain = $domain;
}


function set_lifetime($lifetime)
{
	$this->lifetime = $lifetime;
}


function set_secret($secret)
{
	$this->secret = $secret;
}


function init()
{
	if (empty($this->secret))
		it::fatal('it_session requires secret to be set');

	/* Got a cookie? */
	if ($this->hascookies = isset($_COOKIE[$this->cookiename]) && is_string($_COOKIE[$this->cookiename]))
		$this->cookie = $_COOKIE[$this->cookiename];
	else
		$this->cookie = '';
	#debug("hascookies '$this->hascookies', '$this->cookie', " . $_COOKIE[$this->cookiename]);

	$now = time();
	/*
	 * Valid time range is now - 1/2 lifetime to now + 1/2 lifetime
	 * I.e. session has to be either from start or now
	 */
	$this->now = $now - ($now % ($this->lifetime / 2));
	$this->prev = $this->now - ($this->lifetime / 2);

	/* Set user id from valid session */
	$this->uid = substr($this->cookie, 1, strlen($this->cookie) - 33);

	if (!$this->is_valid())
		$this->uid = "";

	#debug("it_session::new session=$this->cookie, user=$this->uid");
}


/* INTERNAL: Create session id from session data */
function _mkcookie($uid, $timeslot)
{
	return "A" . $uid . md5("$uid,$this->domain,$this->address,$this->secret,$timeslot");
}


/* Check if this session is valid */
function is_valid()
{
	$result = true;

	if ($this->_mkcookie($this->uid, $this->now) != $this->cookie)
	{
		/* Check if using id from previous time slot */
		if ($this->_mkcookie($this->uid, $this->prev) == $this->cookie)
			$this->set_valid();	/* Rejuvenate session */
		else
			$result = false;
	}

	return $result;
}


/*
 * Validate this session
 * @param $valid Should this session be validated or invalidated?
 * @param $login_identifier_required Does session validation require login magic?
 * @param $login_identifier Session validation magic cookie to be checked
 * @return true if successful
 */
function set_valid($valid = true, $login_identifier_required = false, $login_identifier = "")
{
	$result = false;

	if ($valid && (!$login_identifier_required || ($login_identifier == $this->_mkcookie("", $this->cookie))))
	{
		$this->cookie = $this->_mkcookie($this->uid, $this->now);
		$result = true;
	}
	else
	{
		$this->cookie = bin2hex(random_bytes(16));	/* random garbage */
		$result = !$valid;	/* Setting to invalid succeeded or setting to valid failed */
	}

	it::setcookie($this->cookiename, $this->cookie, [ 'expires' => _IT_SESSION_COOKIE_EXPIRY, 'path' => "/", 'domain' => $this->domain, 'secure' => $this->ssl, 'httponly' => true, 'samesite' => _IT_USER_COOKIE_SAMESITE ]);
	$_COOKIE[$this->cookiename] = $this->cookie;

	return $result;
}


function purge()
{
	$this->cookie = "";
	$_COOKIE[$this->cookiename] = "";
	$this->uid = "";
}


/*
 * Create a login identifier and set session to login identifier 'secret' value
 * Returns a value to be put into the login <form> which has to be passed to 
 * set_valid() to create a valid session
 */
function create_login_identifier()
{
	if (!$this->cookie)
	{
		$this->cookie = bin2hex(random_bytes(16));	/* random garbage */
		it::setcookie($this->cookiename, $this->cookie, [ 'expires' => _IT_SESSION_COOKIE_EXPIRY, 'path' => "/", 'domain' => $this->domain, 'secure' => $this->ssl, 'httponly' => true, 'samesite' => _IT_USER_COOKIE_SAMESITE ]);
	}

	$login_identifier = $this->_mkcookie("", $this->cookie);

	return $login_identifier;
}

/*
 * Check if cookies are enabled.
 * NOTE: Only works if you used create_login_identifier() on previous page
 */
function has_cookies()
{
	return $this->hascookies;
}


/*
 * Sign string for current session
 * @param $text Text to be signed
 * @return Signature for $text
 */
function _sign($text, $timeslot)
{
	return "B" . md5("$text,$this->uid,$this->domain,$this->address,$this->secret,$timeslot");
}

/*
 * Sign string for current session
 * @param $text Text to be signed
 * @return Signature for $text
 */
function create_signature($text)
{
	return $this->_sign($text, $this->now);
}

/*
 * Check signature for string for current session
 * @param $text Text which was signed
 * @param $signature Signature to be checked
 * @return True if signature ok, false otherwise
 */
function check_signature($text, $signature)
{
	return (($this->_sign($text, $this->now) == $signature) ||
		($this->_sign($text, $this->prev) == $signature));
}

} /* End class it_session */