<?php
/**
 * Elgg web services API
 * Functions and objects for exposing custom web services.
 *
 * @package    Elgg.Core
 * @subpackage WebServicesAPI
 */

// Primary Services API Server functions

/**
 * A global array holding API methods.
 * The structure of this is
 * 	$API_METHODS = array (
 * 		$method => array (
 * 			"description" => "Some human readable description"
 * 			"function" = 'my_function_callback'
 * 			"parameters" = array (
 * 				"variable" = array ( // the order should be the same as the function callback
 * 					type => 'int' | 'bool' | 'float' | 'string'
 * 					required => true (default) | false
 *					default => value // optional
 * 				)
 * 			)
 * 			"call_method" = 'GET' | 'POST'
 * 			"require_api_auth" => true | false (default)
 * 			"require_user_auth" => true | false (default)
 * 		)
 *  )
 */
global $API_METHODS;
$API_METHODS = array();

/**
 * Expose a function as a services api call.
 *
 * Limitations: Currently cannot expose functions which expect objects.
 * It also cannot handle arrays of bools or arrays of arrays.
 * Also, input will be filtered to protect against XSS attacks through the API.
 *
 * @param string $method            The api name to expose - for example "myapi.dosomething"
 * @param string $function          Your function callback.
 * @param array  $parameters        (optional) List of parameters in the same order as in
 *                                  your function. Default values may be set for parameters which
 *                                  allow REST api users flexibility in what parameters are passed.
 *                                  Generally, optional parameters should be after required
 *                                  parameters.
 *
 *                                  This array should be in the format
 *                                    "variable" = array (
 *                                  					type => 'int' | 'bool' | 'float' | 'string' | 'array'
 *                                  					required => true (default) | false
 *                                  					default => value (optional)
 *                                  	 )
 * @param string $description       (optional) human readable description of the function.
 * @param string $call_method       (optional) Define what http method must be used for
 *                                  this function. Default: GET
 * @param bool   $require_api_auth  (optional) (default is false) Does this method
 *                                  require API authorization? (example: API key)
 * @param bool   $require_user_auth (optional) (default is false) Does this method
 *                                  require user authorization?
 *
 * @return bool
 */
function expose_function($method, $function, array $parameters = NULL, $description = "",
$call_method = "GET", $require_api_auth = false, $require_user_auth = false) {

	global $API_METHODS;

	if (($method == "") || ($function == "")) {
		$msg = elgg_echo('InvalidParameterException:APIMethodOrFunctionNotSet');
		throw new InvalidParameterException($msg);
	}

	// does not check whether this method has already been exposed - good idea?
	$API_METHODS[$method] = array();

	$API_METHODS[$method]["description"] = $description;

	// does not check whether callable - done in execute_method()
	$API_METHODS[$method]["function"] = $function;

	if ($parameters != NULL) {
		if (!is_array($parameters)) {
			$msg = elgg_echo('InvalidParameterException:APIParametersArrayStructure', array($method));
			throw new InvalidParameterException($msg);
		}

		// catch common mistake of not setting up param array correctly
		$first = current($parameters);
		if (!is_array($first)) {
			$msg = elgg_echo('InvalidParameterException:APIParametersArrayStructure', array($method));
			throw new InvalidParameterException($msg);
		}
	}

	if ($parameters != NULL) {
		// ensure the required flag is set correctly in default case for each parameter
		foreach ($parameters as $key => $value) {
			// check if 'required' was specified - if not, make it true
			if (!array_key_exists('required', $value)) {
				$parameters[$key]['required'] = true;
			}
		}

		$API_METHODS[$method]["parameters"] = $parameters;
	}

	$call_method = strtoupper($call_method);
	switch ($call_method) {
		case 'POST' :
			$API_METHODS[$method]["call_method"] = 'POST';
			break;
		case 'GET' :
			$API_METHODS[$method]["call_method"] = 'GET';
			break;
		default :
			$msg = elgg_echo('InvalidParameterException:UnrecognisedHttpMethod',
			array($call_method, $method));

			throw new InvalidParameterException($msg);
	}

	$API_METHODS[$method]["require_api_auth"] = $require_api_auth;

	$API_METHODS[$method]["require_user_auth"] = $require_user_auth;

	return true;
}

/**
 * Unregister an API method
 *
 * @param string $method The api name that was exposed
 *
 * @since 1.7.0
 *
 * @return void
 */
function unexpose_function($method) {
	global $API_METHODS;

	if (isset($API_METHODS[$method])) {
		unset($API_METHODS[$method]);
	}
}

/**
 * Check that the method call has the proper API and user authentication
 *
 * @param string $method The api name that was exposed
 *
 * @return true or throws an exception
 * @throws APIException
 * @since 1.7.0
 * @access private
 */
function authenticate_method($method) {
	global $API_METHODS;

	// method must be exposed
	if (!isset($API_METHODS[$method])) {
		throw new APIException(elgg_echo('APIException:MethodCallNotImplemented', array($method)));
	}

	// check API authentication if required
	if ($API_METHODS[$method]["require_api_auth"] == true) {
		$api_pam = new ElggPAM('api');
		if ($api_pam->authenticate() !== true) {
			throw new APIException(elgg_echo('APIException:APIAuthenticationFailed'));
		}
	}

	$user_pam = new ElggPAM('user');
	$user_auth_result = $user_pam->authenticate(array());

	// check if user authentication is required
	if ($API_METHODS[$method]["require_user_auth"] == true) {
		if ($user_auth_result == false) {
			throw new APIException($user_pam->getFailureMessage());
		}
	}

	return true;
}

/**
 * Executes a method.
 * A method is a function which you have previously exposed using expose_function.
 *
 * @param string $method Method, e.g. "foo.bar"
 *
 * @return GenericResult The result of the execution.
 * @throws APIException, CallException
 * @access private
 */
function execute_method($method) {
	global $API_METHODS, $CONFIG;

	// method must be exposed
	if (!isset($API_METHODS[$method])) {
		$msg = elgg_echo('APIException:MethodCallNotImplemented', array($method));
		throw new APIException($msg);
	}

	// function must be callable
	if (!(isset($API_METHODS[$method]["function"]))
	|| !(is_callable($API_METHODS[$method]["function"]))) {

		$msg = elgg_echo('APIException:FunctionDoesNotExist', array($method));
		throw new APIException($msg);
	}

	// check http call method
	if (strcmp(get_call_method(), $API_METHODS[$method]["call_method"]) != 0) {
		$msg = elgg_echo('CallException:InvalidCallMethod', array($method,
		$API_METHODS[$method]["call_method"]));

		throw new CallException($msg);
	}

	$parameters = get_parameters_for_method($method);

	if (verify_parameters($method, $parameters) == false) {
		// if verify_parameters fails, it throws exception which is not caught here
	}

	$serialised_parameters = serialise_parameters($method, $parameters);

	// Execute function: Construct function and calling parameters
	$function = $API_METHODS[$method]["function"];
	$serialised_parameters = trim($serialised_parameters, ", ");

	// @todo document why we cannot use call_user_func_array here
	$result = eval("return $function($serialised_parameters);");

	// Sanity check result
	// If this function returns an api result itself, just return it
	if ($result instanceof GenericResult) {
		return $result;
	}

	if ($result === false) {
		$msg = elgg_echo('APIException:FunctionParseError', array($function, $serialised_parameters));
		throw new APIException($msg);
	}

	if ($result === NULL) {
		// If no value
		$msg = elgg_echo('APIException:FunctionNoReturn', array($function, $serialised_parameters));
		throw new APIException($msg);
	}

	// Otherwise assume that the call was successful and return it as a success object.
	return SuccessResult::getInstance($result);
}

/**
 * Get the request method.
 *
 * @return string HTTP request method
 * @access private
 */
function get_call_method() {
	return $_SERVER['REQUEST_METHOD'];
}

/**
 * This function analyses all expected parameters for a given method
 *
 * This function sanitizes the input parameters and returns them in
 * an associated array.
 *
 * @param string $method The method
 *
 * @return array containing parameters as key => value
 * @access private
 */
function get_parameters_for_method($method) {
	global $API_METHODS;

	$sanitised = array();

	// if there are parameters, sanitize them
	if (isset($API_METHODS[$method]['parameters'])) {
		foreach ($API_METHODS[$method]['parameters'] as $k => $v) {
			$param = get_input($k); // Make things go through the sanitiser
			if ($param !== '' && $param !== null) {
				$sanitised[$k] = $param;
			} else {
				// parameter wasn't passed so check for default
				if (isset($v['default'])) {
					$sanitised[$k] = $v['default'];
				}
			}
		}
	}

	return $sanitised;
}

/**
 * Get POST data
 * Since this is called through a handler, we need to manually get the post data
 *
 * @return POST data as string encoded as multipart/form-data
 * @access private
 */
function get_post_data() {

	$postdata = file_get_contents('php://input');

	return $postdata;
}

/**
 * Verify that the required parameters are present
 *
 * @param string $method     Method name
 * @param array  $parameters List of expected parameters
 *
 * @return true on success or exception
 * @throws APIException
 * @since 1.7.0
 * @access private
 */
function verify_parameters($method, $parameters) {
	global $API_METHODS;

	// are there any parameters for this method
	if (!(isset($API_METHODS[$method]["parameters"]))) {
		return true; // no so return
	}

	// check that the parameters were registered correctly and all required ones are there
	foreach ($API_METHODS[$method]['parameters'] as $key => $value) {
		// this tests the expose structure: must be array to describe parameter and type must be defined
		if (!is_array($value) || !isset($value['type'])) {

			$msg = elgg_echo('APIException:InvalidParameter', array($key, $method));
			throw new APIException($msg);
		}

		// Check that the variable is present in the request if required
		if ($value['required'] && !array_key_exists($key, $parameters)) {
			$msg = elgg_echo('APIException:MissingParameterInMethod', array($key, $method));
			throw new APIException($msg);
		}
	}

	return true;
}

/**
 * Serialize an array of parameters for an API method call
 *
 * @param string $method     API method name
 * @param array  $parameters Array of parameters
 *
 * @return string or exception
 * @throws APIException
 * @since 1.7.0
 * @access private
 */
function serialise_parameters($method, $parameters) {
	global $API_METHODS;

	// are there any parameters for this method
	if (!(isset($API_METHODS[$method]["parameters"]))) {
		return ''; // if not, return
	}

	$serialised_parameters = "";
	foreach ($API_METHODS[$method]['parameters'] as $key => $value) {

		// avoid warning on parameters that are not required and not present
		if (!isset($parameters[$key])) {
			continue;
		}

		// Set variables casting to type.
		switch (strtolower($value['type']))
		{
			case 'int':
			case 'integer' :
				$serialised_parameters .= "," . (int)trim($parameters[$key]);
				break;
			case 'bool':
			case 'boolean':
				// change word false to boolean false
				if (strcasecmp(trim($parameters[$key]), "false") == 0) {
					$serialised_parameters .= ',false';
				} else if ($parameters[$key] == 0) {
					$serialised_parameters .= ',false';
				} else {
					$serialised_parameters .= ',true';
				}

				break;
			case 'string':
				$serialised_parameters .= ",'" . addcslashes(trim($parameters[$key]), "'") . "'";
				break;
			case 'float':
				$serialised_parameters .= "," . (float)trim($parameters[$key]);
				break;
			case 'array':
				// we can handle an array of strings, maybe ints, definitely not booleans or other arrays
				if (!is_array($parameters[$key])) {
					$msg = elgg_echo('APIException:ParameterNotArray', array($key));
					throw new APIException($msg);
				}

				$array = "array(";

				foreach ($parameters[$key] as $k => $v) {
					$k = sanitise_string($k);
					$v = sanitise_string($v);

					$array .= "'$k'=>'$v',";
				}

				$array = trim($array, ",");

				$array .= ")";
				$array = ",$array";

				$serialised_parameters .= $array;
				break;
			default:
				$msg = elgg_echo('APIException:UnrecognisedTypeCast', array($value['type'], $key, $method));
				throw new APIException($msg);
		}
	}

	return $serialised_parameters;
}

// API authorization handlers /////////////////////////////////////////////////////////////////////

/**
 * PAM: Confirm that the call includes a valid API key
 *
 * @return true if good API key - otherwise throws exception
 *
 * @return mixed
 * @throws APIException
 * @since 1.7.0
 * @access private
 */
function api_auth_key() {
	global $CONFIG;

	// check that an API key is present
	$api_key = get_input('api_key');
	if ($api_key == "") {
		throw new APIException(elgg_echo('APIException:MissingAPIKey'));
	}

	// check that it is active
	$api_user = get_api_user($CONFIG->site_id, $api_key);
	if (!$api_user) {
		// key is not active or does not exist
		throw new APIException(elgg_echo('APIException:BadAPIKey'));
	}

	// can be used for keeping stats
	// plugin can also return false to fail this authentication method
	return elgg_trigger_plugin_hook('api_key', 'use', $api_key, true);
}


/**
 * PAM: Confirm the HMAC signature
 *
 * @return true if success - otherwise throws exception
 *
 * @throws SecurityException
 * @since 1.7.0
 * @access private
 */
function api_auth_hmac() {
	global $CONFIG;

	// Get api header
	$api_header = get_and_validate_api_headers();

	// Pull API user details
	$api_user = get_api_user($CONFIG->site_id, $api_header->api_key);

	if (!$api_user) {
		throw new SecurityException(elgg_echo('SecurityException:InvalidAPIKey'),
		ErrorResult::$RESULT_FAIL_APIKEY_INVALID);
	}

	// Get the secret key
	$secret_key = $api_user->secret;

	// get the query string
	$query = substr($_SERVER['REQUEST_URI'], strpos($_SERVER['REQUEST_URI'], '?') + 1);

	// calculate expected HMAC
	$hmac = calculate_hmac(	$api_header->hmac_algo,
							$api_header->time,
							$api_header->nonce,
							$api_header->api_key,
							$secret_key,
							$query,
							$api_header->method == 'POST' ? $api_header->posthash : "");


	if ($api_header->hmac !== $hmac) {
		throw new SecurityException("HMAC is invalid.  {$api_header->hmac} != [calc]$hmac");
	}

	// Now make sure this is not a replay
	if (cache_hmac_check_replay($hmac)) {
		throw new SecurityException(elgg_echo('SecurityException:DupePacket'));
	}

	// Validate post data
	if ($api_header->method == "POST") {
		$postdata = get_post_data();
		$calculated_posthash = calculate_posthash($postdata, $api_header->posthash_algo);

		if (strcmp($api_header->posthash, $calculated_posthash) != 0) {
			$msg = elgg_echo('SecurityException:InvalidPostHash',
			array($calculated_posthash, $api_header->posthash));

			throw new SecurityException($msg);
		}
	}

	return true;
}

// HMAC /////////////////////////////////////////////////////////////////////

/**
 * This function looks at the super-global variable $_SERVER and extracts the various
 * header variables needed for the HMAC PAM
 *
 * @return stdClass Containing all the values.
 * @throws APIException Detailing any error.
 * @access private
 */
function get_and_validate_api_headers() {
	$result = new stdClass;

	$result->method = get_call_method();
	// Only allow these methods
	if (($result->method != "GET") && ($result->method != "POST")) {
		throw new APIException(elgg_echo('APIException:NotGetOrPost'));
	}

	$result->api_key = $_SERVER['HTTP_X_ELGG_APIKEY'];
	if ($result->api_key == "") {
		throw new APIException(elgg_echo('APIException:MissingAPIKey'));
	}

	$result->hmac = $_SERVER['HTTP_X_ELGG_HMAC'];
	if ($result->hmac == "") {
		throw new APIException(elgg_echo('APIException:MissingHmac'));
	}

	$result->hmac_algo = $_SERVER['HTTP_X_ELGG_HMAC_ALGO'];
	if ($result->hmac_algo == "") {
		throw new APIException(elgg_echo('APIException:MissingHmacAlgo'));
	}

	$result->time = $_SERVER['HTTP_X_ELGG_TIME'];
	if ($result->time == "") {
		throw new APIException(elgg_echo('APIException:MissingTime'));
	}

	// Must have been sent within 25 hour period.
	// 25 hours is more than enough to handle server clock drift.
	// This values determines how long the HMAC cache needs to store previous
	// signatures. Heavy use of HMAC is better handled with a shorter sig lifetime.
	// See cache_hmac_check_replay()
	if (($result->time < (time() - 90000)) || ($result->time > (time() + 90000))) {
		throw new APIException(elgg_echo('APIException:TemporalDrift'));
	}

	$result->nonce = $_SERVER['HTTP_X_ELGG_NONCE'];
	if ($result->nonce == "") {
		throw new APIException(elgg_echo('APIException:MissingNonce'));
	}

	if ($result->method == "POST") {
		$result->posthash = $_SERVER['HTTP_X_ELGG_POSTHASH'];
		if ($result->posthash == "") {
			throw new APIException(elgg_echo('APIException:MissingPOSTHash'));
		}

		$result->posthash_algo = $_SERVER['HTTP_X_ELGG_POSTHASH_ALGO'];
		if ($result->posthash_algo == "") {
			throw new APIException(elgg_echo('APIException:MissingPOSTAlgo'));
		}

		$result->content_type = $_SERVER['CONTENT_TYPE'];
		if ($result->content_type == "") {
			throw new APIException(elgg_echo('APIException:MissingContentType'));
		}
	}

	return $result;
}

/**
 * Map various algorithms to their PHP equivs.
 * This also gives us an easy way to disable algorithms.
 *
 * @param string $algo The algorithm
 *
 * @return string The php algorithm
 * @throws APIException if an algorithm is not supported.
 * @access private
 */
function map_api_hash($algo) {
	$algo = strtolower(sanitise_string($algo));
	$supported_algos = array(
		"md5" => "md5",	// @todo Consider phasing this out
		"sha" => "sha1", // alias for sha1
		"sha1" => "sha1",
		"sha256" => "sha256"
	);

	if (array_key_exists($algo, $supported_algos)) {
		return $supported_algos[$algo];
	}

	throw new APIException(elgg_echo('APIException:AlgorithmNotSupported', array($algo)));
}

/**
 * Calculate the HMAC for the http request.
 * This function signs an api request using the information provided. The signature returned
 * has been base64 encoded and then url encoded.
 *
 * @param string $algo          The HMAC algorithm used
 * @param string $time          String representation of unix time
 * @param string $nonce         Nonce
 * @param string $api_key       Your api key
 * @param string $secret_key    Your private key
 * @param string $get_variables URLEncoded string representation of the get variable parameters,
 *                              eg "method=user&guid=2"
 * @param string $post_hash     Optional sha1 hash of the post data.
 *
 * @return string The HMAC signature
 * @access private
 */
function calculate_hmac($algo, $time, $nonce, $api_key, $secret_key,
$get_variables, $post_hash = "") {

	global $CONFIG;

	elgg_log("HMAC Parts: $algo, $time, $api_key, $secret_key, $get_variables, $post_hash");

	$ctx = hash_init(map_api_hash($algo), HASH_HMAC, $secret_key);

	hash_update($ctx, trim($time));
	hash_update($ctx, trim($nonce));
	hash_update($ctx, trim($api_key));
	hash_update($ctx, trim($get_variables));
	if (trim($post_hash) != "") {
		hash_update($ctx, trim($post_hash));
	}

	return urlencode(base64_encode(hash_final($ctx, true)));
}

/**
 * Calculate a hash for some post data.
 *
 * @todo Work out how to handle really large bits of data.
 *
 * @param string $postdata The post data.
 * @param string $algo     The algorithm used.
 *
 * @return string The hash.
 * @access private
 */
function calculate_posthash($postdata, $algo) {
	$ctx = hash_init(map_api_hash($algo));

	hash_update($ctx, $postdata);

	return hash_final($ctx);
}

/**
 * This function will do two things. Firstly it verifies that a HMAC signature
 * hasn't been seen before, and secondly it will add the given hmac to the cache.
 *
 * @param string $hmac The hmac string.
 *
 * @return bool True if replay detected, false if not.
 * @access private
 */
function cache_hmac_check_replay($hmac) {
	// cache lifetime is 25 hours (this should be related to the time drift
	// allowed in get_and_validate_headers
	$cache = new ElggHMACCache(90000);

	if (!$cache->load($hmac)) {
		$cache->save($hmac, $hmac);

		return false;
	}

	return true;
}

// API key functions /////////////////////////////////////////////////////////////////////

/**
 * Generate a new API user for a site, returning a new keypair on success.
 *
 * @param int $site_guid The GUID of the site. (default is current site)
 *
 * @return stdClass object or false
 */
function create_api_user($site_guid) {
	global $CONFIG;

	if (!isset($site_guid)) {
		$site_guid = $CONFIG->site_id;
	}

	$site_guid = (int)$site_guid;

	$public = sha1(rand() . $site_guid . microtime());
	$secret = sha1(rand() . $site_guid . microtime() . $public);

	$insert = insert_data("INSERT into {$CONFIG->dbprefix}api_users
		(site_guid, api_key, secret) values
		($site_guid, '$public', '$secret')");

	if ($insert) {
		return get_api_user($site_guid, $public);
	}

	return false;
}

/**
 * Find an API User's details based on the provided public api key.
 * These users are not users in the traditional sense.
 *
 * @param int    $site_guid The GUID of the site.
 * @param string $api_key   The API Key
 *
 * @return mixed stdClass representing the database row or false.
 */
function get_api_user($site_guid, $api_key) {
	global $CONFIG;

	$api_key = sanitise_string($api_key);
	$site_guid = (int)$site_guid;

	$query = "SELECT * from {$CONFIG->dbprefix}api_users"
	. " where api_key='$api_key' and site_guid=$site_guid and active=1";

	return get_data_row($query);
}

/**
 * Revoke an api user key.
 *
 * @param int    $site_guid The GUID of the site.
 * @param string $api_key   The API Key (public).
 *
 * @return bool
 */
function remove_api_user($site_guid, $api_key) {
	global $CONFIG;

	$keypair = get_api_user($site_guid, $api_key);
	if ($keypair) {
		return delete_data("DELETE from {$CONFIG->dbprefix}api_users where id={$keypair->id}");
	}

	return false;
}


// User Authorization functions

/**
 * Check the user token
 * This examines whether an authentication token is present and returns true if
 * it is present and is valid. The user gets logged in so with the current
 * session code of Elgg, that user will be logged out of all other sessions.
 *
 * @return bool
 * @access private
 */
function pam_auth_usertoken() {
	global $CONFIG;

	$token = get_input('auth_token');
	if (!$token) {
		return false;
	}

	$validated_userid = validate_user_token($token, $CONFIG->site_id);

	if ($validated_userid) {
		$u = get_entity($validated_userid);

		// Could we get the user?
		if (!$u) {
			return false;
		}

		// Not an elgg user
		if ((!$u instanceof ElggUser)) {
			return false;
		}

		// User is banned
		if ($u->isBanned()) {
			return false;
		}

		// Fail if we couldn't log the user in
		if (!login($u)) {
			return false;
		}

		return true;
	}

	return false;
}

/**
 * See if the user has a valid login sesson
 *
 * @return bool
 * @access private
 */
function pam_auth_session() {
	return elgg_is_logged_in();
}

// user token functions

/**
 * Obtain a token for a user.
 *
 * @param string $username The username
 * @param int    $expire   Minutes until token expires (default is 60 minutes)
 *
 * @return bool
 */
function create_user_token($username, $expire = 60) {
	global $CONFIG;

	$site_guid = $CONFIG->site_id;
	$user = get_user_by_username($username);
	$time = time();
	$time += 60 * $expire;
	$token = md5(rand() . microtime() . $username . $time . $site_guid);

	if (!$user) {
		return false;
	}

	if (insert_data("INSERT into {$CONFIG->dbprefix}users_apisessions
				(user_guid, site_guid, token, expires) values
				({$user->guid}, $site_guid, '$token', '$time')
				on duplicate key update token='$token', expires='$time'")) {
		return $token;
	}

	return false;
}

/**
 * Get all tokens attached to a user
 *
 * @param int $user_guid The user GUID
 * @param int $site_guid The ID of the site (default is current site)
 *
 * @return false if none available or array of stdClass objects
 * 		(see users_apisessions schema for available variables in objects)
 * @since 1.7.0
 */
function get_user_tokens($user_guid, $site_guid) {
	global $CONFIG;

	if (!isset($site_guid)) {
		$site_guid = $CONFIG->site_id;
	}

	$site_guid = (int)$site_guid;
	$user_guid = (int)$user_guid;

	$tokens = get_data("SELECT * from {$CONFIG->dbprefix}users_apisessions
		where user_guid=$user_guid and site_guid=$site_guid");

	return $tokens;
}

/**
 * Validate a token against a given site.
 *
 * A token registered with one site can not be used from a
 * different apikey(site), so be aware of this during development.
 *
 * @param string $token     The Token.
 * @param int    $site_guid The ID of the site (default is current site)
 *
 * @return mixed The user id attached to the token if not expired or false.
 */
function validate_user_token($token, $site_guid) {
	global $CONFIG;

	if (!isset($site_guid)) {
		$site_guid = $CONFIG->site_id;
	}

	$site_guid = (int)$site_guid;
	$token = sanitise_string($token);

	$time = time();

	$user = get_data_row("SELECT * from {$CONFIG->dbprefix}users_apisessions
		where token='$token' and site_guid=$site_guid and $time < expires");

	if ($user) {
		return $user->user_guid;
	}

	return false;
}

/**
 * Remove user token
 *
 * @param string $token     The toekn
 * @param int    $site_guid The ID of the site (default is current site)
 *
 * @return bool
 * @since 1.7.0
 */
function remove_user_token($token, $site_guid) {
	global $CONFIG;

	if (!isset($site_guid)) {
		$site_guid = $CONFIG->site_id;
	}

	$site_guid = (int)$site_guid;
	$token = sanitise_string($token);

	return delete_data("DELETE from {$CONFIG->dbprefix}users_apisessions
		where site_guid=$site_guid and token='$token'");
}

/**
 * Remove expired tokens
 *
 * @return bool
 * @since 1.7.0
 */
function remove_expired_user_tokens() {
	global $CONFIG;

	$site_guid = $CONFIG->site_id;

	$time = time();

	return delete_data("DELETE from {$CONFIG->dbprefix}users_apisessions
		where site_guid=$site_guid and expires < $time");
}

// Client api functions

/**
 * Utility function to serialise a header array into its text representation.
 *
 * @param array $headers The array of headers "key" => "value"
 *
 * @return string
 * @access private
 */
function serialise_api_headers(array $headers) {
	$headers_str = "";

	foreach ($headers as $k => $v) {
		$headers_str .= trim($k) . ": " . trim($v) . "\r\n";
	}

	return trim($headers_str);
}

/**
 * Send a raw API call to an elgg api endpoint.
 *
 * @param array  $keys         The api keys.
 * @param string $url          URL of the endpoint.
 * @param array  $call         Associated array of "variable" => "value"
 * @param string $method       GET or POST
 * @param string $post_data    The post data
 * @param string $content_type The content type
 *
 * @return string
 */
function send_api_call(array $keys, $url, array $call, $method = 'GET', $post_data = '',
$content_type = 'application/octet-stream') {

	global $CONFIG;

	$headers = array();
	$encoded_params = array();

	$method = strtoupper($method);
	switch (strtoupper($method)) {
		case 'GET' :
		case 'POST' :
			break;
		default:
			$msg = elgg_echo('NotImplementedException:CallMethodNotImplemented', array($method));
			throw new NotImplementedException($msg);
	}

	// Time
	$time = time();

	// Nonce
	$nonce = uniqid('');

	// URL encode all the parameters
	foreach ($call as $k => $v) {
		$encoded_params[] = urlencode($k) . '=' . urlencode($v);
	}

	$params = implode('&', $encoded_params);

	// Put together the query string
	$url = $url . "?" . $params;

	// Construct headers
	$posthash = "";
	if ($method == 'POST') {
		$posthash = calculate_posthash($post_data, 'md5');
	}

	if ((isset($keys['public'])) && (isset($keys['private']))) {
		$headers['X-Elgg-apikey'] = $keys['public'];
		$headers['X-Elgg-time'] = $time;
		$headers['X-Elgg-nonce'] = $nonce;
		$headers['X-Elgg-hmac-algo'] = 'sha1';
		$headers['X-Elgg-hmac'] = calculate_hmac('sha1',
			$time,
			$nonce,
			$keys['public'],
			$keys['private'],
			$params,
			$posthash
		);
	}
	if ($method == 'POST') {
		$headers['X-Elgg-posthash'] = $posthash;
		$headers['X-Elgg-posthash-algo'] = 'md5';

		$headers['Content-type'] = $content_type;
		$headers['Content-Length'] = strlen($post_data);
	}

	// Opt array
	$http_opts = array(
		'method' => $method,
		'header' => serialise_api_headers($headers)
	);
	if ($method == 'POST') {
		$http_opts['content'] = $post_data;
	}

	$opts = array('http' => $http_opts);

	// Send context
	$context = stream_context_create($opts);

	// Send the query and get the result and decode.
	elgg_log("APICALL: $url");
	$results = file_get_contents($url, false, $context);

	return $results;
}

/**
 * Send a GET call
 *
 * @param string $url  URL of the endpoint.
 * @param array  $call Associated array of "variable" => "value"
 * @param array  $keys The keys dependant on chosen authentication method
 *
 * @return string
 */
function send_api_get_call($url, array $call, array $keys) {
	return send_api_call($keys, $url, $call);
}

/**
 * Send a GET call
 *
 * @param string $url          URL of the endpoint.
 * @param array  $call         Associated array of "variable" => "value"
 * @param array  $keys         The keys dependant on chosen authentication method
 * @param string $post_data    The post data
 * @param string $content_type The content type
 *
 * @return string
 */
function send_api_post_call($url, array $call, array $keys, $post_data,
$content_type = 'application/octet-stream') {

	return send_api_call($keys, $url, $call, 'POST', $post_data, $content_type);
}

/**
 * Return a key array suitable for the API client using the standard
 * authentication method based on api-keys and secret keys.
 *
 * @param string $secret_key Your secret key
 * @param string $api_key    Your api key
 *
 * @return array
 */
function get_standard_api_key_array($secret_key, $api_key) {
	return array('public' => $api_key, 'private' => $secret_key);
}

// System functions

/**
 * Simple api to return a list of all api's installed on the system.
 *
 * @return array
 * @access private
 */
function list_all_apis() {
	global $API_METHODS;

	// sort first
	ksort($API_METHODS);

	return $API_METHODS;
}

/**
 * The auth.gettoken API.
 * This API call lets a user log in, returning an authentication token which can be used
 * to authenticate a user for a period of time. It is passed in future calls as the parameter
 * auth_token.
 *
 * @param string $username Username
 * @param string $password Clear text password
 *
 * @return string Token string or exception
 * @throws SecurityException
 * @access private
 */
function auth_gettoken($username, $password) {
	if (true === elgg_authenticate($username, $password)) {
		$token = create_user_token($username);
		if ($token) {
			return $token;
		}
	}

	throw new SecurityException(elgg_echo('SecurityException:authenticationfailed'));
}

// Error handler functions

/** Define a global array of errors */
$ERRORS = array();

/**
 * API PHP Error handler function.
 * This function acts as a wrapper to catch and report PHP error messages.
 *
 * @see http://uk3.php.net/set-error-handler
 *
 * @param int    $errno    Error number
 * @param string $errmsg   Human readable message
 * @param string $filename Filename
 * @param int    $linenum  Line number
 * @param array  $vars     Vars
 *
 * @return void
 * @access private
 * 
 * @throws Exception
 */
function _php_api_error_handler($errno, $errmsg, $filename, $linenum, $vars) {
	global $ERRORS;

	$error = date("Y-m-d H:i:s (T)") . ": \"" . $errmsg . "\" in file "
	. $filename . " (line " . $linenum . ")";

	switch ($errno) {
		case E_USER_ERROR:
			error_log("ERROR: " . $error);
			$ERRORS[] = "ERROR: " . $error;

			// Since this is a fatal error, we want to stop any further execution but do so gracefully.
			throw new Exception("ERROR: " . $error);
			break;

		case E_WARNING :
		case E_USER_WARNING :
			error_log("WARNING: " . $error);
			$ERRORS[] = "WARNING: " . $error;
			break;

		default:
			error_log("DEBUG: " . $error);
			$ERRORS[] = "DEBUG: " . $error;
	}
}

/**
 * API PHP Exception handler.
 * This is a generic exception handler for PHP exceptions. This will catch any
 * uncaught exception, end API execution and return the result to the requestor
 * as an ErrorResult in the requested format.
 *
 * @param Exception $exception Exception
 *
 * @return void
 * @access private
 */
function _php_api_exception_handler($exception) {

	error_log("*** FATAL EXCEPTION (API) *** : " . $exception);

	$code   = $exception->getCode() == 0 ? ErrorResult::$RESULT_FAIL : $exception->getCode();
	$result = new ErrorResult($exception->getMessage(), $code, NULL);

	echo elgg_view_page($exception->getMessage(), elgg_view("api/output", array("result" => $result)));
}


// Services handler

/**
 * Services handler - turns request over to the registered handler
 * If no handler is found, this returns a 404 error
 *
 * @param string $handler Handler name
 * @param array  $request Request string
 *
 * @return void
 * @access private
 */
function service_handler($handler, $request) {
	global $CONFIG;

	elgg_set_context('api');

	$request = explode('/', $request);

	// after the handler, the first identifier is response format
	// ex) http://example.org/services/api/rest/xml/?method=test
	$reponse_format = array_shift($request);
	// Which view - xml, json, ...
	if ($reponse_format) {
		elgg_set_viewtype($reponse_format);
	} else {
		// default to xml
		elgg_set_viewtype("xml");
	}

	if (!isset($CONFIG->servicehandler) || empty($handler)) {
		// no handlers set or bad url
		header("HTTP/1.0 404 Not Found");
		exit;
	} else if (isset($CONFIG->servicehandler[$handler]) && is_callable($CONFIG->servicehandler[$handler])) {
		$function = $CONFIG->servicehandler[$handler];
		call_user_func($function, $request, $handler);
	} else {
		// no handler for this web service
		header("HTTP/1.0 404 Not Found");
		exit;
	}
}

/**
 * Registers a web services handler
 *
 * @param string $handler  Web services type
 * @param string $function Your function name
 *
 * @return bool Depending on success
 * @since 1.7.0
 */
function register_service_handler($handler, $function) {
	global $CONFIG;

	if (!isset($CONFIG->servicehandler)) {
		$CONFIG->servicehandler = array();
	}
	if (is_callable($function, true)) {
		$CONFIG->servicehandler[$handler] = $function;
		return true;
	}

	return false;
}

/**
 * Remove a web service
 * To replace a web service handler, register the desired handler over the old on
 * with register_service_handler().
 *
 * @param string $handler web services type
 *
 * @return void
 * @since 1.7.0
 */
function unregister_service_handler($handler) {
	global $CONFIG;

	if (isset($CONFIG->servicehandler, $CONFIG->servicehandler[$handler])) {
		unset($CONFIG->servicehandler[$handler]);
	}
}

/**
 * REST API handler
 *
 * @return void
 * @access private
 *
 * @throws SecurityException|APIException
 */
function rest_handler() {
	global $CONFIG;

	// Register the error handler
	error_reporting(E_ALL);
	set_error_handler('_php_api_error_handler');

	// Register a default exception handler
	set_exception_handler('_php_api_exception_handler');

	// Check to see if the api is available
	if ((isset($CONFIG->disable_api)) && ($CONFIG->disable_api == true)) {
		throw new SecurityException(elgg_echo('SecurityException:APIAccessDenied'));
	}

	// plugins should return true to control what API and user authentication handlers are registered
	if (elgg_trigger_plugin_hook('rest', 'init', null, false) == false) {
		// for testing from a web browser, you can use the session PAM
		// do not use for production sites!!
		//register_pam_handler('pam_auth_session');

		// user token can also be used for user authentication
		register_pam_handler('pam_auth_usertoken');

		// simple API key check
		register_pam_handler('api_auth_key', "sufficient", "api");
		// hmac
		register_pam_handler('api_auth_hmac', "sufficient", "api");
	}

	// Get parameter variables
	$method = get_input('method');
	$result = null;

	// this will throw an exception if authentication fails
	authenticate_method($method);

	$result = execute_method($method);


	if (!($result instanceof GenericResult)) {
		throw new APIException(elgg_echo('APIException:ApiResultUnknown'));
	}

	// Output the result
	echo elgg_view_page($method, elgg_view("api/output", array("result" => $result)));
}

// Initialization

/**
 * Unit tests for API
 *
 * @param string  $hook   unit_test
 * @param string $type   system
 * @param mixed  $value  Array of tests
 * @param mixed  $params Params
 *
 * @return array
 * @access private
 */
function api_unit_test($hook, $type, $value, $params) {
	global $CONFIG;

	$value[] = $CONFIG->path . 'engine/tests/services/api.php';
	return $value;
}

/**
 * Initialise the API subsystem.
 *
 * @return void
 * @access private
 */
function api_init() {
	// Register a page handler, so we can have nice URLs
	register_service_handler('rest', 'rest_handler');

	elgg_register_plugin_hook_handler('unit_test', 'system', 'api_unit_test');

	// expose the list of api methods
	expose_function("system.api.list", "list_all_apis", NULL,
	elgg_echo("system.api.list"), "GET", false, false);

	// The authentication token api
	expose_function(
		"auth.gettoken",
		"auth_gettoken",
		array(
			'username' => array ('type' => 'string'),
			'password' => array ('type' => 'string'),
		),
		elgg_echo('auth.gettoken'),
		'POST',
		false,
		false
	);
}


elgg_register_event_handler('init', 'system', 'api_init');