<?php
/**
 * Copyright 2011 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License. You may obtain
 * a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

if (!function_exists('curl_init')) {
  throw new Exception('Facebook needs the CURL PHP extension.');
}
if (!function_exists('json_decode')) {
  throw new Exception('Facebook needs the JSON PHP extension.');
}

/**
 * Thrown when an API call returns an exception.
 *
 * @author Naitik Shah <naitik@facebook.com>
 */
class FacebookApiException extends Exception
{
  /**
   * The result from the API server that represents the exception information.
   */
  protected $result;

  /**
   * Make a new API Exception with the given result.
   *
   * @param Array $result the result from the API server
   */
  public function __construct($result) {
    $this->result = $result;

    $code = isset($result['error_code']) ? $result['error_code'] : 0;

    if (isset($result['error_description'])) {
      // OAuth 2.0 Draft 10 style
      $msg = $result['error_description'];
    } else if (isset($result['error']) && is_array($result['error'])) {
      // OAuth 2.0 Draft 00 style
      $msg = $result['error']['message'];
    } else if (isset($result['error_msg'])) {
      // Rest server style
      $msg = $result['error_msg'];
    } else {
      $msg = 'Unknown Error. Check getResult()';
    }

    parent::__construct($msg, $code);
  }

  /**
   * Return the associated result object returned by the API server.
   *
   * @returns Array the result from the API server
   */
  public function getResult() {
    return $this->result;
  }

  /**
   * Returns the associated type for the error. This will default to
   * 'Exception' when a type is not available.
   *
   * @return String
   */
  public function getType() {
    if (isset($this->result['error'])) {
      $error = $this->result['error'];
      if (is_string($error)) {
        // OAuth 2.0 Draft 10 style
        return $error;
      } else if (is_array($error)) {
        // OAuth 2.0 Draft 00 style
        if (isset($error['type'])) {
          return $error['type'];
        }
      }
    }

    return 'Exception';
  }

  /**
   * To make debugging easier.
   *
   * @returns String the string representation of the error
   */
  public function __toString() {
    $str = $this->getType() . ': ';
    if ($this->code != 0) {
      $str .= $this->code . ': ';
    }
    return $str . $this->message;
  }
}

/**
 * Provides access to the Facebook Platform.  This class provides
 * a majority of the functionality needed, but the class is abstract
 * because it is designed to be subclassed.  The subclass must
 * implement the three abstract methods listed at the bottom of
 * the file.
 *
 * @author Naitik Shah <naitik@facebook.com>
 */
abstract class BaseFacebook
{
  /**
   * Version.
   */
  const VERSION = '3.0.0';

  /**
   * Default options for curl.
   */
  public static $CURL_OPTS = array(
    CURLOPT_CONNECTTIMEOUT => 10,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT        => 60,
    CURLOPT_USERAGENT      => 'facebook-php-3.0',
  );

  /**
   * List of query parameters that get automatically dropped when rebuilding
   * the current URL.
   */
  protected static $DROP_QUERY_PARAMS = array(
    'code',
    'state',
    'signed_request',
  );

  /**
   * Maps aliases to Facebook domains.
   */
  public static $DOMAIN_MAP = array(
    'api'       => 'https://api.facebook.com/',
    'api_video' => 'https://api-video.facebook.com/',
    'api_read'  => 'https://api-read.facebook.com/',
    'graph'     => 'https://graph.facebook.com/',
    'www'       => 'https://www.facebook.com/',
  );

  /**
   * The Application ID.
   */
  protected $appId;

  /**
   * The Application API Secret.
   */
  protected $apiSecret;

  /**
   * The ID of the Facebook user, or 0 if the user is logged out.
   */
  protected $user;

  /**
   * The data from the signed_request token.
   */
  protected $signedRequest;

  /**
   * A CSRF state variable to assist in the defense against
   * CSRF attacks.
   */
  protected $state;

  /**
   * The OAuth access token received in exchange for a valid authorization
   * code.  null means the access token has yet to be determined.
   */
  protected $accessToken = null;

  /**
   * Indicates if the CURL based @ syntax for file uploads is enabled.
   */
  protected $fileUploadSupport = false;

  /**
   * Initialize a Facebook Application.
   *
   * The configuration:
   * - appId: the application ID
   * - secret: the application secret
   * - fileUpload: (optional) boolean indicating if file uploads are enabled
   *
   * @param Array $config the application configuration
   */
  public function __construct($config) {
    $this->setAppId($config['appId']);
    $this->setApiSecret($config['secret']);
    if (isset($config['fileUpload'])) {
      $this->setFileUploadSupport($config['fileUpload']);
    }
    if (isset($_COOKIE[$this->getCSRFTokenCookieName()])) {
      $this->state = $_COOKIE[$this->getCSRFTokenCookieName()];
    }
  }

  /**
   * Set the Application ID.
   *
   * @param String $appId the Application ID
   */
  public function setAppId($appId) {
    $this->appId = $appId;
    return $this;
  }

  /**
   * Get the Application ID.
   *
   * @return String the Application ID
   */
  public function getAppId() {
    return $this->appId;
  }

  /**
   * Set the API Secret.
   *
   * @param String $appId the API Secret
   */
  public function setApiSecret($apiSecret) {
    $this->apiSecret = $apiSecret;
    return $this;
  }

  /**
   * Get the API Secret.
   *
   * @return String the API Secret
   */
  public function getApiSecret() {
    return $this->apiSecret;
  }

  /**
   * Set the file upload support status.
   *
   * @param Boolean the file upload support status.
   */
  public function setFileUploadSupport($fileUploadSupport) {
    $this->fileUploadSupport = $fileUploadSupport;
    return $this;
  }

  /**
   * Get the file upload support status.
   *
   * @return Boolean true if and only if the server supports
   * file upload.
   */
  public function useFileUploadSupport() {
    return $this->fileUploadSupport;
  }

  /**
   * Sets the access token for api calls.  Use this if you get
   * your access token by other means and just want the SDK
   * to use it.
   *
   * @param String $access_token an access token.
   */
  public function setAccessToken($access_token) {
    $this->accessToken = $access_token;
    return $this;
  }

  /**
   * Determines the access token that should be used for API calls.
   * The first time this is called, $this->accessToken is set equal
   * to either a valid user access token, or it's set to the application
   * access token if a valid user access token wasn't available.  Subsequent
   * calls return whatever the first call returned.
   *
   * @return String the access token
   */
  public function getAccessToken() {
    if ($this->accessToken !== null) {
      // we've done this already and cached it.  Just return.
      return $this->accessToken;
    }

    // first establish access token to be the application
    // access token, in case we navigate to the /oauth/access_token
    // endpoint, where SOME access token is required.
    $this->setAccessToken($this->getApplicationAccessToken());
    if ($user_access_token = $this->getUserAccessToken()) {
      $this->setAccessToken($user_access_token);
    }

    return $this->accessToken;
  }

  /**
   * Determines and returns the user access token, first using
   * the signed request if present, and then falling back on
   * the authorization code if present.  The intent is to
   * return a valid user access token, or false if one is determined
   * to not be available.
   *
   * @return String a valid user access token, or false if one
   *         could not be determined.
   */
  protected function getUserAccessToken() {
    // first, consider a signed request if it's supplied.
    // if there is a signed request, then it alone determines
    // the access token.
    $signed_request = $this->getSignedRequest();
    if ($signed_request) {
      if (array_key_exists('oauth_token', $signed_request)) {
        $access_token = $signed_request['oauth_token'];
        $this->setPersistentData('access_token', $access_token);
        return $access_token;
      }

      // signed request states there's no access token, so anything
      // stored should be cleared.
      $this->clearAllPersistentData();
      return false; // respect the signed request's data, even
                    // if there's an authorization code or something else
    }

    $code = $this->getCode();
    if ($code && $code != $this->getPersistentData('code')) {
      $access_token = $this->getAccessTokenFromCode($code);
      if ($access_token) {
        $this->setPersistentData('code', $code);
        $this->setPersistentData('access_token', $access_token);
        return $access_token;
      }

      // code was bogus, so everything based on it should be invalidated.
      $this->clearAllPersistentData();
      return false;
    }

    // as a fallback, just return whatever is in the persistent
    // store, knowing nothing explicit (signed request, authorization
    // code, etc.) was present to shadow it (or we saw a code in $_REQUEST,
    // but it's the same as what's in the persistent store)
    return $this->getPersistentData('access_token');
  }

  /**
   * Get the data from a signed_request token.
   *
   * @return String the base domain
   */
  public function getSignedRequest() {
    if (!$this->signedRequest) {
      if (isset($_REQUEST['signed_request'])) {
        $this->signedRequest = $this->parseSignedRequest(
          $_REQUEST['signed_request']);
      }
    }
    return $this->signedRequest;
  }

  /**
   * Get the UID of the connected user, or 0
   * if the Facebook user is not connected.
   *
   * @return String the UID if available.
   */
  public function getUser() {
    if ($this->user !== null) {
      // we've already determined this and cached the value.
      return $this->user;
    }

    return $this->user = $this->getUserFromAvailableData();
  }

  /**
   * Determines the connected user by first examining any signed
   * requests, then considering an authorization code, and then
   * falling back to any persistent store storing the user.
   *
   * @return Integer the id of the connected Facebook user, or 0
   * if no such user exists.
   */
  protected function getUserFromAvailableData() {
    // if a signed request is supplied, then it solely determines
    // who the user is.
    $signed_request = $this->getSignedRequest();
    if ($signed_request) {
      if (array_key_exists('user_id', $signed_request)) {
        $user = $signed_request['user_id'];
        $this->setPersistentData('user_id', $signed_request['user_id']);
        return $user;
      }

      // if the signed request didn't present a user id, then invalidate
      // all entries in any persistent store.
      $this->clearAllPersistentData();
      return 0;
    }

    $user = $this->getPersistentData('user_id', $default = 0);
    $persisted_access_token = $this->getPersistentData('access_token');

    // use access_token to fetch user id if we have a user access_token, or if
    // the cached access token has changed.
    $access_token = $this->getAccessToken();
    if ($access_token &&
        $access_token != $this->getApplicationAccessToken() &&
        !($user && $persisted_access_token == $access_token)) {
      $user = $this->getUserFromAccessToken();
      if ($user) {
        $this->setPersistentData('user_id', $user);
      } else {
        $this->clearAllPersistentData();
      }
    }

    return $user;
  }

  /**
   * Get a Login URL for use with redirects. By default, full page redirect is
   * assumed. If you are using the generated URL with a window.open() call in
   * JavaScript, you can pass in display=popup as part of the $params.
   *
   * The parameters:
   * - redirect_uri: the url to go to after a successful login
   * - scope: comma separated list of requested extended perms
   *
   * @param Array $params provide custom parameters
   * @return String the URL for the login flow
   */
  public function getLoginUrl($params=array()) {
    $this->establishCSRFTokenState();
    $currentUrl = $this->getCurrentUrl();
    return $this->getUrl(
      'www',
      'dialog/oauth',
      array_merge(array(
                    'client_id' => $this->getAppId(),
                    'redirect_uri' => $currentUrl, // possibly overwritten
                    'state' => $this->state),
                  $params));
  }

  /**
   * Get a Logout URL suitable for use with redirects.
   *
   * The parameters:
   * - next: the url to go to after a successful logout
   *
   * @param Array $params provide custom parameters
   * @return String the URL for the logout flow
   */
  public function getLogoutUrl($params=array()) {
    return $this->getUrl(
      'www',
      'logout.php',
      array_merge(array(
        'next' => $this->getCurrentUrl(),
        'access_token' => $this->getAccessToken(),
      ), $params)
    );
  }

  /**
   * Get a login status URL to fetch the status from Facebook.
   *
   * The parameters:
   * - ok_session: the URL to go to if a session is found
   * - no_session: the URL to go to if the user is not connected
   * - no_user: the URL to go to if the user is not signed into facebook
   *
   * @param Array $params provide custom parameters
   * @return String the URL for the logout flow
   */
  public function getLoginStatusUrl($params=array()) {
    return $this->getUrl(
      'www',
      'extern/login_status.php',
      array_merge(array(
        'api_key' => $this->getAppId(),
        'no_session' => $this->getCurrentUrl(),
        'no_user' => $this->getCurrentUrl(),
        'ok_session' => $this->getCurrentUrl(),
        'session_version' => 3,
      ), $params)
    );
  }

  /**
   * Make an API call.
   *
   * @param Array $params the API call parameters
   * @return the decoded response
   */
  public function api(/* polymorphic */) {
    $args = func_get_args();
    if (is_array($args[0])) {
      return $this->_restserver($args[0]);
    } else {
      return call_user_func_array(array($this, '_graph'), $args);
    }
  }

  /**
   * Get the authorization code from the query parameters, if it exists,
   * and otherwise return false to signal no authorization code was
   * discoverable.
   *
   * @return mixed the authorization code, or false if the authorization
   * code could not be determined.
   */
  protected function getCode() {
    if (isset($_REQUEST['code'])) {
      if ($this->state !== null &&
          isset($_REQUEST['state']) &&
          $this->state === $_REQUEST['state']) {

        // CSRF state has done its job, so clear it
        $this->state = null;
        unset($_COOKIE[$this->getCSRFTokenCookieName()]);
        return $_REQUEST['code'];
      } else {
        self::errorLog('CSRF state token does not match one provided.');
        return false;
      }
    }

    return false;
  }

  /**
   * Retrieves the UID with the understanding that
   * $this->accessToken has already been set and is
   * seemingly legitimate.  It relies on Facebook's Graph API
   * to retreive user information and then extract
   * the user ID.
   *
   * @return Integer returns the UID of the Facebook user, or
   * 0 if the Facebook user could not be determined.
   */
  protected function getUserFromAccessToken() {
    try {
      $user_info = $this->api('/me');
      return $user_info['id'];
    } catch (FacebookApiException $e) {
      return 0;
    }
  }

  /**
   * Returns the access token that should be used for logged out
   * users when no authorization code is available.
   *
   * @return String the application access token, useful for
   * gathering public information about users and applications.
   */
  protected function getApplicationAccessToken() {
    return $this->appId.'|'.$this->apiSecret;
  }

  /**
   * Lays down a CSRF state token for this process.  We
   * only generate a new CSRF token if one isn't currently
   * circulating in the domain's cookie jar.
   *
   * @return void
   */
  protected function establishCSRFTokenState() {
    if ($this->state === null) {
      $this->state = md5(uniqid(mt_rand(), true));
      setcookie($name = $this->getCSRFTokenCookieName(),
                $value = $this->state,
                $expires = time() + 3600); // sticks for an hour
    }
  }

  /**
   * Retreives an access token for the given authorization code
   * (previously generated from www.facebook.com on behalf of
   * a specific user).  The authorization code is sent to graph.facebook.com
   * and a legitimate access token is generated provided the access token
   * and the user for which it was generated all match, and the user is
   * either logged in to Facebook or has granted an offline access permission.
   *
   * @param String $code an authorization code.
   * @return mixed an access token exchanged for the authorization code, or
   * false if an access token could not be generated.
   */
  protected function getAccessTokenFromCode($code) {
    if (empty($code)) {
      return false;
    }

    try {
      // need to circumvent json_decode by calling _oauthRequest
      // directly, since response isn't JSON format.
      $access_token_response =
        $this->_oauthRequest(
          $this->getUrl('graph', '/oauth/access_token'),
          $params = array('client_id' => $this->getAppId(),
                          'client_secret' => $this->getApiSecret(),
                          'redirect_uri' => $this->getCurrentUrl(),
                          'code' => $code));
    } catch (FacebookApiException $e) {
      // most likely that user very recently revoked authorization.
      // In any event, we don't have an access token, so say so.
      return false;
    }

    if (empty($access_token_response)) {
      return false;
    }

    $response_params = array();
    parse_str($access_token_response, $response_params);
    if (!isset($response_params['access_token'])) {
      return false;
    }

    return $response_params['access_token'];
  }

  /**
   * Invoke the old restserver.php endpoint.
   *
   * @param Array $params method call object
   * @return the decoded response object
   * @throws FacebookApiException
   */
  protected function _restserver($params) {
    // generic application level parameters
    $params['api_key'] = $this->getAppId();
    $params['format'] = 'json-strings';

    $result = json_decode($this->_oauthRequest(
      $this->getApiUrl($params['method']),
      $params
    ), true);

    // results are returned, errors are thrown
    if (is_array($result) && isset($result['error_code'])) {
      throw new FacebookApiException($result);
    }

    return $result;
  }

  /**
   * Invoke the Graph API.
   *
   * @param String $path the path (required)
   * @param String $method the http method (default 'GET')
   * @param Array $params the query/post data
   * @return the decoded response object
   * @throws FacebookApiException
   */
  protected function _graph($path, $method = 'GET', $params = array()) {
    if (is_array($method) && empty($params)) {
      $params = $method;
      $method = 'GET';
    }
    $params['method'] = $method; // method override as we always do a POST

    $result = json_decode($this->_oauthRequest(
      $this->getUrl('graph', $path),
      $params
    ), true);

    // results are returned, errors are thrown
    if (is_array($result) && isset($result['error'])) {
      $this->throwAPIException($result);
    }

    return $result;
  }

  /**
   * Make a OAuth Request.
   *
   * @param String $path the path (required)
   * @param Array $params the query/post data
   * @return the decoded response object
   * @throws FacebookApiException
   */
  protected function _oauthRequest($url, $params) {
    if (!isset($params['access_token'])) {
      $params['access_token'] = $this->getAccessToken();
    }

    // json_encode all params values that are not strings
    foreach ($params as $key => $value) {
      if (!is_string($value)) {
        $params[$key] = json_encode($value);
      }
    }

    return $this->makeRequest($url, $params);
  }

  /**
   * Makes an HTTP request. This method can be overriden by subclasses if
   * developers want to do fancier things or use something other than curl to
   * make the request.
   *
   * @param String $url the URL to make the request to
   * @param Array $params the parameters to use for the POST body
   * @param CurlHandler $ch optional initialized curl handle
   * @return String the response text
   */
  protected function makeRequest($url, $params, $ch=null) {
    if (!$ch) {
      $ch = curl_init();
    }

    $opts = self::$CURL_OPTS;
    if ($this->useFileUploadSupport()) {
      $opts[CURLOPT_POSTFIELDS] = $params;
    } else {
      $opts[CURLOPT_POSTFIELDS] = http_build_query($params, null, '&');
    }
    $opts[CURLOPT_URL] = $url;

    // disable the 'Expect: 100-continue' behaviour. This causes CURL to wait
    // for 2 seconds if the server does not support this header.
    if (isset($opts[CURLOPT_HTTPHEADER])) {
      $existing_headers = $opts[CURLOPT_HTTPHEADER];
      $existing_headers[] = 'Expect:';
      $opts[CURLOPT_HTTPHEADER] = $existing_headers;
    } else {
      $opts[CURLOPT_HTTPHEADER] = array('Expect:');
    }

    curl_setopt_array($ch, $opts);
    $result = curl_exec($ch);

    if (curl_errno($ch) == 60) { // CURLE_SSL_CACERT
      self::errorLog('Invalid or no certificate authority found, '.
                     'using bundled information');
      curl_setopt($ch, CURLOPT_CAINFO,
                  dirname(__FILE__) . '/fb_ca_chain_bundle.crt');
      $result = curl_exec($ch);
    }

    if ($result === false) {
      $e = new FacebookApiException(array(
        'error_code' => curl_errno($ch),
        'error' => array(
        'message' => curl_error($ch),
        'type' => 'CurlException',
        ),
      ));
      curl_close($ch);
      throw $e;
    }
    curl_close($ch);
    return $result;
  }

  /**
   * The name of the cookie housing the CSRF protection value.
   *
   * @return String the cookie name
   */
  protected function getCSRFTokenCookieName() {
    return 'fbcsrf_'.$this->getAppId();
  }

  /**
   * Parses a signed_request and validates the signature.
   *
   * @param String A signed token
   * @return Array the payload inside it or null if the sig is wrong
   */
  protected function parseSignedRequest($signed_request) {
    list($encoded_sig, $payload) = explode('.', $signed_request, 2);

    // decode the data
    $sig = self::base64UrlDecode($encoded_sig);
    $data = json_decode(self::base64UrlDecode($payload), true);

    if (strtoupper($data['algorithm']) !== 'HMAC-SHA256') {
      self::errorLog('Unknown algorithm. Expected HMAC-SHA256');
      return null;
    }

    // check sig
    $expected_sig = hash_hmac('sha256', $payload,
                              $this->getApiSecret(), $raw = true);
    if ($sig !== $expected_sig) {
      self::errorLog('Bad Signed JSON signature!');
      return null;
    }

    return $data;
  }

  /**
   * Build the URL for api given parameters.
   *
   * @param $method String the method name.
   * @return String the URL for the given parameters
   */
  protected function getApiUrl($method) {
    static $READ_ONLY_CALLS =
      array('admin.getallocation' => 1,
            'admin.getappproperties' => 1,
            'admin.getbannedusers' => 1,
            'admin.getlivestreamvialink' => 1,
            'admin.getmetrics' => 1,
            'admin.getrestrictioninfo' => 1,
            'application.getpublicinfo' => 1,
            'auth.getapppublickey' => 1,
            'auth.getsession' => 1,
            'auth.getsignedpublicsessiondata' => 1,
            'comments.get' => 1,
            'connect.getunconnectedfriendscount' => 1,
            'dashboard.getactivity' => 1,
            'dashboard.getcount' => 1,
            'dashboard.getglobalnews' => 1,
            'dashboard.getnews' => 1,
            'dashboard.multigetcount' => 1,
            'dashboard.multigetnews' => 1,
            'data.getcookies' => 1,
            'events.get' => 1,
            'events.getmembers' => 1,
            'fbml.getcustomtags' => 1,
            'feed.getappfriendstories' => 1,
            'feed.getregisteredtemplatebundlebyid' => 1,
            'feed.getregisteredtemplatebundles' => 1,
            'fql.multiquery' => 1,
            'fql.query' => 1,
            'friends.arefriends' => 1,
            'friends.get' => 1,
            'friends.getappusers' => 1,
            'friends.getlists' => 1,
            'friends.getmutualfriends' => 1,
            'gifts.get' => 1,
            'groups.get' => 1,
            'groups.getmembers' => 1,
            'intl.gettranslations' => 1,
            'links.get' => 1,
            'notes.get' => 1,
            'notifications.get' => 1,
            'pages.getinfo' => 1,
            'pages.isadmin' => 1,
            'pages.isappadded' => 1,
            'pages.isfan' => 1,
            'permissions.checkavailableapiaccess' => 1,
            'permissions.checkgrantedapiaccess' => 1,
            'photos.get' => 1,
            'photos.getalbums' => 1,
            'photos.gettags' => 1,
            'profile.getinfo' => 1,
            'profile.getinfooptions' => 1,
            'stream.get' => 1,
            'stream.getcomments' => 1,
            'stream.getfilters' => 1,
            'users.getinfo' => 1,
            'users.getloggedinuser' => 1,
            'users.getstandardinfo' => 1,
            'users.hasapppermission' => 1,
            'users.isappuser' => 1,
            'users.isverified' => 1,
            'video.getuploadlimits' => 1);
    $name = 'api';
    if (isset($READ_ONLY_CALLS[strtolower($method)])) {
      $name = 'api_read';
    } else if (strtolower($method) == 'video.upload') {
      $name = 'api_video';
    }
    return self::getUrl($name, 'restserver.php');
  }

  /**
   * Build the URL for given domain alias, path and parameters.
   *
   * @param $name String the name of the domain
   * @param $path String optional path (without a leading slash)
   * @param $params Array optional query parameters
   * @return String the URL for the given parameters
   */
  protected function getUrl($name, $path='', $params=array()) {
    $url = self::$DOMAIN_MAP[$name];
    if ($path) {
      if ($path[0] === '/') {
        $path = substr($path, 1);
      }
      $url .= $path;
    }
    if ($params) {
      $url .= '?' . http_build_query($params, null, '&');
    }

    return $url;
  }

  /**
   * Returns the Current URL, stripping it of known FB parameters that should
   * not persist.
   *
   * @return String the current URL
   */
  protected function getCurrentUrl() {
    $protocol = isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on'
      ? 'https://'
      : 'http://';
    $currentUrl = $protocol . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
    $parts = parse_url($currentUrl);

    // drop known fb params
    $query = '';
    if (!empty($parts['query'])) {
      $params = array();
      parse_str($parts['query'], $params);
      foreach(self::$DROP_QUERY_PARAMS as $key) {
        unset($params[$key]);
      }
      if (!empty($params)) {
        $query = '?' . http_build_query($params, null, '&');
      }
    }

    // use port if non default
    $port =
      isset($parts['port']) &&
      (($protocol === 'http://' && $parts['port'] !== 80) ||
       ($protocol === 'https://' && $parts['port'] !== 443))
      ? ':' . $parts['port'] : '';

    // rebuild
    return $protocol . $parts['host'] . $port . $parts['path'] . $query;
  }

  /**
   * Analyzes the supplied result to see if it was thrown
   * because the access token is no longer valid.  If that is
   * the case, then the persistent store is cleared.
   *
   * @param $result a record storing the error message returned
   *        by a failed API call.
   */
  protected function throwAPIException($result) {
    $e = new FacebookApiException($result);
    switch ($e->getType()) {
      // OAuth 2.0 Draft 00 style
      case 'OAuthException':
        // OAuth 2.0 Draft 10 style
      case 'invalid_token':
        $message = $e->getMessage();
      if ((strpos($message, 'Error validating access token') !== false) ||
          (strpos($message, 'Invalid OAuth access token') !== false)) {
        $this->setAccessToken(null);
        $this->user = 0;
        $this->clearAllPersistentData();
      }
    }

    throw $e;
  }


  /**
   * Prints to the error log if you aren't in command line mode.
   *
   * @param String log message
   */
  protected static function errorLog($msg) {
    // disable error log if we are running in a CLI environment
    // @codeCoverageIgnoreStart
    if (php_sapi_name() != 'cli') {
      error_log($msg);
    }
    // uncomment this if you want to see the errors on the page
    // print 'error_log: '.$msg."\n";
    // @codeCoverageIgnoreEnd
  }

  /**
   * Base64 encoding that doesn't need to be urlencode()ed.
   * Exactly the same as base64_encode except it uses
   *   - instead of +
   *   _ instead of /
   *
   * @param String base64UrlEncodeded string
   */
  protected static function base64UrlDecode($input) {
    return base64_decode(strtr($input, '-_', '+/'));
  }

  /**
   * Each of the following three methods should be overridden in
   * a concrete subclass, as they are in the provided Facebook class.
   * The Facebook class uses PHP sessions to provide a primitive
   * persistent store, but another subclass--one that you implement--
   * might use a database, memcache, or an in-memory cache.
   *
   * @see Facebook
   */
  abstract protected function setPersistentData($key, $value);
  abstract protected function getPersistentData($key, $default = false);
  abstract protected function clearAllPersistentData();
}