<?php
/**
 * Facebook connector
 *
 * $Id$
 *
 * @author gERD Schaufelberger <gerd@php-tools.net>
 * @license PHP License
 * @package WB
 * @subpackage base
 */

 WBClass::load('WBStream');

/**
 * Facebook connector
 *
 * @version 0.1.0
 * @package WB
 * @subpackage base
 */
class WBFacebook
{
    /**
     * configuration
     * @var WBConfig
     */
    private $conf;

    /**
     * Graph base URL
     */
    const FB_GRAPH_BASE_URL =   'https://graph.facebook.com';

    /**
     * current facebook access token
     * @var string
     */
    private $token = '';

    /**
     * facebook application id
     * @var string
     */
    private $appId;

    /**
     * stream context
     * @var array
     */
    private $streamContextOption;

    /**
     * constructor
     *
     * Load facebook config and get stream context options
     */
    public function __construct($params = array())
    {
        $this->conf =   WBClass::create('WBConfig');
        $this->conf->load('facebook');

        $this->appId    =   $this->conf->get('account/appid');
        $this->streamContextOption  =   WBStream::getStreamContextOptions(self::FB_GRAPH_BASE_URL);
    }

    /**
     * publish a wall post
     *
     * @see http://developers.facebook.com/docs/reference/api/post/
     *
     * @param array $data
     * @param array %actions
     * @return string $id
     */
    public function postOnWall($data = array(), $actions = array())
    {
        if (empty($data) || !is_array($data) || !isset($data['message']) || empty($data['message'])) {
            WBClass::load('WBException_Argument');
            throw new WBException_Argument('Invalid argument. $data must be an associative array with "message" set', 1, __CLASS__);
        }

        $keys   =   array(
                            'message',
                            'link',
                            'picture',
                            'name',
                            'caption',
                            'description',
                            'privacy',
                            'targeting'
                        );
        $post   =   array();
        foreach ($keys as $key) {
            if (!isset($data[$key]) || empty($data[$key])) {
                continue;
            }
            $post[$key] =   $data[$key];
        }

        // actions
        if (!empty($actions)) {
            $post['actions']    =   json_encode($actions);
        }

        $this->fetchAccessToken();
        $url    =   sprintf('%s/%s/feed'
                    , self::FB_GRAPH_BASE_URL
                    , $this->appId);

        $res    =   $this->request($url, $data);
        if (is_array($res) && isset($res['id'])) {
            return $res['id'];
        }
        return null;
    }

    /**
     * fetch access token for further requests
     *
     * Use appid and appsecret to create session like access token
     */
    private function fetchAccessToken()
    {
        if (!empty($this->token)) {
            return;
        }
        $url    =   sprintf('%s/oauth/access_token?client_id=%s&client_secret=%s&grant_type=client_credentials'
                    , self::FB_GRAPH_BASE_URL
                    , $this->appId
                    , $this->conf->get('account/appsecret')
                    );

        $token  =   trim($this->request($url, array(), true));
        $token  =   explode('=', $token);
        $this->token    =   $token[1];
    }

    /**
     * Send GET or POST request to facebook
     *
     * Auxillary method to build facebook requests. Send request and receive response.
     *
     * @param string $url
     * @param array $post optional post data
     * @param bool $raw whether to decode JSON string (default) or return raw data
     * @return array
     */
    private function request($url, $post = array(), $raw = false)
    {
        $option =   $this->streamContextOption;
        if (!empty($post)) {
            $post['access_token']       =   $this->token;
            $option['http']['method']   =   'POST';
            $option['http']['header']   =   'Content-type: application/x-www-form-urlencoded';
            $option['http']['content']  =   http_build_query($post);
        }

        $context    =   stream_context_create($option);
        $res        =   file_get_contents($url, false, $context);
        if (false === $res) {
            WBClass::load('WBException_Net');
            throw new WBException_Net('Facebook request failed.', 2, __CLASS__);
        }
        if ($raw) {
            return $res;
        }
        if (!strlen($res)) {
            return array();
        }
        return json_decode($res, true);
    }
}
?>