<?php
/**
 * Facebook Login - Log in via Facebook
 * @author Daniel15 <dan.cx>
 */

class FacebookLogin
{
    const AUTHORIZE_URL = 'https://graph.facebook.com/oauth/authorize';
    const TOKEN_URL = 'https://graph.facebook.com/oauth/access_token';
    const PROFILE_URL = 'https://graph.facebook.com/me';

    private $client_id;
    private $client_secret;
    private $my_url;
    private $user_data;

    /**
     * Create an instance of the FacebookLogin class
     */
    public function __construct($client_id, $client_secret)
    {
        $this->client_id = $client_id;
        $this->client_secret = $client_secret;
        $this->my_url = 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['PHP_SELF'];
    }

    /**
     * Do a Facebook login - either redirects to Facebook or reads the returned result
     */
    public function doLogin()
    {
        // Are we not returning from Facebook (ie. starting the login)?
        return !isset($_GET['code']) ? $this->startLogin() : $this->verifyLogin();
    }

    /**
     * Start a login with Facebook - Redirect to their authentication URL
     */
    private function startLogin()
    {
        $data = array(
            'client_id' => $this->client_id,
            'redirect_uri' => $this->my_url,
            'type' => 'web_server',
        );

        header('Location: ' . self::AUTHORIZE_URL . '?' . http_build_query($data));
        die();
    }

    /**
     * Verify the token we receive from Facebook is valid, and get the user's details
     */
    private function verifyLogin()
    {
        $data = array(
            'client_id' => $this->client_id,
            'redirect_uri' => $this->my_url,
            'client_secret' => $this->client_secret,
            'code' => $_GET['code'],
        );

        // Get an access token
        $result = @file_get_contents(self::TOKEN_URL . '?' . http_build_query($data));
        parse_str($result, $result_array);

        // Make sure we actually have a token
        if (empty($result_array['access_token']))
            throw new Exception('Invalid response received from Facebook. Response = "' . $result . '"');

        // Grab the user's data
        $this->access_token = $result_array['access_token'];
        $this->user_data = json_decode(file_get_contents(self::PROFILE_URL . '?access_token=' . $this->access_token));
        return $this->user_data;
    }

    /**
     * Helper function to get the user's Facebook info
     */
    public function getUser()
    {
        return $this->user_data;
    }
}

//code paste
$facebook = new FacebookLogin('*******************', '*****************************');
$user = $facebook->doLogin();
echo 'User\'s URL: ', $user->link, '<br />';
echo 'User\'s name: ', $user->name, '<br />';
echo 'Full details:<br /><pre>', print_r($user, true), '</ pre>';