<?php
/*
 * Copyright 2014 Google 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.
 */
/*
 * WARNING - this class depends on the Google App Engine PHP library
 * which is 5.3 and above only, so if you include this in a PHP 5.2
 * setup or one without 5.3 things will blow up.
 */
use google\appengine\api\app_identity\AppIdentityService;
require_once realpath(dirname(__FILE__) . '/../../../autoload.php');

/**
 * Authentication via the Google App Engine App Identity service.
 */
class Google_Auth_AppIdentity extends Google_Auth_Abstract
{

    const CACHE_PREFIX = "Google_Auth_AppIdentity::";

    private $key = null;

    private $client;

    private $token = false;

    private $tokenScopes = false;

    public function __construct(Google_Client $client, $config = null)
    {
        $this->client = $client;
    }

    /**
     * Retrieve an access token for the scopes supplied.
     */
    public function authenticateForScope($scopes)
    {
        if ($this->token && $this->tokenScopes == $scopes) {
            return $this->token;
        }
        $cacheKey = self::CACHE_PREFIX;
        if (is_string($scopes)) {
            $cacheKey .= $scopes;
        } else 
            if (is_array($scopes)) {
                $cacheKey .= implode(":", $scopes);
            }
        $this->token = $this->client->getCache()->get($cacheKey);
        if (! $this->token) {
            $this->token = AppIdentityService::getAccessToken($scopes);
            if ($this->token) {
                $this->client->getCache()->set($cacheKey, $this->token);
            }
        }
        $this->tokenScopes = $scopes;
        return $this->token;
    }

    /**
     * Perform an authenticated / signed apiHttpRequest.
     * This function takes the apiHttpRequest, calls apiAuth->sign on it
     * (which can modify the request in what ever way fits the auth mechanism)
     * and then calls apiCurlIO::makeRequest on the signed request
     *
     * @param Google_Http_Request $request            
     * @return Google_Http_Request The resulting HTTP response including the
     *         responseHttpCode, responseHeaders and responseBody.
     */
    public function authenticatedRequest(Google_Http_Request $request)
    {
        $request = $this->sign($request);
        return $this->client->getIo()->makeRequest($request);
    }

    public function sign(Google_Http_Request $request)
    {
        if (! $this->token) {
            // No token, so nothing to do.
            return $request;
        }
        $this->client->getLogger()->debug('App Identity authentication');
        // Add the OAuth2 header to the request
        $request->setRequestHeaders(array(
            'Authorization' => 'Bearer ' . $this->token['access_token']
        ));
        return $request;
    }
}
