<?php
/*
 * Copyright 2015 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.
 */

namespace Google\Auth\Credentials;

use Google\Auth\CredentialsLoader;
use Google\Auth\OAuth2;

/**
 * ServiceAccountCredentials supports authorization using a Google service
 * account.
 *
 * (cf https://developers.google.com/accounts/docs/OAuth2ServiceAccount)
 *
 * It's initialized using the json key file that's downloadable from developer
 * console, which should contain a private_key and client_email fields that it
 * uses.
 *
 * Use it with AuthTokenMiddleware to authorize http requests:
 *
 *   use Google\Auth\Credentials\ServiceAccountCredentials;
 *   use Google\Auth\Middleware\AuthTokenMiddleware;
 *   use GuzzleHttp\Client;
 *   use GuzzleHttp\HandlerStack;
 *
 *   $sa = new ServiceAccountCredentials(
 *       'https://www.googleapis.com/auth/taskqueue',
 *       '/path/to/your/json/key_file.json'
 *   );
 *   $middleware = new AuthTokenMiddleware($sa);
 *   $stack = HandlerStack::create();
 *   $stack->push($middleware);
 *
 *   $client = new Client([
 *       'handler' => $stack,
 *       'base_uri' => 'https://www.googleapis.com/taskqueue/v1beta2/projects/',
 *       'auth' => 'google_auth' // authorize all requests
 *   ]);
 *
 *   $res = $client->get('myproject/taskqueues/myqueue');
 */
class ServiceAccountCredentials extends CredentialsLoader
{
    /**
     * The OAuth2 instance used to conduct authorization.
     *
     * @var OAuth2
     */
    protected $auth;

    /**
     * Create a new ServiceAccountCredentials.
     *
     * @param string|array $scope the scope of the access request, expressed
     *   either as an Array or as a space-delimited String.
     * @param string|array $jsonKey JSON credential file path or JSON credentials
     *   as an associative array
     * @param string $sub an email address account to impersonate, in situations when
     *   the service account has been delegated domain wide access.
     */
    public function __construct(
        $scope,
        $jsonKey,
        $sub = null
    ) {
        if (is_string($jsonKey)) {
            if (!file_exists($jsonKey)) {
                throw new \InvalidArgumentException('file does not exist');
            }
            $jsonKeyStream = file_get_contents($jsonKey);
            if (!$jsonKey = json_decode($jsonKeyStream, true)) {
                throw new \LogicException('invalid json for auth config');
            }
        }
        if (!array_key_exists('client_email', $jsonKey)) {
            throw new \InvalidArgumentException(
                'json key is missing the client_email field');
        }
        if (!array_key_exists('private_key', $jsonKey)) {
            throw new \InvalidArgumentException(
                'json key is missing the private_key field');
        }
        $this->auth = new OAuth2([
            'audience' => self::TOKEN_CREDENTIAL_URI,
            'issuer' => $jsonKey['client_email'],
            'scope' => $scope,
            'signingAlgorithm' => 'RS256',
            'signingKey' => $jsonKey['private_key'],
            'sub' => $sub,
            'tokenCredentialUri' => self::TOKEN_CREDENTIAL_URI,
        ]);
    }

    /**
     * @param callable $httpHandler
     *
     * @return array
     */
    public function fetchAuthToken(callable $httpHandler = null)
    {
        return $this->auth->fetchAuthToken($httpHandler);
    }

    /**
     * @return string
     */
    public function getCacheKey()
    {
        $key = $this->auth->getIssuer() . ':' . $this->auth->getCacheKey();
        if ($sub = $this->auth->getSub()) {
            $key .= ':' . $sub;
        }

        return $key;
    }

    /**
     * @return array
     */
    public function getLastReceivedToken()
    {
        return $this->auth->getLastReceivedToken();
    }

    /**
     * Updates metadata with the authorization token.
     *
     * @param array $metadata metadata hashmap
     * @param string $authUri optional auth uri
     * @param callable $httpHandler callback which delivers psr7 request
     *
     * @return array updated metadata hashmap
     */
    public function updateMetadata(
        $metadata,
        $authUri = null,
        callable $httpHandler = null
    ) {
        // scope exists. use oauth implementation
        $scope = $this->auth->getScope();
        if (!is_null($scope)) {
            return parent::updateMetadata($metadata, $authUri, $httpHandler);
        }

        // no scope found. create jwt with the auth uri
        $credJson = array(
            'private_key' => $this->auth->getSigningKey(),
            'client_email' => $this->auth->getIssuer(),
        );
        $jwtCreds = new ServiceAccountJwtAccessCredentials($credJson);

        return $jwtCreds->updateMetadata($metadata, $authUri, $httpHandler);
    }

    /**
     * @param string $sub an email address account to impersonate, in situations when
     *   the service account has been delegated domain wide access.
     */
    public function setSub($sub)
    {
        $this->auth->setSub($sub);
    }
}