<?php

/**

 * Copyright 2010-2013 Amazon.com, Inc. or its affiliates. All Rights Reserved.

 *

 * Licensed under the Apache License, Version 2.0 (the "License").

 * You may not use this file except in compliance with the License.

 * A copy of the License is located at

 *

 * http://aws.amazon.com/apache2.0

 *

 * or in the "license" file accompanying this file. This file 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 Aws\S3;



use Aws\Common\Exception\RuntimeException;

use Aws\Common\Exception\UnexpectedValueException;

use Guzzle\Http\EntityBody;

use Guzzle\Http\ReadLimitEntityBody;

use Guzzle\Http\EntityBodyInterface;

use Guzzle\Service\Resource\Model;



/**

 * Allows you to resume the download of a partially downloaded object.

 *

 * Downloads objects from Amazon S3 in using "Range" downloads. This allows a partially downloaded object to be resumed

 * so that only the remaining portion of the object is downloaded.

 */

class ResumableDownload

{

    /** @var S3Client The S3 client to use to download objects and issue HEAD requests */

    protected $client;



    /** @var \Guzzle\Service\Resource\Model Model object returned when the initial HeadObject operation was called */

    protected $meta;



    /** @var array Array of parameters to pass to a GetObject operation */

    protected $params;



    /** @var \Guzzle\Http\EntityBody Where the object will be downloaded */

    protected $target;



    /**

     * @param S3Client                            $client Client to use when executing requests

     * @param string                              $bucket Bucket that holds the object

     * @param string                              $key    Key of the object

     * @param string|resource|EntityBodyInterface $target Where the object should be downloaded to. Pass a string to

     *                                                    save the object to a file, pass a resource returned by

     *                                                    fopen() to save the object to a stream resource, or pass a

     *                                                    Guzzle EntityBody object to save the contents to an

     *                                                    EntityBody.

     * @param array                               $params Any additional GetObject or HeadObject parameters to use

     *                                                    with each command issued by the client. (e.g. pass "Version"

     *                                                    to download a specific version of an object)

     * @throws RuntimeException if the target variable points to a file that cannot be opened

     */

    public function __construct(S3Client $client, $bucket, $key, $target, array $params = array())

    {

        $this->params = $params;

        $this->client = $client;

        $this->params['Bucket'] = $bucket;

        $this->params['Key'] = $key;



        // If a string is passed, then assume that the download should stream to a file on disk

        if (is_string($target)) {

            if (!($target = fopen($target, 'a+'))) {

                throw new RuntimeException("Unable to open {$target} for writing");

            }

            // Always append to the file

            fseek($target, 0, SEEK_END);

        }



        // Get the metadata and Content-MD5 of the object

        $this->target = EntityBody::factory($target);

    }



    /**

     * Get the bucket of the download

     *

     * @return string

     */

    public function getBucket()

    {

        return $this->params['Bucket'];

    }



    /**

     * Get the key of the download

     *

     * @return string

     */

    public function getKey()

    {

        return $this->params['Key'];

    }



    /**

     * Get the file to which the contents are downloaded

     *

     * @return string

     */

    public function getFilename()

    {

        return $this->target->getUri();

    }



    /**

     * Download the remainder of the object from Amazon S3

     *

     * Performs a message integrity check if possible

     *

     * @return Model

     */

    public function __invoke()

    {

        $command = $this->client->getCommand('HeadObject', $this->params);

        $this->meta = $command->execute();



        if ($this->target->ftell() >= $this->meta['ContentLength']) {

            return false;

        }



        $this->meta['ContentMD5'] = (string) $command->getResponse()->getHeader('Content-MD5');



        // Use a ReadLimitEntityBody so that rewinding the stream after an error does not cause the file pointer

        // to enter an inconsistent state with the data being downloaded

        $this->params['SaveAs'] = new ReadLimitEntityBody(

            $this->target,

            $this->meta['ContentLength'],

            $this->target->ftell()

        );



        $result = $this->getRemaining();

        $this->checkIntegrity();



        return $result;

    }



    /**

     * Send the command to get the remainder of the object

     *

     * @return Model

     */

    protected function getRemaining()

    {

        $current = $this->target->ftell();

        $targetByte = $this->meta['ContentLength'] - 1;

        $this->params['Range'] = "bytes={$current}-{$targetByte}";



        // Set the starting offset so that the body is never seeked to before this point in the event of a retry

        $this->params['SaveAs']->setOffset($current);

        $command = $this->client->getCommand('GetObject', $this->params);



        return $command->execute();

    }



    /**

     * Performs an MD5 message integrity check if possible

     *

     * @throws UnexpectedValueException if the message does not validate

     */

    protected function checkIntegrity()

    {

        if ($this->target->isReadable() && $expected = $this->meta['ContentMD5']) {

            $actual = $this->target->getContentMd5();

            if ($actual != $expected) {

                throw new UnexpectedValueException(

                    "Message integrity check failed. Expected {$expected} but got {$actual}."

                );

            }

        }

    }

}