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<?php

namespace Aws;

use GuzzleHttp\Psr7\StreamDecoratorTrait;

use Psr\Http\Message\StreamInterface;

/**

 * Stream decorator that calculates a rolling hash of the stream as it is read.

 */

class HashingStream implements StreamInterface

{

    use StreamDecoratorTrait;

    /** @var StreamInterface */

    private $stream;

    /** @var HashInterface */

    private $hash;

    /** @var callable|null */

    private $callback;

    /**

     * @param StreamInterface $stream     Stream that is being read.

     * @param HashInterface   $hash       Hash used to calculate checksum.

     * @param callable        $onComplete Optional function invoked when the

     *                                    hash calculation is completed.

     */

    public function __construct(

        StreamInterface $stream,

        HashInterface $hash,

        ?callable $onComplete = null

    ) {

        $this->stream = $stream;

        $this->hash = $hash;

        $this->callback = $onComplete;

    }

    public function read($length): string

    {

        $data = $this->stream->read($length);

        $this->hash->update($data);

        if ($this->eof()) {

            $result = $this->hash->complete();

            if ($this->callback) {

                call_user_func($this->callback, $result);

            }

        }

        return $data;

    }

    public function seek($offset, $whence = SEEK_SET): void

    {

        // Seeking arbitrarily is not supported.

        if ($offset !== 0) {

            return;

        }

        $this->hash->reset();

        $this->stream->seek($offset);

    }

}