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<?php

namespace GuzzleHttp\Psr7;

use Psr\Http\Message\StreamInterface;

/**

 * Stream decorator that can cache previously read bytes from a sequentially

 * read stream.

 */

class CachingStream implements StreamInterface

{

    use StreamDecoratorTrait;

    /** @var StreamInterface Stream being wrapped */

    private $remoteStream;

    /** @var int Number of bytes to skip reading due to a write on the buffer */

    private $skipReadBytes = 0;

    /**

     * We will treat the buffer object as the body of the stream

     *

     * @param StreamInterface $stream Stream to cache

     * @param StreamInterface $target Optionally specify where data is cached

     */

    public function __construct(

        StreamInterface $stream,

        StreamInterface $target = null

    ) {

        $this->remoteStream = $stream;

        $this->stream = $target ?: new Stream(fopen('php://temp', 'r+'));

    }

    public function getSize()

    {

        return max($this->stream->getSize(), $this->remoteStream->getSize());

    }

    public function rewind()

    {

        $this->seek(0);

    }

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

    {

        if ($whence == SEEK_SET) {

            $byte = $offset;

        } elseif ($whence == SEEK_CUR) {

            $byte = $offset + $this->tell();

        } elseif ($whence == SEEK_END) {

            $size = $this->remoteStream->getSize();

            if ($size === null) {

                $size = $this->cacheEntireStream();

            }

            $byte = $size + $offset;

        } else {

            throw new \InvalidArgumentException('Invalid whence');

        }

        $diff = $byte - $this->stream->getSize();

        if ($diff > 0) {

            // Read the remoteStream until we have read in at least the amount

            // of bytes requested, or we reach the end of the file.

            while ($diff > 0 && !$this->remoteStream->eof()) {

                $this->read($diff);

                $diff = $byte - $this->stream->getSize();

            }

        } else {

            // We can just do a normal seek since we've already seen this byte.

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

        }

    }

    public function read($length)

    {

        // Perform a regular read on any previously read data from the buffer

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

        $remaining = $length - strlen($data);

        // More data was requested so read from the remote stream

        if ($remaining) {

            // If data was written to the buffer in a position that would have

            // been filled from the remote stream, then we must skip bytes on

            // the remote stream to emulate overwriting bytes from that

            // position. This mimics the behavior of other PHP stream wrappers.

            $remoteData = $this->remoteStream->read(

                $remaining + $this->skipReadBytes

            );

            if ($this->skipReadBytes) {

                $len = strlen($remoteData);

                $remoteData = substr($remoteData, $this->skipReadBytes);

                $this->skipReadBytes = max(0, $this->skipReadBytes - $len);

            }

            $data .= $remoteData;

            $this->stream->write($remoteData);

        }

        return $data;

    }

    public function write($string)

    {

        // When appending to the end of the currently read stream, you'll want

        // to skip bytes from being read from the remote stream to emulate

        // other stream wrappers. Basically replacing bytes of data of a fixed

        // length.

        $overflow = (strlen($string) + $this->tell()) - $this->remoteStream->tell();

        if ($overflow > 0) {

            $this->skipReadBytes += $overflow;

        }

        return $this->stream->write($string);

    }

    public function eof()

    {

        return $this->stream->eof() && $this->remoteStream->eof();

    }

    /**

     * Close both the remote stream and buffer stream

     */

    public function close()

    {

        $this->remoteStream->close() && $this->stream->close();

    }

    private function cacheEntireStream()

    {

        $target = new FnStream(['write' => 'strlen']);

        copy_to_stream($this, $target);

        return $this->tell();

    }

}