<?php

namespace GuzzleHttp\Psr7;

use Psr\Http\Message\StreamInterface;

/**
* Stream decorator that can cache previously read bytes from a sequentially
* read stream.
*
* @final
*/
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. The cursor is assumed to be at the beginning of the stream.
* @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(Utils::tryFopen('php://temp', 'r+'));
}

public function getSize()
{
$remoteSize = $this->remoteStream->getSize();

if (null === $remoteSize) {
return null;
}

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

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()
{
$target = new FnStream(['write' => 'strlen']);
Utils::copyToStream($this, $target);

return $this->tell();
}
}