<?php

namespace GuzzleHttp\Psr7;

use Psr\Http\Message\StreamInterface;

/**
* Provides a buffer stream that can be written to to fill a buffer, and read
* from to remove bytes from the buffer.
*
* This stream returns a "hwm" metadata value that tells upstream consumers
* what the configured high water mark of the stream is, or the maximum
* preferred size of the buffer.
*
* @final
*/
class BufferStream implements StreamInterface
{
private $hwm;
private $buffer = '';

/**
* @param int $hwm High water mark, representing the preferred maximum
* buffer size. If the size of the buffer exceeds the high
* water mark, then calls to write will continue to succeed
* but will return false to inform writers to slow down
* until the buffer has been drained by reading from it.
*/
public function __construct($hwm = 16384)
{
$this->hwm = $hwm;
}

public function __toString()
{
return $this->getContents();
}

public function getContents()
{
$buffer = $this->buffer;
$this->buffer = '';

return $buffer;
}

public function close()
{
$this->buffer = '';
}

public function detach()
{
$this->close();

return null;
}

public function getSize()
{
return strlen($this->buffer);
}

public function isReadable()
{
return true;
}

public function isWritable()
{
return true;
}

public function isSeekable()
{
return false;
}

public function rewind()
{
$this->seek(0);
}

public function seek($offset, $whence = SEEK_SET)
{
throw new \RuntimeException('Cannot seek a BufferStream');
}

public function eof()
{
return strlen($this->buffer) === 0;
}

public function tell()
{
throw new \RuntimeException('Cannot determine the position of a BufferStream');
}

/**
* Reads data from the buffer.
*/
public function read($length)
{
$currentLength = strlen($this->buffer);

if ($length >= $currentLength) {
// No need to slice the buffer because we don't have enough data.
$result = $this->buffer;
$this->buffer = '';
} else {
// Slice up the result to provide a subset of the buffer.
$result = substr($this->buffer, 0, $length);
$this->buffer = substr($this->buffer, $length);
}

return $result;
}

/**
* Writes data to the buffer.
*/
public function write($string)
{
$this->buffer .= $string;

// TODO: What should happen here?
if (strlen($this->buffer) >= $this->hwm) {
return false;
}

return strlen($string);
}

public function getMetadata($key = null)
{
if ($key == 'hwm') {
return $this->hwm;
}

return $key ? null : [];
}
}