<?php

namespace GuzzleHttp\Psr7;

use Psr\Http\Message\StreamInterface;
use RuntimeException;


/**
 * Decorator used to return only a subset of a stream
 */
class LimitStream implements StreamInterface {
	use StreamDecoratorTrait;

	/** @var int Offset to start reading from */
	private $offset;

	/** @var int Limit the number of bytes that can be read */
	private $limit;

	/**
	 * @param StreamInterface $stream Stream to wrap
	 * @param int $limit Total number of bytes to allow to be read
	 *                                from the stream. Pass -1 for no limit.
	 * @param int $offset Position to seek to before reading (only
	 *                                works on seekable streams).
	 */
	public function __construct(
		StreamInterface $stream,
		$limit = - 1,
		$offset = 0
	) {
		$this->stream = $stream;
		$this->setLimit( $limit );
		$this->setOffset( $offset );
	}

	/**
	 * Set the limit of bytes that the decorator allows to be read from the
	 * stream.
	 *
	 * @param int $limit Number of bytes to allow to be read from the stream.
	 *                   Use -1 for no limit.
	 */
	public function setLimit( $limit ) {
		$this->limit = $limit;
	}

	/**
	 * Set the offset to start limiting from
	 *
	 * @param int $offset Offset to seek to and begin byte limiting from
	 *
	 * @throws RuntimeException if the stream cannot be seeked.
	 */
	public function setOffset( $offset ) {
		$current = $this->stream->tell();

		if ( $current !== $offset ) {
			// If the stream cannot seek to the offset position, then read to it
			if ( $this->stream->isSeekable() ) {
				$this->stream->seek( $offset );
			} elseif ( $current > $offset ) {
				throw new RuntimeException( "Could not seek to stream offset $offset" );
			} else {
				$this->stream->read( $offset - $current );
			}
		}

		$this->offset = $offset;
	}

	public function eof() {
		// Always return true if the underlying stream is EOF
		if ( $this->stream->eof() ) {
			return true;
		}

		// No limit and the underlying stream is not at EOF
		if ( $this->limit == - 1 ) {
			return false;
		}

		return $this->stream->tell() >= $this->offset + $this->limit;
	}

	/**
	 * Returns the size of the limited subset of data
	 * {@inheritdoc}
	 */
	public function getSize() {
		if ( null === ( $length = $this->stream->getSize() ) ) {
			return null;
		} elseif ( $this->limit == - 1 ) {
			return $length - $this->offset;
		} else {
			return min( $this->limit, $length - $this->offset );
		}
	}

	/**
	 * Allow for a bounded seek on the read limited stream
	 * {@inheritdoc}
	 */
	public function seek( $offset, $whence = SEEK_SET ) {
		if ( $whence !== SEEK_SET || $offset < 0 ) {
			throw new RuntimeException( sprintf(
				'Cannot seek to offset %s with whence %s',
				$offset,
				$whence
			) );
		}

		$offset += $this->offset;

		if ( $this->limit !== - 1 ) {
			if ( $offset > $this->offset + $this->limit ) {
				$offset = $this->offset + $this->limit;
			}
		}

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

	/**
	 * Give a relative tell()
	 * {@inheritdoc}
	 */
	public function tell() {
		return $this->stream->tell() - $this->offset;
	}

	public function read( $length ) {
		if ( $this->limit == - 1 ) {
			return $this->stream->read( $length );
		}

		// Check if the current position is less than the total allowed
		// bytes + original offset
		$remaining = ( $this->offset + $this->limit ) - $this->stream->tell();
		if ( $remaining > 0 ) {
			// Only return the amount of requested data, ensuring that the byte
			// limit is not exceeded
			return $this->stream->read( min( $remaining, $length ) );
		}

		return '';
	}
}
