<?php

/*

 * This file is part of the Symfony package.

 *

 * (c) Fabien Potencier <fabien@symfony.com>

 *

 * For the full copyright and license information, please view the LICENSE

 * file that was distributed with this source code.

 */

namespace Symfony\Component\CssSelector;

/**

 * TokenStream represents a stream of CSS Selector tokens.

 *

 * This component is a port of the Python lxml library,

 * which is copyright Infrae and distributed under the BSD license.

 *

 * @author Fabien Potencier <fabien@symfony.com>

 */

class TokenStream

{

    private $used;

    private $tokens;

    private $source;

    private $peeked;

    private $peeking;

    /**

     * Constructor.

     *

     * @param array $tokens The tokens that make the stream.

     * @param mixed $source The source of the stream.

     */

    public function __construct($tokens, $source = null)

    {

        $this->used = array();

        $this->tokens = $tokens;

        $this->source = $source;

        $this->peeked = null;

        $this->peeking = false;

    }

    /**

     * Gets the tokens that have already been visited in this stream.

     *

     * @return array

     */

    public function getUsed()

    {

        return $this->used;

    }

    /**

     * Gets the next token in the stream or null if there is none.

     * Note that if this stream was set to be peeking its behavior

     * will be restored to not peeking after this operation.

     *

     * @return mixed

     */

    public function next()

    {

        if ($this->peeking) {

            $this->peeking = false;

            $this->used[] = $this->peeked;

            return $this->peeked;

        }

        if (!count($this->tokens)) {

            return null;

        }

        $next = array_shift($this->tokens);

        $this->used[] = $next;

        return $next;

    }

    /**

     * Peeks for the next token in this stream. This means that the next token

     * will be returned but it won't be considered as used (visited) until the

     * next() method is invoked.

     * If there are no remaining tokens null will be returned.

     *

     * @see next()

     *

     * @return mixed

     */

    public function peek()

    {

        if (!$this->peeking) {

            if (!count($this->tokens)) {

                return null;

            }

            $this->peeked = array_shift($this->tokens);

            $this->peeking = true;

        }

        return $this->peeked;

    }

}