<?php
class Context
{
    private $_commands;
    private $_currentIndex = 0;

    public function __construct($command)
    {
        $this->_commands = preg_split('/ +/', trim($command));
    }

    public function next()
    {
        $this->_currentIndex++;

        return $this;
    }

    public function getCurrentCommand()
    {
        if (!array_key_exists($this->_currentIndex, $this->_commands)) {
            return null;
        }
        return trim($this->_commands[$this->_currentIndex]);
    }
}