iterator

<?php

class Collection implements \Iterator
{
    /**
     * @var Room[][]
     */
    private $rooms = [];

    /**
     * @return Room|false
     */
    public function current()
    {
        if (null === $key = key($this->rooms)) {
            return false;
        }

        return current($this->rooms[$key]);
    }

    public function next()
    {
        if (null === $key = key($this->rooms)) {
            return;
        }

        if (next($this->rooms[$key]) !== false) {
            return;
        }

        next($this->rooms);
        if (null === $key = key($this->rooms)) {
            return;
        }

        reset($this->rooms[$key]);
    }

    /**
     * @return Identifier|null
     */
    public function key()
    {
        if (false === $room = $this->current()) {
            return null;
        }

        return $room->getIdentifier();
    }

    public function valid()
    {
        return $this->current() !== false;
    }

    public function rewind()
    {
        reset($this->rooms);

        if (null !== $key = key($this->rooms)) {
            reset($this->rooms[$key]);
        }
    }
}