Iterator over combinations of array elements.

Combinator.php

<?php

class Combinator implements \Iterator
{
    /**
     * @var array
     */
    private $data;

    /**
     * @var array
     */
    private $levels;

    /**
     * @var int
     */
    private $position;

    /**
     * Constructor.
     *
     * @param array $data
     */
    public function __construct(array $data)
    {
        $this->data = $data;
        $this->rewind();
    }

    public function rewind()
    {
        $this->levels = array_fill(0, count($this->data), 0);
        $this->position = 0;
    }

    public function current()
    {
        $data = $this->data;
        $comb = [];

        foreach ($this->levels as $level => $idx) {
            $comb[] = array_splice($data, $idx, 1)[0];
        }

        return $comb;
    }

    public function key()
    {
        return $this->position;
    }

    public function valid()
    {
        return 0 == $this->position || array_sum($this->levels) > 0;
    }

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

        foreach ($this->levels as $level => $idx) {
            ++$idx;

            if ($idx >= count($this->levels) - $level) {
                $idx = 0;
            }

            $this->levels[$level] = $idx;
        }
    }
}