PHP `itertools.groupby` implementation

GroupIterator.php

<?php

class GroupIterator implements Iterator
{
    protected $keyfunc;
    protected $iter;

    protected $key = null;
    protected $value = null;

    protected $group = null;

    public function __construct(Iterator $iterator, Closure $key = null) {
        if ($key === null) {
            $key = function($k) {
                return $k;
            };
        }

        $this->keyfunc = $key;
        $this->iter = $iterator;
    }

    protected function grouper($group) {
        while ($group === $this->key) {
            yield $this->value;

            next($this->iter);

            $this->value = current($this->iter);
            $this->key = call_user_func($this->keyfunc, $this->value);
        }
    }

    public function current() {
        return $this->grouper($this->group);
    }

    public function next() {
        while ($this->group === $this->key) {
            next($this->iter);

            $this->value = current($this->iter);
            $this->key = call_user_func($this->keyfunc, $this->value);
        }

        $this->group = $this->key;
    }

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

    public function valid() {
        return key($this->iter) !== null;
    }

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

        $this->value = current($this->iter);
        $this->group = $this->key = call_user_func($this->keyfunc, $this->value);
    }
}

GroupIteratorAggregate.php

<?php

class GroupIteratorAggregate implements \IteratorAggregate
{
    protected $keyfunc;
    protected $iter;

    public function __construct(Iterator $iterator, Closure $key = null) {
        if ($key === null) {
            $key = function($k) {
                return $k;
            };
        }

        $this->keyfunc = $key;
        $this->iter = $iterator;
    }

    public function getIterator()
    {
        $array = array();

        foreach ($this->iter as $value) {
            $group = call_user_func($this->keyfunc, $value);
            $array[$group] = $this->grouper($group, $value);
        }

        return new \ArrayIterator($array);
    }

    protected function grouper($group, $value) {
        do {
            yield $value;

            next($this->iter);

            $value = current($this->iter);
            $key = call_user_func($this->keyfunc, $value);
        } while ($key === $group);
    }
}

GroupIteratorTest.php

<?php

// @see https://docs.python.org/2/library/itertools.html#itertools.groupby

include 'GroupIterator.php';
include 'GroupIteratorAggregate.php';

function iterator_to_array_deep(\Traversable $iterator, $use_keys = true) {
    $array = array();
    foreach ($iterator as $key => $value) {
        if ($value instanceof \Iterator) {
            $value = iterator_to_array_deep($value, $use_keys);
        }
        if ($use_keys) {
            $array[$key] = $value;
        } else {
            $array[] = $value;
        }
    }
    return $array;
}

class GroupIteratorTest extends \PHPUnit_Framework_TestCase
{
    /**
     * @dataProvider provide
     */
    public function test($string, array $expected)
    {
        $array = new ArrayIterator(str_split($string));
        $group = new GroupIterator($array);

        $this->assertEquals($expected, iterator_to_array_deep($group));
    }

    /**
     * @dataProvider provide
     */
    public function testAggregate($string, array $expected)
    {
        $array = new ArrayIterator(str_split($string));
        $group = new GroupIteratorAggregate($array);

        $this->assertEquals($expected, iterator_to_array_deep($group));
    }

    public function provide()
    {
        return array(
            array('A', array('A' => array('A'))),
            array('AA', array('A' => array('A', 'A'))),
            array('AAB', array('A' => array('A', 'A'), 'B' => array('B'))),
        );
    }
}