IteratorPropertySorterIterator.php

<?php
/**
 * @author     Michael Calcinai <michael@calcin.ai>
 */

class IteratorPropertySorterIterator implements \Iterator
{

    /**
     * @var \Iterator[]
     */
    private $iterators;
    /**
     * @var callable
     */
    private $sort_callback;


    /**
     * IteratorPropertySorterIterator constructor.
     * @param callable $sort_callback
     */
    public function __construct(callable $sort_callback)
    {
        $this->iterators = array_slice(func_get_args(), 1);
        $this->sort_callback = $sort_callback;
    }

    public function addIterator(\Iterator $iterator)
    {
        $this->iterators[] = $iterator;
        return $this;
    }


    /**
     * @return \Iterator|null
     */
    public function getLeadingIterator()
    {

        /** @var \Iterator $leading_iterator */
        $leading_iterator = null;

        foreach ($this->iterators as $iterator) {

            //Skip any that have run out
            if (!$iterator->valid()) {
                continue;
            }

            //First iteration or higher value
            if ($leading_iterator === null || call_user_func($this->sort_callback, $iterator->current(),
                    $leading_iterator->current())
            ) {
                $leading_iterator = $iterator;
            }
        }

        return $leading_iterator;
    }


    /**
     * Return the current element
     * @link http://php.net/manual/en/iterator.current.php
     * @return mixed Can return any type.
     * @since 5.0.0
     */
    public function current()
    {
        $leading_iterator = $this->getLeadingIterator();

        if ($leading_iterator !== null) {
            return $leading_iterator->current();
        }

        return null;
    }

    /**
     * Move forward to next element
     * @link http://php.net/manual/en/iterator.next.php
     * @return void Any returned value is ignored.
     * @since 5.0.0
     */
    public function next()
    {
        $leading_iterator = $this->getLeadingIterator();

        if ($leading_iterator !== null) {
            $leading_iterator->next();
        }
    }

    /**
     * Return the key of the current element
     * @link http://php.net/manual/en/iterator.key.php
     * @return mixed scalar on success, or null on failure.
     * @since 5.0.0
     */
    public function key()
    {
        $leading_iterator = $this->getLeadingIterator();

        if ($leading_iterator !== null) {
            return $leading_iterator->key();
        }

        return null;
    }

    /**
     * Checks if current position is valid
     * @link http://php.net/manual/en/iterator.valid.php
     * @return boolean The return value will be casted to boolean and then evaluated.
     * Returns true on success or false on failure.
     * @since 5.0.0
     */
    public function valid()
    {
        //Only need one to be valid
        foreach ($this->iterators as $iterator) {
            if ($iterator->valid()) {
                return true;
            }
        }
        return false;
    }

    /**
     * Rewind the Iterator to the first element
     * @link http://php.net/manual/en/iterator.rewind.php
     * @return void Any returned value is ignored.
     * @since 5.0.0
     */
    public function rewind()
    {
        //Will throw an exception if any have been started
        foreach ($this->iterators as $iterator) {
            $iterator->rewind();
        }
    }
}