Domain helper stuff

DiffObjectCollections.php

<?php

use Assert\Assertion;

trait DiffObjectCollections
{
    /**
     * @var object[]
     */
    protected $items;

    /**
     * Returns the difference between the collections.
     *
     * @param object $other
     *
     * @return array[]
     */
    public function diff($other)
    {
        $removed = [];
        $added = [];

        Assertion::isInstanceOf($other, get_class($this));

        // This is a two stage process, first check for items present in $this->items
        // but not present in $other. They are removed.
        // Then loop trough $other and add none-matched items to $this->items

        // Look for removed items.
        foreach ($this->items as $item) {
            foreach ($other->toArray() as $item2) {
                if ($item->equals($item2)) {
                    // Unchanged, continue with the next item in the main loop.
                    // Else the item is none-matched and removed.
                    continue 2;
                }
            }

            // None of the existing items matched the $item, so the item is removed.
            $removed[] = $item;
        }

        // Look for newly added items.
        foreach ($other->toArray() as $item) {
            foreach ($this->items as $item2) {
                if ($item->equals($item2)) {
                    // Unchanged, continue with the next item in the main loop.
                    // Else the item is none-matched and added.
                    continue 2;
                }
            }

            // None of the existing items matched so its a new one (added).
            $added[] = $item;
        }

        return ['removed' => $removed, 'added' => $added];
    }

    /**
     * @return object[]
     */
    public function toArray()
    {
        return $this->items;
    }

    /**
     * Retrieve an external iterator.
     *
     * @return \ArrayIterator
     */
    public function getIterator()
    {
        return new \ArrayIterator($this->items);
    }
}