A JSON Diff object

JSONUtil.php

<?php
/**
 * This class works on arrays, not on JSON strings
 * directly. You have to use json_encode/json_decode
 * for doing this.
 *
 * @author wrey75@gmail.com
 *
 */

namespace App\Http\Controllers;

class JSONUtil extends Controller
{
    const OLD_ITEM = 'old';
    const NEW_ITEM = 'new';

    /**
     * Compute the difference between $arr1 and $arr2.
     * The result is an array (can be empty) giving the
     * differences between the 2 arrays.
     *
     * Note the differences are expressed in a form you
     * can use the resulting array to "patch" $arr1 to
     * obtain $arr2.
     *
     * This is basically the same stuff than for "diff"
     * command (from UNIX).
     *
     * @param array $arr1 the first array
     * @param array $arr2 the second array
     */
    public static function diff($arr1, $arr2)
    {
        $diff = array();

        // Check the similarities
        foreach ($arr1 as $k1 => $v1) {
            if (isset($arr2[$k1])) {
                $v2 = $arr2[$k1];
                if (is_array($v1) && is_array($v2)) {
                    // 2 arrays: just go further...
                    // .. and explain it's an update!
                    $changes = self::diff($v1, $v2);
                    if (count($changes) > 0) {
                        // If we have no change, simply ignore
                        $diff[$k1] = array('upd' => $changes);
                    }
                    unset($arr2[$k1]); // don't forget
                } else if ($v2 === $v1) {
                    // unset the value on the second array
                    // for the "surplus"
                    unset($arr2[$k1]);
                } else {
                    // Don't mind if arrays or not.
                    $diff[$k1] = array('old' => $v1, 'new' => $v2);
                    unset($arr2[$k1]);
                }
            } else {
                // remove information
                $diff[$k1] = array('old' => $v1);
            }
        }

        // Now, check for new stuff in $arr2
        reset($arr2); // Don't argue it's unnecessary (even I believe you)
        foreach ($arr2 as $k => $v) {
            // OK, it is quite stupid my friend
            $diff[$k] = array('new' => $v);
        }
        return $diff;
    }

    /**
     * @param $arr
     * @param $patch
     * @return mixed
     */
    public static function patch($arr, $patch)
    {
        $dest = $arr;
        foreach ($patch as $k => $v) {
            // $k is the key to change
            // $v contains 'old' and 'new'.

            if (!is_array($v)) {
                error_log('$patch is a bad argument.');
            } else if (isset($v['upd'])) {
                // Update...!
                $dest[$k] = self::patch($arr[$k], $v['upd']);
            } else if (!isset($v['new'])) {
                // Remove the entry
                unset($dest[$k]);
            } else {
                // A new value (can be array by the way).
                $dest[$k] = $v['new'];
            }
        }
        return $dest;
    }

}