IBAN validation in PHP - example use for new Respect rule

Iban.php

<?php

/**
  * Based on https://stackoverflow.com/a/20983340 and improved
  */

namespace OpenAPIServer\ValidationRules;

use Respect\Validation\Rules\AbstractRule;

/**
 * This custom rule will check valid IBAN (coutnry code, length and checksum). Expects trimmed input!
 */

class Iban extends AbstractRule
{
    public function validate($input)
    {
        $iban = strtolower($input);

        // The official min length is 5. Also prevents substringing too short input.
        if(strlen($iban) < 5) return false;

        // lengths of iban per country
        $Countries = array(
            'al'=>28,'ad'=>24,'at'=>20,'az'=>28,'bh'=>22,'be'=>16,'ba'=>20,'br'=>29,'bg'=>22,'cr'=>21,'hr'=>21,'cy'=>28,'cz'=>24,
            'dk'=>18,'do'=>28,'ee'=>20,'fo'=>18,'fi'=>18,'fr'=>27,'ge'=>22,'de'=>22,'gi'=>23,'gr'=>27,'gl'=>18,'gt'=>28,'hu'=>28,
            'is'=>26,'ie'=>22,'il'=>23,'it'=>27,'jo'=>30,'kz'=>20,'kw'=>30,'lv'=>21,'lb'=>28,'li'=>21,'lt'=>20,'lu'=>20,'mk'=>19,
            'mt'=>31,'mr'=>27,'mu'=>30,'mc'=>27,'md'=>24,'me'=>22,'nl'=>18,'no'=>15,'pk'=>24,'ps'=>29,'pl'=>28,'pt'=>25,'qa'=>29,
            'ro'=>24,'sm'=>27,'sa'=>24,'rs'=>22,'sk'=>24,'si'=>19,'es'=>24,'se'=>24,'ch'=>21,'tn'=>24,'tr'=>26,'ae'=>23,'gb'=>22,'vg'=>24
        );
        // subsitution scheme for letters
        $Chars = array(
            'a'=>10,'b'=>11,'c'=>12,'d'=>13,'e'=>14,'f'=>15,'g'=>16,'h'=>17,'i'=>18,'j'=>19,'k'=>20,'l'=>21,'m'=>22,
            'n'=>23,'o'=>24,'p'=>25,'q'=>26,'r'=>27,'s'=>28,'t'=>29,'u'=>30,'v'=>31,'w'=>32,'x'=>33,'y'=>34,'z'=>35
        );

        // Check input country code is known
        if (!isset($Countries[ substr($iban,0,2) ])) return false;

        // Check total length for given country code
        if (strlen($iban) != $Countries[ substr($iban,0,2) ]) { return false; }

        // Move first 4 chars to end
        $MovedChar = substr($iban, 4) . substr($iban,0,4);

        // Replace letters by their numeric variant
        $MovedCharArray = str_split($MovedChar);
        $NewString = "";
        foreach ($MovedCharArray as $k => $v) {
            if ( !is_numeric($MovedCharArray[$k]) ) {
                // if any other cahracter then the known letters, its bogus
                if(!isset($Chars[$MovedCharArray[$k]])) return false;
                $MovedCharArray[$k] = $Chars[$MovedCharArray[$k]];
            }
            $NewString .= $MovedCharArray[$k];
        }

        // Now we just need to validate the checksum
        // Use bcmod if available
        if (function_exists("bcmod")) { return bcmod($NewString, '97') == 1; }

        // Else use this workaround
        // http://au2.php.net/manual/en/function.bcmod.php#38474
        $x = $NewString; $y = "97";
        $take = 5; $mod = "";
        do {
            $a = (int)$mod . substr($x, 0, $take);
            $x = substr($x, $take);
            $mod = $a % $y;
        }
        while (strlen($x));
        return (int)$mod == 1;

    }
}