Create IBAN from bank account in PHP

BankAccountConverter.php

<?php
/**
 * BankAccountConverter class
 *
 * @author aaronfc <[email protected]>
 */

class BankAccountConverter {

	/**
	 * Static constructor
	 * @return BankAccountConverter
	 */
	public static function create() {
		return new static();
	}

	/**
	 * Get a bank account as a plain string and a country code and returns its IBAN equivalent.
	 * @param string $fullBankAccount
	 * @return string
	 */
	public function toIban($fullBankAccount, $countryCode) {
		$checksum = $this->calculateChecksum($fullBankAccount, $countryCode);
		return $countryCode . $checksum . $fullBankAccount;
	}

	/**
	 * Calculates checksum for a given bank account and its country code.
	 * @param $fullBankAccount
	 * @param string $countryCode
	 * @return string
	 */
	private function calculateChecksum($fullBankAccount, $countryCode)
	{
		$asArray = str_split(strtoupper($fullBankAccount . str_pad($countryCode, 4 , "0")));
		$numeric = array_map(array($this, "castAlphabeticCharToEquivalentNumber"), $asArray);
		$numeric = join('', $numeric);
		// bcmod used because regular mod operator can't handle such a big number (overflowed int)
		return str_pad(98 - bcmod($numeric,97), 2, "0", STR_PAD_LEFT);
	}

	/**
	 * Cast alphabetic character to number as required by IBAN generation algorithm.
	 * Thus: A=10, B=11, ... Z=35
	 *
	 * @param $char
	 * @return int
	 */
	private function castAlphabeticCharToEquivalentNumber($char) {
		if (ctype_alpha($char)){
			return ord($char) - 55;
		}
		return $char;
	}
}