Extension function to format IBAN Strings

FormatIBAN.kt

fun String.formatIBAN(): String {
    val iban = replace("\\s+".toRegex(), "").uppercase(Locale.getDefault())
    val maxLength = (iban.length * 1.25).roundToInt()
    val result = StringBuilder(maxLength)
    iban.forEachIndexed { index, c ->
        when {
            index > 0 && index % 4 == 0 -> result.append(" $c")
            else -> result.append(c)
        }
    }
    return result.toString()
}