MRZ validate algorithm for passports. http://en.wikipedia.org/wiki/Machine-readable_passport

MrzValidator.kt

object MrzValidator {

    private val COEFFICIENTS = listOf(7, 3, 1)
    private const val EMPTY = '<'

    /**
     * Samples:
     * - Document number: isValid("D123456785", 0, 9) actual document number is "D12345678" check character is "5"
     * - Date: isValid("7903063", 0, 6)) actual date is "790306" check character is "3"
     */
    fun isValid(str: String, start: Int, end: Int): Boolean {
        if (str.length > end && end > start) {
            val data = str.substring(start, end)
            val check = str.substring(end, end + 1)
            return try {
                val calculatedCheck = calculateCheck(data)
                println("Data: $data check character: $check calculated check character: $calculatedCheck")
                calculatedCheck == check.toInt()
            } catch (e: Exception) {
                false
            }
        }
        return false
    }

    private fun calculateCheck(str: String): Int {
        var total = 0
        str.forEachIndexed { index, c ->
            total += getCharValue(c) * COEFFICIENTS[index % COEFFICIENTS.size]
        }
        return total % 10
    }

    private fun getCharValue(char: Char): Int {
        return when (char) {
            EMPTY -> 0
            in '0'..'9' -> char - '0'
            in 'A'..'Z' -> char - 'A' + 10
            else -> throw RuntimeException("Not valid character")
        }
    }
}