/**
 * The `CardNumberGenerator` class generates random credit card numbers adhering to the Luhn algorithm.
 *
 * @property cartIdLength The length of the card ID portion in the generated card number.
 * @property bin The BIN (Bank Identification Number) value representing the card network.
 */
class CardNumberGenerator {

    private var cartIdLength: Int = DEFAULT_CARD_ID_LENGTH
    private var bin: Int = DEFAULT_BIN

    // Constants and ranges for configuration
    companion object {
        private const val LUHN_CHECKSUM_LENGTH = 1
        private const val MIN_DIGIT = 0
        private const val MAX_DIGIT = 9
        private const val CARD_NUMBER_MIN_LENGTH = 13
        private const val CARD_NUMBER_MAX_LENGTH = 19

        private val MIR_BIN_RANGE = 220000..220499
        private val MASTERCARD_BIN_RANGE = 510000..559999
        private val VISA_BIN_RANGE = 450000..459999
        private val DEFAULT_BIN = Bin.entries.random().getValue()

        private val CARD_ID_MIN_LENGTH = CARD_NUMBER_MIN_LENGTH - DEFAULT_BIN.toString().length - LUHN_CHECKSUM_LENGTH
        private val CARD_ID_MAX_LENGTH = CARD_NUMBER_MIN_LENGTH - DEFAULT_BIN.toString().length - LUHN_CHECKSUM_LENGTH
        private val CARD_NUMBER_LENGTH_RANGE = CARD_NUMBER_MIN_LENGTH..CARD_NUMBER_MAX_LENGTH
        private val CARD_ID_LENGTH_RANGE = CARD_ID_MIN_LENGTH..CARD_ID_MAX_LENGTH
        private val DEFAULT_CARD_ID_LENGTH = CARD_ID_LENGTH_RANGE.random()
        private val DIGIT_RANGE = MIN_DIGIT..MAX_DIGIT
    }

    /**
     * Enum representing different card networks.
     */
    enum class Bin {
        MASTERCARD {
            override fun getValue(): Int {
                return MASTERCARD_BIN_RANGE.random()
            }
        },
        VISA {
            override fun getValue(): Int {
                return VISA_BIN_RANGE.random()
            }
        },
        MIR {
            override fun getValue(): Int {
                return MIR_BIN_RANGE.random()
            }
        };

        abstract fun getValue(): Int
    }

    /**
     * Sets the bin value for the card network.
     *
     * @param bin The card network represented by the `Bin` enum.
     * @return The current instance of `CardNumberGenerator`.
     */
    fun setBin(bin: Bin): CardNumberGenerator {
        this.bin = bin.getValue()
        return this
    }

    /**
     * Sets the custom length for the generated card number.
     *
     * @param customLength The desired length of the generated card number.
     * @return The current instance of `CardNumberGenerator`.
     * @throws IllegalArgumentException if the specified length is not in the valid range.
     */
    fun setLength(customLength: Int): CardNumberGenerator {
        if (customLength in CARD_NUMBER_LENGTH_RANGE) {
            this.cartIdLength = customLength - LUHN_CHECKSUM_LENGTH - bin.toString().length
            return this
        } else {
            throw IllegalArgumentException("Length is not in valid range: $CARD_NUMBER_LENGTH_RANGE")
        }
    }

    /**
     * Generates a random card number based on the configured parameters.
     *
     * @return The randomly generated card number.
     */
    fun generate(): String {
        val preparedNumber = bin.toString() + getRandomCardId()
        return preparedNumber + luhnCalculate(preparedNumber).toString()
    }

    // Internal utility functions for Luhn algorithm
    private fun luhnCheckSum(number: String): Int {
        var sum = 0
        val parity = number.length % 2
        for (i in number.length - 1 downTo 0) {
            var digit = Character.getNumericValue(number[i])

            if (i % 2 == parity) {
                digit *= 2
            }
            if (digit > 9) {
                digit -= 9
            }
            sum += digit
        }
        return sum % 10
    }

    private fun luhnCalculate(partNumber: String): Int {
        val checksum = luhnCheckSum(partNumber + '0')
        return if ((checksum % 10) == 0) 0 else 10 - (checksum % 10)
    }

    // Internal utility functions for generating random card ID
    private fun getRandomCardId(): String {
        var cardID = ""
        while (cardID.length < this.cartIdLength) {
            cardID += DIGIT_RANGE.random().toString()
        }
        return cardID
    }
}