module Workarea
  module Kount
    ##
    # This class implements the Kount KHASH for cards and gift cards.
    class SecurityMash
      # @param plain_text [String] String to be hashed
      # @param ptyp [String] Payment type code: CARD, GIFT, or OTHER
      # @return [String] KHASH version of string
      def self.hash_token(plain_text, ptyp, ksalt, merchant_id = '')
        if ptyp == 'CARD'
          hash_credit_card(plain_text, ksalt)
        else
          hash_gift_card(plain_text, ksalt, merchant_id)
        end
      end

      # Hash a credit card number.
      # Preserves first six characters of the input so that hashed cards can be
      # categorized by Bank Identification Number (BIN).
      #
      # Example usage:
      #   hashed = Kount::SecurityMash.hash_credit_card("4111111111111111")
      #     Expect: 411111WMS5YA6FUZA1KC
      #   hashed = Kount::SecurityMash.hash_credit_card("5199185454061655")
      #     Expect: 5199182NOQRXNKTTFL11
      #   hashed = Kount::SecurityMash.hash_credit_card("4259344583883")
      #     Expect: 425934FEXQI1QS6TH2O5
      #
      # @param plain_text [String] String to be hashed
      # @return [String] KHASH version of string
      def self.hash_credit_card(plain_text, ksalt)
        return plain_text if khashed?(plain_text)
        first_six = plain_text[0..5]
        mashed = mash(plain_text, 14, ksalt)
        "#{first_six}#{mashed}"
      end

      # Hash a gift card number.
      # Use the six characters of the merchant id so that hashed cards can be
      # unique across the entire domain.
      #
      # Example usage:
      #   hashed = Kount::SecurityMash.hash_gift_card("123456", "3245876")
      #     Expect: 1234569HXH32Y5NNJCGB

      # @param plain_text [String] String to be hashed
      # @return [String] KHASH version of string
      def self.hash_gift_card(plain_text, ksalt, merchant_id)
        mashed = mash(plain_text, 14, ksalt)
        "#{merchant_id}#{mashed}"
      end

      # Compute a base64 hash of the provided data.
      #
      # @param data [String] Data to hash
      # @param len [int] Length of hash to retain
      # @return [String] Hashed data
      def self.mash(data, len, m)
        a = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'
        r = Digest::SHA1.hexdigest("#{data}.#{m}")
        c = ''
        len = 17 if len > 17
        limit = 2 * len
        i = 0
        while i < limit
          c << a[r[i..i + 6].to_i(16) % 36]
          i += 2
        end
        c
      end

      # @param val [String] Token that may or may not be khashed
      # @return [Boolean] True if token is already khashed
      def self.khashed?(val)
        true if val =~ /(\d{6}[A-Z0-9]{14})/
      end
    end
  end
end