# frozen_string_literal: true

module SecId
  # https://en.wikipedia.org/wiki/CUSIP
  class CUSIP < Base
    ID_REGEX = /\A
      (?<identifier>
        (?<cusip6>[A-Z0-9]{5}[A-Z0-9*@#])
        (?<issue>[A-Z0-9*@#]{2}))
      (?<check_digit>\d)?
    \z/x

    attr_reader :cusip6, :issue

    def initialize(cusip)
      cusip_parts = parse cusip
      @identifier = cusip_parts[:identifier]
      @cusip6 = cusip_parts[:cusip6]
      @issue = cusip_parts[:issue]
      @check_digit = cusip_parts[:check_digit]&.to_i
    end

    def calculate_check_digit
      unless valid_format?
        raise InvalidFormatError, "CUSIP '#{full_number}' is invalid and check-digit cannot be calculated!"
      end

      mod10(modified_luhn_sum)
    end

    def to_isin(country_code)
      unless ISIN::CGS_COUNTRY_CODES.include?(country_code)
        raise(InvalidFormatError, "'#{country_code}' is not a CGS country code!")
      end

      restore!
      isin = ISIN.new(country_code + full_number)
      isin.restore!
      isin
    end

    # CUSIP International Numbering System
    def cins?
      cusip6[0] < '0' || cusip6[0] > '9'
    end

    private

    # https://en.wikipedia.org/wiki/Luhn_algorithm
    def modified_luhn_sum
      reversed_id_digits.each_slice(2).reduce(0) do |sum, (even, odd)|
        double_even = (even || 0) * 2
        sum + div10mod10(double_even) + div10mod10(odd || 0)
      end
    end

    def reversed_id_digits
      identifier.each_char.map(&method(:char_to_digit)).reverse!
    end
  end
end