module Dixon
  module Validators
    class Taiwan

      INVALID_MESSAGE = 'Invalid ID number.'

      LETTER_ISSUED_BY = {
        ##
        # Active Letters
        'A' => 'Taipei City'     , 'B' => 'Taichung City',
        'C' => 'Keelung City'    , 'D' => 'Tainan City',
        'E' => 'Kaohsiung City'  , 'F' => 'New Taipei City',
        'G' => 'Yilan County'    , 'H' => 'Taoyuan County',
        'I' => 'Chiayi City'     , 'J' => 'Hsinchu County',
        'K' => 'Miaoli County'   , 'M' => 'Nantou County',
        'N' => 'Changhua County' , 'O' => 'Hsinchu City',
        'P' => 'Yunlin County'   , 'Q' => 'Chiayi County',
        'T' => 'Pingtung County' , 'U' => 'Hualien County',
        'V' => 'Taitung County'  , 'W' => 'Kinmen County',
        'X' => 'Penghu County'   , 'Z' => 'Lienchiang County',
        ##
        # Letters no longer issued
        'L' => 'Taichung County' ,
        'R' => 'Tainan County'   ,
        'S' => 'Kaohsiung County',
        'Y' => 'Yangmingshan Management Bureau'
      }

      LETTER_NUMBERS = {
        'A' => '10', 'B' => '11', 'C' => '12', 'D' => '13', 'E' => '14',
        'F' => '15', 'G' => '16', 'H' => '17', 'J' => '18', 'K' => '19',
        'L' => '20', 'M' => '21', 'N' => '22', 'P' => '23', 'Q' => '24',
        'R' => '25', 'S' => '26', 'T' => '27', 'U' => '28', 'V' => '29',
        'X' => '30', 'Y' => '31', 'W' => '32', 'Z' => '33', 'I' => '34',
        'O' => '35'
      }

      RULE_NUMBERS = [1, 9, 8, 7, 6, 5, 4, 3, 2, 1, 1]

      ##
      # Check if a given ID is valid.
      # `id` must be a string, case is insensitive.
      # First convert ID into all numbers, then multiply to RULE_NUMBERS
      # element by element. Sum up and take a 10 modulo then check
      # if remainder is 0. If it's, return true, false otherwise.
      def checks(id)
        # "F127337575" => [1, 5, 1, 2, 7, 3, 3, 7, 5, 7, 5]
        converted = convert id.to_s
        #    [1,  5,  1,  2,  7,  3,  3,  7,  5,  7, 5]
        #  * [1,  9,  8,  7,  6,  5,  4,  3,  2,  1, 1]
        #  --------------------------------------------
        # sum 1, 45,  8, 14, 43, 15, 12, 21, 10,  7, 5
        # => 180
        # 180 mod 10, is the remainder equal to zero? If so, return true.
        return (mapcar(-> (a,b) { a * b }, converted, RULE_NUMBERS).reduce(:+).divmod 10)[1] == 0
      end

      ##
      # Returns gender for given ID.
      # By check the second digit of ID.
      # 1 is male, 2 is female.
      def gender(id)
        case id[1]
          when '1' then 'male'
          when '2' then 'female'
          else puts INVALID_MESSAGE
        end
      end

      ##
      # Returns local agencies who issued your id.
      def issued_by(id)
        LETTER_ISSUED_BY[id[0]]
      end

      private

      ##
      # Convert array of strings into integer array.
      def to_i_array(str_arr)
        str_arr.map(&:to_i)
      end

      ##
      # Convert an identification number to array of strings
      # First letter conversion rules is defined in LETTER_NUMBERS
      # `convert 'F127337575'` will result in
      # [1, 5, 1, 2, 7, 3, 3, 7, 5, 7, 5]
      def convert(id)
        to_i_array((LETTER_NUMBERS[id[0]] + id[1..-1]).split(''))
      end

      ##
      # mapcar operates on successive elements of the arrays.
      # fn is applied to the first element of each array,
      # then to the secondf element of each array, and so on.
      # The iteration terminates when the shortest array runs out,
      # and excess elements in other arrays are ignored.
      # The value returned by mapcar is a array of the results of
      # successive calls to function.
      def mapcar(fn, *arrs)
        return [] if arrs.empty? or arrs.include? []
        transposed = if arrs.element_of_same_size
                       arrs.transpose
                     else
                       arrs[0].zip(*arrs.drop(1))
                     end
        transposed.map do |e|
          e.reduce(&fn) unless e.include? nil
        end
      end
    end
  end
end

module ValidateFormat

  ##
  # A123456789
  TAIWAN_ID_REGEXP = /[a-zA-Z][1|2][0-9]+/i

  ##
  # Check if given id's format is valid.
  # The current ID number has exact 10 digits
  # The first digit is one capital English letter and
  # is followed by nine Arabic numerals.
  # returns
  #   'Empty ID.' for empty string
  #   'Valid ID.' if the format is correct.
  #   otherwise, 'Invalid ID number.'
  def validate_id_format(id)
    id_str = id.to_s
    return 'Empty ID.' if id_str.empty?
    return 'Valid ID.' if id_str =~ TAIWAN_ID_REGEXP and id_str.size == 10
    return Dixon::Validators::Taiwan::INVALID_MESSAGE
  end

  ##
  # Add a before_hook for methods that
  # defined in literal symbol array.
  %i(checks gender issued_by convert).each do |m|
    define_method(m) do |id|
      is_it_valid = validate_id_format id
      if is_it_valid == 'Valid ID.'
        super(id)
      else
        return is_it_valid
      end
    end
  end

  private :convert

end

module Dixon
  module Validators
    class Taiwan
      prepend ValidateFormat
    end
  end
end