module ActiveSupport
  module NumberHelper
    class NumberToRoundedConverter < NumberConverter # :nodoc:
      self.namespace      = :precision
      self.validate_float = true

      def convert
        precision = options.delete :precision
        significant = options.delete :significant

        case number
        when Float, String
          @number = BigDecimal(number.to_s)
        when Rational
          if significant
            @number = BigDecimal(number, digit_count(number.to_i) + precision)
          else
            @number = BigDecimal(number, precision)
          end
        else
          @number = number.to_d
        end

        if significant && precision > 0
          digits, rounded_number = digits_and_rounded_number(precision)
          precision -= digits
          precision = 0 if precision < 0 # don't let it be negative
        else
          rounded_number = number.round(precision)
          rounded_number = rounded_number.to_i if precision == 0
          rounded_number = rounded_number.abs if rounded_number.zero? # prevent showing negative zeros
        end

        formatted_string =
          if BigDecimal === rounded_number && rounded_number.finite?
            s = rounded_number.to_s('F') + '0'*precision
            a, b = s.split('.', 2)
            a + '.' + b[0, precision]
          else
            "%01.#{precision}f" % rounded_number
          end

        delimited_number = NumberToDelimitedConverter.convert(formatted_string, options)
        format_number(delimited_number)
      end

      private

        def digits_and_rounded_number(precision)
          if zero?
            [1, 0]
          else
            digits = digit_count(number)
            multiplier = 10 ** (digits - precision)
            rounded_number = calculate_rounded_number(multiplier)
            digits = digit_count(rounded_number) # After rounding, the number of digits may have changed
            [digits, rounded_number]
          end
        end

        def calculate_rounded_number(multiplier)
          (number / BigDecimal.new(multiplier.to_f.to_s)).round * multiplier
        end

        def digit_count(number)
          (Math.log10(absolute_number(number)) + 1).floor
        end

        def strip_insignificant_zeros
          options[:strip_insignificant_zeros]
        end

        def format_number(number)
          if strip_insignificant_zeros
            escaped_separator = Regexp.escape(options[:separator])
            number.sub(/(#{escaped_separator})(\d*[1-9])?0+\z/, '\1\2').sub(/#{escaped_separator}\z/, '')
          else
            number
          end
        end

        def absolute_number(number)
          number.respond_to?(:abs) ? number.abs : number.to_d.abs
        end

        def zero?
          number.respond_to?(:zero?) ? number.zero? : number.to_d.zero?
        end
    end
  end
end
