irobayna/stupidedi

# frozen_string_literal: true
require "bigdecimal"
require "rational"

module Stupidedi
  module Refinements
    refine BigDecimal do
      # @return [BigDecimal] self
      def to_d
        self
      end
    end

    BIGDECIMAL = /\A[+-]?            (?# optional leading sign            )
                  (?:
                    (?:\d+\.?\d*)  | (?# whole with optional decimal or ..)
                    (?:\d*?\.?\d+) ) (?# optional whole with decimal      )
                  (?:E[+-]?\d+)?     (?# optional exponent                )
                 \Z/ix

    refine String do
      # Converts the string to a BigDecimal after validating the format. If the
      # string does not match the pattern for a valid number, an `ArgumentError`
      # is raised.
      #
      # @example
      #   "1.0".to_d  #=> BigDecimal("1.0")
      #
      # @return [BigDecimal]
      def to_d
        if BIGDECIMAL =~ self
          BigDecimal(to_s)
        else
          raise ArgumentError, "#{inspect} is not a valid number"
        end
      end
    end

    refine Integer do
      # Converts the integer to a BigDecimal
      #
      # @example
      #   10.to_d   #=> BigDecimal("10")
      #
      # @return [BigDecimal]
      def to_d
        BigDecimal(to_s)
      end
    end

    refine Rational do
      # Converts the rational to a BigDecimal
      #
      # @example
      #   Rational(3, 4).to_d   #=> BigDecimal("3") / BigDecimal("4")
      #
      # @return [BigDecimal]
      def to_d
        numerator.to_d / denominator.to_d
      end
    end

    refine Float do
      # Raises a `TypeError` exception. The reason this method is defined at
      # all is to produce a more meaningful error than `NoSuchMethod`.
      #
      # @return [void]
      def to_d
        # The problem is there isn't a way to know the correct precision,
        # since there are (many) values that cannot be represented exactly
        # using Floats. For instance, we can't assume which value is correct
        #
        #   "%0.10f" % 1.8 #=> "1.8000000000"
        #   "%0.20f" % 1.8 #=> "1.80000000000000004441"
        #
        # The programmer should convert the Float to a String using whatever
        # precision he chooses, and call #to_d on the String.
        raise TypeError, "cannot convert Float to BigDecimal"
      end
    end
  end
end