module Rpn
  module Core
    module Operations
      module_function

      # addition
      def add( stack )
        addable = %i[numeric string name]
        stack, args = Rpn::Core.stack_extract( stack, [addable, addable] )

        result = { type: case args[0][:type]
                         when :name
                           :name
                         when :string
                           :string
                         when :numeric
                           if args[1][:type] == :numeric
                             :numeric
                           else
                             :string
                           end
                         end }

        args.each do |elt|
          elt[:value] = elt[:value][1..-2] unless elt[:type] == :numeric
        end

        result[:value] = case result[:type]
                         when :name
                           "'#{args[0][:value]}#{args[1][:value]}'"
                         when :string
                           "\"#{args[0][:value]}#{args[1][:value]}\""
                         when :numeric
                           args[0][:value] + args[1][:value]
                         end

        stack << result
      end

      # substraction
      def subtract( stack )
        stack, args = Rpn::Core.stack_extract( stack, [%i[numeric], %i[numeric]] )

        stack << { type: :numeric,
                   value: args[0][:value] - args[1][:value] }
      end

      # negation
      def negate( stack )
        stack, args = Rpn::Core.stack_extract( stack, [%i[numeric]] )

        stack << { type: :numeric,
                   value: args[0][:value] * -1 }
      end

      # multiplication
      def multiply( stack )
        stack, args = Rpn::Core.stack_extract( stack, [%i[numeric], %i[numeric]] )

        stack << { type: :numeric,
                   value: args[0][:value] * args[1][:value] }
      end

      # division
      def divide( stack )
        stack, args = Rpn::Core.stack_extract( stack, [%i[numeric], %i[numeric]] )

        raise 'Division by 0' if args[0][:value].zero?

        stack << { type: :numeric,
                   value: args[0][:value] / args[1][:value] }
      end

      # inverse
      def inverse( stack )
        stack, args = Rpn::Core.stack_extract( stack, [%i[numeric]] )

        raise 'Division by 0' if args[0][:value].zero?

        stack << { type: :numeric,
                   value: 1.0 / args[0][:value] }
      end

      # power
      def power( stack )
        stack, args = Rpn::Core.stack_extract( stack, [%i[numeric], %i[numeric]] )

        stack << { type: :numeric,
                   value: args[0][:value]**args[1][:value] }
      end
    end
  end
end