service.rb

service.rb

# app/utils/calculator.rb
class StatelessCalculator
  def self.add(x, y)
    x + y
  end

  # ...subtract, divide, multiply, etc.
end

# app/services/calculation_isolate.rb
class CalculationService
  def initialize(logger)
    @logger = logger
  end
 
  def calculate(operation, x, y)
    result = StatelessCalculator.send operation, x, y
    @logger.log operation, x, y, result
    result
  end
end
 
# app/controllers/calculation.rb
def create
  h = ActiveSupport::JSON.decode(request.body)
  @result = MyApp::Services.calculation.calculate h["operation"], h["x"], h["y"]
  render :calculation_view
end