Persisting Calculator

_repository.rb

# a fake repository

class Repository
  def self.save_calculation(op, n1, n2, result)
    puts "just saved #{op}, #{n1}, #{n2}, #{result}"
  end
end

higher_order.rb

# implemented in the controller action, result from the 
# calculator operation is passed to the Repository
 
# app/controllers/calculation.rb
def create
  h = ActiveSupport::JSON.decode(request.body)
  
  fx = lambda do |op, mod, repo|
    lambda do |x, y|
      result = mod.method(op.to_sym).to_proc[x, y]
      repo.save_calculation op, x, y, result
      result
    end
  end
 
  @result = fx[h["operation"], StatelessCalculator, Repository][h["x"], h["y"]]
  
  render :calculation_view
end

lambda.rb

# implemented in the controller action, result from the 
# calculator operation is passed to the Repository

# app/controllers/calculation.rb
def create
  h = ActiveSupport::JSON.decode(request.body)
  
  fx = lambda do |op, x, y|
    result = StatelessCalculator.send op, x, y
    Repository.save_calculation op, x, y, result
    result
  end

  @result = fx[h["operation"], h["x"], h["y"]]
  
  render :calculation_view
end

service.rb

# app/services/calculation_service.rb
class CalculationService
  def initialize(repository)
    @repository = repository
  end
  
  def calculate(operation, x, y)
    result = StatelessCalculator.send operation, x, y
    @repository.save_calculation 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

stateless_calculator_decorator.rb

# a decorator for the StatelessCalculator, wrapping each method 
# with some code to pass results to the injected repository

# app/decorators/calculator.rb
class StatelessCalculatorDecorator
  def initialize(calculator, repository)
    @calculator = calculator
    @repository = repository
  end

  def method_missing(m, *args, &block)
    return super unless [:add, :sub, :mul, :div].include? m

    result = @calculator.send m.to_s, *args
    @repository.save_calculation m, *args[0], *args[1], result
    result
  end
end

# app/controllers/calculation.rb
def create
  h = ActiveSupport::JSON.decode(request.body)
  c = StatelessCalculatorDecorator.new(StatelessCalculator, Repository)
  @result = c.send h["operation"], h["x"], h["y"]
  
  render :calculation_view
end