simple_railway.rb

module SimpleRailway
  class Result
    attr_accessor :success, :data
    def initialize(success, data)
      @success = success
      @data = data
    end

    def success?; !!success; end
    def failure?; !success?; end

    def self.success(data = nil)
      new(true, data)
    end

    def self.failure(data = nil)
      new(false, data)
    end
  end

  class Chain
    def initialize
      @result = Result.success
      @store = []
    end

    def call
      while !@store.empty?
        @store.shift.tap do |action|
          @result = action.call unless @result.failure?
        end
      end
      @result
    end

    def push(&block)
      @store << block
    end
  end

  def initialize(*)
    reset_chain!
    super
  end

  def reset_chain!
    @chain = Chain.new
  end

  def run
    @chain.call
  end

  def chain
    @chain.push { yield(self) } if block_given?; self
  end

  def when_success
    yield(run.data) if run.success?; self
  end

  def when_failure
    yield(run.data) if run.failure?; self
  end

  protected

  def Success(data)
    Result.success(data)
  end

  def Failure(data)
    Result.failure(data)
  end
end

class Counter
  prepend SimpleRailway

  attr_reader :count
  def initialize
    reset!
  end

  def reset!
    @count = 0
  end

  def increment
    return Failure("Overflow !@$^&") if @count >= 3
    puts "+1"
    Success(@count += 1)
  end
end