Trailing Stop Loss kata extracts for the Celluloid mailing list

market_agent.rb

require 'celluloid'

require_relative 'timers/null_timer'
require_relative 'timers/too_late_timer'

class MarketAgent
  include Celluloid

  class ActionError < RuntimeError; end

  def initialize(dependencies)
    @market = dependencies.fetch(:market)
    @delay  = dependencies.fetch(:delay)
    @timer  = NullTimer.new
  end

  def sell
    @timer.cancel
    @timer = after(@delay) do
      @market.sell
      @timer = too_late_timer
    end
  end

  def belay
    @timer.cancel
  end

  private

  def null_timer
    NullTimer.new
  end

  def too_late_timer
    TooLateTimer.new(
      ActionError.new("Sell order has already been issued")
    )
  end
end

market_agent_spec.rb

require 'spec_helper'

require 'market_agent'

describe MarketAgent, focus: true do
  include CelluloidHelpers

  let(:market)    { MockMarket.new(sell_action: ->{ sleep 0.07 }) }
  subject(:agent) { MarketAgent.new(market: market, delay: 0.05) }

  # Most examples removed

  context "after the time specified" do
    it "sells" do
      agent.sell
      sleep 0.06
      expect(market.actions).to be == [ :sell ]
    end

    context "when told to belay" do
      it "raises an error", focus: true do
        agent.sell
        sleep 0.06

        expect {
          agent.belay
        }.to raise_error(MarketAgent::ActionError, "Sell order has already been issued")
      end
    end
  end
end

mock_market.rb

require 'celluloid'

class MockMarketAgent
  include Celluloid

  def initialize(options = { })
    @actions = [ ]
    @sell_action = options.fetch(:sell_action, -> { })
  end

  def sell
    @sell_action.call
    @actions << :sell
  end

  def belay
    @actions << :belay
  end

  def actions
    @actions.dup
  end
end

# It just turned out they're the exact same thing
MockMarket = MockMarketAgent

null_timer.rb

class NullTimer
  def cancel
    # NOOP
  end
end

too_late_timer.rb

class TooLateTimer
  def initialize(error)
    @error = error
  end

  def cancel
    raise @error
  end
end