greeting_mvc.rb

class GreetingView
  def initialize env
    @env = env
  end

  def new
    flash
    print "Enter your name: "
  end

  def show
    flash
    puts "Hello, #{@env[:greeter].name}!"
  end

  def error
    puts "Sorry, something went wrong: #{@env.delete(:flash)}"
  end

  def flash
    puts @env.delete(:flash) if @env[:flash]
  end
end

class GreetingController
  def initialize router
    @router = router
  end

  def new
    GreetingView.new(@router.env).new

    response = gets.strip

    unless response.empty? then
      @router.go_to 'greeting/create'
    else
      @router.env[:flash] = "Try again!"
      @router.go_to 'greeting/new'
    end

    response
  end

  def create
    if @router.response.is_a? String then
      @router.env[:greeter] = Greeter.new(@router.response)
      @router.go_to 'greeting/show'
    else
      @router.env[:flash] = "I don't know what do do with #{@router.response.inspect}!"
      @router.go_to 'greeting/error'
    end

    [email protected][:greeter]
  end

  def show
    GreetingView.new(@router.env).show
    @router.done!
  end

  def error
    GreetingView.new(@router.env).error
    @router.go_to :default
  end
end

class Greeter
  def initialize name
    @name = name
  end
  attr_accessor :name
end

class GreetingRouter
  def initialize env = Hash.new
    @env = env
  end

  def route!
    route_to :default
    until @env[:done]
      route_to @env[:destination]
    end
  rescue => error
    @env[:flash] = "Encountered error in route #{@env[:destination]}: #{error.inspect}"
    go_to 'greeting/error'
    retry
  end

  def env
    @env
  end

  def go_to destination
    @env[:destination] = destination
  end

  def response
    @env[:response]
  end

  def done!
    @env[:done] = true
  end

  private

  def route_to destination
    route = map[destination]

    if route then
      @env[:response] = route.first.new(self).send route.last
    else
      @env[:flash] = "Unknown route: #{destination.inspect}"
      route_to 'greeting/error'
    end
  end

  def map
    {
      :default          => [GreetingController, :new],
      'greeting/new'    => [GreetingController, :new],
      'greeting/create' => [GreetingController, :create],
      'greeting/show'   => [GreetingController, :show],
      'greeting/error'  => [GreetingController, :error]
    }
  end
end

GreetingRouter.new.route!