Dependency Injection

dance.rb

#!/usr/bin/env ruby

require './dancer'
require './gangnam_style'

dancer = Dancer.new('PSY', GangnamStyle.new)
dancer.dance!

dancer.rb

class Dancer
  attr_reader :name

  def initialize(name, dance_style)
    @name        = name
    @dance_style = dance_style
  end

  def dance!
    @dance_style.dance!(self.name)
  end

end

gangnam_style.rb

# encoding: UTF-8
class GangnamStyle

  def initialize(delay = true)
    @delay = delay
  end

  def dance!(name)
    take_stage(name)
    cue_music
    perform_steps
    stop_music
  rescue SystemExit, Interrupt => e
    exit if SystemExit === e
  ensure
    stop_music if @music_pid
    clear_screen
  end

  def injected(base)
    dance_style = self
    base.singleton_class.class_eval do
      define_method :dance! do
        dance_style.dance!(base.name)
      end
    end
  end

  private

  def take_stage(name)
    clear_screen
    print "\n" * 5
    center_print "#{name} has taken the stage..."
    print "\n" * 5
    center_print '/(゜_ ゜)\  '
  end

  def clear_screen
    print "\e[2J\e[f"
  end

  def perform_steps
    while true do
      steps.each do |step|
        center_print step
        sleep 1
      end
    end
  end

  def center_print(message)
    indent = ' ' * (39 - message.length.to_f / 2)
    print "#{' ' * 80}\r#{indent}#{message}\r"
  end

  def cue_music
    with_delay do
      @music_pid = spawn 'mpg123 -q music.mp3'
      Process.detach @music_pid
    end
  end

  def with_delay(&block)
    if @delay
      sleep 5
      yield
      sleep 8
    else
      yield
    end
  end

  def stop_music
    Process.kill('QUIT', @music_pid)
  end

  def steps
    [
      'ヽ(゜∇ ゜)ノ  ',
      'ヘ(￣ー￣ヘ)  ',
      '  (ノ￣ー￣)ノ',
      '  (〜￣▽￣)〜 ',
      '〜(￣△￣〜)   ',
      '  (☞ ﾟ∀ ﾟ)☞   '
    ]
  end

end