Play Selected Track Next.rb

#!/usr/bin/env ruby
# encoding: UTF-8

pid = fork and (Process.detach(pid); exit) # Go to background.

require 'appscript'

SRC_MACRUBY_WAIT_FOR_PLAYER_NOTIFICATION = <<-RUBY
  framework "Cocoa"
  def playerInfo(notification); exit; end
  NSDistributedNotificationCenter.defaultCenter.addObserver(self, selector:"playerInfo:", name:"com.apple.iTunes.playerInfo", object:nil)
  NSRunLoop.currentRunLoop.run
RUBY

class << $itunes = Appscript::app("iTunes")
  def wait_for_track_to_end(track)
    @track_to_wait_for = track
    wait_for_player_info_notification until track_to_wait_for_has_started_playing? && !track_to_wait_for_is_currently_playing?
  end

  private

  def track_to_wait_for_is_currently_playing?
    @track_to_wait_for == (current_track.get rescue nil)
  end

  def track_to_wait_for_has_started_playing?
    @track_to_wait_for_has_started_playing ||= track_to_wait_for_is_currently_playing?
  end

  def wait_for_player_info_notification
    system "macruby", "-e", SRC_MACRUBY_WAIT_FOR_PLAYER_NOTIFICATION
  end
end

next_track = $itunes.selection.get.first or ($stderr.puts "no tracks selected"; exit 1)

$itunes.wait_for_track_to_end($itunes.current_track.get)
$itunes.play(next_track)