using System;

delegate void WorkStarted();
delegate void WorkProgressing();
delegate int WorkCompleted();

class Worker {
  public event WorkStarted Started;
  public event WorkProgressing Progressing;
  public event WorkCompleted Completed;

  public void DoWork() {
    Console.WriteLine("Worker: work started");
    if( this.Started != null )
      this.Started();

    Console.WriteLine("Worker: work progressing");
    if( this.Progressing != null )
      this.Progressing();

    Console.WriteLine("Worker: work completed");
    if( this.Completed != null ) {
      foreach( WorkCompleted wc in this.Completed.GetInvocationList() ) {
        // Create an unchanging variable referencing the current wc
        WorkCompleted wc2 = wc;
        wc.BeginInvoke(delegate(IAsyncResult result) {
          // Use wc2 variable from surrounding context
          int grade = wc2.EndInvoke(result);
          Console.WriteLine("Worker grade= {0}", grade);
        },
        null);
      }
    }
  }
}

class Boss {
  public int WorkCompleted() {
    System.Threading.Thread.Sleep(5000);
    Console.WriteLine("It's about time!");
    return 4; // out of 10
  }
}

class Universe {
  static void WorkerStartedWork() {
    Console.WriteLine("Universe notices worker starting work");
  }

  static int WorkerCompletedWork() {
    System.Threading.Thread.Sleep(10000);
    Console.WriteLine("Universe pleased with worker's work");
    return 7;
  }

  static void Main() {
    Worker peter = new Worker();
    Boss boss = new Boss();

    //peter.Completed = boss.WorkCompleted;
    peter.Completed += boss.WorkCompleted;
    peter.Started += Universe.WorkerStartedWork;
    peter.Completed += Universe.WorkerCompletedWork;

    peter.DoWork();

    Console.WriteLine("Main: worker completed work");
    Console.ReadLine();
  }
}