using System;

namespace DemoApp

{

  // This interface helps decouple the concept of

  // "writing output" from the Console class. We

  // don't really "care" how the Write operation

  // happens, just that we can write.

  public interface IOutput

  {

    void Write(string content);

  }

  // This implementation of the IOutput interface

  // is actually how we write to the Console. Technically

  // we could also implement IOutput to write to Debug

  // or Trace... or anywhere else.

  public class ConsoleOutput : IOutput

  {

    public void Write(string content)

    {

      Console.WriteLine(content);

    }

  }

  // This interface decouples the notion of writing

  // a date from the actual mechanism that performs

  // the writing. Like with IOutput, the process

  // is abstracted behind an interface.

  public interface IDateWriter

  {

    void WriteDate();

  }

  // This TodayWriter is where it all comes together.

  // Notice it takes a constructor parameter of type

  // IOutput - that lets the writer write to anywhere

  // based on the implementation. Further, it implements

  // WriteDate such that today's date is written out;

  // you could have one that writes in a different format

  // or a different date.

  public class TodayWriter : IDateWriter

  {

    private IOutput _output;

    public TodayWriter(IOutput output)

    {

      this._output = output;

    }

    public void WriteDate()

    {

      this._output.Write(DateTime.Today.ToShortDateString());

    }

  }

}