Page History

using System.Collections.Immutable;
using Akka.Persistence;

#region MessageData
public class Shutdown { }

//커멘드와 이벤트를 분리합니다. 커멘드는 이벤트를 발생시키는 명령이며
//1 커멘드는 n개의 이벤트로 복제가 될수 있습니다.
public class Cmd
{
    public Cmd(string data)
    {
        Data = data;
    }

    public string Data { get; }
}

public class Evt
{
    public Evt(string data)
    {
        Data = data;
    }

    public string Data { get; }
}

public class ExampleState
{
    private readonly ImmutableList<string> _events;

    public ExampleState(ImmutableList<string> events)
    {
        _events = events;
    }

    public ExampleState() : this(ImmutableList.Create<string>())
    {
    }

    public ExampleState Updated(Evt evt)
    {
        return new ExampleState(_events.Add(evt.Data));
    }

    public int Size => _events.Count;

    public override string ToString()
    {
        return string.Join(", ", _events.Reverse());
    }
}

#endregion

#region Actor
public class PersistentActor : UntypedPersistentActor
{
    private ExampleState _state = new ExampleState();

    private void UpdateState(Evt evt)
    {
        _state = _state.Updated(evt);
    }

    private int NumEvents => _state.Size;

    public override Recovery Recovery => new Recovery(fromSnapshot: SnapshotSelectionCriteria.None);
    protected override void OnRecover(object message)
    {
        switch (message)
        {
            case Evt evt:
                UpdateState(evt);
                break;
            case SnapshotOffer snapshot when snapshot.Snapshot is ExampleState:
            _state = (ExampleState)snapshot.Snapshot;
                break;
        }
    }

    protected override void OnCommand(object message)
    {
        switch (message)
        {
            case Cmd cmd:
                Persist(new Evt($"{cmd.Data}-{NumEvents}"), UpdateState);
                Persist(new Evt($"{cmd.Data}-{NumEvents + 1}"), evt =>   //이코드는 복제와 추가행동 전략과 관련있습니다.
                {
                    UpdateState(evt);
                    Context.System.EventStream.Publish(evt);
                });
                break;
            case "snap":
                SaveSnapshot(_state);
                break;
            case "print":
                Console.WriteLine("Try print");
                Console.WriteLine(_state);
                break;
            case Shutdown down:
                Context.Stop(Self);
                break;
        }
    }

    public override string PersistenceId { get; } = "sample-id-1";  //영속성을 위한 고유한 아이디값을 가집니다.
}


#endregion