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Saga

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gistfile1.cs
C#
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namespace Sagas
{
using System;
using System.Collections.Generic;
 
class Program
{
static ActivityHost[] processes;
 
static void Main(string[] args)
{
var routingSlip = new RoutingSlip(new WorkItem[]
{
new WorkItem<ReserveCarActivity>(new WorkItemArguments{{"vehicleType", "Compact"}}),
new WorkItem<ReserveHotelActivity>(new WorkItemArguments{{"roomType", "Suite"}}),
new WorkItem<ReserveFlightActivity>(new WorkItemArguments{{"destination", "DUS"}})
});
 
 
// imagine these being completely separate processes with queues between them
processes = new ActivityHost[]
{
new ActivityHost<ReserveCarActivity>(Send),
new ActivityHost<ReserveHotelActivity>(Send),
new ActivityHost<ReserveFlightActivity>(Send)
};
 
// hand off to the first address
Send(routingSlip.ProgressUri, routingSlip);
}
 
static void Send(Uri uri, RoutingSlip routingSlip)
{
// this is effectively the network dispatch
foreach (var process in processes)
{
if (process.AcceptMessage(uri, routingSlip))
{
break;
}
}
}
 
}
 
 
class ReserveCarActivity : Activity
{
static Random rnd = new Random(2);
 
public override WorkLog DoWork(WorkItem workItem)
{
Console.WriteLine("Reserving car");
var car = workItem.Arguments["vehicleType"];
var reservationId = rnd.Next(100000);
Console.WriteLine("Reserved car {0}", reservationId);
return new WorkLog(this, new WorkResult { { "reservationId", reservationId } });
}
 
public override bool Compensate(WorkLog item, RoutingSlip routingSlip)
{
var reservationId = item.Result["reservationId"];
Console.WriteLine("Cancelled car {0}", reservationId);
return true;
}
 
public override Uri WorkItemQueueAddress
{
get { return new Uri("sb://./carReservations"); }
}
 
public override Uri CompensationQueueAddress
{
get { return new Uri("sb://./carCancellactions"); }
}
}
 
class ReserveHotelActivity : Activity
{
static Random rnd = new Random(1);
 
public override WorkLog DoWork(WorkItem workItem)
{
Console.WriteLine("Reserving hotel");
var car = workItem.Arguments["roomType"];
var reservationId = rnd.Next(100000);
Console.WriteLine("Reserved hotel {0}", reservationId);
return new WorkLog(this, new WorkResult { { "reservationId", reservationId } });
}
 
public override bool Compensate(WorkLog item, RoutingSlip routingSlip)
{
var reservationId = item.Result["reservationId"];
Console.WriteLine("Cancelled hotel {0}", reservationId);
return true;
}
 
public override Uri WorkItemQueueAddress
{
get { return new Uri("sb://./hotelReservations"); }
}
 
public override Uri CompensationQueueAddress
{
get { return new Uri("sb://./hotelCancellations"); }
}
}
 
class ReserveFlightActivity : Activity
{
static Random rnd = new Random(3);
 
public override WorkLog DoWork(WorkItem workItem)
{
Console.WriteLine("Reserving flight");
var car = workItem.Arguments["fatzbatz"]; // this throws
var reservationId = rnd.Next(100000);
Console.WriteLine("Reserved flight {0}", reservationId);
return new WorkLog(this, new WorkResult { { "reservationId", reservationId } });
}
 
public override bool Compensate(WorkLog item, RoutingSlip routingSlip)
{
var reservationId = item.Result["reservationId"];
Console.WriteLine("Cancelled flight {0}", reservationId);
return true;
}
 
public override Uri WorkItemQueueAddress
{
get { return new Uri("sb://./flightReservations"); }
}
 
public override Uri CompensationQueueAddress
{
get { return new Uri("sb://./flightCancellations"); }
}
}
 
 
abstract class Activity
{
public abstract WorkLog DoWork(WorkItem item);
public abstract bool Compensate(WorkLog item, RoutingSlip routingSlip);
public abstract Uri WorkItemQueueAddress { get; }
public abstract Uri CompensationQueueAddress { get; }
}
 
class WorkLog
{
readonly Type activityType;
readonly WorkResult result;
 
public WorkLog(Activity activity, WorkResult result)
{
this.result = result;
this.activityType = activity.GetType();
}
 
public WorkResult Result
{
get { return this.result; }
}
 
public Type ActivityType
{
get { return this.activityType; }
}
}
 
class WorkItemArguments : Dictionary<string, object>
{
}
 
class WorkResult : Dictionary<string, object>
{
}
 
 
abstract class WorkItem
{
protected WorkItem(WorkItemArguments arguments)
{
this.Arguments = arguments;
}
 
public RoutingSlip RoutingSlip { get; set; }
public WorkItemArguments Arguments { get; set; }
public abstract Type ActivityType { get; }
}
 
class WorkItem<T> : WorkItem where T : Activity
{
public WorkItem(WorkItemArguments args) : base(args)
{
}
 
public override Type ActivityType
{
get { return typeof (T); }
}
}
 
class RoutingSlip
{
readonly Stack<WorkLog> completedWorkLogs = new Stack<WorkLog>();
readonly Queue<WorkItem> nextWorkItem = new Queue<WorkItem>();
 
public RoutingSlip()
{
}
 
public RoutingSlip(IEnumerable<WorkItem> workItems)
{
foreach (var workItem in workItems)
{
this.nextWorkItem.Enqueue(workItem);
}
}
 
public bool IsCompleted
{
get { return this.nextWorkItem.Count == 0; }
}
 
public bool IsInProgress
{
get { return this.completedWorkLogs.Count > 0; }
}
 
public bool ProcessNext()
{
if (this.IsCompleted)
{
throw new InvalidOperationException();
}
 
var currentItem = this.nextWorkItem.Dequeue();
var activity = (Activity) Activator.CreateInstance(currentItem.ActivityType);
try
{
var result = activity.DoWork(currentItem);
if (result != null)
{
this.completedWorkLogs.Push(result);
return true;
}
}
catch (Exception e)
{
Console.WriteLine("Exception {0}", e.Message);
}
return false;
}
 
public Uri ProgressUri
{
get
{
if (IsCompleted)
{
return null;
}
else
{
return
((Activity) Activator.CreateInstance(this.nextWorkItem.Peek().ActivityType)).
WorkItemQueueAddress;
}
}
}
 
public Uri CompensationUri
{
get
{
if (!IsInProgress)
{
return null;
}
else
{
return
((Activity) Activator.CreateInstance(this.completedWorkLogs.Peek().ActivityType)).
CompensationQueueAddress;
}
}
}
 
public bool UndoLast()
{
if (!this.IsInProgress)
{
throw new InvalidOperationException();
}
 
var currentItem = this.completedWorkLogs.Pop();
var activity = (Activity) Activator.CreateInstance(currentItem.ActivityType);
try
{
return activity.Compensate(currentItem, this);
}
catch (Exception e)
{
Console.WriteLine("Exception {0}", e.Message);
throw;
}
}
}
 
abstract class ActivityHost
{
Action<Uri, RoutingSlip> send;
 
public ActivityHost(Action<Uri, RoutingSlip> send)
{
this.send = send;
}
 
public void ProcessForwardMessage(RoutingSlip routingSlip)
{
if (!routingSlip.IsCompleted)
{
// if the current step is successful, proceed
// otherwise go to the Unwind path
if (routingSlip.ProcessNext())
{
// recursion stands for passing context via message
// the routing slip can be fully serialized and passed
// between systems.
this.send(routingSlip.ProgressUri, routingSlip);
}
else
{
// pass message to unwind message route
this.send(routingSlip.CompensationUri, routingSlip);
}
}
}
 
public void ProcessBackwardMessage(RoutingSlip routingSlip)
{
if (routingSlip.IsInProgress)
{
// UndoLast can put new work on the routing slip
// and return false to go back on the forward
// path
if (routingSlip.UndoLast())
{
// recursion stands for passing context via message
// the routing slip can be fully serialized and passed
// between systems
this.send(routingSlip.CompensationUri, routingSlip);
}
else
{
this.send(routingSlip.ProgressUri, routingSlip);
}
}
}
 
public abstract bool AcceptMessage(Uri uri, RoutingSlip routingSlip);
}
 
class ActivityHost<T> : ActivityHost where T : Activity, new()
{
public ActivityHost(Action<Uri, RoutingSlip> send)
: base(send)
{
}
 
public override bool AcceptMessage(Uri uri, RoutingSlip routingSlip)
{
var activity = new T();
if (activity.CompensationQueueAddress.Equals(uri))
{
this.ProcessBackwardMessage(routingSlip);
return true;
}
if (activity.WorkItemQueueAddress.Equals(uri))
{
this.ProcessForwardMessage(routingSlip);
return true;
}
return false;
}
 
}
}

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