fix: design the service envelope to only contain a single service

Author: corstian

src/Whaally.Domain/Abstractions/IMessageMetadata.cs

@@ -9,7 +9,10 @@ public interface IMessageMetadata
     public DateTimeOffset CreatedAt { get; set; }
 }
 
-public interface IServiceMetadata : IMessageMetadata;
+public interface IServiceMetadata : IMessageMetadata
+{
+    public Type? ServiceType { get; set; }
+}
 
 public interface ICommandMetadata : IMessageMetadata
 {

src/Whaally.Domain/Abstractions/Service/IServiceEnvelope.cs

@@ -2,9 +2,9 @@
 
 public interface IServiceEnvelope : IMessageEnvelope
 {
-    public new IEnumerable<IService> Messages { get; }
+    public IService Message { get; }
     public new IServiceMetadata Metadata { get; }
 
-    IEnumerable<IMessage> IMessageEnvelope.Messages => Messages;
+    IEnumerable<IMessage> IMessageEnvelope.Messages => [ Message ];
     IMessageMetadata IMessageEnvelope.Metadata => Metadata;
 }

src/Whaally.Domain/DefaultContextFactory.cs

@@ -15,10 +15,9 @@ public ISagaContext CreateSagaContext(IEventMetadata metadata)
         };
 
     public IServiceHandlerContext CreateServiceHandlerContext(IServiceMetadata metadata)
-        => new ServiceHandlerContext(services)
+        => new ServiceHandlerContext(services, metadata)
         {
             Attributes = new ReadOnlyDictionary<string, object>(metadata.Attributes),
-            ParentContext = metadata.ParentContext
         };
 
     public ICommandHandlerContext<TAggregate> CreateCommandHandlerContext<TAggregate>(

src/Whaally.Domain/DefaultEvaluationAgent.cs

@@ -34,24 +34,13 @@ public async Task<IResult<ICommandEnvelope[]>> Evaluate(IServiceEnvelope service
         if (serviceEnvelope.Messages.Count() != 1)
             throw new ArgumentException($"Expected {nameof(serviceEnvelope)} to contain one message");
 
-        using var activity = DomainContext.ActivitySource.StartActivity(
-            ActivityKind.Internal,
-            name: $"Evaluate {serviceEnvelope.Messages.Single().GetType().Name}",
-            parentContext: serviceEnvelope.Metadata.ParentContext ?? default,
-            tags: new Dictionary<string, object?>
-            {
-                
-            });
-        
-        serviceEnvelope.Metadata.ParentContext = activity?.Context;
-        
         var serviceContext = _contextFactory.CreateServiceHandlerContext(serviceEnvelope.Metadata);
 
         var result = await _domainContext
             .GetServiceHandler(serviceEnvelope.Messages.Single().GetType())
             .Handle(
                 serviceContext,
-                serviceEnvelope.Messages.Single());
+                serviceEnvelope.Message);
 
         return new Result<ICommandEnvelope[]>()
             .WithValue(serviceContext.Commands.ToArray())

src/Whaally.Domain/Service/ServiceEnvelope.cs

@@ -2,24 +2,6 @@
 
 namespace Whaally.Domain;
 
-public record ServiceEnvelope : IServiceEnvelope
-{
-    public ServiceEnvelope(
-        IServiceMetadata metadata,
-        IEnumerable<IService> messages)
-    {
-        Metadata = metadata;
-        Messages = messages;
-    }
-
-    public ServiceEnvelope(
-        IServiceMetadata metadata,
-        params IService[] messages)
-    {
-        Metadata = metadata;
-        Messages = messages;
-    }
-    
-    public IServiceMetadata Metadata { get; init; }
-    public IEnumerable<IService> Messages { get; init; }
-}
+public record ServiceEnvelope(
+    IServiceMetadata Metadata,
+    IService Message) : IServiceEnvelope;

src/Whaally.Domain/Service/ServiceHandlerContext.cs

@@ -12,13 +12,25 @@ public class ServiceHandlerContext : IServiceHandlerContext
     private readonly IEvaluationAgent _evaluationAgent;
     private readonly DomainContext _domainContext;
 
+    private readonly Activity? _activity;
     // ToDo: Add an activity here to track service evaluation
 
-    public ServiceHandlerContext(IServiceProvider services)
+    public ServiceHandlerContext(IServiceProvider services, IServiceMetadata metadata)
     {
         _services = services;
         _evaluationAgent = services.GetRequiredService<IEvaluationAgent>();
         _domainContext = services.GetRequiredService<DomainContext>();
+        
+        _activity = DomainContext.ActivitySource.StartActivity(
+            ActivityKind.Internal,
+            name: $"Evaluate {metadata.ServiceType?.Name}",
+            parentContext: metadata.ParentContext ?? default,
+            tags: new Dictionary<string, object?>
+            {
+                
+            });
+        
+        ParentContext = _activity?.Context;
     }
 
     public ActivityContext? ParentContext { get; init; }

src/Whaally.Domain/Service/ServiceMetadata.cs

@@ -11,4 +11,6 @@ public record ServiceMetadata : IServiceMetadata
     public ActivityContext? ParentContext { get; set; }
 
     public DateTimeOffset CreatedAt { get; set; }
+
+    public Type? ServiceType { get; set; }
 }

tests/Whaally.Domain.Tests/RecursiveServiceInvocationTest.cs

@@ -60,7 +60,7 @@ public async Task RecursiveServiceCanBeEvaluated()
 
         var serviceHandler = _services.GetRequiredService<IServiceHandler<RecursiveService>>();
         var serviceHandlerContext =
-            new ServiceHandlerContext(_services);
+            new ServiceHandlerContext(_services, new ServiceMetadata());
 
         var result = await serviceHandler.Handle(serviceHandlerContext, service);
 

tests/Whaally.Domain.Tests/ServiceTests.cs

@@ -1,6 +1,4 @@
-using Microsoft.Extensions.DependencyInjection;
-using Whaally.Domain.Abstractions;
-using Whaally.Domain.Tests.Domain;
+using Whaally.Domain.Tests.Domain;
 
 namespace Whaally.Domain.Tests;
 
@@ -11,7 +9,7 @@ public class ServiceTests
     [Fact]
     public async Task ServiceCanBeEvaluated()
     {
-        var context = new ServiceHandlerContext(_services);
+        var context = new ServiceHandlerContext(_services, new ServiceMetadata());
         var service = new TestService
         {
             Id = Guid.NewGuid().ToString()
@@ -27,7 +25,7 @@ public async Task ServiceCanBeEvaluated()
     [Fact]
     public async Task ServiceCanInvokeOtherServices()
     {
-        var context = new ServiceHandlerContext(_services);
+        var context = new ServiceHandlerContext(_services, new ServiceMetadata());
         var service = new TestParentService
         {
             Id1 = Guid.NewGuid().ToString(),