Initial commit carried over from private repo. This is V2.

code/MessengerApi/Handlers/Endpoint/AckEndpointHandler.cs

@@ -0,0 +1,40 @@
+using MessengerApi.Contracts.Models.Scoped;
+using MessengerApi.Models.Scoped;
+
+namespace MessengerApi.Handlers.Endpoint
+{
+    public class AckEndpointHandler
+    {
+        private readonly ILogger logger;
+        private readonly IUnitOfWork unitOfWork;
+        private readonly Identity identity;
+
+        public AckEndpointHandler(
+            ILogger logger,
+            IUnitOfWork unitOfWork,
+            Identity identity)
+        {
+            this.logger = logger;
+            this.unitOfWork = unitOfWork;
+            this.identity = identity;
+        }
+
+        public async Task AckMessage(Guid messageId)
+        {
+            var message = unitOfWork.Messages.GetById(messageId);
+            
+            // Authorize.
+            if (message.ToId != this.identity.User.Id)
+            {
+                throw new InvalidOperationException("It's not your message to ack.");
+            }
+            else if(!message.IsDelivered)
+            {
+                throw new InvalidOperationException("Can't ack undelivered message.");
+            }
+
+            // Act.
+            message.IsAcknowledged = true;
+        }
+    }
+}