1️⃣1️⃣ 🧙 supporting files: durable entities, change feed

src/backend/Entities/ITodoItemEntity.cs

@@ -0,0 +1,14 @@
+using System;
+using System.Threading.Tasks;
+using backend.Models;
+
+namespace backend.Entities;
+
+public interface ITodoItemEntity
+{
+    Task Create(TodoItem todoItem);
+
+    Task Sync();
+
+    Task Delete();
+}

src/backend/Entities/TodoItemEntity.cs

@@ -0,0 +1,113 @@
+using System;
+using System.Threading.Tasks;
+using Microsoft.Azure.Cosmos;
+using Microsoft.Extensions.Logging;
+using Newtonsoft.Json;
+using Microsoft.Azure.WebJobs;
+using Microsoft.Azure.WebJobs.Extensions.DurableTask;
+using backend.Models;
+
+namespace backend.Entities;
+
+public class TodoItemEntity : ITodoItemEntity
+{
+    [JsonIgnore]
+    private ILogger _logger;
+
+    [JsonIgnore]
+    private CosmosClient _cosmosClient;
+
+    [JsonProperty("id")]
+    public string Id { get; set; }
+
+    [JsonProperty("todoItem")]
+    public TodoItem TodoItem { get; set; }
+
+    public TodoItemEntity(ILogger<TodoItemEntity> logger, CosmosClient cosmosClient)
+    {
+        _logger = logger;
+        _cosmosClient = cosmosClient;
+    }
+
+    public Task Create(TodoItem todoItem)
+    {
+        if (todoItem.DueDate is null || todoItem.IsOverdue())
+        {
+            Entity.Current.SignalEntity<ITodoItemEntity>(todoItem.Id, e => e.Delete());
+            return Task.CompletedTask;
+        }
+
+        Id = todoItem.Id;
+        TodoItem = todoItem;
+
+        SetTimer();
+
+        return Task.CompletedTask;
+    }
+
+    public async Task Sync()
+    {
+        var container = _cosmosClient.GetContainer("Todo", "TodoItem");
+
+        try
+        {
+            ItemResponse<TodoItem> readResponse = await container.ReadItemAsync<TodoItem>(
+            id: TodoItem.Id,
+            partitionKey: new PartitionKey(TodoItem.Id));
+
+            if (readResponse.StatusCode != System.Net.HttpStatusCode.OK)
+            {
+                return;
+            }
+
+            TodoItem todoItem = readResponse.Resource;
+
+            // Update entity state
+            TodoItem = todoItem;
+
+            if (!todoItem.IsTimerRequired())
+            {
+                Entity.Current.SignalEntity<ITodoItemEntity>(Id, e => e.Delete());
+                return;
+            }
+
+            if (todoItem.IsOverdue())
+            {
+                todoItem.State = "overdue";
+                todoItem.UpdatedDate = DateTimeOffset.UtcNow.DateTime;
+                await container.UpsertItemAsync(todoItem);
+
+                Entity.Current.SignalEntity<ITodoItemEntity>(Id, e => e.Delete());
+                return;
+            }
+
+            SetTimer();
+        }
+        catch (CosmosException ex) when (ex.StatusCode == System.Net.HttpStatusCode.NotFound)
+        {
+            _logger.LogWarning($"Missing ToDo item in db, id: {TodoItem.Id}.");
+        }
+    }
+
+    public Task Delete()
+    {
+        _logger.LogInformation($"Deleting entity, id=[{Id}]");
+
+        Entity.Current.DeleteState();
+
+        return Task.CompletedTask;
+    }
+
+    private void SetTimer()
+    {
+        DateTime alarm = TodoItem.DueDate.GetValueOrDefault().DateTime;
+        Entity.Current.SignalEntity<ITodoItemEntity>(TodoItem.Id, alarm, e => e.Sync());
+    }
+
+    [FunctionName(nameof(TodoItemEntity))]
+    public static Task Run(
+        [EntityTrigger] IDurableEntityContext context)
+    {
+        return context.DispatchAsync<TodoItemEntity>();
+    }
+}

src/backend/Startup.cs

@@ -3,6 +3,8 @@
 using System.Threading.Tasks;
 using Azure.Identity;
 using Azure.Security.KeyVault.Secrets;
+using Microsoft.Azure.Cosmos;
+using Microsoft.Azure.Cosmos.Fluent;
 using Microsoft.Azure.Functions.Extensions.DependencyInjection;
 using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.DependencyInjection;
@@ -34,7 +36,14 @@ public override void Configure(IFunctionsHostBuilder builder)
 
                     return new VirusTotalClient(virusTotalApiKey, httpClient, memoryCache);
                 })
-                .AddSingleton<Healthz>();
+                .AddSingleton<Healthz>()
+                .AddSingleton<CosmosClient>(serviceProvider =>
+                {
+                    var accountEndpoint = Environment.GetEnvironmentVariable("CosmosConnectionOptions__accountEndpoint");
+                    var defaultAzureCredentials = serviceProvider.GetService<DefaultAzureCredential>();
+
+                    return new CosmosClientBuilder(accountEndpoint, defaultAzureCredentials).Build();
+                });
         }
     }
 }

src/backend/Todo.Backend.csproj

@@ -6,8 +6,10 @@
   <ItemGroup>
     <PackageReference Include="Azure.Identity" Version="1.10.4" />
     <PackageReference Include="Azure.Security.KeyVault.Secrets" Version="4.5.0" />
+    <PackageReference Include="Microsoft.Azure.Cosmos" Version="3.35.3" />
     <PackageReference Include="Microsoft.Azure.Functions.Extensions" Version="1.1.0" />
     <PackageReference Include="Microsoft.Azure.WebJobs.Extensions.CosmosDB" Version="4.3.0" />
+    <PackageReference Include="Microsoft.Azure.WebJobs.Extensions.DurableTask" Version="2.11.1" />
     <PackageReference Include="Microsoft.Azure.WebJobs.Extensions.EventHubs" Version="5.4.0" />
     <PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="6.0.1" />
     <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="7.0.0" />

src/backend/host.json

@@ -5,6 +5,11 @@
             // "default": "Information"
             "backend.Healthz": "Information"
         },
+        "extensions": {
+            "durableTask": {
+                "hubName": "ToDoApp"
+            }
+        },
         "applicationInsights": {
             "samplingSettings": {
                 "isEnabled": true,