Add support for dependency injection's IHttpClientFactory. (#56)

* Added a constructor for `TodoistRestClient` that takes an `HttpClient` argument.

* Added a `TodoistClientFactory` that builds `TodoistClients` with tokens.

* Added an extension method to add the `TodoistClientFactory` to DI container.

* Disabled the added extension method and its dependency for net462 target framework.

Author: AhmedZaki99

src/Todoist.Net/Extensions/TodoistServiceCollectionExtensions.cs

@@ -0,0 +1,27 @@
+#if NETSTANDARD2_0
+
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Todoist.Net.Extensions
+{
+    /// <summary>
+    /// Extension methods for setting up todoist client services in an <see cref="IServiceCollection" />.
+    /// </summary>
+    public static class TodoistServiceCollectionExtensions
+    {
+        /// <summary>
+        /// Adds todoist client services to the specified <see cref="IServiceCollection" />.
+        /// </summary>
+        /// <param name="services">The <see cref="IServiceCollection" /> to add services to.</param>
+        /// <returns>The <see cref="IServiceCollection" /> so that additional calls can be chained.</returns>
+        public static IServiceCollection AddTodoistClient(this IServiceCollection services)
+        {
+            services.AddHttpClient();
+            services.AddSingleton<ITodoistClientFactory, TodoistClientFactory>();
+
+            return services;
+        }
+    }
+}
+
+#endif

src/Todoist.Net/ITodoistClientFactory.cs

@@ -0,0 +1,15 @@
+namespace Todoist.Net
+{
+    /// <summary>
+    /// A factory abstraction for a component that can create <see cref="TodoistClient"/> instances with user tokens.
+    /// </summary>
+    public interface ITodoistClientFactory
+    {
+        /// <summary>
+        /// Creates a new instance of <see cref="TodoistClient"/> with the specified user token."/>
+        /// </summary>
+        /// <param name="token">The user token to use.</param>
+        /// <returns>The created <see cref="TodoistClient"/></returns>
+        TodoistClient CreateClient(string token);
+    }
+}

src/Todoist.Net/Todoist.Net.csproj

@@ -29,6 +29,10 @@
     <PackageReference Include="System.Text.Json" Version="8.0.4" />
   </ItemGroup>
 
+  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
+    <PackageReference Include="Microsoft.Extensions.Http" Version="6.0.0"/>
+  </ItemGroup>
+
   <ItemGroup Condition=" '$(TargetFramework)' == 'net462' ">
     <Reference Include="System.Net.Http" />
   </ItemGroup>

src/Todoist.Net/TodoistClientFactory.cs

@@ -0,0 +1,27 @@
+#if NETSTANDARD2_0
+
+using System.Net.Http;
+
+namespace Todoist.Net
+{
+    internal sealed class TodoistClientFactory : ITodoistClientFactory
+    {
+        private readonly IHttpClientFactory _httpClientFactory;
+
+        public TodoistClientFactory(IHttpClientFactory httpClientFactory)
+        {
+            _httpClientFactory = httpClientFactory;
+        }
+
+        /// <inheritdoc/>
+        public TodoistClient CreateClient(string token)
+        {
+            var httpClient = _httpClientFactory.CreateClient();
+            var todoistRestClient = new TodoistRestClient(token, httpClient);
+
+            return new TodoistClient(todoistRestClient);
+        }
+    }
+}
+
+#endif

src/Todoist.Net/TodoistRestClient.cs

@@ -11,12 +11,13 @@ namespace Todoist.Net
     internal sealed class TodoistRestClient : ITodoistRestClient
     {
         private readonly HttpClient _httpClient;
+        private readonly bool _disposeHttpClient;
 
-        public TodoistRestClient() : this(null, null)
+        public TodoistRestClient() : this(null, (IWebProxy)null)
         {
         }
 
-        public TodoistRestClient(string token) : this(token, null)
+        public TodoistRestClient(string token) : this(token, (IWebProxy)null)
         {
         }
 
@@ -43,11 +44,27 @@ public TodoistRestClient(string token, IWebProxy proxy)
             {
                 _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
             }
+
+            _disposeHttpClient = true;
+        }
+
+        public TodoistRestClient(string token, HttpClient httpClient)
+        {
+            _httpClient = httpClient;
+
+            _httpClient.BaseAddress = new Uri("https://api.todoist.com/sync/v9/");
+            if (!string.IsNullOrEmpty(token))
+            {
+                _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
+            }
         }
 
         public void Dispose()
         {
-            _httpClient?.Dispose();
+            if (_disposeHttpClient)
+            {
+                _httpClient?.Dispose(); 
+            }
         }