make ScratchLinkApp to take the place of MAUI app

Note that this builds and runs, but doesn't work: the Xamarin.Mac
implementation of `System.Net` always sets `IsWebSocketRequest` to
`false` and doesn't actually support WebSockets connections as a server.

scratch-link-common/BLE/BLESession.cs

@@ -11,6 +11,7 @@ using System.Net.WebSockets;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using System.Threading.Tasks;
+using Microsoft.Extensions.DependencyInjection;
 using ScratchLink.Extensions;
 using ScratchLink.JsonRpc;
 
@@ -28,7 +29,7 @@ internal abstract class BLESession<TUUID> : Session
     public BLESession(WebSocketContext context)
         : base(context)
     {
-        this.GattHelpers = IPlatformApplication.Current.Services.GetService<GattHelpers<TUUID>>();
+        this.GattHelpers = ScratchLinkApp.Current.Services.GetService<GattHelpers<TUUID>>();
         this.AllowedServices = new ();
         this.Handlers["discover"] = this.HandleDiscover;
         this.Handlers["connect"] = this.HandleConnect;

scratch-link-common/ScratchLinkApp.cs

@@ -0,0 +1,150 @@
+// <copyright file="ScratchLinkApp.cs" company="Scratch Foundation">
+// Copyright (c) Scratch Foundation. All rights reserved.
+// </copyright>
+
+namespace ScratchLink;
+
+using System;
+using System.Diagnostics;
+using System.Net;
+using System.Net.WebSockets;
+using System.Text;
+using System.Threading;
+using Microsoft.Extensions.DependencyInjection;
+using ScratchLink.BLE;
+
+/// <summary>
+/// Main entry point for Scratch Link and central service provider for dependency injection.
+/// </summary>
+public class ScratchLinkApp
+{
+    private const int WebSocketPort = 20111;
+
+    private readonly SessionManager sessionManager;
+    private readonly WebSocketListener webSocketListener;
+
+    private ScratchLinkApp(IServiceProvider platformServicesProvider)
+    {
+        this.Services = platformServicesProvider;
+        if (Current != null)
+        {
+            throw new InvalidOperationException("Attempt to create a second app instance");
+        }
+
+        Current = this;
+
+        this.sessionManager = this.Services.GetService<SessionManager>();
+        this.webSocketListener = new ()
+        {
+            OnWebSocketConnection = (webSocketContext) =>
+            {
+                this.sessionManager.ClientDidConnect(webSocketContext);
+            },
+            OnOtherConnection = (context) =>
+            {
+                context.Response.Headers.Clear();
+                context.Response.SendChunked = false;
+                context.Response.StatusCode = 426; // Upgrade Required
+                context.Response.OutputStream.Write(Encoding.UTF8.GetBytes("WebSockets required"));
+                context.Response.OutputStream.Close();
+            },
+        };
+    }
+
+    /// <summary>
+    /// Gets the current app instance.
+    /// </summary>
+    public static ScratchLinkApp Current { get; private set; }
+
+    /// <summary>
+    /// Gets the platform-specific services provider.
+    /// This provides access to services like the session manager or GATT helpers.
+    /// </summary>
+    public IServiceProvider Services { get; private set; }
+
+    /// <summary>
+    /// Run the app.
+    /// </summary>
+    public void Run()
+    {
+        if (!HttpListener.IsSupported)
+        {
+            // TODO: pop up an error message
+            return;
+        }
+
+        this.webSocketListener.Start(new[]
+        {
+            string.Format("http://127.0.0.1:{0}/", WebSocketPort),
+            string.Format("http://localhost:{0}/", WebSocketPort),
+        });
+    }
+
+    private void HandleSessionDebug(WebSocketContext context)
+    {
+        var origin = context.Headers.Get("origin");
+        var socket = context.WebSocket;
+        Debug.Print("New connection");
+        socket.CloseAsync(WebSocketCloseStatus.NormalClosure, null, CancellationToken.None);
+    }
+
+    /// <summary>
+    /// Builds a Scratch Link app instance.
+    /// Fills the role of the .NET generic host or <c>MauiAppBuilder</c>.
+    /// </summary>
+    public class Builder
+    {
+        private string[] arguments;
+        private Type sessionManagerType;
+        private Type gattHelpersBaseType;
+        private Type gattHelpersType;
+
+        /// <summary>
+        /// Sets the arguments which will be passed to the app host.
+        /// Must be called before Build().
+        /// </summary>
+        /// <param name="arguments">Command line arguments from app invocation.</param>
+        public void SetArguments(string[] arguments)
+        {
+            this.arguments = arguments;
+        }
+
+        /// <summary>
+        /// Sets the type which will be used to build the platform-specific session manager.
+        /// </summary>
+        /// <typeparam name="TSessionManager">The platform-specific session manager type.</typeparam>
+        internal void SetSessionManager<TSessionManager>()
+            where TSessionManager : SessionManager
+        {
+            this.sessionManagerType = typeof(TSessionManager);
+        }
+
+        /// <summary>
+        /// Sets the types which will be used to build the BLE GATT helpers.
+        /// </summary>
+        /// <typeparam name="TGattHelpers">The platform-specific GATT helpers type.</typeparam>
+        /// <typeparam name="TUUID">The platform-specific type for BLE UUID values.</typeparam>
+        internal void SetGattHelpers<TGattHelpers, TUUID>()
+            where TGattHelpers : GattHelpers<TUUID>
+        {
+            this.gattHelpersBaseType = typeof(GattHelpers<TUUID>);
+            this.gattHelpersType = typeof(TGattHelpers);
+        }
+
+        /// <summary>
+        /// Builds a Scratch Link app host.
+        /// </summary>
+        /// <returns>A new Scratch Link app host.</returns>
+        internal ScratchLinkApp Build()
+        {
+            var serviceCollection = new ServiceCollection();
+            var serviceProviderOptions = new ServiceProviderOptions { ValidateOnBuild = true, ValidateScopes = true };
+            var servicesProvider = new DefaultServiceProviderFactory(serviceProviderOptions)
+                .CreateBuilder(serviceCollection)
+                .AddSingleton(typeof(SessionManager), this.sessionManagerType)
+                .AddSingleton(this.gattHelpersBaseType, this.gattHelpersType)
+                .BuildServiceProvider();
+            return new ScratchLinkApp(servicesProvider);
+        }
+    }
+}

scratch-link-common/scratch-link-common.projitems

@@ -27,5 +27,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)Session.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)SessionManager.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)WebSocketListener.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)ScratchLinkApp.cs" />
   </ItemGroup>
 </Project>

scratch-link-mac/AppDelegate.cs

@@ -5,7 +5,9 @@
 namespace ScratchLink.Mac;
 
 using AppKit;
+using CoreBluetooth;
 using Foundation;
+using ScratchLink.Mac.BLE;
 
 /// <summary>
 /// Scratch Link's implementation of the NSApplicationDelegate protocol.
@@ -19,7 +21,14 @@ public class AppDelegate : NSApplicationDelegate
     /// <param name="notification">A notification named <c>didFinishLaunchingNotification</c>.</param>
     public override void DidFinishLaunching(NSNotification notification)
     {
-        // Insert code here to initialize your application
+        var appBuilder = new ScratchLinkApp.Builder();
+        appBuilder.SetArguments(new NSProcessInfo().Arguments);
+        appBuilder.SetSessionManager<MacSessionManager>();
+        appBuilder.SetGattHelpers<MacGattHelpers, CBUUID>();
+
+        var app = appBuilder.Build();
+
+        app.Run();
     }
 
     /// <summary>

scratch-link-mac/scratch-link-mac.csproj

@@ -105,6 +105,9 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <AdditionalFiles Include="$(SolutionDir)stylecop.json" />
+    <PackageReference Include="Fleck">
+      <Version>1.2.0</Version>
+    </PackageReference>
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="System.Text.Json">

scratch-link/ScratchLinkApp.xaml

@@ -1,25 +0,0 @@
-<Application xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
-             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
-             xmlns:local="clr-namespace:ScratchLink"
-             x:Class="ScratchLink.ScratchLinkApp">
-    <Application.Resources>
-        <ResourceDictionary>
-
-            <Color x:Key="PrimaryColor">#512bdf</Color>
-            <Color x:Key="SecondaryColor">White</Color>
-
-            <Style TargetType="Label">
-                <Setter Property="TextColor" Value="{DynamicResource PrimaryColor}" />
-                <Setter Property="FontFamily" Value="OpenSansRegular" />
-            </Style>
-
-            <Style TargetType="Button">
-                <Setter Property="TextColor" Value="{DynamicResource SecondaryColor}" />
-                <Setter Property="FontFamily" Value="OpenSansRegular" />
-                <Setter Property="BackgroundColor" Value="{DynamicResource PrimaryColor}" />
-                <Setter Property="Padding" Value="14,10" />
-            </Style>
-
-        </ResourceDictionary>
-    </Application.Resources>
-</Application>

scratch-link/ScratchLinkApp.xaml.cs

@@ -1,72 +0,0 @@
-// <copyright file="ScratchLinkApp.xaml.cs" company="Scratch Foundation">
-// Copyright (c) Scratch Foundation. All rights reserved.
-// </copyright>
-
-namespace ScratchLink;
-
-using ScratchLink.Resources.Strings;
-
-using System.Net;
-using System.Net.WebSockets;
-
-/// <summary>
-/// The <see cref="ScratchLinkApp"/> class contains the cross-platform entry point for the application.
-/// </summary>
-public partial class ScratchLinkApp : Application
-{
-    private const int WebSocketPort = 20111;
-
-    private readonly SessionManager sessionManager;
-    private readonly WebSocketListener webSocketListener;
-
-    /// <summary>
-    /// Initializes a new instance of the <see cref="ScratchLinkApp"/> class.
-    /// This is the cross-platform entry point.
-    /// </summary>
-    public ScratchLinkApp()
-    {
-        this.InitializeComponent();
-
-        this.MainPage = new MainPage();
-
-        if (!HttpListener.IsSupported)
-        {
-            // TODO: this doesn't work right
-            this.MainPage.DisplayAlert("Error", AppResource.HTTP_Listener_not_supported, "Quit").ContinueWith(task =>
-            {
-                this.Quit();
-            });
-            return;
-        }
-
-        this.sessionManager = IPlatformApplication.Current.Services.GetService<SessionManager>();
-
-        this.webSocketListener = new ()
-        {
-            OnWebSocketConnection = (webSocketContext) =>
-            {
-                this.sessionManager.ClientDidConnect(webSocketContext);
-            },
-            OnOtherConnection = (context) =>
-            {
-                throw new NotImplementedException();
-            },
-        };
-        this.webSocketListener.Start(new[]
-        {
-            string.Format("http://127.0.0.1:{0}/", WebSocketPort),
-            string.Format("http://localhost:{0}/", WebSocketPort),
-        });
-    }
-
-    private void HandleSessionDebug(WebSocketContext context)
-    {
-        var origin = context.Headers.Get("origin");
-        var socket = context.WebSocket;
-        this.Dispatcher.Dispatch(() =>
-        {
-            this.MainPage.DisplayAlert("New connection", string.Format("Path: {0}\nOrigin: {1}", context.RequestUri.AbsolutePath, origin), "OK");
-        });
-        socket.CloseAsync(WebSocketCloseStatus.NormalClosure, null, CancellationToken.None);
-    }
-}