Add basic speech synthesis, with a Linux Speech Dispatcher backend.

Signed-off-by: Ritchie Frodomar <alkalinethunder@gmail.com>

src/Ritchie.Toolbox/Accessibility/ISpeechHandler.cs

@@ -0,0 +1,15 @@
+namespace Ritchie.Toolbox.Accessibility;
+
+/// <summary>
+///     Interface for a class that can be used as a speech synthesis backend for the <see cref="TextToSpeech"/> accessibility API.
+/// </summary>
+public interface ISpeechHandler
+{
+    /// <summary>
+    ///     Speak the specified text aloud.
+    /// </summary>
+    /// <param name="textToSpeak">The text to speak.</param>
+    /// <param name="interruptToken">A <see cref="CancellationToken"/> that will be cancelled if speech is interrupted.</param>
+    /// <returns></returns>
+    Task SpeakAsync(string textToSpeak, CancellationToken interruptToken);
+}

src/Ritchie.Toolbox/Accessibility/SpeechDispatcherBackend.cs

@@ -0,0 +1,42 @@
+using System.Diagnostics;
+
+namespace Ritchie.Toolbox.Accessibility;
+
+/// <summary>
+///     Implementation of <see cref="ISpeechHandler"/> that uses the Speech Dispatcher daemon (speechd).
+/// </summary>
+public sealed class SpeechDispatcherBackend : ISpeechHandler
+{
+    private readonly string SayCommandName = "/usr/bin/spd-say";
+    
+    /// <inheritdoc />
+    public async Task SpeakAsync(string textToSpeak, CancellationToken interruptToken)
+    {
+        var startInfo = new ProcessStartInfo();
+        startInfo.FileName = SayCommandName;
+        startInfo.UseShellExecute = false;
+        startInfo.RedirectStandardInput = true;
+        startInfo.ArgumentList.Add("-w"); // Tells it to wait for speech to finish, since the game expects that.
+        startInfo.ArgumentList.Add("--pipe-mode"); // Allows us to stream text in, instead of passing it by CLI args, which is safer.
+
+        var process = Process.Start(startInfo);
+        if (process == null)
+            throw new InvalidOperationException($"Could not start the spd-say process. Ensure that Speech Dispatcher is installed on this computer and that spd-say is in PATH.");
+
+        try
+        {
+            await process.StandardInput.WriteAsync(textToSpeak);
+            process.StandardInput.Close();
+            
+            await process.WaitForExitAsync(interruptToken);
+        }
+        catch (OperationCanceledException)
+        {
+            process.Kill();
+        }
+        finally
+        {
+            process.Dispose();
+        }
+    }
+}

src/Ritchie.Toolbox/Accessibility/TextToSpeech.cs

@@ -0,0 +1,57 @@
+using System.Runtime.CompilerServices;
+using Silk.NET.SDL;
+
+namespace Ritchie.Toolbox.Accessibility;
+
+/// <summary>
+///     Accessibility API for reading text aloud with a speech synthesis backend.
+/// </summary>
+public static class TextToSpeech
+{
+    private static ISpeechHandler?          speechHandler;
+    private static CancellationTokenSource? currentSpeechToken;
+
+    /// <summary>
+    ///     Switch the current speech backend.
+    /// </summary>
+    /// <param name="newSpeechHandler">The new backend to use. If null is provided, speech synthesis support will be disabled.</param>
+    public static void SetSpeechHandler(ISpeechHandler? newSpeechHandler)
+    {
+        StopSpeaking();
+
+        if (speechHandler is IDisposable disposable)
+            disposable.Dispose();
+
+        speechHandler = newSpeechHandler;
+    }
+
+    /// <summary>
+    ///     Tries to read the specified text aloud with the current speech backend.
+    /// </summary>
+    /// <param name="textToSpeak">The text to speak.</param>
+    /// <returns>A task that waits for speech to finish, and returns true if speech was successful.</returns>
+    public static async Task<bool> TrySpeakAsync(string textToSpeak)
+    {
+        if (speechHandler == null)
+            return false;
+
+        StopSpeaking();
+
+        try
+        {
+            currentSpeechToken = new();
+            await speechHandler.SpeakAsync(textToSpeak, currentSpeechToken.Token);
+            return true;
+        }
+        catch (Exception ex)
+        {
+            return false;
+        }
+    }
+
+    private static void StopSpeaking()
+    {
+        currentSpeechToken?.Cancel();
+        currentSpeechToken = null;
+    }
+}

src/SociallyDistant/Commands/Misc/SayCommand.cs

@@ -0,0 +1,27 @@
+using Ritchie.Toolbox.Accessibility;
+using SociallyDistant.Architecture;
+using SociallyDistant.Core.Modules;
+using SociallyDistant.Core.OS.Tasks;
+
+namespace SociallyDistant.Commands.Misc;
+
+[Command("say")]
+public sealed class SayCommand : ScriptableCommand
+{
+    public SayCommand(IGameContext gameContext) : base(gameContext)
+    {
+    }
+
+    public override string Name => "say";
+
+    protected override async Task DefaultHandler()
+    {
+        string textToSpeak = string.Join(" ", Arguments);
+
+        bool didSpeak = await TextToSpeech.TrySpeakAsync(textToSpeak);
+        if (!didSpeak)
+        {
+            Console.WriteLine("Speech service is unavailable.");
+        }
+    }
+}

src/SociallyDistant/GameApplication.cs

@@ -1,6 +1,7 @@
 using System.Diagnostics;
 using System.Runtime.InteropServices;
 using Microsoft.Xna.Framework;
+using Ritchie.Toolbox.Accessibility;
 using Serilog;
 using Silk.NET.SDL;
 using SociallyDistant.Core.Config;
@@ -23,6 +24,11 @@ internal sealed class GameApplication : Application
     
     public GameApplication()
     {
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+        {
+            TextToSpeech.SetSpeechHandler(new SpeechDispatcherBackend());
+        }
+        
         var videoDriversSupported = GetSdlDrivers();
         var sdlSupportsWayland = videoDriversSupported.Contains("wayland");