Add plugin isolation IPC scaffolding and host phase one docs (#5)

LanMountainDesktop.PluginIsolation.Ipc/PluginIpcServer.cs

@@ -0,0 +1,113 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace LanMountainDesktop.PluginIsolation.Ipc;
+
+public sealed class PluginIpcServer
+{
+    private readonly Dictionary<string, Func<JsonElement?, CancellationToken, Task<JsonElement?>>> _requestHandlers =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    private readonly Dictionary<string, Func<JsonElement?, CancellationToken, Task>> _notificationHandlers =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    public PluginIpcServer(PluginIpcServerOptions options)
+    {
+        Options = options ?? throw new ArgumentNullException(nameof(options));
+        SerializerContext = options.SerializerContext ?? throw new ArgumentNullException(nameof(options.SerializerContext));
+        SerializerOptions = SerializerContext.Options;
+    }
+
+    public PluginIpcServerOptions Options { get; }
+
+    public JsonSerializerContext SerializerContext { get; }
+
+    public JsonSerializerOptions SerializerOptions { get; }
+
+    public void MapRequest<TRequest, TResponse>(
+        string route,
+        Func<TRequest, CancellationToken, Task<TResponse>> handler)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(route);
+        ArgumentNullException.ThrowIfNull(handler);
+
+        _requestHandlers[route] = async (payload, cancellationToken) =>
+        {
+            var request = Deserialize<TRequest>(payload);
+            var response = await handler(request, cancellationToken).ConfigureAwait(false);
+            return Serialize(response);
+        };
+    }
+
+    public void MapNotification<TPayload>(
+        string route,
+        Func<TPayload, CancellationToken, Task> handler)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(route);
+        ArgumentNullException.ThrowIfNull(handler);
+
+        _notificationHandlers[route] = (payload, cancellationToken) =>
+        {
+            var notification = Deserialize<TPayload>(payload);
+            return handler(notification, cancellationToken);
+        };
+    }
+
+    public async Task<JsonElement?> HandleRequestAsync(
+        string route,
+        JsonElement? payload,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(route);
+
+        if (!_requestHandlers.TryGetValue(route, out var handler))
+        {
+            throw new InvalidOperationException($"No IPC request handler is registered for route '{route}'.");
+        }
+
+        return await handler(payload, cancellationToken).ConfigureAwait(false);
+    }
+
+    public Task HandleNotificationAsync(
+        string route,
+        JsonElement? payload,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(route);
+
+        if (!_notificationHandlers.TryGetValue(route, out var handler))
+        {
+            throw new InvalidOperationException($"No IPC notification handler is registered for route '{route}'.");
+        }
+
+        return handler(payload, cancellationToken);
+    }
+
+    private JsonElement Serialize<T>(T payload)
+    {
+        return JsonSerializer.SerializeToElement(payload, SerializerOptions);
+    }
+
+    private T Deserialize<T>(JsonElement? payload)
+    {
+        if (payload is null)
+        {
+            if (default(T) is null)
+            {
+                return default!;
+            }
+
+            throw new InvalidOperationException(
+                $"IPC payload is required for '{typeof(T).FullName}', but the caller provided no payload.");
+        }
+
+        var value = payload.Value.Deserialize<T>(SerializerOptions);
+        if (value is null && default(T) is not null)
+        {
+            throw new InvalidOperationException(
+                $"Failed to deserialize IPC payload to '{typeof(T).FullName}'.");
+        }
+
+        return value!;
+    }
+}