Add SharedEventService

Forgot to put in b4db1fc

Services/SharedEventService/SharedEventService.cs

@@ -0,0 +1,48 @@
+using System.Threading.Channels;
+
+namespace RegexBot.Services.SharedEventService;
+/// <summary>
+/// Implements a queue which any service or module may send objects into,
+/// which are then sent to subscribing services and/or modules. Allows for simple,
+/// basic sharing of information between separate parts of the program.
+/// </summary>
+class SharedEventService : Service {
+    private readonly Channel<ISharedEvent> _items;
+    //private readonly Task _itemPropagationWorker;
+
+    internal SharedEventService(RegexbotClient bot) : base(bot) {
+        _items = Channel.CreateUnbounded<ISharedEvent>();
+        _ = Task.Factory.StartNew(ItemPropagator, CancellationToken.None,
+                                  TaskCreationOptions.LongRunning, TaskScheduler.Default);
+    }
+
+    // Hooked (lock this on self)
+    internal event RegexbotClient.IncomingSharedEventHandler? Subscribers;
+
+    internal async Task PushSharedEventAsync(ISharedEvent ev) {
+        await _items.Writer.WriteAsync(ev);
+    }
+
+    private async Task ItemPropagator() {
+        while (true) {
+            var ev = await _items.Reader.ReadAsync();
+
+            Delegate[]? subscribed;
+            lock (this) {
+                subscribed = Subscribers?.GetInvocationList();
+                if (subscribed == null || subscribed.Length == 0) return;
+            }
+
+            foreach (var handler in subscribed) {
+                // Fire and forget!
+                _ = Task.Run(async () => {
+                    try {
+                        await (Task)handler.DynamicInvoke(ev)!;
+                    } catch (Exception ex) {
+                        Log("Unhandled exception in shared event handler:" + ex.ToString());
+                    }
+                });
+            }
+        }
+    }
+}