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packages/pubsub/src/index.ts

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+/**
+ * @wrnexus/pubsub — topic-based publish/subscribe with a pluggable driver.
+ * The default is in-process; swap in a Redis/NATS driver for cross-instance
+ * messaging (it also backs @wrnexus/core's realtime bridge).
+ *
+ *   const bus = createPubSub();
+ *   const off = bus.subscribe("order:*", (msg, topic) => {...});
+ *   await bus.publish("order:created", { id: 7 });
+ *
+ * Subscriptions match exact topics, "ns:*" prefixes, and "*" (everything).
+ */
+
+export type Handler<T = unknown> = (message: T, topic: string) => void | Promise<void>;
+
+export interface PubSubDriver {
+  publish(topic: string, message: unknown): void | Promise<void>;
+  subscribe(pattern: string, handler: Handler): () => void;
+}
+
+export interface PubSub {
+  publish<T = unknown>(topic: string, message: T): Promise<void>;
+  subscribe<T = unknown>(pattern: string, handler: Handler<T>): () => void;
+}
+
+function patternMatches(pattern: string, topic: string): boolean {
+  if (pattern === "*" || pattern === topic) return true;
+  if (pattern.endsWith(":*")) return topic.startsWith(pattern.slice(0, -1)); // "post:" prefix
+  return false;
+}
+
+/** In-process pub/sub driver (default). */
+export function memoryDriver(): PubSubDriver {
+  const subs = new Map<string, Set<Handler>>();
+  return {
+    publish(topic, message) {
+      for (const [pattern, handlers] of subs) {
+        if (!patternMatches(pattern, topic)) continue;
+        for (const handler of handlers) void handler(message, topic);
+      }
+    },
+    subscribe(pattern, handler) {
+      let set = subs.get(pattern);
+      if (!set) subs.set(pattern, (set = new Set()));
+      set.add(handler);
+      return () => {
+        set!.delete(handler);
+        if (!set!.size) subs.delete(pattern);
+      };
+    },
+  };
+}
+
+/** Create a pub/sub bus over a driver (in-memory by default). */
+export function createPubSub(driver: PubSubDriver = memoryDriver()): PubSub {
+  return {
+    async publish(topic, message) {
+      await driver.publish(topic, message);
+    },
+    subscribe(pattern, handler) {
+      return driver.subscribe(pattern, handler as Handler);
+    },
+  };
+}