add broker so eventually events can span client/worker and maybe minion

src/moto/broker.js

@@ -0,0 +1,49 @@
+class Broker {
+    constructor() {
+        this.topics = {};
+    }
+
+    topics() {
+        return Object.keys(this.topics);
+    }
+
+    subscribe(topic, listener) {
+        let topics = this.topics;
+        let channel = topics[topic];
+        if (!channel) {
+            channel = topics[topic] = [];
+        }
+        if (channel.indexOf(listener) < 0) {
+            channel.push(listener);
+            this.publish(".topic.add", topic);
+        }
+    }
+
+    unsubscribe(topic, listener) {
+        let channel = this.topics[topic];
+        if (!channel) {
+            return;
+        }
+        let index = channel.indexOf(listener);
+        if (index < 0) {
+            return;
+        }
+        channel.splice(index,1);
+        if (channel.length === 0) {
+            delete this.topics[topic];
+            this.publish(".topic.remove", topic);
+        }
+    }
+
+    publish(topic, message, options = {}) {
+        if (topic !== ".topic.publish") {
+            this.publish(".topic.publish", {topic, message, options});
+        }
+        let channel = this.topics[topic];
+        if (channel && channel.length) {
+            for (let listener of channel) {
+                listener(message, topic, options);
+            }
+        }
+    }
+}