1 files changed, 79 insertions, 0 deletions
diff --git a/js/src/bus/index.ts b/js/src/bus/index.ts
new file mode 100644
index 000000000..5359debd9
--- /dev/null
+++ b/js/src/bus/index.ts
@@ -0,0 +1,79 @@
+import type { z, ZodSchema } from "zod/v4";
+import { App } from "../app";
+import { Log } from "../util/log";
+
+export namespace Bus {
+  const log = Log.create({ service: "bus" });
+  type Subscription = (event: any) => void;
+
+  const state = App.state("bus", () => {
+    const subscriptions = new Map<any, Subscription[]>();
+
+    return {
+      subscriptions,
+    };
+  });
+
+  export type EventDefinition = ReturnType<typeof event>;
+
+  export function event<Type extends string, Properties extends ZodSchema>(
+    type: Type,
+    properties: Properties,
+  ) {
+    return {
+      type,
+      properties,
+    };
+  }
+
+  export function publish<Definition extends EventDefinition>(
+    def: Definition,
+    properties: z.output<Definition["properties"]>,
+  ) {
+    const payload = {
+      type: def.type,
+      properties,
+    };
+    log.info("publishing", {
+      type: def.type,
+      ...properties,
+    });
+    for (const key of [def.type, "*"]) {
+      const match = state().subscriptions.get(key);
+      for (const sub of match ?? []) {
+        sub(payload);
+      }
+    }
+  }
+
+  export function subscribe<Definition extends EventDefinition>(
+    def: Definition,
+    callback: (event: {
+      type: Definition["type"];
+      properties: z.infer<Definition["properties"]>;
+    }) => void,
+  ) {
+    return raw(def.type, callback);
+  }
+
+  export function subscribeAll(callback: (event: any) => void) {
+    return raw("*", callback);
+  }
+
+  function raw(type: string, callback: (event: any) => void) {
+    log.info("subscribing", { type });
+    const subscriptions = state().subscriptions;
+    let match = subscriptions.get(type) ?? [];
+    match.push(callback);
+    subscriptions.set(type, match);
+
+    return () => {
+      log.info("unsubscribing", { type });
+      const match = subscriptions.get(type);
+      if (!match) return;
+      const index = match.indexOf(callback);
+      if (index === -1) return;
+      match.splice(index, 1);
+    };
+  }
+}