/**
* emitter.ts — Typed pub/sub base class for services.
*
* Replaces `document.dispatchEvent(new CustomEvent(...))` with typed,
* scoped event emitters. Services extend Emitter<T> where T defines
* the event contract as a record of event names → payload types.
*
* ```ts
* class NavigationEvents extends Emitter<{
* select: { id: string };
* filter: { filter: string };
* }> {}
*
* const nav = inject(NavigationEvents);
* nav.emit('select', { id: 'TASK-1' }); // typed
* nav.on('select', ({ id }) => console.log(id)); // typed
* const selectedId = nav.toSignal('select', e => e.id, null);
* ```
*/
import { signal, type Signal } from './signal.js';
import { hasContext, getCurrentComponent } from './context.js';
// ── Types ───────────────────────────────────────────────────────────
type EventMap = Record<string, unknown>;
type Listener<T> = (payload: T) => void;
// ── Emitter base class ──────────────────────────────────────────────
export class Emitter<Events extends EventMap> {
private listeners = new Map<keyof Events, Set<Listener<any>>>();
/**
* Emit a typed event. All subscribers for this event name are called
* synchronously. If a subscriber throws, other subscribers still fire.
*/
emit<K extends keyof Events>(event: K, payload: Events[K]): void {
const set = this.listeners.get(event);
if (!set) return;
// Iterate a copy to allow unsubscribe during callback
for (const fn of [...set]) {
try {
fn(payload);
} catch (err) {
console.error(`Emitter: subscriber for '${String(event)}' threw:`, err);
}
}
}
/**
* Subscribe to a typed event. Returns an unsubscribe function.
*
* If called during component setup, the subscription is automatically
* disposed on disconnectedCallback.
*/
on<K extends keyof Events>(event: K, fn: Listener<Events[K]>): () => void {
let set = this.listeners.get(event);
if (!set) {
set = new Set();
this.listeners.set(event, set);
}
set.add(fn);
const unsubscribe = () => {
set!.delete(fn);
if (set!.size === 0) {
this.listeners.delete(event);
}
};
// Auto-dispose if inside component setup context
if (hasContext()) {
getCurrentComponent().addDisposer(unsubscribe);
}
return unsubscribe;
}
/**
* Bridge an event into the signal system.
* Returns a signal that updates whenever the event fires.
*
* @param event - Event name to subscribe to
* @param selector - Transform the payload into the signal value
* @param initial - Initial signal value before any event fires
*/
toSignal<K extends keyof Events, V>(
event: K,
selector: (payload: Events[K]) => V,
initial: V,
): Signal<V> {
const s = signal(initial);
this.on(event, (payload) => {
s.value = selector(payload);
});
return s;
}
/**
* Remove all subscribers. Useful for testing cleanup.
*/
clear(): void {
this.listeners.clear();
}
}
