Initial commit

src/utils/event-emitter.ts

@@ -0,0 +1,152 @@
+// TODO: You'll probably want to use WeakRef's here.
+
+export type EventMap = Record<string, unknown>;
+
+type Listener<T> = (detail: T) => void;
+
+interface ListenerEntry<T> {
+  listener: Listener<T>;
+  wrappedListener: Listener<T>;
+  debounceTime?: number;
+  once?: boolean;
+}
+
+export type OffCallback = () => void;
+
+export class EventEmitter<T extends EventMap> {
+  private listeners: Map<keyof T, Set<ListenerEntry<T[keyof T]>>> = new Map();
+
+  on<K extends keyof T>(
+    type: K,
+    listener: Listener<T[K]>,
+    debounceMilliseconds?: number,
+  ): OffCallback {
+    const wrappedListener =
+      debounceMilliseconds && debounceMilliseconds > 0
+        ? this.debounce(listener, debounceMilliseconds)
+        : listener;
+
+    if (!this.listeners.has(type)) {
+      this.listeners.set(type, new Set());
+    }
+
+    const listenerEntry: ListenerEntry<T[K]> = {
+      listener,
+      wrappedListener,
+      debounceTime: debounceMilliseconds,
+    };
+
+    this.listeners.get(type)?.add(listenerEntry as ListenerEntry<T[keyof T]>);
+
+    // Return an "off" callback that can be called to stop listening for events.
+    return () => this.off(type, listener);
+  }
+
+  once<K extends keyof T>(
+    type: K,
+    listener: Listener<T[K]>,
+    debounceMilliseconds?: number,
+  ): OffCallback {
+    const wrappedListener: Listener<T[K]> = (detail: T[K]) => {
+      this.off(type, listener);
+      listener(detail);
+    };
+
+    const debouncedListener =
+      debounceMilliseconds && debounceMilliseconds > 0
+        ? this.debounce(wrappedListener, debounceMilliseconds)
+        : wrappedListener;
+
+    if (!this.listeners.has(type)) {
+      this.listeners.set(type, new Set());
+    }
+
+    const listenerEntry: ListenerEntry<T[K]> = {
+      listener,
+      wrappedListener: debouncedListener,
+      debounceTime: debounceMilliseconds,
+      once: true,
+    };
+
+    this.listeners.get(type)?.add(listenerEntry as ListenerEntry<T[keyof T]>);
+
+    // Return an "off" callback that can be called to stop listening for events.
+    return () => this.off(type, listener);
+  }
+
+  off<K extends keyof T>(type: K, listener: Listener<T[K]>): void {
+    const listeners = this.listeners.get(type);
+    if (!listeners) return;
+
+    const listenerEntry = Array.from(listeners).find(
+      (entry) =>
+        entry.listener === listener || entry.wrappedListener === listener,
+    );
+
+    if (listenerEntry) {
+      listeners.delete(listenerEntry);
+    }
+  }
+
+  emit<K extends keyof T>(type: K, payload: T[K]): boolean {
+    const listeners = this.listeners.get(type);
+    if (!listeners) return false;
+
+    listeners.forEach((entry) => {
+      entry.wrappedListener(payload);
+    });
+
+    return listeners.size > 0;
+  }
+
+  removeAllListeners(): void {
+    this.listeners.clear();
+  }
+
+  async waitFor<K extends keyof T>(
+    type: K,
+    predicate: (payload: T[K]) => boolean,
+    timeoutMs?: number,
+  ): Promise<T[K]> {
+    return new Promise((resolve, reject) => {
+      let timeoutId: ReturnType<typeof setTimeout> | undefined;
+
+      const listener = (payload: T[K]) => {
+        if (predicate(payload)) {
+          // Clean up
+          this.off(type, listener);
+          if (timeoutId !== undefined) {
+            clearTimeout(timeoutId);
+          }
+          resolve(payload);
+        }
+      };
+
+      // Set up timeout if specified
+      if (timeoutMs !== undefined) {
+        timeoutId = setTimeout(() => {
+          this.off(type, listener);
+          reject(new Error(`Timeout waiting for event "${String(type)}"`));
+        }, timeoutMs);
+      }
+
+      this.on(type, listener);
+    });
+  }
+
+  private debounce<K extends keyof T>(
+    func: Listener<T[K]>,
+    wait: number,
+  ): Listener<T[K]> {
+    let timeout: ReturnType<typeof setTimeout>;
+
+    return (detail: T[K]) => {
+      if (timeout !== null) {
+        clearTimeout(timeout);
+      }
+      timeout = setTimeout(() => {
+        func(detail);
+      }, wait);
+    };
+  }
+}