From 4026b954a6d1dd06d530a1342365cce7de628aae Mon Sep 17 00:00:00 2001
From: ludvigalden <aldenludvig@gmail.com>
Date: Mon, 10 Jan 2022 15:00:10 +0100
Subject: [PATCH] async notifier

---
 src/notifier-async.ts | 49 +++++++++++++++++++++++++++++++++++++++++++
 src/types.ts          |  4 ++++
 2 files changed, 53 insertions(+)
 create mode 100644 src/notifier-async.ts

diff --git a/src/notifier-async.ts b/src/notifier-async.ts
new file mode 100644
index 0000000..beacc99
--- /dev/null
+++ b/src/notifier-async.ts
@@ -0,0 +1,49 @@
+import { AsyncChangeListener, UnsubscribeFn } from "./types";
+
+export class NotifierAsync<T> extends Set<AsyncChangeListener<T>> {
+    subscribe(listener: AsyncChangeListener<T>): UnsubscribeFn {
+        this.add(listener);
+
+        return () => this.unsubscribe(listener);
+    }
+
+    unsubscribe(listener: AsyncChangeListener<T>) {
+        this.delete(listener);
+    }
+
+    notify(value: T): void | Promise<void>;
+    notify(value: T, ...otherArgs: any[]): void | Promise<void>;
+    notify(...args: any[]): void | Promise<void> {
+        const promises: Promise<void>[] = [];
+        Array.from(this.values()).forEach((listener) => {
+            const promiseOrVoid = listener(...(args as [T]));
+            if (isPromise(promiseOrVoid)) {
+                promises.push(promiseOrVoid);
+            }
+        });
+        if (promises.length) {
+            return Promise.all(promises).then(() => {});
+        }
+    }
+
+    static get<T>(abon: any): NotifierAsync<T> {
+        return (abon as any)[KEY];
+    }
+
+    static define<T>(abon: T): T {
+        Object.defineProperty(abon, KEY, {
+            value: new NotifierAsync(),
+            configurable: false,
+            writable: false,
+            enumerable: false,
+        });
+
+        return abon;
+    }
+}
+
+const KEY = "__notifier";
+
+function isPromise(v: any): v is Promise<any> {
+    return Boolean(v && typeof v["then"] === "function");
+}
diff --git a/src/types.ts b/src/types.ts
index b1759bf..e8e6b4e 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -38,3 +38,7 @@ export type SubscriberFlexResult = UnsubscribeFn | boolean | undefined | null |
 export type ComposedSubscriberFlexResult = SubscriberFlexResult | Iterable<SubscriberFlexResult>;
 
 export type ComposedSubscriberFlex = (listener: () => void) => ComposedSubscriberFlexResult;
+
+export interface AsyncChangeListener<T> {
+    (current: T): void | Promise<void>;
+}