Add named callbacks to the js promise construct

(used for async communication which needs to callback many different times before the promise resolves)

android/app/src/main/java/io/freetubeapp/freetube/FreeTubeJavaScriptInterface.kt

@@ -578,6 +578,15 @@ class FreeTubeJavaScriptInterface {
     syncMessages.remove(promise)
     return value!!
   }
+  private fun addNamedCallbackToPromise(promise: String, name: String) {
+    context.runOnUiThread {
+      context.webView.loadUrl("javascript: window['${promise}'].callbacks = window['${promise}'].callbacks || {};  window['${promise}'].callbacks.notify = (key, message) => window['${promise}'].callbacks[key].forEach(callback => callback(message)); window['${promise}'].callbacks['${name}'] = window['${promise}'].callbacks['${name}'] || []")
+    }
+  }
+
+  private fun notifyNamedCallback(promise: String, name: String, message: String) {
+    context.webView.loadUrl("javascript: window['${promise}'].callbacks.notify(${context.btoa(name)}, ${context.btoa(message)})")
+  }
 
   /**
    * @return the id of a promise on the window

src/index.ejs

@@ -41,12 +41,15 @@
         window.clearAllMediaSessionEventListeners = function () {
           window.mediaSessionListeners = {}
         }
-        window.awaitAsyncResult = function (id) {
+        window.awaitAsyncResult = function (id, callbacks = {}) {
           return new Promise((resolve, reject) => {
             const interval = setInterval(async () => {
               if (id in window) {
                 clearInterval(interval)
                 try {
+                  if ('callbacks' in window[id]) {
+                    Object.assign(window[id].callbacks, callbacks)
+                  }
                   const result = await window[id].promise
                   resolve(Android.getSyncMessage(id))
                 } catch (ex) {