fix: parallax replacer might fail to find shadow root on its first try

frontend/app/src/app/util/ion-content-parallax.directive.ts

@@ -13,6 +13,7 @@
  * this program. If not, see <https://www.gnu.org/licenses/>.
  */
 import {Directive, ElementRef, HostBinding, Input, OnDestroy, OnInit} from '@angular/core';
+import {waitForElement} from './ion-icon/shadow-attacher';
 
 type IonicColor =
   | 'danger'
@@ -86,31 +87,39 @@ export class IonContentParallaxDirective implements OnInit, OnDestroy {
 
   constructor(private element: ElementRef) {}
 
-  ngOnInit() {
-    this.mutationObserver = new MutationObserver(() => {
-      const inner = this.element.nativeElement.shadowRoot.querySelector('.inner-scroll') as
-        | HTMLDivElement
-        | undefined;
-      if (!inner) return;
-
-      // eslint-disable-next-line unicorn/no-array-for-each
-      inner.childNodes.forEach(node => node.remove());
-
-      inner.part.add('parallax-scroll');
-      const parallaxParentElement = document.createElement('div');
-      parallaxParentElement.part.add('parallax-parent');
-      const parallaxElement = document.createElement('div');
-      parallaxElement.part.add('parallax');
-
-      inner.append(parallaxParentElement);
-      parallaxParentElement.append(parallaxElement, document.createElement('slot'));
-    });
-    this.mutationObserver.observe(this.element.nativeElement.shadowRoot, {
-      childList: true,
-    });
+  async ngOnInit() {
+    this.mutationObserver = new MutationObserver(this.replace.bind(this));
+    const element = this.element.nativeElement;
+    if (element.shadowRoot) {
+      this.mutationObserver.observe(element.shadowRoot, {childList: true});
+    } else {
+      console.warn("Shadow root didn't exist for parallax, retrying...");
+      await waitForElement(() => this.element.nativeElement.shadowRoot);
+      this.mutationObserver.observe(element.shadowRoot, {childList: true});
+      this.replace();
+    }
   }
 
   ngOnDestroy() {
     this.mutationObserver.disconnect();
   }
+
+  replace() {
+    const inner = this.element.nativeElement.shadowRoot.querySelector('.inner-scroll') as
+      | HTMLDivElement
+      | undefined;
+    if (!inner) return;
+
+    // eslint-disable-next-line unicorn/no-array-for-each
+    inner.childNodes.forEach(node => node.remove());
+
+    inner.part.add('parallax-scroll');
+    const parallaxParentElement = document.createElement('div');
+    parallaxParentElement.part.add('parallax-parent');
+    const parallaxElement = document.createElement('div');
+    parallaxElement.part.add('parallax');
+
+    inner.append(parallaxParentElement);
+    parallaxParentElement.append(parallaxElement, document.createElement('slot'));
+  }
 }

frontend/app/src/app/util/ion-icon/replace-util.ts

@@ -16,6 +16,7 @@
 import {ComponentRef, Directive, ElementRef, OnDestroy, OnInit, ViewContainerRef} from '@angular/core';
 import {IonIcon} from '@ionic/angular';
 import {IonIconDirective} from './ion-icon.directive';
+import {waitForElement} from './shadow-attacher';
 
 export type IconData = Omit<
   Partial<IonIconDirective>,
@@ -79,25 +80,15 @@ export abstract class IconReplacer implements OnInit, OnDestroy {
     // noop
   }
 
-  ngOnInit() {
+  async ngOnInit() {
     this.init();
 
     if (this.host) {
       this.attachObserver();
     } else {
-      let tries = 0;
-      console.warn('IconReplacer: host not found, trying again');
-      const interval = setInterval(() => {
-        if (tries > this.maxAttempts) {
-          clearInterval(interval);
-          throw new Error('IconReplacer: host not found');
-        }
-        if (this.host) {
-          clearInterval(interval);
-          this.replace();
-        }
-        tries++;
-      }, this.retryAfterMs);
+      console.warn("Shadow root didn't exist for ion icon replacer, retrying...");
+      await waitForElement(() => this.host);
+      this.replace();
     }
   }
 

frontend/app/src/app/util/ion-icon/shadow-attacher.ts

@@ -0,0 +1,23 @@
+/**
+ * Waits for an element to appear
+ *
+ * In normal circumstances *please* use the mutation observer for these kinds of tasks.
+ * However, shadowDom attachment is **not** covered by the mutation observer,
+ * so a solution like this is required.
+ */
+export async function waitForElement(query: () => HTMLElement, maxAttempts = 10, retryAfterMs = 10) {
+  let tries = 0;
+  return new Promise<void>(resolve => {
+    const interval = setInterval(() => {
+      if (tries > maxAttempts) {
+        clearInterval(interval);
+        throw new Error('Element not found');
+      }
+      if (query()) {
+        clearInterval(interval);
+        resolve();
+      }
+      tries++;
+    }, retryAfterMs);
+  });
+}