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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { LitElement } from "chrome://global/content/vendor/lit.all.mjs";
+
+/**
+ * Helper for our replacement of @query. Used with `static queries` property.
+ *
+ * https://github.com/lit/lit/blob/main/packages/reactive-element/src/decorators/query.ts
+ */
+function query(el, selector) {
+  return () => el.renderRoot.querySelector(selector);
+}
+
+/**
+ * Helper for our replacement of @queryAll. Used with `static queries` property.
+ *
+ * https://github.com/lit/lit/blob/main/packages/reactive-element/src/decorators/query-all.ts
+ */
+function queryAll(el, selector) {
+  return () => el.renderRoot.querySelectorAll(selector);
+}
+
+/**
+ * MozLitElement provides extensions to the lit-provided LitElement class.
+ *
+ *******
+ *
+ * `@query` support (define a getter for a querySelector):
+ *
+ * static get queries() {
+ *   return {
+ *     propertyName: ".aNormal .cssSelector",
+ *     anotherName: { all: ".selectorFor .querySelectorAll" },
+ *   };
+ * }
+ *
+ * This example would add properties that would be written like this without
+ * using `queries`:
+ *
+ * get propertyName() {
+ *   return this.renderRoot?.querySelector(".aNormal .cssSelector");
+ * }
+ *
+ * get anotherName() {
+ *   return this.renderRoot?.querySelectorAll(".selectorFor .querySelectorAll");
+ * }
+ *******
+ *
+ * Automatic Fluent support for shadow DOM.
+ *
+ * Fluent requires that a shadowRoot be connected before it can use Fluent.
+ * Shadow roots will get connected automatically.
+ *
+ *******
+ *
+ * Test helper for sending events after a change: `dispatchOnUpdateComplete`
+ *
+ * When some async stuff is going on and you want to wait for it in a test, you
+ * can use `this.dispatchOnUpdateComplete(myEvent)` and have the test wait on
+ * your event.
+ *
+ * The component will then wait for your reactive property change to take effect
+ * and dispatch the desired event.
+ *
+ * Example:
+ *
+ * async onClick() {
+ *   let response = await this.getServerResponse(this.data);
+ *   // Show the response status to the user.
+ *   this.responseStatus = respose.status;
+ *   this.dispatchOnUpdateComplete(
+ *     new CustomEvent("status-shown")
+ *   );
+ * }
+ *
+ * add_task(async testButton() {
+ *   let button = this.setupAndGetButton();
+ *   button.click();
+ *   await BrowserTestUtils.waitForEvent(button, "status-shown");
+ * });
+ */
+export class MozLitElement extends LitElement {
+  constructor() {
+    super();
+    let { queries } = this.constructor;
+    if (queries) {
+      for (let [selectorName, selector] of Object.entries(queries)) {
+        if (selector.all) {
+          Object.defineProperty(this, selectorName, {
+            get: queryAll(this, selector.all),
+          });
+        } else {
+          Object.defineProperty(this, selectorName, {
+            get: query(this, selector),
+          });
+        }
+      }
+    }
+  }
+
+  connectedCallback() {
+    super.connectedCallback();
+    if (
+      this.renderRoot == this.shadowRoot &&
+      !this._l10nRootConnected &&
+      document.l10n
+    ) {
+      document.l10n.connectRoot(this.renderRoot);
+      this._l10nRootConnected = true;
+    }
+  }
+
+  async dispatchOnUpdateComplete(event) {
+    await this.updateComplete;
+    this.dispatchEvent(event);
+  }
+
+  update() {
+    super.update();
+    if (document.l10n) {
+      document.l10n.translateFragment(this.renderRoot);
+    }
+  }
+}