1 files changed, 54 insertions, 0 deletions
diff --git a/browser/components/backup/actors/BackupUIChild.sys.mjs b/browser/components/backup/actors/BackupUIChild.sys.mjs
new file mode 100644
index 0000000000..25d013fa8e
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+++ b/browser/components/backup/actors/BackupUIChild.sys.mjs
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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/. */
+
+/**
+ * A JSWindowActor that is responsible for marshalling information between
+ * the BackupService singleton and any registered UI widgets that need to
+ * represent data from that service. Any UI widgets that want to receive
+ * state updates from BackupService should emit a BackupUI:InitWidget
+ * event in a document that this actor pair is registered for.
+ */
+export class BackupUIChild extends JSWindowActorChild {
+  #inittedWidgets = new WeakSet();
+
+  /**
+   * Handles BackupUI:InitWidget custom events fired by widgets that want to
+   * register with BackupUIChild. Firing this event sends a message to the
+   * parent to request the BackupService state which will result in a
+   * `backupServiceState` property of the widget to be set when that state is
+   * received. Subsequent state updates will also cause that state property to
+   * be set.
+   *
+   * @param {Event} event
+   *   The BackupUI:InitWidget custom event that the widget fired.
+   */
+  handleEvent(event) {
+    if (event.type == "BackupUI:InitWidget") {
+      this.#inittedWidgets.add(event.target);
+      this.sendAsyncMessage("RequestState");
+    }
+  }
+
+  /**
+   * Handles messages sent by BackupUIParent.
+   *
+   * @param {ReceiveMessageArgument} message
+   *   The message received from the BackupUIParent.
+   */
+  receiveMessage(message) {
+    if (message.name == "StateUpdate") {
+      let widgets = ChromeUtils.nondeterministicGetWeakSetKeys(
+        this.#inittedWidgets
+      );
+      for (let widget of widgets) {
+        if (widget.isConnected) {
+          // Note: we might need to switch to using Cu.cloneInto here in the
+          // event that these widgets are embedded in a non-parent-process
+          // context, like in an onboarding card.
+          widget.backupServiceState = message.data.state;
+        }
+      }
+    }
+  }
+}