1 files changed, 52 insertions, 0 deletions
diff --git a/browser/components/syncedtabs/SyncedTabsDeckStore.sys.mjs b/browser/components/syncedtabs/SyncedTabsDeckStore.sys.mjs
new file mode 100644
index 0000000000..392e0fea99
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+++ b/browser/components/syncedtabs/SyncedTabsDeckStore.sys.mjs
@@ -0,0 +1,52 @@
+/* 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 { EventEmitter } from "resource:///modules/syncedtabs/EventEmitter.sys.mjs";
+
+/**
+ * SyncedTabsDeckStore
+ *
+ * This store keeps track of the deck view state, including the panels and which
+ * one is selected. The view listens for change events on the store, which are
+ * triggered whenever the state changes. If it's a small change, the state
+ * will have `isUpdatable` set to true so the view can skip rerendering the whole
+ * DOM.
+ */
+export function SyncedTabsDeckStore() {
+  EventEmitter.call(this);
+  this._panels = [];
+}
+
+Object.assign(SyncedTabsDeckStore.prototype, EventEmitter.prototype, {
+  _change(isUpdatable = false) {
+    let panels = this._panels.map(panel => {
+      return { id: panel, selected: panel === this._selectedPanel };
+    });
+    this.emit("change", { panels, isUpdatable });
+  },
+
+  /**
+   * Sets the selected panelId and triggers a change event.
+   * @param {String} panelId - ID of the panel to select.
+   */
+  selectPanel(panelId) {
+    if (!this._panels.includes(panelId) || this._selectedPanel === panelId) {
+      return;
+    }
+    this._selectedPanel = panelId;
+    this._change(true);
+  },
+
+  /**
+   * Update the set of panels in the deck and trigger a change event.
+   * @param {Array} panels - an array of IDs for each panel in the deck.
+   */
+  setPanels(panels) {
+    if (panels === this._panels) {
+      return;
+    }
+    this._panels = panels || [];
+    this._change();
+  },
+});