1 files changed, 142 insertions, 0 deletions
diff --git a/remote/cdp/observers/TargetObserver.sys.mjs b/remote/cdp/observers/TargetObserver.sys.mjs
new file mode 100644
index 0000000000..dfd9e2d9dc
--- /dev/null
+++ b/remote/cdp/observers/TargetObserver.sys.mjs
@@ -0,0 +1,142 @@
+/* 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/. */
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  EventEmitter: "resource://gre/modules/EventEmitter.sys.mjs",
+
+  EventPromise: "chrome://remote/content/shared/Sync.sys.mjs",
+});
+
+// TODO(ato):
+//
+// The DOM team is working on pulling browsing context related behaviour,
+// such as window and tab handling, out of product code and into the platform.
+// This will have implication for the remote agent,
+// and as the platform gains support for product-independent events
+// we can likely get rid of this entire module.
+
+/**
+ * Observe Firefox tabs as they open and close.
+ *
+ * "open" fires when a tab opens.
+ * "close" fires when a tab closes.
+ */
+export class TabObserver {
+  /**
+   * @param {boolean?} [false] registerExisting
+   *     Events will be fired for ChromeWIndows and their respective tabs
+   *     at the time when the observer is started.
+   */
+  constructor({ registerExisting = false } = {}) {
+    lazy.EventEmitter.decorate(this);
+
+    this.registerExisting = registerExisting;
+
+    this.onTabOpen = this.onTabOpen.bind(this);
+    this.onTabClose = this.onTabClose.bind(this);
+  }
+
+  async start() {
+    Services.wm.addListener(this);
+
+    if (this.registerExisting) {
+      // Start listening for events on already open windows
+      for (const win of Services.wm.getEnumerator("navigator:browser")) {
+        this._registerDOMWindow(win);
+      }
+    }
+  }
+
+  stop() {
+    Services.wm.removeListener(this);
+
+    // Stop listening for events on still opened windows
+    for (const win of Services.wm.getEnumerator("navigator:browser")) {
+      this._unregisterDOMWindow(win);
+    }
+  }
+
+  // Event emitters
+
+  onTabOpen({ target }) {
+    this.emit("open", target);
+  }
+
+  onTabClose({ target }) {
+    this.emit("close", target);
+  }
+
+  // Internal methods
+
+  _registerDOMWindow(win) {
+    for (const tab of win.gBrowser.tabs) {
+      // a missing linkedBrowser means the tab is still initialising,
+      // and a TabOpen event will fire once it is ready
+      if (!tab.linkedBrowser) {
+        continue;
+      }
+
+      this.onTabOpen({ target: tab });
+    }
+
+    win.gBrowser.tabContainer.addEventListener("TabOpen", this.onTabOpen);
+    win.gBrowser.tabContainer.addEventListener("TabClose", this.onTabClose);
+  }
+
+  _unregisterDOMWindow(win) {
+    for (const tab of win.gBrowser.tabs) {
+      // a missing linkedBrowser means the tab is still initialising
+      if (!tab.linkedBrowser) {
+        continue;
+      }
+
+      // Emulate custom "TabClose" events because that event is not
+      // fired for each of the tabs when the window closes.
+      this.onTabClose({ target: tab });
+    }
+
+    win.gBrowser.tabContainer.removeEventListener("TabOpen", this.onTabOpen);
+    win.gBrowser.tabContainer.removeEventListener("TabClose", this.onTabClose);
+  }
+
+  // nsIWindowMediatorListener
+
+  async onOpenWindow(xulWindow) {
+    const win = xulWindow.docShell.domWindow;
+
+    await new lazy.EventPromise(win, "load");
+
+    // Return early if it's not a browser window
+    if (
+      win.document.documentElement.getAttribute("windowtype") !=
+      "navigator:browser"
+    ) {
+      return;
+    }
+
+    this._registerDOMWindow(win);
+  }
+
+  onCloseWindow(xulWindow) {
+    const win = xulWindow.docShell.domWindow;
+
+    // Return early if it's not a browser window
+    if (
+      win.document.documentElement.getAttribute("windowtype") !=
+      "navigator:browser"
+    ) {
+      return;
+    }
+
+    this._unregisterDOMWindow(win);
+  }
+
+  // XPCOM
+
+  get QueryInterface() {
+    return ChromeUtils.generateQI(["nsIWindowMediatorListener"]);
+  }
+}