1 files changed, 113 insertions, 0 deletions
diff --git a/toolkit/jetpack/sdk/tabs/observer.js b/toolkit/jetpack/sdk/tabs/observer.js
new file mode 100644
index 000000000..4e935cd62
--- /dev/null
+++ b/toolkit/jetpack/sdk/tabs/observer.js
@@ -0,0 +1,113 @@
+/* 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/. */
+'use strict';
+
+module.metadata = {
+  "stability": "unstable"
+};
+
+const { EventTarget } = require("../event/target");
+const { emit } = require("../event/core");
+const { DOMEventAssembler } = require("../deprecated/events/assembler");
+const { Class } = require("../core/heritage");
+const { getActiveTab, getTabs } = require("./utils");
+const { browserWindowIterator } = require("../deprecated/window-utils");
+const { isBrowser, windows, getMostRecentBrowserWindow } = require("../window/utils");
+const { observer: windowObserver } = require("../windows/observer");
+const { when } = require("../system/unload");
+
+const EVENTS = {
+  "TabOpen": "open",
+  "TabClose": "close",
+  "TabSelect": "select",
+  "TabMove": "move",
+  "TabPinned": "pinned",
+  "TabUnpinned": "unpinned"
+};
+
+const selectedTab = Symbol("observer/state/selectedTab");
+
+// Event emitter objects used to register listeners and emit events on them
+// when they occur.
+const Observer = Class({
+  implements: [EventTarget, DOMEventAssembler],
+  initialize() {
+    this[selectedTab] = null;
+    // Currently Gecko does not dispatch any event on the previously selected
+    // tab before / after "TabSelect" is dispatched. In order to work around this
+    // limitation we keep track of selected tab and emit "deactivate" event with
+    // that before emitting "activate" on selected tab.
+    this.on("select", tab => {
+      const selected = this[selectedTab];
+      if (selected !== tab) {
+        if (selected) {
+          emit(this, 'deactivate', selected);
+        }
+
+        if (tab) {
+          this[selectedTab] = tab;
+          emit(this, 'activate', this[selectedTab]);
+        }
+      }
+    });
+
+
+    // We also observe opening / closing windows in order to add / remove it's
+    // containers to the observed list.
+    windowObserver.on("open", chromeWindow => {
+      if (isBrowser(chromeWindow)) {
+        this.observe(chromeWindow);
+      }
+    });
+
+    windowObserver.on("close", chromeWindow => {
+      if (isBrowser(chromeWindow)) {
+        // Bug 751546: Emit `deactivate` event on window close immediatly
+        // Otherwise we are going to face "dead object" exception on `select` event
+        if (getActiveTab(chromeWindow) === this[selectedTab]) {
+          emit(this, "deactivate", this[selectedTab]);
+          this[selectedTab] = null;
+        }
+        this.ignore(chromeWindow);
+      }
+    });
+
+
+    // Currently gecko does not dispatches "TabSelect" events when different
+    // window gets activated. To work around this limitation we emulate "select"
+    // event for this case.
+    windowObserver.on("activate", chromeWindow => {
+      if (isBrowser(chromeWindow)) {
+        emit(this, "select", getActiveTab(chromeWindow));
+      }
+    });
+
+    // We should synchronize state, since probably we already have at least one
+    // window open.
+    for (let chromeWindow of browserWindowIterator()) {
+      this.observe(chromeWindow);
+    }
+
+    when(_ => {
+      // Don't dispatch a deactivate event during unload.
+      this[selectedTab] = null;
+    });
+  },
+  /**
+   * Events that are supported and emitted by the module.
+   */
+  supportedEventsTypes: Object.keys(EVENTS),
+  /**
+   * Function handles all the supported events on all the windows that are
+   * observed. Method is used to proxy events to the listeners registered on
+   * this event emitter.
+   * @param {Event} event
+   *    Keyboard event being emitted.
+   */
+  handleEvent: function handleEvent(event) {
+    emit(this, EVENTS[event.type], event.target, event);
+  }
+});
+
+exports.observer = new Observer();