1 files changed, 64 insertions, 0 deletions
diff --git a/app/lib/window-state-observer.js b/app/lib/window-state-observer.js
new file mode 100644
index 0000000000..67252d8f6a
--- /dev/null
+++ b/app/lib/window-state-observer.js
@@ -0,0 +1,64 @@
+// @flow
+
+import { remote } from 'electron';
+
+type EventListener = () => void;
+
+// Tiny helper for detecting the window state.
+export default class WindowStateObserver {
+  _onShow: ?EventListener;
+  _onHide: ?EventListener;
+
+  get onShow() {
+    return this._onShow;
+  }
+
+  set onShow(listener: ?EventListener) {
+    const currentWindow = remote.getCurrentWindow();
+    const oldListener = this._onShow;
+    if (oldListener) {
+      currentWindow.removeListener('show', oldListener);
+    }
+
+    if (listener) {
+      currentWindow.addListener('show', listener);
+    }
+
+    this._onShow = listener;
+  }
+
+  get onHide() {
+    return this._onHide;
+  }
+
+  set onHide(listener: ?EventListener) {
+    const currentWindow = remote.getCurrentWindow();
+    const oldListener = this._onHide;
+    if (oldListener) {
+      currentWindow.removeListener('hide', oldListener);
+    }
+
+    if (listener) {
+      currentWindow.addListener('hide', listener);
+    }
+
+    this._onHide = listener;
+  }
+
+  constructor() {
+    // Because BrowserWindow persists between page reloads,
+    // it's important to release event handlers when that happens.
+    window.addEventListener('beforeunload', this._onBeforeUnload);
+  }
+
+  _onBeforeUnload = () => {
+    this.dispose();
+  };
+
+  dispose() {
+    this.onShow = null;
+    this.onHide = null;
+
+    window.removeEventListener('beforeunload', this._onBeforeUnload);
+  }
+}