style on proximity of windows

src/events/eventManager.js

@@ -5,6 +5,7 @@ class EventManager {
         this.evenIds = {}; // event name -> {target, eventID}
         this.monitoredWindows = {}; // windowID -> {eventName -> eventID}
         this.unlockHandlerId = null;
+        this.positionCallbacks = new Set(); // Set of callbacks for position changes
     }
 
     attachGlobalEventOnce(eventName, target, callback) {
@@ -23,6 +24,7 @@ class EventManager {
             event.target.disconnect(event.id);
         });
         this.detachUnlockScreenEvent();
+        this.positionCallbacks.clear();
         this.evenIds = {};
     }
 
@@ -61,6 +63,50 @@ class EventManager {
             this.unlockHandlerId = null;
         }
     }
+
+    attachWindowPositionCallback(window, callback) {
+        const eventName = 'position-changed';
+        this.attachWindowEventOnce(eventName, window, callback);
+        this.positionCallbacks.add(callback);
+        return callback;
+    }
+
+    isPositionCallbackAttached(callback) {
+        return this.positionCallbacks.has(callback);
+    }
+
+    attachGlobalPositionCallback(target, callback) {
+        const eventName = 'position-changed';
+        this.attachGlobalEventOnce(eventName, target, callback);
+        this.positionCallbacks.add(callback);
+        return callback;
+    }
+
+    detachGlobalPositionCallback(callback) {
+        if (this.evenIds['position-changed'] && this.positionCallbacks.has(callback)) {
+            const event = this.evenIds['position-changed'];
+            event.target.disconnect(event.id);
+            delete this.evenIds['position-changed'];
+            this.positionCallbacks.delete(callback);
+        }
+    }
+
+    detachWindowPositionCallback(window, callback) {
+        const windowId = window.get_id();
+        const eventName = 'position-changed';
+
+        if (this.monitoredWindows[windowId] &&
+            this.monitoredWindows[windowId][eventName] !== undefined) {
+            window.disconnect(this.monitoredWindows[windowId][eventName]);
+            delete this.monitoredWindows[windowId][eventName];
+
+            // If no more events for this window, clean up the entry
+            if (Object.keys(this.monitoredWindows[windowId]).length === 0)
+                delete this.monitoredWindows[windowId];
+        }
+
+        this.positionCallbacks.delete(callback);
+    }
 }
 
 export default EventManager;