Replacing the display link with an AXObserver solution

For lower CPU usage

Author: intitni

Core/Package.swift

@@ -58,6 +58,7 @@ let package = Package(
                 "CGEventObserver",
                 "DisplayLink",
                 "ActiveApplicationMonitor",
+                "AXNotificationStream",
             ]
         ),
         .target(
@@ -72,5 +73,6 @@ let package = Package(
         .target(name: "LaunchAgentManager"),
         .target(name: "DisplayLink"),
         .target(name: "ActiveApplicationMonitor"),
+        .target(name: "AXNotificationStream"),
     ]
 )

Core/Sources/AXNotificationStream/AXNotificationStream.swift

@@ -0,0 +1,76 @@
+import AppKit
+import ApplicationServices
+import Foundation
+
+public final class AXNotificationStream: AsyncSequence {
+    public typealias Stream = AsyncStream<Element>
+    public typealias Continuation = Stream.Continuation
+    public typealias AsyncIterator = Stream.AsyncIterator
+    public typealias Element = (String, CFDictionary)
+
+    private var continuation: Continuation
+    private let stream: Stream
+
+    public func makeAsyncIterator() -> Stream.AsyncIterator {
+        stream.makeAsyncIterator()
+    }
+
+    deinit {
+        continuation.finish()
+    }
+
+    public init(
+        app: NSRunningApplication,
+        element: AXUIElement? = nil,
+        notificationNames: String...
+    ) {
+        var cont: Continuation!
+        stream = Stream { continuation in
+            cont = continuation
+        }
+        continuation = cont
+        var observer: AXObserver?
+
+        func callback(
+            observer: AXObserver,
+            element: AXUIElement,
+            notificationName: CFString,
+            userInfo: CFDictionary,
+            pointer: UnsafeMutableRawPointer?
+        ) {
+            guard let pointer = pointer?.assumingMemoryBound(to: Continuation.self)
+            else { return }
+            pointer.pointee.yield((notificationName as String, userInfo))
+        }
+
+        _ = AXObserverCreateWithInfoCallback(
+            app.processIdentifier,
+            callback,
+            &observer
+        )
+        guard let observer else {
+            continuation.finish()
+            return
+        }
+
+        let observingElement = element ?? AXUIElementCreateApplication(app.processIdentifier)
+        continuation.onTermination = { @Sendable _ in
+            for name in notificationNames {
+                AXObserverRemoveNotification(observer, observingElement, name as CFString)
+            }
+            CFRunLoopRemoveSource(
+                CFRunLoopGetMain(),
+                AXObserverGetRunLoopSource(observer),
+                .commonModes
+            )
+        }
+        for name in notificationNames {
+            AXObserverAddNotification(observer, observingElement, name as CFString, &continuation)
+        }
+        CFRunLoopAddSource(
+            CFRunLoopGetMain(),
+            AXObserverGetRunLoopSource(observer),
+            .commonModes
+        )
+    }
+}

Core/Sources/ActiveApplicationMonitor/ActiveApplicationMonitor.swift

@@ -34,6 +34,7 @@ public final class ActiveApplicationMonitor {
             continuation.onTermination = { _ in
                 ActiveApplicationMonitor.shared.removeContinuation(id: id)
             }
+            continuation.yield(activeApplication)
         }
     }
 

Core/Sources/Service/GUI/SuggestionPanelController.swift

@@ -1,5 +1,6 @@
 import ActiveApplicationMonitor
 import AppKit
+import AXNotificationStream
 import DisplayLink
 import SwiftUI
 
@@ -25,25 +26,47 @@ final class SuggestionPanelController {
         return it
     }()
 
-    private var displayLinkTask: Task<Void, Never>?
-    private var activeApplicationMonitorTask: Task<Void, Never>?
     let viewModel = SuggestionPanelViewModel()
+
+    private var windowChangeObservationTask: Task<Void, Error>?
+    private var activeApplicationMonitorTask: Task<Void, Error>?
     private var activeApplication: NSRunningApplication? {
         ActiveApplicationMonitor.activeApplication
     }
 
     nonisolated init() {
         Task { @MainActor in
-            displayLinkTask = Task {
-                for await _ in DisplayLink.createStream() {
+            activeApplicationMonitorTask = Task { [weak self] in
+                guard let self else { return }
+                var previousApp: NSRunningApplication?
+                for await app in ActiveApplicationMonitor.createStream() {
+                    try Task.checkCancellation()
+                    defer { previousApp = app }
+                    if let app, app.bundleIdentifier == "com.apple.dt.Xcode" {
+                        if app != previousApp {
+                            windowChangeObservationTask?.cancel()
+                            windowChangeObservationTask = nil
+                            self.observeXcodeWindowChangeIfNeeded()
+                        }
+                    }
+
                     self.updateWindowLocation()
                 }
             }
+        }
+    }
 
-            activeApplicationMonitorTask = Task {
-                for await _ in ActiveApplicationMonitor.createStream() {
-                    self.updateWindowLocation()
-                }
+    private func observeXcodeWindowChangeIfNeeded() {
+        guard windowChangeObservationTask == nil else { return }
+        windowChangeObservationTask = Task { [weak self] in
+            guard let self else { return }
+            let notifications = AXNotificationStream(
+                app: activeApplication!,
+                notificationNames: kAXMovedNotification
+            )
+            for await _ in notifications {
+                try Task.checkCancellation()
+                self.updateWindowLocation()
             }
         }
     }
@@ -91,6 +114,8 @@ final class SuggestionPanelController {
     }
 }
 
+#warning("MUSTDO: Update when editing file is changed.")
+
 @MainActor
 final class SuggestionPanelViewModel: ObservableObject {
     @Published var startLineIndex: Int = 0