refactor: replace main-queue callbacks with structured concurrency

Author: cantpr09ram

app/dauphin/View/LibSSoLoginView.swift

@@ -10,12 +10,19 @@ struct LibSSOLoginView: UIViewRepresentable {
     class Coordinator: NSObject, WKNavigationDelegate, WKScriptMessageHandler {
         var parent: LibSSOLoginView
         private let allowedHosts: Set<String> = ["sso.tku.edu.tw"]
+        private var evaluateTokenTask: Task<Void, Never>?
 
         init(parent: LibSSOLoginView) { self.parent = parent }
 
+        deinit { evaluateTokenTask?.cancel() }
+
         func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
             // Web page loaded
-            DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
+            evaluateTokenTask?.cancel()
+            evaluateTokenTask = Task { @MainActor in
+                try? await Task.sleep(nanoseconds: 500_000_000)
+                guard !Task.isCancelled else { return }
+
                 let javascript = """
                         try {
                             var token = getSsoLoginToken();
@@ -26,11 +33,9 @@ struct LibSSOLoginView: UIViewRepresentable {
                         }
                     """
 
-                webView.evaluateJavaScript(javascript) { (result, error) in
-                    if let error = error {
-                        LibSSOLoginView.logger.error(
-                            "JavaScript execution error: \(error.localizedDescription)")
-                    }
+                do { _ = try await webView.evaluateJavaScript(javascript) } catch {
+                    LibSSOLoginView.logger.error(
+                        "JavaScript execution error: \(error.localizedDescription)")
                 }
             }
         }

app/dauphin/View/Setting/ClearCacheView.swift

@@ -41,7 +41,8 @@ struct ClearCacheView: View {
 
         withAnimation(.spring()) { cacheCleared = true }
 
-        DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
+        Task {
+            try? await Task.sleep(nanoseconds: 3_000_000_000)
             withAnimation { cacheCleared = false }
         }
     }

app/dauphin/ViewModels/CourseViewModel.swift

@@ -66,8 +66,8 @@ import SwiftUI
 
     private func startNetworkMonitor() {
         monitor.pathUpdateHandler = { [weak self] path in
-            guard let self = self else { return }
-            DispatchQueue.main.async {
+            Task { @MainActor [weak self] in
+                guard let self = self else { return }
                 self.isNetworkAvailable = (path.status == .satisfied)
                 if self.isNetworkAvailable {
                     Self.logger.debug("Network is available")
@@ -147,7 +147,8 @@ import SwiftUI
             self.cacheUpdateMessage =
                 forceRefresh ? "Refreshed successfully" : "Course data updated"
 
-            DispatchQueue.main.asyncAfter(deadline: .now() + 2) { [weak self] in
+            Task { @MainActor [weak self] in
+                try? await Task.sleep(nanoseconds: 2_000_000_000)
                 self?.cacheUpdateMessage = nil
             }
         } catch {
@@ -158,7 +159,8 @@ import SwiftUI
                 self.errorMessage = "Failed to fetch courses."
             } else if forceRefresh {
                 self.cacheUpdateMessage = "Refresh failed"
-                DispatchQueue.main.asyncAfter(deadline: .now() + 2) { [weak self] in
+                Task { @MainActor [weak self] in
+                    try? await Task.sleep(nanoseconds: 2_000_000_000)
                     self?.cacheUpdateMessage = nil
                 }
             }