refactored timetable

lib/api/requestCache.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:convert';
 
 import 'package:localstore/localstore.dart';
@@ -17,29 +18,41 @@ abstract class RequestCache<T extends ApiResponse?> {
   void Function(Exception) onError;
   bool? renew;
 
+  final Completer<void> _ready = Completer<void>();
+
+  /// Resolves when [start] has finished, regardless of whether the network
+  /// call succeeded, failed, or was skipped due to a fresh cache. Callers
+  /// can await this to know when both the cache lookup and the network
+  /// attempt have settled.
+  Future<void> get ready => _ready.future;
+
   RequestCache(this.maxCacheTime, this.onUpdate, {this.onError = ignore, this.renew = false});
 
   static void ignore(Exception e) {}
 
   Future<void> start(String document) async {
-    final tableData = await Localstore.instance.collection(collection).doc(document).get();
-    if (tableData != null) {
-      onUpdate?.call(onLocalData(tableData['json']));
-    }
-
-    if (DateTime.now().millisecondsSinceEpoch - (maxCacheTime * 1000) < (tableData?['lastupdate'] ?? 0)) {
-      if (renew == null || !renew!) return;
-    }
-
     try {
-      final newValue = await onLoad();
-      onUpdate?.call(newValue);
-      Localstore.instance.collection(collection).doc(document).set({
-        'json': jsonEncode(newValue),
-        'lastupdate': DateTime.now().millisecondsSinceEpoch,
-      });
-    } on Exception catch (e) {
-      onError(e);
+      final tableData = await Localstore.instance.collection(collection).doc(document).get();
+      if (tableData != null) {
+        onUpdate?.call(onLocalData(tableData['json']));
+      }
+
+      if (DateTime.now().millisecondsSinceEpoch - (maxCacheTime * 1000) < (tableData?['lastupdate'] ?? 0)) {
+        if (renew == null || !renew!) return;
+      }
+
+      try {
+        final newValue = await onLoad();
+        onUpdate?.call(newValue);
+        Localstore.instance.collection(collection).doc(document).set({
+          'json': jsonEncode(newValue),
+          'lastupdate': DateTime.now().millisecondsSinceEpoch,
+        });
+      } on Exception catch (e) {
+        onError(e);
+      }
+    } finally {
+      if (!_ready.isCompleted) _ready.complete();
     }
   }