implemented a 1-minute in-memory cache for the EmergencyNoticeClient to prevent redundant network requests on app resume

lib/api/emergency/emergency_notice.dart

@@ -1,21 +1,10 @@
-/// A backend-independent emergency notice, loaded from a foreign server URL.
-///
-/// Deliberately decoupled from MarianumConnect: if that backend is unreachable
-/// (the disaster case this exists for), a plain text file on any other host can
-/// still surface a message. The file is a small YAML-ish frontmatter followed
-/// by a free Markdown body, so it stays hand-writable in an emergency — no JSON
-/// escaping of the (multi-line) content.
-///
-/// See [parse] for the exact format.
+/// A backend-independent emergency notice loaded from a foreign server URL —
+/// frontmatter (control fields) plus a free Markdown body, so it stays
+/// hand-writable in an outage. See [parse] for the format.
 class EmergencyNotice {
-  /// Whether the notice can be dismissed. `false` renders it full-screen and
-  /// blocks back/barrier taps.
+  /// `false` renders full-screen and blocks back/barrier taps.
   final bool dismissible;
-
-  /// Optional heading shown above the body.
   final String? title;
-
-  /// Markdown body (the message itself).
   final String body;
 
   const EmergencyNotice({
@@ -24,38 +13,24 @@ class EmergencyNotice {
     required this.body,
   });
 
-  /// Parses the raw file into a displayable notice, or returns `null` when
-  /// there is nothing to show. Never throws — any malformed input yields `null`
-  /// so a broken file can never break the app.
+  /// Parses the raw file, or returns `null` when there is nothing to show.
+  /// Never throws — malformed input yields `null` so a broken file can't break
+  /// the app.
   ///
-  /// Format:
   /// ```
   /// ---
-  /// active: true
-  /// # dismissible: false   <- comment lines (# ...) are ignored
-  /// dismissible: true
-  /// title: Störung
+  /// active: true          # required truthy, else null; # lines are comments
+  /// dismissible: true     # default true
+  /// title: Störung        # optional
   /// ---
-  /// # Markdown heading
-  /// Free **markdown** body.
+  /// Free **markdown** body (everything after the closing ---).
   /// ```
-  ///
-  /// Rules:
-  /// - The frontmatter is everything between the first `---` line and the next
-  ///   `---` line. Both delimiters are required.
-  /// - Frontmatter entries are `key: value`; a line whose trimmed form starts
-  ///   with `#` is a comment. Unknown keys are ignored.
-  /// - `active` (default `false`) must be explicitly true, else `null`.
-  /// - `dismissible` defaults to `true`.
-  /// - `title` is optional. The rest after the closing `---` is the Markdown
-  ///   body; an empty body yields `null`.
   static EmergencyNotice? parse(String raw) {
     final lines = raw
         .replaceAll('\r\n', '\n')
         .replaceAll('\r', '\n')
         .split('\n');
 
-    // Locate the opening `---` (skipping any leading blank lines).
     var i = 0;
     while (i < lines.length && lines[i].trim().isEmpty) {
       i++;
@@ -63,7 +38,6 @@ class EmergencyNotice {
     if (i >= lines.length || lines[i].trim() != '---') return null;
     final openIndex = i;
 
-    // Locate the closing `---`.
     var closeIndex = -1;
     for (var j = openIndex + 1; j < lines.length; j++) {
       if (lines[j].trim() == '---') {

lib/api/emergency/emergency_notice_client.dart

@@ -2,17 +2,30 @@ import 'package:dio/dio.dart';
 
 import 'emergency_notice.dart';
 
-/// Loads the emergency notice from a foreign URL over a standalone [Dio]
-/// instance — no MarianumConnect interceptors, base URL or auth. That keeps the
-/// fallback fully independent of the backend it is meant to survive.
+/// Loads the emergency notice from a foreign URL over a standalone [Dio] — no
+/// MarianumConnect interceptors/base URL/auth, so it survives a backend outage.
+/// Never throws: any failure yields `null` (nothing shown).
 ///
-/// Fail-safe by contract: if the server is unreachable, times out, answers with
-/// a non-2xx status or delivers unparsable content, [fetch] returns `null` and
-/// nothing is shown. It never throws.
+/// A [cacheTtl] in-memory throttle keeps rapid resumes from hammering the host;
+/// it lives only for the process, so a cold start always fetches fresh.
 class EmergencyNoticeClient {
-  const EmergencyNoticeClient();
+  EmergencyNoticeClient();
+
+  static const Duration cacheTtl = Duration(minutes: 1);
+
+  EmergencyNotice? _cached;
+  String? _cachedUrl;
+  DateTime? _cachedAt;
 
   Future<EmergencyNotice?> fetch(String url) async {
+    final cachedAt = _cachedAt;
+    if (cachedAt != null &&
+        _cachedUrl == url &&
+        DateTime.now().difference(cachedAt) < cacheTtl) {
+      return _cached;
+    }
+
+    EmergencyNotice? result;
     try {
       final dio = Dio(
         BaseOptions(
@@ -24,11 +37,15 @@ class EmergencyNoticeClient {
       );
       final response = await dio.get<String>(url);
       final raw = response.data;
-      if (raw == null || raw.isEmpty) return null;
-      return EmergencyNotice.parse(raw);
+      result = (raw == null || raw.isEmpty) ? null : EmergencyNotice.parse(raw);
     } catch (_) {
-      // Server down / timeout / bad status / malformed body: show nothing.
-      return null;
+      result = null;
     }
+
+    // Cache failures too, so a down server isn't retried on every resume.
+    _cached = result;
+    _cachedUrl = url;
+    _cachedAt = DateTime.now();
+    return result;
   }
 }