Group contacts by last seen

lib/services/mesh_map_nodes_service.dart

@@ -1,5 +1,7 @@
+import 'dart:async';
 import 'dart:convert';
 import 'package:http/http.dart' as http;
+import 'package:shared_preferences/shared_preferences.dart';
 
 class MeshMapNode {
   final int type;
@@ -33,25 +35,35 @@ class MeshMapNode {
 class MeshMapNodesService {
   static const String _nodesEndpoint =
       'https://api.meshcore.nz/api/v1/map/nodes';
-  static const Duration _cacheTtl = Duration(minutes: 2);
-  static const Duration traceCacheTtl = Duration(minutes: 10);
+  static const Duration _cacheTtl = Duration(hours: 24);
+  static const Duration traceCacheTtl = _cacheTtl;
   static const Duration traceTimeout = Duration(seconds: 30);
+  static const String _cacheKey = 'mesh_map_nodes_cache_v1';
+  static const String _cacheTimestampKey = 'mesh_map_nodes_cache_timestamp_v1';
   static List<MeshMapNode>? _cachedNodes;
   static DateTime? _cachedAt;
+  static Future<void>? _ongoingSync;
 
   static Future<List<MeshMapNode>> fetchNodes({
     bool forceRefresh = false,
     Duration cacheTtl = _cacheTtl,
+    bool allowNetwork = true,
+    http.Client? client,
   }) async {
     final now = DateTime.now();
+    final cached = await loadCachedNodes(cacheTtl: cacheTtl);
     if (!forceRefresh &&
-        _cachedNodes != null &&
+        cached.isNotEmpty &&
         _cachedAt != null &&
         now.difference(_cachedAt!) < cacheTtl) {
-      return _cachedNodes!;
+      return cached;
     }
 
-    final response = await http
+    if (!allowNetwork) {
+      return cached;
+    }
+
+    final response = await (client ?? http.Client())
         .get(Uri.parse(_nodesEndpoint))
         .timeout(traceTimeout);
     if (response.statusCode < 200 || response.statusCode >= 300) {
@@ -69,8 +81,131 @@ class MeshMapNodesService {
         )
         .toList();
 
-    _cachedNodes = nodes;
-    _cachedAt = now;
+    await _storeCache(nodes, cachedAt: now);
     return nodes;
   }
+
+  static Future<List<MeshMapNode>> loadCachedNodes({
+    Duration cacheTtl = _cacheTtl,
+  }) async {
+    final now = DateTime.now();
+    if (_cachedNodes != null &&
+        _cachedAt != null &&
+        now.difference(_cachedAt!) < cacheTtl) {
+      return _cachedNodes!;
+    }
+
+    final prefs = await SharedPreferences.getInstance();
+    final cachedAtMs = prefs.getInt(_cacheTimestampKey);
+    final cachedJson = prefs.getString(_cacheKey);
+    if (cachedAtMs == null || cachedJson == null) {
+      _cachedNodes = null;
+      _cachedAt = null;
+      return const [];
+    }
+
+    final cachedAt = DateTime.fromMillisecondsSinceEpoch(cachedAtMs);
+    if (now.difference(cachedAt) >= cacheTtl) {
+      _cachedNodes = null;
+      _cachedAt = cachedAt;
+      return const [];
+    }
+
+    final decoded = jsonDecode(cachedJson) as List<dynamic>;
+    final nodes = decoded
+        .whereType<Map<String, dynamic>>()
+        .map(MeshMapNode.fromJson)
+        .where(
+          (n) => n.publicKey.isNotEmpty && n.latitude != 0 && n.longitude != 0,
+        )
+        .toList();
+    _cachedNodes = nodes;
+    _cachedAt = cachedAt;
+    return nodes;
+  }
+
+  static Future<bool> hasFreshCache({Duration cacheTtl = _cacheTtl}) async {
+    final nodes = await loadCachedNodes(cacheTtl: cacheTtl);
+    return nodes.isNotEmpty;
+  }
+
+  static Future<void> syncInBackgroundIfStale({
+    Duration cacheTtl = _cacheTtl,
+    http.Client? client,
+  }) async {
+    final now = DateTime.now();
+    if (_cachedAt != null && now.difference(_cachedAt!) < cacheTtl) {
+      return;
+    }
+
+    final cached = await loadCachedNodes(cacheTtl: cacheTtl);
+    if (cached.isNotEmpty && _cachedAt != null) {
+      return;
+    }
+
+    if (_ongoingSync != null) {
+      return _ongoingSync!;
+    }
+
+    _ongoingSync = () async {
+      try {
+        await fetchNodes(
+          forceRefresh: true,
+          cacheTtl: cacheTtl,
+          allowNetwork: true,
+          client: client,
+        );
+      } catch (_) {
+        // Background refresh is best-effort only.
+      } finally {
+        _ongoingSync = null;
+      }
+    }();
+
+    return _ongoingSync!;
+  }
+
+  static Future<void> clearCache() async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.remove(_cacheKey);
+    await prefs.remove(_cacheTimestampKey);
+    _cachedNodes = null;
+    _cachedAt = null;
+  }
+
+  static Future<DateTime?> cachedAt() async {
+    if (_cachedAt != null) return _cachedAt;
+    final prefs = await SharedPreferences.getInstance();
+    final cachedAtMs = prefs.getInt(_cacheTimestampKey);
+    if (cachedAtMs == null) return null;
+    _cachedAt = DateTime.fromMillisecondsSinceEpoch(cachedAtMs);
+    return _cachedAt;
+  }
+
+  static Future<void> _storeCache(
+    List<MeshMapNode> nodes, {
+    required DateTime cachedAt,
+  }) async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(
+      _cacheKey,
+      jsonEncode(
+        nodes
+            .map(
+              (node) => {
+                'type': node.type,
+                'name': node.name,
+                'public_key': node.publicKey,
+                'latitude': node.latitude,
+                'longitude': node.longitude,
+                'updated_at': node.updatedAtMs,
+              },
+            )
+            .toList(),
+      ),
+    );
+    await prefs.setInt(_cacheTimestampKey, cachedAt.millisecondsSinceEpoch);
+    _cachedNodes = nodes;
+    _cachedAt = cachedAt;
+  }
 }