feat: add request caching service (TBD54566975#280)

lib/shared/services/request_cache_service.dart

@@ -0,0 +1,100 @@
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:collection/collection.dart';
+import 'package:hive/hive.dart';
+import 'package:http/http.dart' as http;
+
+class RequestCacheService<T> {
+  final T Function(Map<String, dynamic>) fromJson;
+  final Map<String, dynamic> Function(T) toJson;
+  final Duration cacheDuration;
+  final String networkCacheKey;
+
+  RequestCacheService({
+    required this.fromJson,
+    required this.toJson,
+    this.cacheDuration = const Duration(minutes: 1),
+    this.networkCacheKey = 'network_cache',
+  });
+
+  /// Fetches data from the cache and API.
+  Stream<T> fetchData(String url) async* {
+    final box = await Hive.openBox(networkCacheKey);
+    final cacheKey = _generateCacheKey(url);
+    bool cacheEmitted = false;
+
+    try {
+      // Check for cached data
+      final cachedEntry = await box.get(cacheKey);
+      if (cachedEntry != null && cachedEntry is Map) {
+        final cachedMap = Map<String, dynamic>.from(cachedEntry);
+        final cachedTimestamp =
+            DateTime.parse(cachedMap['timestamp'] as String);
+        final cachedDataJson =
+            Map<String, dynamic>.from(cachedMap['data'] ?? {});
+        final cachedData = fromJson(cachedDataJson);
+        // Emit cached data
+        yield cachedData;
+        cacheEmitted = true;
+
+        final now = DateTime.now();
+        // Decide whether to fetch new data based on cache validity
+        if (now.difference(cachedTimestamp) < cacheDuration) {
+          // Cache is still valid, but we'll fetch new data to check for updates
+          // return; // Uncomment this line to skip fetching new data
+        }
+      }
+
+      // Fetch data from the network
+      try {
+        final response = await http.get(Uri.parse(url));
+
+        if (response.statusCode == 200) {
+          final dataMap = jsonDecode(response.body) as Map<String, dynamic>;
+          final data = fromJson(dataMap);
+
+          // Compare with cached data
+          bool isDataUpdated = true;
+          if (cachedEntry != null && cachedEntry is Map) {
+            final cachedDataJson =
+                Map<String, dynamic>.from(cachedEntry['data'] ?? {});
+            // Use DeepCollectionEquality for deep comparison
+            const equalityChecker = DeepCollectionEquality();
+            if (equalityChecker.equals(cachedDataJson, dataMap)) {
+              isDataUpdated = false;
+            }
+          }
+
+          // Cache the new data with a timestamp
+          final cacheEntry = {
+            'data': toJson(data),
+            'timestamp': DateTime.now().toIso8601String(),
+          };
+          await box.put(cacheKey, cacheEntry);
+
+          if (isDataUpdated) {
+            yield data;
+          }
+        } else {
+          throw Exception(
+            'Failed to load data from $url. Status code: ${response.statusCode}',
+          );
+        }
+      } catch (e) {
+        if (!cacheEmitted) {
+          // No cached data was emitted before, so we need to throw an error
+          throw Exception('Error fetching data from $url: $e');
+        }
+        // Else, we have already emitted cached data, so we can silently fail or log the error
+      }
+    } finally {
+      await box.close();
+    }
+  }
+
+  /// Generates a cache key by hashing the URL.
+  String _generateCacheKey(String url) {
+    return url.hashCode.toString();
+  }
+}