feat: implementation of the 'contains' method

Closes #92

Author: rafamizes

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- implementation of the 'contains' method —
+  [92](https://github.com/dartoos-dev/json_cache/issues/92).
+
 ## [1.2.6] - 2022-08-01
 
 ### Changed

README.md

@@ -91,6 +91,11 @@ abstract class JsonCache {
   ///
   /// **Note**: [value] must be json encodable.
   Future<void> refresh(String key, Map<String, dynamic> value);
+
+  /// Checks whether there is cached data at [key].
+  ///
+  /// Returns `true` if there is cached data at [key]; `false` otherwise.
+  Future<bool> contains(String key);
 }
 ```
 

lib/json_cache.dart

@@ -1,4 +1,4 @@
-/// Collection of json cache decorators.
+/// A collection of [JsonCache] decorators.
 library json_cache;
 
 export 'src/json_cache.dart';

lib/src/json_cache.dart

@@ -20,4 +20,9 @@ abstract class JsonCache {
   ///
   /// **Note**: [value] must be json encodable.
   Future<void> refresh(String key, Map<String, dynamic> value);
+
+  /// Checks whether there is cached data at [key].
+  ///
+  /// Returns `true` if there is cached data at [key]; `false` otherwise.
+  Future<bool> contains(String key);
 }

lib/src/json_cache_cross_local_storage.dart

@@ -43,4 +43,10 @@ class JsonCacheCrossLocalStorage implements JsonCache {
         ? null
         : json.decode(strJson) as Map<String, dynamic>;
   }
+
+  /// Checks whether there is cached data at [key].
+  @override
+  Future<bool> contains(String key) async {
+    return _prefs.containsKey(key);
+  }
 }

lib/src/json_cache_enc_prefs.dart

@@ -40,4 +40,9 @@ class JsonCacheEncPrefs implements JsonCache {
     }
     return null;
   }
+
+  @override
+  Future<bool> contains(String key) async {
+    return (await _encPrefs.getInstance()).containsKey(key);
+  }
 }

lib/src/json_cache_fake.dart

@@ -23,21 +23,31 @@ class JsonCacheFake implements JsonCache {
 
   /// Clears its internal in-memory storage.
   @override
-  Future<void> clear() async => _memory.clear();
+  Future<void> clear() async {
+    _memory.clear();
+  }
 
   /// Updates data located at [key].
   @override
-  Future<void> refresh(String key, Map<String, dynamic> data) async =>
-      _memory[key] = Map<String, dynamic>.of(data);
+  Future<void> refresh(String key, Map<String, dynamic> data) async {
+    _memory[key] = Map<String, dynamic>.of(data);
+  }
 
   /// Removes data located at [key].
   @override
-  Future<void> remove(String key) async => _memory.remove(key);
+  Future<void> remove(String key) async {
+    _memory.remove(key);
+  }
 
   /// Retrieves a copy of the data at [key] or `null` if there is no data.
   @override
   Future<Map<String, dynamic>?> value(String key) async {
     final cached = _memory[key];
     return cached == null ? null : Map<String, dynamic>.of(cached);
   }
+
+  @override
+  Future<bool> contains(String key) async {
+    return _memory.containsKey(key);
+  }
 }

lib/src/json_cache_hive.dart

@@ -10,7 +10,6 @@ class JsonCacheHive implements JsonCache {
   /// Sets the Hive [Box] instance.
   const JsonCacheHive(this._box);
 
-  // final Box<String> _box;
   final Box<String> _box;
 
   @override
@@ -33,4 +32,9 @@ class JsonCacheHive implements JsonCache {
     final data = _box.get(key);
     return data == null ? null : json.decode(data) as Map<String, dynamic>;
   }
+
+  @override
+  Future<bool> contains(String key) async {
+    return _box.containsKey(key);
+  }
 }

lib/src/json_cache_hollow.dart

@@ -31,7 +31,11 @@ class JsonCacheHollow implements JsonCache {
   @override
   Future<void> remove(String key) async {}
 
-  /// Always returns null.
+  /// Always returns `null`.
   @override
   Future<Map<String, dynamic>?> value(String key) async => null;
+
+  /// Always returns `false`.
+  @override
+  Future<bool> contains(String key) async => false;
 }

lib/src/json_cache_local_storage.dart

@@ -35,4 +35,11 @@ class JsonCacheLocalStorage implements JsonCache {
     await _getReady;
     return await _storage.getItem(key) as Map<String, dynamic>?;
   }
+
+  @override
+  Future<bool> contains(String key) async {
+    await _getReady;
+    final Object? item = _storage.getItem(key);
+    return item != null;
+  }
 }