feat(storage): Add support for EncoderBackedStore (#129)

packages/langchain/lib/src/documents/embeddings/base.dart

@@ -6,7 +6,7 @@ abstract interface class Embeddings {
   const Embeddings();
 
   /// Embed search docs.
-  Future<List<List<double>>> embedDocuments(final List<String> documents);
+  Future<List<List<double>>> embedDocuments(final List<String> texts);
 
   /// Embed query text.
   Future<List<double>> embedQuery(final String query);

packages/langchain/lib/src/storage/encoder_backed.dart

@@ -0,0 +1,78 @@
+import 'base.dart';
+
+/// {@template encoder_backed_store}
+/// Wraps a store with key and value encoders/decoders.
+///
+/// This is useful for stores that only support certain types of keys and
+/// values. You can wrap the store with an encoder that converts the keys and
+/// values to the supported types.
+/// {@endtemplate}
+class EncoderBackedStore<K, V, EK, EV> implements BaseStore<K, V> {
+  /// {@macro encoder_backed_store}
+  EncoderBackedStore({
+    required this.store,
+    required this.encoder,
+  });
+
+  /// The underlying store.
+  final BaseStore<EK, EV> store;
+
+  /// The encoder/decoder for keys and values.
+  final Encoder<K, V, EK, EV> encoder;
+
+  @override
+  Future<List<V?>> get(final List<K> keys) async {
+    final encodedKeys = keys.map(encoder.encodeKey).toList(growable: false);
+    final encodedValues = await store.get(encodedKeys);
+    return encodedValues
+        .map((final value) => value == null ? null : encoder.decodeValue(value))
+        .toList(growable: false);
+  }
+
+  @override
+  Future<void> set(final List<(K, V)> keyValuePairs) async {
+    final encodedKeyValuePairs = keyValuePairs
+        .map(
+          (final pair) => (
+            encoder.encodeKey(pair.$1),
+            encoder.encodeValue(pair.$2),
+          ),
+        )
+        .toList(growable: false);
+    await store.set(encodedKeyValuePairs);
+  }
+
+  @override
+  Future<void> delete(final List<K> keys) async {
+    final encodedKeys = keys.map(encoder.encodeKey).toList(growable: false);
+    await store.delete(encodedKeys);
+  }
+
+  @override
+  Stream<K> yieldKeys({final String? prefix}) async* {
+    final encodedKeys = store.yieldKeys(prefix: prefix);
+    await for (final encodedKey in encodedKeys) {
+      yield encoder.decodeKey(encodedKey);
+    }
+  }
+}
+
+/// {@template encoder}
+/// Encoder/decoder for keys and values.
+/// {@endtemplate}
+abstract class Encoder<K, V, EK, EV> {
+  /// {@macro encoder}
+  const Encoder();
+
+  /// Encodes a key.
+  EK encodeKey(final K key);
+
+  /// Encodes a value.
+  EV encodeValue(final V value);
+
+  /// Decodes a key.
+  K decodeKey(final EK key);
+
+  /// Decodes a value.
+  V decodeValue(final EV value);
+}

packages/langchain/lib/src/storage/storage.dart

@@ -1,2 +1,3 @@
 export 'base.dart';
+export 'encoder_backed.dart';
 export 'in_memory.dart';

packages/langchain/test/storage/encoder_backed.dart

@@ -0,0 +1,57 @@
+import 'package:langchain/langchain.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('EncoderBackedStore tests', () {
+    test(
+        'EncoderBackedStore should encode and decode key-value pairs using InMemoryStore',
+        () async {
+      final encoderBackedStore = EncoderBackedStore(
+        store: InMemoryStore<String, String>(),
+        encoder: SampleEncoder(),
+      );
+
+      final keyValuePairs = [(1, 'One'), (2, 'Two'), (3, 'Three')];
+
+      await encoderBackedStore.set(keyValuePairs);
+
+      // Verify if the key-value pairs are properly encoded and stored
+      final keys = keyValuePairs.map((final pair) => pair.$1).toList();
+      final values = await encoderBackedStore.get(keys);
+
+      for (int i = 0; i < keyValuePairs.length; i++) {
+        expect(values[i], equals(keyValuePairs[i].$2));
+      }
+
+      // Test for delete function
+      await encoderBackedStore.delete([keyValuePairs[0].$1]);
+
+      // Check if the first key is deleted
+      final deletedValues = await encoderBackedStore.get(keys);
+      expect(deletedValues[0], equals(null));
+
+      // Test yieldKeys
+      final stream = encoderBackedStore.yieldKeys();
+      await for (final key in stream) {
+        expect(key, isNot(equals(keyValuePairs[0].$1)));
+      }
+    });
+  });
+}
+
+class SampleEncoder extends Encoder<int, String, String, String> {
+  @override
+  String encodeKey(final int key) => '$key';
+
+  @override
+  String encodeValue(final String value) => "'$value'";
+
+  @override
+  int decodeKey(final String encodedKey) => int.parse(encodedKey);
+
+  @override
+  String decodeValue(final String encodedValue) => encodedValue.substring(
+        1,
+        encodedValue.length - 1,
+      );
+}