feat: add toJson method to Timestamp

packages/google_cloud_firestore/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## Unreleased
 
 - Updated `Transaction.delete` and `Transaction.update` type constraints to accept `DocumentReference<Object?>`. (thanks to @Levin-Me)
+- Made `Timestamp` encodable by adding `toJson` method. (thanks to @OutdatedGuy)
 
 ## 0.5.2
 

packages/google_cloud_firestore/lib/src/timestamp.dart

@@ -197,4 +197,18 @@ final class Timestamp implements _Serializable {
   String toString() {
     return 'Timestamp(seconds=$seconds, nanoseconds=$nanoseconds)';
   }
+
+  /// Converts this Timestamp to a JSON representation.
+  ///
+  /// Returns a Map\<String, int\> containing the seconds and nanoseconds.
+  ///
+  /// Example:
+  /// ```dart
+  /// final timestamp = Timestamp(seconds: 1234567890, nanoseconds: 123456789);
+  /// final json = timestamp.toJson();
+  /// print(json); // {'_seconds': 1234567890, '_nanoseconds': 123456789}
+  /// ```
+  Map<String, int> toJson() {
+    return {'_seconds': seconds, '_nanoseconds': nanoseconds};
+  }
 }

packages/google_cloud_firestore/test/timestamp_test.dart

@@ -106,5 +106,11 @@ void main() {
       final timestamp = Timestamp.fromMillis(millis);
       expect(timestamp.toMillis(), millis);
     });
+
+    test('toJson() returns correct JSON representation', () {
+      final timestamp = Timestamp(seconds: 1234567890, nanoseconds: 123456789);
+      final json = timestamp.toJson();
+      expect(json, {'_seconds': 1234567890, '_nanoseconds': 123456789});
+    });
   });
 }