api [nfc]: Pull out a method Anchor.toJson

Author: sirpengi

lib/api/route/messages.dart

@@ -92,12 +92,7 @@ Future<GetMessagesResult> getMessages(ApiConnection connection, {
 }) {
   return connection.get('getMessages', GetMessagesResult.fromJson, 'messages', {
     'narrow': resolveLegacyElements(narrow, connection),
-    'anchor': switch (anchor) {
-      NumericAnchor(:var messageId) => messageId,
-      AnchorCode.newest             => RawParameter('newest'),
-      AnchorCode.oldest             => RawParameter('oldest'),
-      AnchorCode.firstUnread        => RawParameter('first_unread'),
-    },
+    'anchor': RawParameter(anchor.toJson()),
     if (includeAnchor != null) 'include_anchor': includeAnchor,
     'num_before': numBefore,
     'num_after': numAfter,
@@ -112,17 +107,28 @@ Future<GetMessagesResult> getMessages(ApiConnection connection, {
 sealed class Anchor {
   /// This const constructor allows subclasses to have const constructors.
   const Anchor();
+
+  String toJson();
 }
 
 /// An anchor value for [getMessages] other than a specific message ID.
 ///
 /// https://zulip.com/api/get-messages#parameter-anchor
-enum AnchorCode implements Anchor { newest, oldest, firstUnread }
+@JsonEnum(fieldRename: FieldRename.snake, alwaysCreate: true)
+enum AnchorCode implements Anchor {
+  newest, oldest, firstUnread;
+
+  @override
+  String toJson() => _$AnchorCodeEnumMap[this]!;
+}
 
 /// A specific message ID, used as an anchor in [getMessages].
 class NumericAnchor extends Anchor {
   const NumericAnchor(this.messageId);
   final int messageId;
+
+  @override
+  String toJson() => messageId.toString();
 }
 
 @JsonSerializable(fieldRename: FieldRename.snake)

lib/api/route/messages.g.dart

@@ -200,6 +200,19 @@ void main() {
     });
   });
 
+  test('Anchor.toJson', () {
+    void checkAnchor(Anchor anchor, String expected) {
+      check(anchor.toJson()).equals(expected);
+    }
+
+    checkAnchor(AnchorCode.newest,      'newest');
+    checkAnchor(AnchorCode.oldest,      'oldest');
+    checkAnchor(AnchorCode.firstUnread, 'first_unread');
+    checkAnchor(const NumericAnchor(1), '1');
+    checkAnchor(const NumericAnchor(999999999), '999999999');
+    checkAnchor(const NumericAnchor(10000000000000000), '10000000000000000');
+  });
+
   group('getMessages', () {
     Future<GetMessagesResult> checkGetMessages(
       FakeApiConnection connection, {
@@ -262,27 +275,19 @@ void main() {
       });
     });
 
-    test('anchor', () {
+    test('numeric anchor', () {
       return FakeApiConnection.with_((connection) async {
-        Future<void> checkAnchor(Anchor anchor, String expected) async {
-          connection.prepare(json: fakeResult.toJson());
-          await checkGetMessages(connection,
-            narrow: const AllMessagesNarrow().apiEncode(),
-            anchor: anchor, numBefore: 10, numAfter: 20,
-            expected: {
-              'narrow': jsonEncode([]),
-              'anchor': expected,
-              'num_before': '10',
-              'num_after': '20',
-            });
-        }
-
-        await checkAnchor(AnchorCode.newest,      'newest');
-        await checkAnchor(AnchorCode.oldest,      'oldest');
-        await checkAnchor(AnchorCode.firstUnread, 'first_unread');
-        await checkAnchor(const NumericAnchor(1), '1');
-        await checkAnchor(const NumericAnchor(999999999), '999999999');
-        await checkAnchor(const NumericAnchor(10000000000000000), '10000000000000000');
+        connection.prepare(json: fakeResult.toJson());
+        await checkGetMessages(connection,
+          narrow: const AllMessagesNarrow().apiEncode(),
+          anchor: const NumericAnchor(42),
+          numBefore: 10, numAfter: 20,
+          expected: {
+            'narrow': jsonEncode([]),
+            'anchor': '42',
+            'num_before': '10',
+            'num_after': '20',
+          });
       });
     });
   });