add generic timestamp

lib/src/org/model/org_timestamp.dart

@@ -14,8 +14,12 @@ class OrgDiaryTimestamp extends OrgLeafNode with SingleContentElement {
 typedef OrgDate = ({String year, String month, String day, String? dayName});
 typedef OrgTime = ({String hour, String minute});
 
+sealed class OrgTimestamp extends OrgNode {
+  bool get isActive;
+}
+
 /// A timestamp, like `[2020-05-05 Tue]`
-class OrgSimpleTimestamp extends OrgLeafNode {
+class OrgSimpleTimestamp extends OrgLeafNode implements OrgTimestamp {
   OrgSimpleTimestamp(
     this.prefix,
     this.date,
@@ -30,6 +34,7 @@ class OrgSimpleTimestamp extends OrgLeafNode {
   final List<String> repeaterOrDelay;
   final String suffix;
 
+  @override
   bool get isActive => prefix == '<' && suffix == '>';
 
   @override
@@ -99,13 +104,14 @@ class OrgSimpleTimestamp extends OrgLeafNode {
       );
 }
 
-class OrgDateRangeTimestamp extends OrgParentNode {
+class OrgDateRangeTimestamp extends OrgParentNode implements OrgTimestamp {
   OrgDateRangeTimestamp(this.start, this.delimiter, this.end);
 
   final OrgSimpleTimestamp start;
   final String delimiter;
   final OrgSimpleTimestamp end;
 
+  @override
   bool get isActive => start.isActive && end.isActive;
 
   @override
@@ -146,7 +152,7 @@ class OrgDateRangeTimestamp extends OrgParentNode {
       );
 }
 
-class OrgTimeRangeTimestamp extends OrgLeafNode {
+class OrgTimeRangeTimestamp extends OrgLeafNode implements OrgTimestamp {
   OrgTimeRangeTimestamp(
     this.prefix,
     this.date,
@@ -163,6 +169,7 @@ class OrgTimeRangeTimestamp extends OrgLeafNode {
   final List<String> repeaterOrDelay;
   final String suffix;
 
+  @override
   bool get isActive => prefix == '<' && suffix == '>';
 
   DateTime get startDateTime => DateTime(

test/org/model/timestamp_test.dart

@@ -108,5 +108,51 @@ void main() {
       expect(result.contains('あ'), isFalse);
       expect(result.toMarkup(), markup);
     });
+    group("generic timestamp tests", () {
+      test('OrgSimpleTimestamp', () {
+        final markup = '<2025-05-30>';
+        final result = parser.parse(markup).value as OrgTimestamp;
+
+        expect(result.isActive, isTrue);
+        expect(result, isA<OrgTimestamp>());
+        expect(result, isA<OrgSimpleTimestamp>());
+        expect(result, isNot(isA<OrgDateRangeTimestamp>()));
+        expect(result, isNot(isA<OrgTimeRangeTimestamp>()));
+        expect(result.toMarkup(), markup);
+      });
+      test('OrgTimeRangeTimestamp', () {
+        final markup = '<2025-05-30 15:00-16:00>';
+        final result = parser.parse(markup).value as OrgTimestamp;
+
+        expect(result.isActive, isTrue);
+        expect(result, isA<OrgTimestamp>());
+        expect(result, isA<OrgTimeRangeTimestamp>());
+        expect(result, isNot(isA<OrgSimpleTimestamp>()));
+        expect(result, isNot(isA<OrgDateRangeTimestamp>()));
+        expect(result.toMarkup(), markup);
+      });
+      test('OrgDateRangeTimestamp', () {
+        final markup = '[2025-05-30]--[2025-06-30]';
+        final result = parser.parse(markup).value as OrgTimestamp;
+
+        expect(result.isActive, isFalse);
+        expect(result, isA<OrgTimestamp>());
+        expect(result, isA<OrgDateRangeTimestamp>());
+        expect(result, isNot(isA<OrgSimpleTimestamp>()));
+        expect(result, isNot(isA<OrgTimeRangeTimestamp>()));
+        expect(result.toMarkup(), markup);
+      });
+      test('Exhaustivity', () {
+        final markup = '[2025-05-30]--[2025-06-30]';
+        final result = parser.parse(markup).value as OrgTimestamp;
+
+        final type = switch (result) {
+          OrgTimeRangeTimestamp() => result.toString(),
+          OrgDateRangeTimestamp() => result.toString(),
+          OrgSimpleTimestamp() => result.toString(),
+        };
+        expect(type, isNotEmpty);
+      });
+    });
   });
 }