feat:增加消息记录功能

lib/utils/date_utils.dart

@@ -0,0 +1,26 @@
+import 'package:intl/intl.dart';
+
+String formatChatTime(DateTime time) {
+  final now = DateTime.now();
+  final t = time.toLocal();
+
+  final today = DateTime(now.year, now.month, now.day);
+  final d = DateTime(t.year, t.month, t.day);
+
+  final diff = today.difference(d).inDays;
+  final hm = DateFormat('HH:mm').format(t);
+
+  if (diff == 0) return hm;
+  if (diff == 1) return '昨天 $hm';
+
+  // 本周
+  if (diff < 7 && d.weekday <= now.weekday) {
+    return '${DateFormat('EEEEE', 'zh_CN').format(t)} $hm';
+  }
+
+  if (t.year == now.year) {
+    return DateFormat('M月d日 HH:mm').format(t);
+  }
+
+  return DateFormat('yyyy年M月d日 HH:mm').format(t);
+}