Fix release notification resource and add multiple advance reminders

mobile/lib/services/local_notification_service.dart

@@ -56,47 +56,62 @@ class LocalNotificationService extends NotificationService {
   ) async {
     if (!settings.remindersEnabled || settings.semester == null) {
       await cancelOwned();
-      return const ReminderResult(ReminderStatus.off);
+      return ReminderResult(
+        ReminderStatus.off,
+        message: settings.remindersEnabled ? '请先设置学期开始日和周数，再安排提醒。' : '课前提醒已关闭。',
+      );
     }
     final access = await gateway.permissions(request: false);
     if (!access.notifications) {
       await cancelOwned();
       return const ReminderResult(
         ReminderStatus.permissionDenied,
-        message: '尚未允许通知权限，请在设置中开启。',
+        message: '请允许通知，并检查系统中的“课前提醒”通知类别。',
       );
     }
     final upcoming =
-        occurrences
-            .where(
-              (e) =>
-                  e.course.source != CourseSource.demo &&
-                  e.start
-                      .subtract(Duration(minutes: settings.reminderMinutes))
-                      .isAfter(now),
-            )
-            .toList()
-          ..sort((a, b) {
-            final order = a.start.compareTo(b.start);
-            return order == 0 ? a.key.compareTo(b.key) : order;
-          });
+        <({CourseOccurrence event, int minutes, tz.TZDateTime fireAt})>[
+          for (final event in occurrences)
+            if (event.course.source != CourseSource.demo)
+              for (final minutes in settings.reminderOffsets)
+                if (event.start
+                    .subtract(Duration(minutes: minutes))
+                    .isAfter(now))
+                  (
+                    event: event,
+                    minutes: minutes,
+                    fireAt: event.start.subtract(Duration(minutes: minutes)),
+                  ),
+        ]..sort((a, b) {
+          final order = a.fireAt.compareTo(b.fireAt);
+          if (order != 0) return order;
+          final courseOrder = a.event.key.compareTo(b.event.key);
+          return courseOrder != 0
+              ? courseOrder
+              : a.minutes.compareTo(b.minutes);
+        });
     final limited = upcoming.length > 400;
-    final selected = upcoming.take(400).toList()
-      ..sort((a, b) => a.key.compareTo(b.key));
+    final selected = upcoming.take(400);
     final desired = <int, ReminderRequest>{};
-    for (final event in selected) {
-      var id = notificationId(event.key);
+    for (final reminder in selected) {
+      final event = reminder.event;
+      // Keep the original 15-minute ID; other times need independent IDs so
+      // Android cannot replace an earlier reminder for the same course.
+      var id = notificationId(
+        reminder.minutes == 15
+            ? event.key
+            : '${event.key}/reminder/${reminder.minutes}',
+      );
       while (desired.containsKey(id)) {
         id = (id + 1) & 0x7FFFFFFF;
       }
       desired[id] = ReminderRequest(
         id: id,
         occurrenceKey: event.key,
-        fireAt: event.start.subtract(
-          Duration(minutes: settings.reminderMinutes),
-        ),
+        fireAt: reminder.fireAt,
         title: event.course.name,
-        body: '${event.course.room} · ${event.course.teacher}',
+        body:
+            '${reminder.minutes}分钟后上课 · ${event.course.room} · ${event.course.teacher}',
         exact: access.exactAlarm,
       );
     }
@@ -118,6 +133,11 @@ class LocalNotificationService extends NotificationService {
       _fingerprints[entry.key] = fingerprint;
     }
     final message = [
+      if (desired.isEmpty) '当前没有待提醒的课程，请核对学期日期和上课周次。',
+      if (desired.isNotEmpty) '已安排 ${desired.length} 次课前提醒。',
+      if (upcoming.isNotEmpty)
+        '最近一次：${upcoming.first.fireAt.month}月${upcoming.first.fireAt.day}日 '
+            '${upcoming.first.fireAt.hour.toString().padLeft(2, '0')}:${upcoming.first.fireAt.minute.toString().padLeft(2, '0')}。',
       if (!access.exactAlarm) '未允许精确提醒，系统可能延迟送达。',
       if (limited) '已安排最近 400 次提醒，后续提醒在再次打开时补充。',
     ].join(' ');
@@ -185,8 +205,17 @@ class PluginReminderGateway extends ReminderGateway {
       await _android?.requestNotificationsPermission();
       await _android?.requestExactAlarmsPermission();
     }
+    final channels = await _android?.getNotificationChannels();
+    final courseChannelEnabled =
+        channels == null ||
+        !channels.any(
+          (channel) =>
+              channel.id == 'hepan_lessons' &&
+              channel.importance == Importance.none,
+        );
     return ReminderPermissions(
-      await _android?.areNotificationsEnabled() ?? false,
+      (await _android?.areNotificationsEnabled() ?? false) &&
+          courseChannelEnabled,
       await _android?.canScheduleExactNotifications() ?? false,
     );
   }