add pagination for pages

lib/pages/staff/model/staff_model.dart

@@ -9,53 +9,47 @@ import 'package:fcs/helpers/firebase_helper.dart';
 import 'package:fcs/pages/main/model/base_model.dart';
 import 'package:logging/logging.dart';
 
+import '../../../pagination/paginator_listener.dart';
+
 class StaffModel extends BaseModel {
   final log = Logger('StaffModel');
-  StreamSubscription<QuerySnapshot>? listener;
-  StreamSubscription<QuerySnapshot>? privilegeListener;
+  PaginatorListener<User>? getStaffs;
 
-  List<User> employees = [];
+  StreamSubscription<QuerySnapshot>? privilegeListener;
   List<Privilege> privileges = [];
 
   @override
   void privilegeChanged() {
     super.privilegeChanged();
     _loadPrivileges();
-    _loadEmployees();
   }
 
   @override
   logout() async {
-    if (listener != null) listener!.cancel();
+    getStaffs?.close();
     if (privilegeListener != null) privilegeListener!.cancel();
-    employees = [];
     privileges = [];
   }
 
-  Future<void> _loadEmployees() async {
+  loadPaginationStaffs() {
     if (user == null || !user!.hasStaffs()) return;
 
-    try {
-      if (listener != null) listener!.cancel();
+    String path = "/$user_collection";
+    Query col = FirebaseFirestore.instance
+        .collection(path)
+        .where("is_employee", isEqualTo: true)
+        .where("is_sys_admin", isEqualTo: false);
 
-      listener = FirebaseFirestore.instance
-          .collection("/$user_collection")
-          .where("is_employee", isEqualTo: true)
-          .where("is_sys_admin", isEqualTo: false)
-          .snapshots()
-          .listen((QuerySnapshot snapshot) {
-        employees.clear();
-        employees = snapshot.docs.map((documentSnapshot) {
-          var user = User.fromMap(
-              documentSnapshot.data() as Map<String, dynamic>,
-              documentSnapshot.id);
-          return user;
-        }).toList();
-        notifyListeners();
-      });
-    } catch (e) {
-      log.warning("Error!! $e");
-    }
+    Query pageQuery = FirebaseFirestore.instance
+        .collection(path)
+        .where("is_employee", isEqualTo: true)
+        .where("is_sys_admin", isEqualTo: false)
+        .orderBy("update_time", descending: true);
+
+    getStaffs?.close();
+    getStaffs = PaginatorListener<User>(
+        col, pageQuery, (data, id) => User.fromMap(data, id),
+        rowPerLoad: 30);
   }
 
   Future<void> _loadPrivileges() async {