update invoice page

lib/pages/discount/model/discount_model.dart

@@ -49,9 +49,9 @@ class DiscountModel extends BaseModel {
           .orderBy("code", descending: false)
           .snapshots()
           .listen((snaps) {
-        discounts.clear();
+        _discounts.clear();
         snaps.documents.forEach((d) {
-          discounts.add(Discount.fromMap(d.data, d.documentID));
+          _discounts.add(Discount.fromMap(d.data, d.documentID));
         });
         notifyListeners();
       });
@@ -73,6 +73,27 @@ class DiscountModel extends BaseModel {
     return paginator;
   }
 
+  Future<List<Discount>> getDiscount(String userID) async {
+    String path = "/$discounts_collection";
+    try {
+      var q = Firestore.instance
+          .collection("$path")
+          .where("customer_id", isEqualTo: userID)
+          .where("status", isEqualTo: "available");
+      var snaps = await q.getDocuments(source: Source.server);
+      List<Discount> discounts = snaps.documents.map((snap) {
+        if (snap.exists) {
+          var s = Discount.fromMap(snap.data, snap.documentID);
+          return s;
+        }
+      }).toList();
+      return discounts;
+    } catch (e) {
+      log.warning("Error!! $e");
+    }
+    return null;
+  }
+
   Future<void> loadMore() async {
     if (_used.ended || _selectedIndex == 1) return;
     isLoading = true;