Can save expenses to local list

moneymgr_mobile/lib/services/storage/expenses.dart

@@ -17,7 +17,7 @@ typedef ExpensesList = List<Expense>;
 abstract class BaseExpenseInfo with _$BaseExpenseInfo {
   const factory BaseExpenseInfo({
     required String label,
-    required int cost,
+    required double cost,
     required DateTime time,
   }) = _BaseExpenseInfo;
 }
@@ -36,7 +36,7 @@ abstract class Expense with _$Expense {
     /// The cost shall always be a positive value
     required double cost,
 
-    /// Time associated with the expense
+    /// Time associated with the expense (seconds since epoch)
     required int time,
 
     /// Associated file mime type
@@ -80,21 +80,24 @@ class ExpensesManager {
 
   /// Get the current list of expenses
   Future<ExpensesList> getList() async {
+    // On first save the list does not exists.
+    if (!await expenseFile.exists()) {
+      return [];
+    }
+
     final jsonDec = jsonDecode(await expenseFile.readAsString());
     return List<Expense>.from(jsonDec.map((m) => Expense.fromJson(m)));
   }
 
   /// Save the list of expenses
   Future<void> saveList(ExpensesList list) async {
-    final jsonDoc = jsonEncode(list.map((t) => t.toJson()));
+    final jsonDoc = jsonEncode(list.map((t) => t.toJson()).toList());
     await expenseFile.writeAsString(jsonDoc);
   }
 
   /// Add a new expense to the list
   Future<void> add({
-    required String? label,
-    required double cost,
-    required int time,
+    required BaseExpenseInfo info,
     required List<int> fileContent,
     required String fileMimeType,
   }) async {
@@ -102,9 +105,9 @@ class ExpensesManager {
 
     final exp = Expense(
       id: (list.lastOrNull?.id ?? 0) + Random().nextInt(1000),
-      label: label,
-      cost: cost,
-      time: time,
+      label: info.label,
+      cost: info.cost,
+      time: (info.time.millisecondsSinceEpoch / 1000).floor(),
       mimeType: fileMimeType,
     );