Added Google Drive storage location

lib/models/fuel_entry.dart

@@ -6,6 +6,8 @@ class FuelEntry {
   final double pricePerGallon;
   final double totalCost;
   final String? receiptImagePath;
+  final String? receiptDriveFileId;
+  final DateTime updatedAt;
 
   FuelEntry({
     required this.id,
@@ -14,9 +16,40 @@ class FuelEntry {
     required this.gallons,
     required this.pricePerGallon,
     required this.totalCost,
+    required this.updatedAt,
     this.receiptImagePath,
+    this.receiptDriveFileId,
   });
 
+  /// True once the receipt photo has been uploaded to Drive and the local
+  /// copy removed. Viewing it then requires downloading it on demand.
+  bool get isReceiptUploadedToDrive =>
+      receiptImagePath == null && receiptDriveFileId != null;
+
+  /// True while a receipt photo exists only locally and still needs to be
+  /// uploaded next sync.
+  bool get hasPendingLocalReceipt => receiptImagePath != null;
+
+  FuelEntry copyWith({
+    String? receiptImagePath,
+    String? receiptDriveFileId,
+    DateTime? updatedAt,
+    bool clearReceiptImagePath = false,
+  }) {
+    return FuelEntry(
+      id: id,
+      vehicleId: vehicleId,
+      date: date,
+      gallons: gallons,
+      pricePerGallon: pricePerGallon,
+      totalCost: totalCost,
+      updatedAt: updatedAt ?? this.updatedAt,
+      receiptImagePath:
+          clearReceiptImagePath ? null : (receiptImagePath ?? this.receiptImagePath),
+      receiptDriveFileId: receiptDriveFileId ?? this.receiptDriveFileId,
+    );
+  }
+
   Map<String, dynamic> toJson() => {
         'id': id,
         'vehicleId': vehicleId,
@@ -25,6 +58,8 @@ class FuelEntry {
         'pricePerGallon': pricePerGallon,
         'totalCost': totalCost,
         'receiptImagePath': receiptImagePath,
+        'receiptDriveFileId': receiptDriveFileId,
+        'updatedAt': updatedAt.toIso8601String(),
       };
 
   factory FuelEntry.fromJson(Map<String, dynamic> json) => FuelEntry(
@@ -35,5 +70,9 @@ class FuelEntry {
         pricePerGallon: (json['pricePerGallon'] as num).toDouble(),
         totalCost: (json['totalCost'] as num).toDouble(),
         receiptImagePath: json['receiptImagePath'] as String?,
+        receiptDriveFileId: json['receiptDriveFileId'] as String?,
+        updatedAt: json['updatedAt'] != null
+            ? DateTime.parse(json['updatedAt'] as String)
+            : DateTime.fromMillisecondsSinceEpoch(0),
       );
 }