feat: make server owner of tabs

lib/models/server_tab.dart

@@ -0,0 +1,122 @@
+import 'payment_method.dart';
+
+/// One piece on a line: when it was put on the tab and, if it was taken off
+/// again, when. Kept so history can show every drink with its time.
+class ServerUnit {
+  /// Stable across syncs: `<event id>:<index within that event>`.
+  final String id;
+  final DateTime addedAt;
+  final DateTime? removedAt;
+
+  const ServerUnit({required this.id, required this.addedAt, this.removedAt});
+
+  factory ServerUnit.fromJson(Map<String, dynamic> json) {
+    return ServerUnit(
+      id: json['id'] as String,
+      addedAt: DateTime.parse(json['addedAt'] as String).toLocal(),
+      removedAt: switch (json['removedAt']) {
+        final String value => DateTime.parse(value).toLocal(),
+        _ => null,
+      },
+    );
+  }
+}
+
+class ServerTabLine {
+  final String id;
+  final String productId;
+  final String productName;
+  final int unitPriceInCents;
+  final int quantity;
+  final List<ServerUnit> units;
+
+  const ServerTabLine({
+    required this.id,
+    required this.productId,
+    required this.productName,
+    required this.unitPriceInCents,
+    required this.quantity,
+    this.units = const [],
+  });
+
+  factory ServerTabLine.fromJson(Map<String, dynamic> json) {
+    return ServerTabLine(
+      id: json['id'] as String,
+      productId: json['productId'] as String? ?? '',
+      productName: json['productName'] as String,
+      unitPriceInCents: json['unitPriceInCents'] as int,
+      quantity: json['quantity'] as int,
+      units: [
+        for (final unit in json['units'] as List<dynamic>? ?? [])
+          ServerUnit.fromJson(unit as Map<String, dynamic>),
+      ],
+    );
+  }
+}
+
+/// An open tab as the server holds it: the venue's source of truth.
+class ServerTab {
+  final String id;
+  final String customerName;
+  final DateTime openedAt;
+  final int version;
+  final List<ServerTabLine> lines;
+
+  const ServerTab({
+    required this.id,
+    required this.customerName,
+    required this.openedAt,
+    required this.version,
+    this.lines = const [],
+  });
+
+  factory ServerTab.fromJson(Map<String, dynamic> json) {
+    return ServerTab(
+      id: json['id'] as String,
+      customerName: json['customerName'] as String,
+      openedAt: DateTime.parse(json['openedAt'] as String).toLocal(),
+      version: json['version'] as int? ?? 0,
+      lines: [
+        for (final line in json['lines'] as List<dynamic>? ?? [])
+          ServerTabLine.fromJson(line as Map<String, dynamic>),
+      ],
+    );
+  }
+}
+
+/// A tab settled anywhere in the venue (this tablet, another tablet or the
+/// dashboard), for the local history.
+class ServerSettlement {
+  /// For a settlement made on a tablet: the id of its `settled` event.
+  final String id;
+  final String tabId;
+  final String customerName;
+  final DateTime settledAt;
+  final PaymentMethod paymentMethod;
+  final List<ServerTabLine> lines;
+
+  const ServerSettlement({
+    required this.id,
+    required this.tabId,
+    required this.customerName,
+    required this.settledAt,
+    required this.paymentMethod,
+    this.lines = const [],
+  });
+
+  factory ServerSettlement.fromJson(Map<String, dynamic> json) {
+    return ServerSettlement(
+      id: json['id'] as String,
+      tabId: json['tabId'] as String,
+      customerName: json['customerName'] as String,
+      settledAt: DateTime.parse(json['settledAt'] as String).toLocal(),
+      paymentMethod: PaymentMethod.fromValue(
+        json['paymentMethod'] as String? ?? 'cash',
+      ),
+      lines: [
+        for (final line in json['lines'] as List<dynamic>? ?? [])
+          ServerTabLine.fromJson(line as Map<String, dynamic>),
+      ],
+    );
+  }
+}