feat: make server owner of tabs

lib/models/tab_event.dart

@@ -4,18 +4,33 @@ import 'payment_method.dart';
 
 /// Types of [TabEvent] the server understands.
 enum TabEventType {
+  tabOpened('tab_opened'),
+  tabRenamed('tab_renamed'),
+  tabDeleted('tab_deleted'),
   lineAdded('line_added'),
   lineRemoved('line_removed'),
-  settled('settled');
+  settled('settled'),
+
+  /// A stock count or tracking change made on the tablet. Not about a tab:
+  /// it has no `tabId`.
+  stockSet('stock_set');
 
   final String value;
 
   const TabEventType(this.value);
+
+  static TabEventType? fromValue(String value) {
+    for (final type in TabEventType.values) {
+      if (type.value == value) return type;
+    }
+    return null;
+  }
 }
 
-/// Something that happened on a tab, reported to the server for sales
-/// statistics. [payload] is the JSON object that is stored in the outbox and
-/// sent as is.
+/// Something that happened on a tab. Together the events form the operation
+/// log the server builds the venue's tabs from, and the tablet replays the
+/// ones the server hasn't applied yet on top of the server's tabs. [payload]
+/// is the JSON object that is stored in the outbox and sent as is.
 class TabEvent {
   final String id;
   final Map<String, dynamic> payload;
@@ -25,6 +40,7 @@ class TabEvent {
 
 /// One settled line in a `settled` event.
 typedef SettledLine = ({
+  String productId,
   String productName,
   int quantity,
   int unitPriceInCents,
@@ -37,10 +53,46 @@ class TabEventFactory {
 
   TabEventFactory({DateTime Function()? now}) : _now = now ?? DateTime.now;
 
-  /// [quantity] is how many pieces were added; always positive.
+  TabEvent tabOpened({
+    required String tabId,
+    required String customerName,
+    required DateTime openedAt,
+  }) {
+    return _event(
+      TabEventType.tabOpened,
+      tabId: tabId,
+      customerName: customerName,
+      fields: {'openedAt': openedAt.toUtc().toIso8601String()},
+    );
+  }
+
+  /// [customerName] is the new name.
+  TabEvent tabRenamed({required String tabId, required String customerName}) {
+    return _event(
+      TabEventType.tabRenamed,
+      tabId: tabId,
+      customerName: customerName,
+      fields: const {},
+    );
+  }
+
+  /// Written after a `line_removed` for every line still on the tab.
+  TabEvent tabDeleted({required String tabId, required String customerName}) {
+    return _event(
+      TabEventType.tabDeleted,
+      tabId: tabId,
+      customerName: customerName,
+      fields: const {},
+    );
+  }
+
+  /// [quantity] is how many pieces were added; always positive. [lineId] is
+  /// the local line, so the server can keep its id.
   TabEvent lineAdded({
     required String tabId,
     required String customerName,
+    required String lineId,
+    required String productId,
     required String productName,
     required int unitPriceInCents,
     required int quantity,
@@ -49,6 +101,8 @@ class TabEventFactory {
       TabEventType.lineAdded,
       tabId: tabId,
       customerName: customerName,
+      lineId: lineId,
+      productId: productId,
       productName: productName,
       unitPriceInCents: unitPriceInCents,
       quantity: quantity,
@@ -59,6 +113,8 @@ class TabEventFactory {
   TabEvent lineRemoved({
     required String tabId,
     required String customerName,
+    required String lineId,
+    required String productId,
     required String productName,
     required int unitPriceInCents,
     required int quantity,
@@ -67,6 +123,8 @@ class TabEventFactory {
       TabEventType.lineRemoved,
       tabId: tabId,
       customerName: customerName,
+      lineId: lineId,
+      productId: productId,
       productName: productName,
       unitPriceInCents: unitPriceInCents,
       quantity: quantity,
@@ -92,6 +150,7 @@ class TabEventFactory {
         'items': [
           for (final item in items)
             {
+              'productId': item.productId,
               'productName': item.productName,
               'quantity': item.quantity,
               'unitPriceInCents': item.unitPriceInCents,
@@ -101,6 +160,23 @@ class TabEventFactory {
     );
   }
 
+  /// The stock of [productId] was set to [quantity] on this tablet (a count,
+  /// or a new product's starting stock); null stops tracking it.
+  TabEvent stockSet({required String productId, required int? quantity}) {
+    final id = _uuid.v4();
+
+    return TabEvent(
+      id: id,
+      payload: {
+        'id': id,
+        'type': TabEventType.stockSet.value,
+        'productId': productId,
+        'quantity': quantity,
+        'occurredAt': _now().toUtc().toIso8601String(),
+      },
+    );
+  }
+
   /// The server's payment method names: `cash`, `payconiq`,
   /// `payment_pending` or `other`.
   static String paymentMethodValue(PaymentMethod method) {
@@ -115,6 +191,8 @@ class TabEventFactory {
     TabEventType type, {
     required String tabId,
     required String customerName,
+    required String lineId,
+    required String productId,
     required String productName,
     required int unitPriceInCents,
     required int quantity,
@@ -128,6 +206,8 @@ class TabEventFactory {
       tabId: tabId,
       customerName: customerName,
       fields: {
+        'lineId': lineId,
+        'productId': productId,
         'productName': productName,
         'unitPriceInCents': unitPriceInCents,
         'quantity': quantity,