feat: make server own tabs

apps/api/prisma/schema.prisma

@@ -24,11 +24,17 @@ model Venue {
   tabEvents        TabEvent[]
   products         Product[]
   stockAdjustments StockAdjustment[]
+  tabs             Tab[]
+  settlements      Settlement[]
+  // Set on the first sync after the server started holding the tabs: the tabs were then taken over from the
+  // terminal's own open tabs, once
+  tabsSeededAt     DateTime?
 }
 
 model Device {
   id             String    @id @default(uuid())
-  venueId        String    @unique
+  // A venue can have several terminals
+  venueId        String
   name           String
   tokenHash      String    @unique
   tokenPrefix    String
@@ -42,6 +48,7 @@ model Device {
   tabOwnerships  TabOwnership[]
   remoteCommands RemoteCommand[]
   tabEvents      TabEvent[]
+  settlements    Settlement[]
 
   @@index([venueId, revokedAt])
 }
@@ -105,10 +112,13 @@ model TabOwnership {
   @@id([venueId, tabId])
 }
 
+// A request from the dashboard. close_tab used to be executed by the owning terminal; the server now settles
+// the tab itself and records the command as completed right away, for the history.
 model RemoteCommand {
   id              String    @id @default(uuid())
   venueId         String
-  deviceId        String
+  // Null for a command the server carried out itself
+  deviceId        String?
   targetTabId     String
   customerName    String?
   amountInCents   Int?
@@ -122,8 +132,8 @@ model RemoteCommand {
   createdAt       DateTime  @default(now())
   expiresAt       DateTime
 
-  venue  Venue  @relation(fields: [venueId], references: [id])
-  device Device @relation(fields: [deviceId], references: [id])
+  venue  Venue   @relation(fields: [venueId], references: [id])
+  device Device? @relation(fields: [deviceId], references: [id])
 
   @@index([deviceId, status, createdAt])
   @@index([venueId, status, createdAt])
@@ -188,16 +198,19 @@ model TabReminder {
   @@index([venueId, tabId])
 }
 
-// What happened on a tab, as reported by the terminal: lines added or removed, and settlements.
-// The id is generated by the terminal so a re-sent event is stored only once.
+// What happened on a tab, as reported by the terminal. The id is generated by the terminal so a re-sent event is
+// stored, and applied to the tab state and stock, only once.
 model TabEvent {
   id               String   @id
   venueId          String
   deviceId         String
-  tabId            String
-  customerName     String
-  // line_added | line_removed | settled
+  // Null for stock_set, which is not about a tab
+  tabId            String?
+  customerName     String?
+  // tab_opened | tab_renamed | tab_deleted | line_added | line_removed | settled | stock_set
   type             String
+  lineId           String?
+  productId        String?
   productName      String?
   unitPriceInCents Int?
   // Signed: positive for line_added, negative for line_removed
@@ -207,6 +220,8 @@ model TabEvent {
   paymentMethod    String?
   commandId        String?
   items            Json?
+  // stock_set: the counted stock, null to stop tracking
+  stockSetTo       Int?
   occurredAt       DateTime
   receivedAt       DateTime @default(now())
 
@@ -217,8 +232,9 @@ model TabEvent {
   @@index([venueId, type, occurredAt])
 }
 
-// The terminal's product catalog with its stock, as last reported by the terminal. The terminal owns the
-// stock: it counts sales down offline, so the dashboard only changes it through StockAdjustments.
+// The venue's products as reported by its terminals, with the stock. The server owns the stock: it follows the
+// terminals' line events and stock counts and the dashboard's StockAdjustments. A product is never removed because
+// one terminal doesn't report it.
 model Product {
   venueId           String
   // Generated by the terminal
@@ -226,8 +242,10 @@ model Product {
   name              String
   category          String?
   priceInCents      Int
-  // Null when the terminal doesn't track stock for this product. Can be negative: a sale is never blocked.
+  // Null when stock is not tracked for this product. Can be negative: a sale is never blocked.
   stock             Int?
+  // When the stock was last counted; line events that happened before it are already in the count
+  countedAt         DateTime?
   // Dashboard-only setting, never sent to or overwritten by the terminal
   lowStockThreshold Int?
   reportedAt        DateTime
@@ -237,8 +255,8 @@ model Product {
   @@id([venueId, productId])
 }
 
-// A stock change requested from the dashboard. It is sent to the terminal on every sync until the terminal
-// reports it applied or rejected.
+// A stock change made on the dashboard. The server applies it right away. Older ones may still have been applied
+// by a terminal, which reported the outcome.
 model StockAdjustment {
   id            String    @id @default(uuid())
   venueId       String
@@ -252,7 +270,7 @@ model StockAdjustment {
   requestedById String
   // pending | applied | rejected | cancelled
   status        String    @default("pending")
-  // The terminal's stock right after applying it
+  // The stock right after applying it
   stockAfter    Int?
   result        String?
   createdAt     DateTime  @default(now())
@@ -263,3 +281,49 @@ model StockAdjustment {
   @@index([venueId, status, createdAt])
   @@index([venueId, productId, createdAt])
 }
+
+// An open tab of the venue: the source of truth the terminals replace their own tabs with on every sync. Tabs are
+// never closed, only emptied by a settlement; tab_deleted removes one.
+model Tab {
+  venueId      String
+  // Generated by the terminal that opened it
+  id           String
+  customerName String
+  openedAt     DateTime
+  // Bumped by every change, so the dashboard can refuse to settle a tab that changed since it was shown
+  version      Int      @default(0)
+  // [{ id, productId, productName, unitPriceInCents, units: [{ id, addedAt, removedAt }] }]
+  lines        Json
+  updatedAt    DateTime @updatedAt
+
+  venue Venue @relation(fields: [venueId], references: [id])
+
+  @@id([venueId, id])
+}
+
+// A settlement made on a terminal (id = the settled event's id) or on the dashboard. Terminals read them as a feed
+// after their cursor, which is the sequence number.
+model Settlement {
+  id            String   @id
+  sequence      Int      @unique @default(autoincrement())
+  venueId       String
+  tabId         String
+  customerName  String
+  settledAt     DateTime
+  // cash | payconiq | payment_pending | other
+  paymentMethod String
+  amountInCents Int
+  // The settled lines, in the shape of Tab.lines with each line's settled and removed units
+  lines         Json
+  // Who settled it: a terminal, or a dashboard user
+  deviceId      String?
+  requestedBy   String?
+  commandId     String?
+  createdAt     DateTime @default(now())
+
+  venue  Venue   @relation(fields: [venueId], references: [id])
+  device Device? @relation(fields: [deviceId], references: [id])
+
+  @@index([venueId, sequence])
+  @@index([venueId, settledAt])
+}