Non-Functional Requirements:

Concurrency: Multiple cashiers can create orders simultaneously without conflicts
Thread Safety: Order queue must be thread-safe for concurrent producer-consumer access
Reliability: Orders must not be lost if a barista worker crashes
Performance: Order placement should complete within 2 seconds
Scalability: Support adding more barista workers during peak hours

Assumptions:

Customers always wait for order completion (no order cancellations)
Order queue has unlimited capacity (can be modified for bounded queue)
Each order gets a unique sequential ID serving as the customer token
One barista processes one order at a time (serial processing per worker)

3. Use Case Diagram

Actors:

Customer: Places orders, makes payments, receives notifications, picks up orders
Cashier: Takes orders, processes payments, enqueues orders, issues tokens
Barista: Dequeues orders, prepares drinks, marks orders complete
Administrator: Manages menu items, configures pricing, views reports

Core Use Cases:

Place Order & Pay
Enqueue Order
Dequeue & Prepare Order
Notify Customer
Pick Up Order
Manage Menu

graph TB
    subgraph CoffeeShopSystem["Coffee Shop System"]
        UC1["Place Order & Pay"]
        UC2["Enqueue Order"]
        UC3["Dequeue Order"]
        UC4["Prepare Drink"]
        UC5["Notify Customer"]
        UC6["Pick Up Order"]
        UC7["Manage Menu"]
        UC8["View Reports"]
    end
    
    Customer([Customer])
    Cashier([Cashier])
    Barista([Barista])
    Admin([Administrator])
    System([System])
    
    Customer --> UC1
    Cashier --> UC1
    Cashier --> UC2
    Barista --> UC3
    Barista --> UC4
    System --> UC5
    Customer --> UC6
    Admin --> UC7
    Admin --> UC8
    
    UC1 -.->|includes| UC2
    UC4 -.->|triggers| UC5
    
    style Customer fill:#e1f5ff
    style Cashier fill:#fff3e0
    style Barista fill:#f3e5f5
    style Admin fill:#ffebee
    style System fill:#e8f5e9

4. Class Diagram

Core Classes:

MenuItem: Represents an item on the menu (name, base price, category)
Customization: Add-ons like extra shot, milk type, size (affects price)
Order: Contains order ID, items with customizations, total price, status, timestamps
OrderQueue: Thread-safe queue holding pending orders (BlockingQueue implementation)
Customer: Places orders, receives token, gets notified
Cashier: Creates orders, processes payments, enqueues to queue
Barista: Worker thread that dequeues orders and prepares drinks
Payment: Handles payment processing with amount and method
NotificationService: Publishes order ready notifications (Observer pattern)
OrderStatus: Enum (PENDING, IN_PROGRESS, COMPLETED, PICKED_UP)

classDiagram
    class MenuItem {
        -String id
        -String name
        -double basePrice
        -Category category
        +getPrice() double
    }
    
    class Customization {
        -String name
        -double additionalPrice
    }
    
    class Order {
        -String orderId
        -List~OrderItem~ items
        -double totalAmount
        -OrderStatus status
        -LocalDateTime createdAt
        -LocalDateTime completedAt
        +calculateTotal() double
        +updateStatus(OrderStatus) void
    }
    
    class Order

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