Project 7 — Design Vending Machine

classDiagram
    class VendingMachine {
        -inventory: Inventory
        -payment: PaymentProcessor
        -state: VMState
        -selectedProduct: Product
        -insertedAmount: number
        +selectProduct(code: string): void
        +insertCoin(coin: Coin): void
        +dispense(): Product
        +refund(): number
    }
    class Inventory {
        -products: Map~string, Product~
        +getProduct(code: string): Product
        +updateStock(code: string, quantity: int): void
        +isAvailable(code: string): boolean
    }
    class Product {
        +code: string
        +name: string
        +price: number
        -quantity: int
    }
    class VMState {
        <<interface>>
        +selectProduct(code: string): void
        +insertCoin(coin: Coin): void
        +dispense(): Product
    }
    class IdleState {
        +selectProduct(code: string): void
    }
    class HasSelectionState {
        +insertCoin(coin: Coin): void
    }
    class DispensingState {
        +dispense(): Product
    }
    class Coin {
        <<enumeration>>
        PENNY(0.01) NICKEL(0.05) DIME(0.10) QUARTER(0.25)
    }

    VendingMachine --> Inventory
    VendingMachine --> VMState
    VMState <|.. IdleState
    VMState <|.. HasSelectionState
    VMState <|.. DispensingState
    Inventory *-- Product

enum Coin { PENNY = 0.01, NICKEL = 0.05, DIME = 0.10, QUARTER = 0.25 }

class Product {
  constructor(
    public code: string,
    public name: string,
    public price: number,
    private quantity: number
  ) {}

  isAvailable(): boolean { return this.quantity > 0; }
  dispense(): void { if (this.quantity > 0) this.quantity--; }
}

class Inventory {
  private products: Map<string, Product> = new Map();

  addProduct(product: Product): void { this.products.set(product.code, product); }
  getProduct(code: string): Product | undefined { return this.products.get(code); }
  isAvailable(code: string): boolean { return this.products.get(code)?.isAvailable() ?? false; }
}

class VendingMachine {
  private inventory: Inventory = new Inventory();
  private insertedAmount: number = 0;
  private selectedProduct?: Product;

  selectProduct(code: string): string | null {
    const product = this.inventory.getProduct(code);
    if (!product || !product.isAvailable()) return null;
    this.selectedProduct = product;
    return `Selected ${product.name} — $${product.price}`;
  }

  insertCoin(coin: Coin): number {
    this.insertedAmount += coin;
    return this.insertedAmount;
  }

  dispense(): { product?: Product; change: number } {
    if (!this.selectedProduct) return { change: this.insertedAmount };
    if (this.insertedAmount < this.selectedProduct.price) {
      return { change: this.insertedAmount }; // Not enough money
    }

    this.selectedProduct.dispense();
    const change = this.insertedAmount - this.selectedProduct.price;
    this.insertedAmount = 0;
    this.selectedProduct = undefined;

    return { product: this.selectedProduct, change };
  }
}