The Desynchronized Flash-Sale Inventory Lock

/**
 * Cart Manager
 * Handles item reservations, expiry cleanup, and checkout finalization.
 */

export class CartManager {
  constructor(inventoryLock, inventoryStore) {
    this.inventoryLock = inventoryLock;
    this.inventoryStore = inventoryStore;
    this.carts = new Map();
  }

  createCart(cartId, sku) {
    const lockResult = this.inventoryLock.acquire(sku, cartId);
    if (!lockResult.success) {
      return { success: false, reason: "OUT_OF_STOCK" };
    }
    this.inventoryStore.decrementStock(sku);
    const cart = {
      cartId,
      sku,
      status: "active",
      epoch: lockResult.epoch
    };
    this.carts.set(cartId, cart);
    return { success: true, cart };
  }

  expireCart(cartId) {
    const cart = this.carts.get(cartId);
    if (!cart) return;

    // Return stock to inventory pool
    this.inventoryStore.incrementStock(cart.sku);
    this.inventoryLock.release(cart.sku, cart.epoch);

    // AI Attempt: Cart expired
    // BUG: Does NOT update cart.status = "expired"!
    // A late checkout request holding this cart object can still execute!
  }

  checkout(cartId) {
    const cart = this.carts.get(cartId);
    if (!cart) {
      return { success: false, reason: "CART_NOT_FOUND" };
    }

    // AI Attempt: Finalize order
    // BUG: Missing check for cart.status === "active"!
    // An expired or reclaimed cart proceeds to finalize!
    cart.status = "completed";
    return { success: true, orderId: "order_" + cartId };
  }
}