/**
 * POST /api/cart/items
 *
 * Add a product to the shopping cart
 *
 * Request Body:
 * {
 *   productId: string (UUID)
 *   quantity: number (positive integer, default: 1)
 * }
 *
 * Behavior:
 * - If product already in cart, increments quantity
 * - Validates product exists, is active, and has sufficient stock
 * - Checks role-based visibility permissions
 * - Creates cart if it doesn't exist
 *
 * Response:
 * {
 *   success: true,
 *   message: string,
 *   cart: CartSummary
 * }
 */

import { z } from 'zod'
import { eq, and } from 'drizzle-orm'
import { cartItems } from '../../database/schema'

// Request validation schema
const addToCartSchema = z.object({
  productId: z.string().uuid('Invalid product ID'),
  quantity: z.number().int().positive().default(1),
})

export default defineEventHandler(async (event) => {
  // Validate request body
  const body = await readBody(event)
  const { productId, quantity } = await addToCartSchema.parseAsync(body)

  // Validate product availability and permissions
  const product = await validateProductForCart(event, productId, quantity)

  // Get or create cart
  const cart = await getOrCreateCart(event)

  const db = await useDatabase()

  // Check if product already in cart
  const existingItem = await db.query.cartItems.findFirst({
    where: and(
      eq(cartItems.cartId, cart.id),
      eq(cartItems.productId, productId)
    ),
  })

  if (existingItem) {
    // Product already in cart - increment quantity
    const newQuantity = existingItem.quantity + quantity

    // Validate new quantity against stock
    validateQuantityUpdate(newQuantity, product.stockQuantity)

    // Update quantity
    await db
      .update(cartItems)
      .set({ quantity: newQuantity })
      .where(eq(cartItems.id, existingItem.id))
  } else {
    // Add new item to cart
    await db.insert(cartItems).values({
      cartId: cart.id,
      productId,
      quantity,
    })
  }

  // Update cart timestamp
  await touchCart(cart.id)

  // Return updated cart
  const cartSummary = await getCartWithItems(cart.id)

  return {
    success: true,
    message: existingItem
      ? `Quantity updated to ${existingItem.quantity + quantity}`
      : 'Product added to cart',
    cart: cartSummary,
  }
})