// Custom Hook для корзины e-commerce

function useCart() {
  const [items, setItems] = React.useState(() => {
    const saved = localStorage.getItem('cart')
    return saved ? JSON.parse(saved) : []
  })

  // Сохранение в localStorage
  React.useEffect(() => {
    localStorage.setItem('cart', JSON.stringify(items))
  }, [items])

  // Добавление товара
  const addItem = (product, variant = null) => {
    setItems(prev => {
      const key = variant ? product.id + '-' + variant.id : product.id
      const existing = prev.find(item => item.key === key)

      if (existing) {
        return prev.map(item =>
          item.key === key
            ? { ...item, quantity: item.quantity + 1 }
            : item
        )
      }

      return [...prev, {
        key,
        productId: product.id,
        variantId: variant?.id,
        name: product.name,
        price: product.price,
        image: product.image,
        variant: variant?.name,
        quantity: 1
      }]
    })
  }

  // Обновление количества
  const updateQuantity = (key, quantity) => {
    if (quantity < 1) {
      removeItem(key)
      return
    }
    setItems(prev =>
      prev.map(item =>
        item.key === key ? { ...item, quantity } : item
      )
    )
  }

  // Удаление товара
  const removeItem = (key) => {
    setItems(prev => prev.filter(item => item.key !== key))
  }

  // Очистка корзины
  const clearCart = () => setItems([])

  // Вычисляемые значения
  const itemsCount = items.reduce((sum, item) => sum + item.quantity, 0)
  const subtotal = items.reduce((sum, item) => sum + item.price * item.quantity, 0)
  const shipping = subtotal > 5000 ? 0 : 500
  const total = subtotal + shipping

  return {
    items,
    addItem,
    updateQuantity,
    removeItem,
    clearCart,
    itemsCount,
    subtotal,
    shipping,
    total
  }
}

// === Демонстрация ===
console.log('=== E-commerce Cart Demo ===\n')

// Симуляция хука
let cartState = []
const setCart = (fn) => { cartState = typeof fn === 'function' ? fn(cartState) : fn }

const addToCart = (product) => {
  setCart(prev => {
    const existing = prev.find(item => item.productId === product.id)
    if (existing) {
      return prev.map(item =>
        item.productId === product.id
          ? { ...item, quantity: item.quantity + 1 }
          : item
      )
    }
    return [...prev, { ...product, productId: product.id, quantity: 1 }]
  })
  console.log('🛒 Добавлено:', product.name)
}

// Товары
const products = [
  { id: 1, name: 'React Книга', price: 1500, image: '📕' },
  { id: 2, name: 'TypeScript Курс', price: 3500, image: '💻' },
  { id: 3, name: 'Node.js Гайд', price: 2000, image: '📗' },
]

// Добавляем товары
addToCart(products[0])
addToCart(products[1])
addToCart(products[0]) // Повторно — увеличит quantity

console.log('\nКорзина:')
cartState.forEach(item => {
  console.log(`  ${item.image} ${item.name} x${item.quantity} = ${item.price * item.quantity}₽`)
})

const total = cartState.reduce((sum, item) => sum + item.price * item.quantity, 0)
console.log('\nИтого:', total, '₽')