export interface CartItem {
  sku: string
  name: string
  unitPriceCents: number
  quantity: number
}

export interface Discount {
  code: string
  percentOff: number
}

export function subtotalCents(items: CartItem[]): number {
  return items.reduce((sum, item) => sum + item.unitPriceCents * item.quantity, 0)
}

export function applyDiscount(subtotal: number, discount?: Discount): number {
  if (!discount) return subtotal
  const factor = 1 - discount.percentOff / 100
  return Math.round(subtotal * factor)
}

export function totalCents(items: CartItem[], discount?: Discount): number {
  return applyDiscount(subtotalCents(items), discount)
}