interface OrderItem {
  price: number;
  quantity: number;
}

enum MembershipTypes {
  'gold',
  'silver'
}

const INIT_VALUE = 0;
const GOLD_HIGH_DISCOUNT = 0.20;
const GOLD_LOW_DISCOUNT = 0.10;
const SILVER_HIGH_DISCOUNT = 0.10;
const SILVER_LOW_DISCOUNT = 0.05;
const LARGE_ORDER_THRESHOLD = 100;
const MIN_ORDER_TOTAL = 10;
const INVALID_ORDER = -1;

export function calculateTotal(items: OrderItem[]) : number {
  let total = INIT_VALUE;

  for (let item = INIT_VALUE; item < items.length; item++) {
    total = total + items[item].price * items[item].quantity;
  }

  return total;
}

export function calculateOrderDiscount(items: OrderItem[], membershipType: string): number {
  let discount = INIT_VALUE;
  
  let total = calculateTotal(items);

  if (total < MIN_ORDER_TOTAL) return INVALID_ORDER; 

  if (membershipType === MembershipTypes[0]) {
    if (total >= LARGE_ORDER_THRESHOLD) {
      discount = total * GOLD_HIGH_DISCOUNT;
    } else {
      discount = total * GOLD_LOW_DISCOUNT;
    }
  } else if (membershipType === MembershipTypes[1]) {
    if (total >= LARGE_ORDER_THRESHOLD) {
      discount = total * SILVER_HIGH_DISCOUNT;
    } else {
      discount = total * SILVER_LOW_DISCOUNT;
    }
  }

  return total - discount;
}