import { BillingCycle, BasketItem, ProductDto } from '@/proxy/order/models'

export interface CartState {
  items: BasketItem[]
  subtotal: number
  vatTotal: number
  total: number
  globalBillingCycle: BillingCycle
  globalPeriod: number
}

export const initialCartState: CartState = {
  items: [],
  subtotal: 0,
  vatTotal: 0,
  total: 0,
  globalBillingCycle: 'yearly',
  globalPeriod: 1,
}

export const calculateItemPrice = (
  product: ProductDto,
  quantity: number,
  billingCycle: BillingCycle,
  period: number = 1,
): number => {
  const price = billingCycle === 'monthly' ? product.monthlyPrice! : product.yearlyPrice!
  const vatRate = product.vatRate ?? 0.2
  return roundMoney(price * quantity * period * (1 + vatRate))
}

const roundMoney = (value: number): number => Math.round(value * 100) / 100

const calculateItemVatAmount = (totalPrice: number, vatRate: number = 0.2): number =>
  vatRate > 0 ? roundMoney(totalPrice - totalPrice / (1 + vatRate)) : 0

const withItemVat = (
  product: ProductDto,
  quantity: number,
  billingCycle: BillingCycle,
  period: number,
): BasketItem => {
  const vatRate = product.vatRate ?? 0.2
  const totalPrice = calculateItemPrice(product, quantity, billingCycle, period)
  return {
    product,
    quantity,
    billingCycle,
    vatRate,
    vatAmount: calculateItemVatAmount(totalPrice, vatRate),
    totalPrice,
  }
}

const calculateCartTotals = (items: BasketItem[]) => {
  const total = roundMoney(items.reduce((sum, item) => sum + item.totalPrice, 0))
  const vatTotal = roundMoney(items.reduce((sum, item) => sum + (item.vatAmount ?? 0), 0))
  return {
    subtotal: roundMoney(total - vatTotal),
    vatTotal,
    total,
  }
}

export const addItemToCart = (
  cartState: CartState,
  product: ProductDto,
  quantity: number,
  billingCycle: BillingCycle,
): CartState => {
  const isAlreadyInCart = isItemInCartState(cartState.items, product.id, billingCycle)

  if (!product.isQuantityBased && isAlreadyInCart) {
    return cartState
  }

  const existingItemIndex = cartState.items.findIndex(
    (item) => item.product.id === product.id && item.billingCycle === billingCycle,
  )

  let newItems
  if (existingItemIndex > -1) {
    newItems = [...cartState.items]
    newItems[existingItemIndex].quantity += quantity
    newItems[existingItemIndex] = withItemVat(
      product,
      newItems[existingItemIndex].quantity,
      billingCycle,
      cartState.globalPeriod,
    )
  } else {
    const actualQuantity = !product.isQuantityBased ? 1 : quantity
    newItems = [
      ...cartState.items,
      withItemVat(product, actualQuantity, billingCycle, cartState.globalPeriod),
    ]
  }

  const updatedState = { ...cartState, items: newItems, ...calculateCartTotals(newItems) }
  return updatedState
}

export const removeItemFromCart = (cartState: CartState, id: string): CartState => {
  const newItems = cartState.items.filter((item) => item.product.id !== id)
  const updatedState = { ...cartState, items: newItems, ...calculateCartTotals(newItems) }
  return updatedState
}

export const updateCartItemQuantity = (
  cartState: CartState,
  id: string,
  quantity: number,
): CartState => {
  const newItems = cartState.items
    .map((item) => {
      if (item.product.id === id) {
        if (quantity <= 0) return null
        if (!item.product.isQuantityBased) return item

        return withItemVat(item.product, quantity, item.billingCycle, cartState.globalPeriod)
      }
      return item
    })
    .filter(Boolean) as BasketItem[]

  const updatedState = { ...cartState, items: newItems, ...calculateCartTotals(newItems) }
  return updatedState
}

export const clearCart = (): CartState => {
  return initialCartState
}

export const setCartGlobalBillingCycle = (cartState: CartState, cycle: BillingCycle): CartState => {
  const newItems = cartState.items.map((item) =>
    withItemVat(item.product, item.quantity, cycle, cartState.globalPeriod),
  )
  const updatedState = {
    ...cartState,
    globalBillingCycle: cycle,
    items: newItems,
    ...calculateCartTotals(newItems),
  }
  return updatedState
}

export const setCartGlobalPeriod = (cartState: CartState, period: number): CartState => {
  const newItems = cartState.items.map((item) =>
    withItemVat(item.product, item.quantity, item.billingCycle, period),
  )
  const updatedState = {
    ...cartState,
    globalPeriod: period,
    items: newItems,
    ...calculateCartTotals(newItems),
  }
  return updatedState
}

export const isItemInCart = (
  cartState: CartState,
  productId: string,
  billingCycle: BillingCycle,
): boolean => {
  return cartState.items.some(
    (item) => item.product.id === productId && item.billingCycle === billingCycle,
  )
}

export const isItemInCartState = (
  items: BasketItem[],
  productId: string,
  billingCycle: BillingCycle,
): boolean => {
  return items.some((item) => item.product.id === productId && item.billingCycle === billingCycle)
}