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

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

export const initialBasketData: BasketData = {
  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 calculateBasketTotals = (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 addItemToBasket = (
  basketData: BasketData,
  product: ProductDto,
  quantity: number,
  billingCycle: BillingCycle,
): BasketData => {
  const isAlreadyInBasket = isItemInBasketData(basketData.items, product.id, billingCycle)

  if (!product.isQuantityBased && isAlreadyInBasket) {
    return basketData
  }

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

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

  const updatedState = { ...basketData, items: newItems, ...calculateBasketTotals(newItems) }
  return updatedState
}

export const removeItemFromBasket = (basketData: BasketData, id: string): BasketData => {
  const newItems = basketData.items.filter((item) => item.product.id !== id)
  const updatedState = { ...basketData, items: newItems, ...calculateBasketTotals(newItems) }
  return updatedState
}

export const updateBasketItemQuantity = (
  basketData: BasketData,
  id: string,
  quantity: number,
): BasketData => {
  const newItems = basketData.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, basketData.globalPeriod)
      }
      return item
    })
    .filter(Boolean) as BasketItem[]

  const updatedState = { ...basketData, items: newItems, ...calculateBasketTotals(newItems) }
  return updatedState
}

export const clearBasket = (): BasketData => {
  return initialBasketData
}

export const setBasketGlobalBillingCycle = (basketData: BasketData, cycle: BillingCycle): BasketData => {
  const newItems = basketData.items.map((item) =>
    withItemVat(item.product, item.quantity, cycle, basketData.globalPeriod),
  )
  const updatedState = {
    ...basketData,
    globalBillingCycle: cycle,
    items: newItems,
    ...calculateBasketTotals(newItems),
  }
  return updatedState
}

export const setBasketGlobalPeriod = (basketData: BasketData, period: number): BasketData => {
  const newItems = basketData.items.map((item) =>
    withItemVat(item.product, item.quantity, item.billingCycle, period),
  )
  const updatedState = {
    ...basketData,
    globalPeriod: period,
    items: newItems,
    ...calculateBasketTotals(newItems),
  }
  return updatedState
}

export const isItemInBasket = (
  basketData: BasketData,
  productId: string,
  billingCycle: BillingCycle,
): boolean => {
  return basketData.items.some(
    (item) => item.product.id === productId && item.billingCycle === billingCycle,
  )
}

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