/**
 * 取出优惠券列表中的最优优惠券和次优优惠券 
 * */

class CouponUtils {
    constructor(couponList, productList) {
        this.couponList = this.couponSort(this.getCanBeUseCouponList(couponList, productList))
        this.productList = productList
        this.bestCoupon = null
        this.secondCoupon = null
        this.currentIndex = this.couponList.length
        this.fetchBestCoupon()
    }

    // 获取最高可用金额的优惠券
    fetchBestCoupon() {
        if (this.couponList.length === 0 || this.productList.length === 0) {
            this.bestCoupon = null
            return
        }
        this.bestCoupon = this.couponList.find(coupon => this.couponCanBeUse(coupon, this.productList)) || null
        if (this.bestCoupon) {
            this.currentIndex = this.couponList.findIndex(coupon => coupon.uniqueId === this.bestCoupon.uniqueId)
        }
        this.fetchSecondCoupon()
    }

    // 获取下一阶段可用优惠券
    fetchSecondCoupon() {
        if (this.couponList.length === 0 || this.productList.length === 0) {
            this.secondCoupon = null
            return
        }
        this.secondCoupon = this.currentIndex > 0 ? this.couponList[this.currentIndex - 1] : null
    }

    // 勾选商品满足优惠券使用条件 && 满足使用条件
    couponCanBeUse(coupon, productList) {
        return (
            this.isNoThreshold(coupon) ||
            this.isSomeProductUse(coupon, productList) ||
            this.isAllProductUse(coupon, productList)
        )
    }

    // 获取当前选中商品都能使用的优惠券
    getCanBeUseCouponList(couponList, productList) {
        return couponList.filter(coupon => coupon.productType === 1 || this.isCanUseByAllProduct(coupon,
            productList))
    }

    // 全部商品可用
    isCanUseByAllProduct(coupon, productList) {
        return productList.every(product => coupon.productIds.indexOf(product.productId.toString()) > -1)
    }

    // 优惠券是否无门槛
    isNoThreshold(coupon) {
        return coupon.noThresholdFlag === 1
    }

    // 全部商品可用 && 满足使用条件
    isAllProductUse(coupon, productList) {
        if (coupon.productType !== 1) {
            return false
        }
        const countPrice = productList.reduce((countPrice, product) => {
            return countPrice + this.totalProductPrice(product)
        }, 0)
        return countPrice >= coupon.touchPrice
    }

    // 部分商品可用 && 满足使用条件
    isSomeProductUse(coupon, productList) {
        if (coupon.productType !== 2) {
            return false
        }
        const countPrice = productList.reduce((countPrice, product) => {
            const isIncludes = coupon.productIds.indexOf(product.productId.toString()) > -1
            return isIncludes ? countPrice + this.totalProductPrice(product) : countPrice
        }, 0)
        return countPrice >= coupon.touchPrice
    }

    // 统计商品价格
    totalProductPrice(product) {
        return product.price * product.num
    }

    // 排序
    couponSort(couponList) {
        return couponList.sort((a, b) => b.couponAmount - a.couponAmount)
    }
}

export default CouponUtils