package distribution

import (
	"errors"
	"sync"
	"time"

	"hfb_sys/backend/internal/model"

	"gorm.io/gorm"
)

// distributionTablesPresent 探测分销财务表是否存在，仅首次访问查询 information_schema，
// 兼容尚未执行分销迁移的旧环境，避免每次支付/退款事务都做系统表查询。
var (
	distributionTablePresent   bool
	distributionTableCheckOnce sync.Once
)

func distributionTablesPresent(tx *gorm.DB) bool {
	distributionTableCheckOnce.Do(func() {
		distributionTablePresent = tx.Migrator().HasTable(&model.DistributionOrderFinancial{})
	})
	return distributionTablePresent
}

// resolveDistributionMode 只根据买卖双方站点判定模式，不查库、不猜规则。
// buySiteID / listingSiteID 为 0 表示主站。
func resolveDistributionMode(buySiteID, listingSiteID uint64) string {
	switch {
	case buySiteID == 0 && listingSiteID == 0:
		return ""
	case buySiteID == 0:
		return ModeTwoPartyDistributorReceive
	case listingSiteID == 0:
		return ModeTwoPartyPlatformReceive
	case buySiteID == listingSiteID:
		return ModeSiteSelfSell
	default:
		return ModeThreeParty
	}
}

func derefSiteID(id *uint64) uint64 {
	if id == nil || *id == 0 {
		return 0
	}
	return *id
}

func loadListingSiteID(tx *gorm.DB, listingID uint64) (uint64, error) {
	if listingID == 0 {
		return 0, nil
	}
	var listing model.RentalListing
	if err := tx.Select("id, distribution_site_id").First(&listing, listingID).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return 0, nil
		}
		return 0, err
	}
	return derefSiteID(listing.DistributionSiteID), nil
}

func loadActiveSiteByID(tx *gorm.DB, siteID uint64) (*model.DistributionSite, error) {
	var site model.DistributionSite
	if err := tx.Where("id = ? AND status = 'active'", siteID).First(&site).Error; err != nil {
		return nil, ErrSiteNotFound
	}
	return &site, nil
}

func loadActiveSellSiteByCode(tx *gorm.DB, siteCode string) (*model.DistributionSite, error) {
	var site model.DistributionSite
	if err := tx.Where("site_code = ? AND status = 'active' AND display_account_enabled = ?", siteCode, true).First(&site).Error; err != nil {
		return nil, ErrSiteNotFound
	}
	return &site, nil
}

func ensureAccountDisplayTx(tx *gorm.DB, siteID, listingID, accountID uint64) error {
	var relation model.DistributionSiteAccount
	if err := tx.Where("site_id = ? AND listing_id = ? AND account_id = ? AND display_status = 'enabled'", siteID, listingID, accountID).First(&relation).Error; err != nil {
		return ErrAccountDisplayNotFound
	}
	return nil
}

func findActiveRuleTx(tx *gorm.DB, siteID uint64, mode string, at time.Time) (*model.DistributionRuleVersion, error) {
	var rule model.DistributionRuleVersion
	err := tx.Where("mode = ? AND status = 'active' AND effective_from <= ? AND (effective_to IS NULL OR effective_to > ?)", mode, at, at).
		Where("site_id = ? OR site_id IS NULL", siteID).
		Order("CASE WHEN site_id IS NULL THEN 1 ELSE 0 END, effective_from DESC, id DESC").
		First(&rule).Error
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, ErrRuleNotFound
		}
		return nil, err
	}
	return &rule, nil
}

// ResolveOrderSourceTx 先按买卖站点判定模式，再查该 mode 的生效规则，不再在两方规则之间猜优先级。
func ResolveOrderSourceTx(tx *gorm.DB, siteCode string, listingID, accountID uint64, at time.Time) (*model.DistributionSite, *model.DistributionRuleVersion, error) {
	listingSiteID, err := loadListingSiteID(tx, listingID)
	if err != nil {
		return nil, nil, err
	}

	var buySite *model.DistributionSite
	buySiteID := uint64(0)
	if siteCode != "" {
		buySite, err = loadActiveSellSiteByCode(tx, siteCode)
		if err != nil {
			return nil, nil, err
		}
		if err := ensureAccountDisplayTx(tx, buySite.ID, listingID, accountID); err != nil {
			return nil, nil, err
		}
		buySiteID = buySite.ID
	}

	mode := resolveDistributionMode(buySiteID, listingSiteID)
	if mode == "" {
		return nil, nil, nil
	}

	var anchor *model.DistributionSite
	switch mode {
	case ModeTwoPartyDistributorReceive:
		anchor, err = loadActiveSiteByID(tx, listingSiteID)
		if err != nil {
			return nil, nil, err
		}
	default:
		if buySite == nil {
			return nil, nil, ErrSiteNotFound
		}
		anchor = buySite
	}

	rule, err := findActiveRuleTx(tx, anchor.ID, mode, at)
	if err != nil {
		return nil, nil, err
	}
	return anchor, rule, nil
}

func ruleFromVersion(rule model.DistributionRuleVersion) Rule {
	return Rule{
		Mode:                    rule.Mode,
		PlatformReceiveRatio:    rule.PlatformReceiveRatio,
		PlatformSellRatio:       rule.PlatformSellRatio,
		DistributorReceiveRatio: rule.DistributorReceiveRatio,
		DistributorSellRatio:    rule.DistributorSellRatio,
		DistributorARatio:       rule.DistributorARatio,
		DistributorBRatio:       rule.DistributorBRatio,
		ServiceFeeValue:         rule.ServiceFeeValue,
		ServiceFeeUnit:          rule.ServiceFeeUnit,
		PaymentFeeBPS:           rule.PaymentFeeBPS,
		TaxEnabled:              rule.TaxEnabled,
		TaxRateBPS:              rule.TaxRateBPS,
	}
}

// calculateForRule 按规则快照计算手续费、服务费和分成基数。
func calculateForRule(rule model.DistributionRuleVersion, input SettlementInput) (SettlementResult, error) {
	return CalculateSettlement(ruleFromVersion(rule), input)
}

// SnapshotPaidOrderTx 在支付确认事务内幂等写入财务和参与方快照。
// 参与方金额按规则比例对分成基数拆分，剩余（含尾差）记入 RoundingAdjustmentCent 归平台。
func SnapshotPaidOrderTx(tx *gorm.DB, orderID uint64, grossPaidCent int64) error {
	if !distributionTablesPresent(tx) {
		return nil
	}
	var order model.RentalOrder
	if err := tx.First(&order, orderID).Error; err != nil {
		return err
	}
	if order.DistributionSiteID == nil || order.DistributionRuleVersionID == nil {
		return nil
	}
	var rule model.DistributionRuleVersion
	if err := tx.First(&rule, *order.DistributionRuleVersionID).Error; err != nil {
		return err
	}
	markup := order.ShelfMarkupCent
	if markup < 0 {
		markup = 0
	}
	result, err := calculateForRule(rule, SettlementInput{GrossPaidAmountCent: grossPaidCent, MarkupAmountCent: markup})
	if err != nil {
		return err
	}
	splits := SplitSettlement(ruleFromVersion(rule), result.SplitBaseAmountCent, markup)
	financial := model.DistributionOrderFinancial{OrderID: order.ID, SiteID: *order.DistributionSiteID, RuleVersionID: rule.ID, GrossPaidAmountCent: grossPaidCent, NetPaidAmountCent: result.NetPaidAmountCent, PaymentFeeBPS: rule.PaymentFeeBPS, PaymentFeeCent: result.PaymentFeeCent, ServiceFeeValue: rule.ServiceFeeValue, ServiceFeeUnit: rule.ServiceFeeUnit, ServiceFeeCent: result.ServiceFeeCent, MarkupAmountCent: markup, TaxEnabled: rule.TaxEnabled, TaxRateBPS: rule.TaxRateBPS, TaxAmountCent: result.TaxAmountCent, SplitBaseAmountCent: result.SplitBaseAmountCent, RoundingAdjustmentCent: SplitRemainderCent(result.SplitBaseAmountCent, splits), SettlementStatus: "pending"}
	if err := tx.Where("order_id = ?", order.ID).Assign(financial).FirstOrCreate(&financial).Error; err != nil {
		return err
	}
	var count int64
	if err := tx.Model(&model.DistributionOrderParty{}).Where("order_id = ?", order.ID).Count(&count).Error; err != nil {
		return err
	}
	if count > 0 {
		return nil
	}
	parties := make([]model.DistributionOrderParty, 0, len(splits))
	for _, split := range splits {
		partyType := PartyTypeSite
		if split.PartyRole == "platform_sell" || split.PartyRole == "platform_receive" {
			partyType = PartyTypePlatform
		}
		partyID := *order.DistributionSiteID
		if partyType == PartyTypePlatform {
			partyID = 0
		} else if split.PartyRole == "distributor_a" {
			// 三方模式下 distributor_a 为商品收号站
			var listing model.RentalListing
			if err := tx.Select("distribution_site_id").First(&listing, order.ListingID).Error; err == nil && listing.DistributionSiteID != nil {
				partyID = *listing.DistributionSiteID
			}
		}
		parties = append(parties, model.DistributionOrderParty{OrderID: order.ID, SiteID: *order.DistributionSiteID, PartyRole: split.PartyRole, PartyType: partyType, PartyID: partyID, Ratio: split.Ratio, IncomeAmountCent: split.AmountCent, ProfitAmountCent: split.AmountCent})
	}
	if len(parties) == 0 {
		return nil
	}
	return tx.Create(&parties).Error
}

// ApplyRefundTx 按累计成功退款金额重算手续费、分成基数和各方分成，不覆盖订单创建时的规则版本。
func ApplyRefundTx(tx *gorm.DB, orderID uint64, refundAmountCent int64) error {
	if !distributionTablesPresent(tx) {
		return nil
	}
	var financial model.DistributionOrderFinancial
	if err := tx.Where("order_id = ?", orderID).First(&financial).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil
		}
		return err
	}
	if refundAmountCent < 0 || refundAmountCent > financial.GrossPaidAmountCent {
		return ErrInvalidAmount
	}
	var rule model.DistributionRuleVersion
	if err := tx.First(&rule, financial.RuleVersionID).Error; err != nil {
		return err
	}
	result, err := calculateForRule(rule, SettlementInput{GrossPaidAmountCent: financial.GrossPaidAmountCent, RefundAmountCent: refundAmountCent, MarkupAmountCent: financial.MarkupAmountCent})
	if err != nil {
		return err
	}
	splits := SplitSettlement(ruleFromVersion(rule), result.SplitBaseAmountCent, financial.MarkupAmountCent)
	if err := tx.Model(&financial).Updates(map[string]any{"refund_amount_cent": refundAmountCent, "net_paid_amount_cent": result.NetPaidAmountCent, "payment_fee_cent": result.PaymentFeeCent, "service_fee_cent": result.ServiceFeeCent, "split_base_amount_cent": result.SplitBaseAmountCent, "rounding_adjustment_cent": SplitRemainderCent(result.SplitBaseAmountCent, splits), "settlement_status": "pending"}).Error; err != nil {
		return err
	}
	for _, split := range splits {
		if err := tx.Model(&model.DistributionOrderParty{}).
			Where("order_id = ? AND party_role = ?", orderID, split.PartyRole).
			Updates(map[string]any{"income_amount_cent": split.AmountCent, "profit_amount_cent": split.AmountCent}).Error; err != nil {
			return err
		}
	}
	return nil
}