package services

import (
	"errors"
	"platform/pkg/u"
	"platform/web/core"
	m "platform/web/models"
	q "platform/web/queries"
	"time"

	"gorm.io/gen/field"
	"gorm.io/gorm"
)

var CouponUser = &couponUserService{}

type couponUserService struct{}

func (s *couponUserService) Create(data CreateCouponUserData) error {
	now := time.Now()
	status := u.Else(data.Status, m.CouponUserStatusUnused)
	if err := validateCouponUserStatus(status); err != nil {
		return err
	}

	return q.Q.Transaction(func(tx *q.Query) error {
		coupon, err := tx.Coupon.Where(tx.Coupon.ID.Eq(data.CouponID)).Take()
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return core.NewBizErr("优惠券不存在")
		}
		if err != nil {
			return core.NewServErr("获取优惠券数据失败", err)
		}
		if coupon.Status != m.CouponStatusEnabled {
			return core.NewBizErr("优惠券不可用")
		}
		if coupon.Count <= 0 {
			return core.NewBizErr("优惠券已发放完")
		}

		_, err = tx.User.Where(tx.User.ID.Eq(data.UserID)).Take()
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return core.NewBizErr("用户不存在")
		}
		if err != nil {
			return core.NewServErr("获取用户数据失败", err)
		}

		expireAt := data.ExpireAt
		if expireAt == nil {
			expireAt = couponUserExpireAt(coupon, now)
		}

		usedAt := data.UsedAt
		if status == m.CouponUserStatusUsed && usedAt == nil {
			usedAt = &now
		}
		if status == m.CouponUserStatusUnused {
			usedAt = nil
		}

		err = tx.CouponUser.Create(&m.CouponUser{
			UserID:   data.UserID,
			CouponID: data.CouponID,
			Status:   status,
			ExpireAt: expireAt,
			UsedAt:   usedAt,
		})
		if err != nil {
			return core.NewServErr("发放优惠券失败", err)
		}

		return adjustCouponCount(tx, coupon.ID, -1)
	})
}

type CreateCouponUserData struct {
	CouponID int32               `json:"coupon_id" validate:"required"`
	UserID   int32               `json:"user_id" validate:"required"`
	Status   *m.CouponUserStatus `json:"status"`
	ExpireAt *time.Time          `json:"expire_at"`
	UsedAt   *time.Time          `json:"used_at"`
}

func (s *couponUserService) Update(data UpdateCouponUserData) error {
	return q.Q.Transaction(func(tx *q.Query) error {
		current, err := tx.CouponUser.Where(tx.CouponUser.ID.Eq(data.ID)).Take()
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return core.NewBizErr("已发放优惠券不存在")
		}
		if err != nil {
			return core.NewServErr("获取已发放优惠券失败", err)
		}

		do := make([]field.AssignExpr, 0)
		if data.ExpireAtClear != nil && *data.ExpireAtClear {
			do = append(do, tx.CouponUser.ExpireAt.Null())
		} else if data.ExpireAt != nil {
			do = append(do, tx.CouponUser.ExpireAt.Value(*data.ExpireAt))
		}

		if data.UsedAtClear != nil && *data.UsedAtClear {
			do = append(do, tx.CouponUser.UsedAt.Null())
		} else if data.UsedAt != nil {
			do = append(do, tx.CouponUser.UsedAt.Value(*data.UsedAt))
		}

		if data.Status != nil {
			if err := validateCouponUserStatus(*data.Status); err != nil {
				return err
			}
			if current.Status != *data.Status {
				if current.Status == m.CouponUserStatusUsed {
					return core.NewBizErr("已使用的优惠券不能修改状态")
				}
				if current.Status == m.CouponUserStatusDisabled && *data.Status == m.CouponUserStatusUsed {
					return core.NewBizErr("已禁用的优惠券不能标记为已使用")
				}

				switch *data.Status {
				case m.CouponUserStatusUnused:
					if current.Status == m.CouponUserStatusDisabled {
						if err := adjustCouponCount(tx, current.CouponID, -1); err != nil {
							return err
						}
					}
					if data.UsedAt == nil && (data.UsedAtClear == nil || !*data.UsedAtClear) {
						do = append(do, tx.CouponUser.UsedAt.Null())
					}

				case m.CouponUserStatusUsed:
					if data.UsedAt == nil && (data.UsedAtClear == nil || !*data.UsedAtClear) {
						do = append(do, tx.CouponUser.UsedAt.Value(time.Now()))
					}

				case m.CouponUserStatusDisabled:
					if current.Status == m.CouponUserStatusUnused {
						if err := adjustCouponCount(tx, current.CouponID, 1); err != nil {
							return err
						}
					}
				}
				do = append(do, tx.CouponUser.Status.Value(int(*data.Status)))
			}
		}

		if len(do) == 0 {
			return nil
		}

		result, err := tx.CouponUser.
			Where(
				tx.CouponUser.ID.Eq(data.ID),
				tx.CouponUser.Status.Eq(int(current.Status)),
			).
			UpdateSimple(do...)
		if err != nil {
			return core.NewServErr("更新已发放优惠券失败", err)
		}
		if result.RowsAffected == 0 {
			return core.NewBizErr("已发放优惠券状态已变化，请重试")
		}
		return nil
	})
}

type UpdateCouponUserData struct {
	ID            int32               `json:"id" validate:"required"`
	Status        *m.CouponUserStatus `json:"status"`
	ExpireAt      *time.Time          `json:"expire_at"`
	ExpireAtClear *bool               `json:"expire_at_clear"`
	UsedAt        *time.Time          `json:"used_at"`
	UsedAtClear   *bool               `json:"used_at_clear"`
}

func (s *couponUserService) Delete(id int32) error {
	status := m.CouponUserStatusDisabled
	return s.Update(UpdateCouponUserData{
		ID:     id,
		Status: &status,
	})
}

func (s *couponUserService) DeleteOfUser(id int32, userID int32) error {
	assigned, err := q.CouponUser.Where(
		q.CouponUser.ID.Eq(id),
		q.CouponUser.UserID.Eq(userID),
	).Take()
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return core.NewBizErr("已发放优惠券不存在")
	}
	if err != nil {
		return core.NewServErr("获取已发放优惠券失败", err)
	}
	if assigned.Status != m.CouponUserStatusUnused {
		return core.NewBizErr("只能撤销未使用的优惠券")
	}

	return s.Delete(id)
}

func couponUserExpireAt(coupon *m.Coupon, now time.Time) *time.Time {
	if coupon == nil {
		return nil
	}

	switch coupon.ExpireType {
	case m.CouponExpireTypeFixed:
		return coupon.ExpireAt
	case m.CouponExpireTypeRelative:
		if coupon.ExpireIn == nil {
			return nil
		}
		expireAt := now.Add(time.Duration(*coupon.ExpireIn) * 24 * time.Hour)
		return &expireAt
	default:
		return nil
	}
}

func validateCouponUserStatus(status m.CouponUserStatus) error {
	switch status {
	case m.CouponUserStatusUnused, m.CouponUserStatusUsed, m.CouponUserStatusDisabled:
		return nil
	default:
		return core.NewBizErr("优惠券发放状态无效")
	}
}

func adjustCouponCount(tx *q.Query, couponID int32, delta int32) error {
	coupon, err := tx.Coupon.Where(tx.Coupon.ID.Eq(couponID)).Take()
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return core.NewBizErr("优惠券不存在")
	}
	if err != nil {
		return core.NewServErr("获取优惠券数据失败", err)
	}

	next := coupon.Count + delta
	if next < 0 {
		return core.NewBizErr("优惠券已发放完")
	}

	result, err := tx.Coupon.
		Where(tx.Coupon.ID.Eq(couponID), tx.Coupon.Count_.Eq(coupon.Count)).
		UpdateSimple(tx.Coupon.Count_.Value(next))
	if err != nil {
		return core.NewServErr("更新优惠券数量失败", err)
	}
	if result.RowsAffected == 0 {
		return core.NewBizErr("优惠券库存已变化，请重试")
	}

	return nil
}