package employeecollection

import (
	"context"
	"time"

	"gorm.io/gorm"
	"gorm.io/gorm/clause"

	employeecollectiondomain "github.com/break/junhong_cmp_fiber/internal/domain/employeecollection"
	"github.com/break/junhong_cmp_fiber/internal/model"
	"github.com/break/junhong_cmp_fiber/pkg/constants"
	"github.com/break/junhong_cmp_fiber/pkg/errors"
)

// RefundOffsetSource 是来源订单退款成功的事实快照。
type RefundOffsetSource struct {
	// RefundID 表示本次退款申请 ID。
	RefundID uint
	// OrderID 表示退款关联的来源订单 ID。
	OrderID uint
	// RefundAmount 表示本次退款成功金额（分），与退款入账使用的金额为同一实参。
	RefundAmount int64
}

// RefundOffsetService 在既有退款成功事务内冲销或提示员工代收款账单。
// 只处理来源为后台线下套餐订单的账单，其他订单直接跳过，不阻断退款链路。
type RefundOffsetService struct {
	audit BillAuditWriter
}

// NewRefundOffsetService 创建退款冲销用例。
func NewRefundOffsetService(audit BillAuditWriter) *RefundOffsetService {
	return &RefundOffsetService{audit: audit}
}

// ApplyInTx 在既有退款成功事务内按来源唯一键 order:{id} 查找账单并幂等写入冲销事实。
// 同一退款对同一账单至多一条关联：重复投递时关联写入影响 0 行，不再冲减、不再写审计、
// 也不依赖退款事务的 changed 标志。
func (s *RefundOffsetService) ApplyInTx(ctx context.Context, tx *gorm.DB, source RefundOffsetSource) error {
	if s == nil || tx == nil || s.audit == nil {
		return errors.New(errors.CodeInternalError, "员工代收款退款冲销能力未配置")
	}
	if source.RefundID == 0 || source.OrderID == 0 || source.RefundAmount <= 0 {
		return errors.New(errors.CodeInvalidParam, "员工代收款退款冲销参数无效")
	}
	var bill model.EmployeeCollectionBill
	if err := tx.WithContext(ctx).Clauses(clause.Locking{Strength: "UPDATE"}).
		Where("source_key = ?", employeecollectiondomain.OrderSourceKey(source.OrderID)).
		First(&bill).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			// 来源订单未产生员工代收款账单，跳过而不阻断退款。
			return nil
		}
		return errors.Wrap(errors.CodeDatabaseError, err, "锁定来源订单员工代收款账单失败")
	}
	decision, err := employeecollectiondomain.DecideRefundOffset(billAmounts(&bill), source.RefundAmount)
	if err != nil {
		return err
	}
	record := &model.EmployeeCollectionBillRefund{
		BillID: bill.ID, RefundID: source.RefundID, SourceOrderID: source.OrderID,
		RefundAmount: source.RefundAmount, BillReceivableAmount: bill.ReceivableAmount,
		Outcome: decision.Outcome, ReducedAmount: decision.ReducedAmount,
	}
	result := tx.WithContext(ctx).Clauses(clause.OnConflict{
		Columns:   []clause.Column{{Name: "bill_id"}, {Name: "refund_id"}},
		DoNothing: true,
	}).Create(record)
	if result.Error != nil {
		return errors.Wrap(errors.CodeDatabaseError, result.Error, "写入员工代收款退款冲销关联失败")
	}
	if result.RowsAffected == 0 {
		// 同一退款已冲销过同一账单，保留既有事实。
		return nil
	}
	before := bill
	if err := applyRefundOutcome(ctx, tx, &bill, decision); err != nil {
		return err
	}
	offsetEventID, err := composeAuditEventID(
		"employee_collection", "bill", "order", uintText(source.OrderID), "refund", uintText(source.RefundID))
	if err != nil {
		return err
	}
	return s.audit.WriteEmployeeCollectionBill(ctx, tx, BillAudit{
		EventID:    offsetEventID,
		ActionCode: constants.AuditActionEmployeeCollectionBillRefundOffseted,
		Summary:    constants.GetEmployeeCollectionRefundOutcomeName(decision.Outcome),
		Bill:       &bill,
		BeforeData: map[string]any{
			"receivable_amount": before.ReceivableAmount, "received_amount": before.ReceivedAmount,
			"reserved_amount": before.ReservedAmount, "status": before.Status,
		},
		AfterData: map[string]any{
			"receivable_amount": bill.ReceivableAmount, "received_amount": bill.ReceivedAmount,
			"reserved_amount": bill.ReservedAmount, "status": bill.Status,
			"refund_id": source.RefundID, "refund_amount": source.RefundAmount, "outcome": decision.Outcome,
		},
		CorrelationID: bill.SourceNo,
	})
}

// applyRefundOutcome 按判定结果修改账单：全额退款关闭、部分冲减应收，提示结果不修改金额与状态。
// 关闭与冲减都使用 expected-status 条件更新并检查 RowsAffected，避免并发覆盖。
func applyRefundOutcome(
	ctx context.Context,
	tx *gorm.DB,
	bill *model.EmployeeCollectionBill,
	decision employeecollectiondomain.RefundOffsetDecision,
) error {
	expectedStatus := bill.Status
	switch decision.Outcome {
	case constants.EmployeeCollectionRefundOutcomeHintOnly:
		return nil
	case constants.EmployeeCollectionRefundOutcomeClosedFull:
		closedAt := time.Now().UTC()
		result := tx.WithContext(ctx).Model(&model.EmployeeCollectionBill{}).
			Where("id = ? AND status = ?", bill.ID, expectedStatus).
			Updates(map[string]any{
				"status":        constants.EmployeeCollectionBillStatusClosed,
				"closed_reason": "来源订单全额退款",
				"closed_at":     closedAt,
				"updater":       0,
			})
		if result.Error != nil {
			return errors.Wrap(errors.CodeDatabaseError, result.Error, "关闭来源订单全额退款账单失败")
		}
		if result.RowsAffected != 1 {
			return errors.New(errors.CodeConflict, "员工代收款账单状态已变化，退款冲销未完成")
		}
		bill.Status = constants.EmployeeCollectionBillStatusClosed
		bill.ClosedReason = "来源订单全额退款"
		bill.ClosedAt = &closedAt
		return nil
	case constants.EmployeeCollectionRefundOutcomeReduced:
		amounts, err := billAmounts(bill).ReduceReceivable(decision.ReducedAmount)
		if err != nil {
			return err
		}
		nextStatus := amounts.DerivedStatus()
		result := tx.WithContext(ctx).Model(&model.EmployeeCollectionBill{}).
			Where("id = ? AND status = ?", bill.ID, expectedStatus).
			Updates(map[string]any{
				"receivable_amount": amounts.Receivable,
				"status":            nextStatus,
				"updater":           0,
			})
		if result.Error != nil {
			return errors.Wrap(errors.CodeDatabaseError, result.Error, "冲减来源订单退款账单应收失败")
		}
		if result.RowsAffected != 1 {
			return errors.New(errors.CodeConflict, "员工代收款账单状态已变化，退款冲减未完成")
		}
		bill.ReceivableAmount = amounts.Receivable
		bill.Status = nextStatus
		return nil
	default:
		return errors.New(errors.CodeInternalError, "不支持的退款冲销处理结果")
	}
}