package service

import (
	"errors"
	"time"

	"github.com/shopspring/decimal"
	"github.com/wmms/wmms/internal/model"
	"github.com/wmms/wmms/internal/repository"
)

var ErrInsufficientStock = errors.New("insufficient stock")

type OutboundService struct {
	outboundRepo *repository.OutboundRepo
	materialSvc  *MaterialService
	stockRepo    *repository.StockRepo
}

func NewOutboundService() *OutboundService {
	return &OutboundService{
		outboundRepo: repository.NewOutboundRepo(),
		materialSvc:  NewMaterialService(),
		stockRepo:    repository.NewStockRepo(),
	}
}

func (s *OutboundService) Create(req *model.CreateOutboundRequest, operator string) (*model.OutboundOrder, error) {
	order := &model.OutboundOrder{
		OutboundDate: time.Now(),
		Operator:     operator,
		Handler:      operator,
		Receiver:     req.Receiver,
		Remark:       req.Remark,
		Items:        make([]model.OutboundItem, len(req.Items)),
	}

	// Validate all items first (outside transaction)
	for i, item := range req.Items {
		exists, err := s.materialSvc.Exists(item.MaterialID)
		if err != nil {
			return nil, err
		}
		if !exists {
			return nil, ErrMaterialNotFound
		}
		active, err := s.materialSvc.IsActive(item.MaterialID)
		if err != nil {
			return nil, err
		}
		if !active {
			return nil, ErrMaterialObsolete
		}

		currentStock, err := s.stockRepo.GetStock(item.MaterialID)
		if err != nil {
			return nil, err
		}
		if currentStock.LessThan(decimal.NewFromInt(int64(item.Quantity))) {
			return nil, ErrInsufficientStock
		}

		order.Items[i] = model.OutboundItem{
			MaterialID: item.MaterialID,
			Quantity:   item.Quantity,
		}
	}

	// Start transaction for stock update (prevents race condition)
	tx, err := repository.BeginTx()
	if err != nil {
		return nil, err
	}
	defer func() {
		if err != nil {
			tx.Rollback()
		}
	}()

	// Re-check stock with row lock (SELECT FOR UPDATE) to prevent overselling
	for i := range order.Items {
		item := &order.Items[i]
		lockedStock, err := s.stockRepo.GetStockForUpdateTx(tx, item.MaterialID)
		if err != nil {
			return nil, err
		}
		if lockedStock.LessThan(decimal.NewFromInt(int64(item.Quantity))) {
			err = ErrInsufficientStock
			return nil, err
		}
	}

	// Create outbound order
	err = s.outboundRepo.CreateTx(tx, order)
	if err != nil {
		return nil, err
	}

	// Update stock and create logs within transaction
	for i := range order.Items {
		item := &order.Items[i]
		material, err := s.materialSvc.GetByID(item.MaterialID)
		if err != nil {
			return nil, err
		}
		item.MaterialCode = material.MaterialCode
		item.MaterialName = material.Name

		// Update stock within transaction
		err = s.stockRepo.UpdateStockTx(tx, item.MaterialID, decimal.NewFromInt(int64(-item.Quantity)))
		if err != nil {
			return nil, err
		}

		// Create stock log within transaction
		stockLog := &model.StockLog{
			MaterialID:       item.MaterialID,
			Type:             "out",
			Quantity:         item.Quantity,
			RelatedOrderType: "outbound",
			RelatedOrderID:   order.ID,
		}
		err = s.stockRepo.CreateLogTx(tx, stockLog)
		if err != nil {
			return nil, err
		}
	}

	// Commit transaction
	if err = tx.Commit(); err != nil {
		return nil, err
	}

	order.Status = "completed"
	return order, nil
}

func (s *OutboundService) GetByID(id int64) (*model.OutboundOrder, error) {
	return s.outboundRepo.GetByID(id)
}

func (s *OutboundService) List(search string, limit, offset int) ([]model.OutboundOrder, int64, error) {
	return s.outboundRepo.List(search, limit, offset)
}

func (s *OutboundService) GetByMaterialID(materialID int64) ([]model.OutboundRecord, error) {
	return s.outboundRepo.GetByMaterialID(materialID)
}

func (s *OutboundService) Delete(id int64) error {
	// Get the outbound order with items
	order, err := s.outboundRepo.GetByID(id)
	if err != nil {
		return err
	}

	// Start transaction
	tx, err := repository.BeginTx()
	if err != nil {
		return err
	}
	defer func() {
		if err != nil {
			tx.Rollback()
		}
	}()

	// Reverse stock for each item (add back) within transaction
	for _, item := range order.Items {
		err = s.stockRepo.UpdateStockTx(tx, item.MaterialID, decimal.NewFromInt(int64(item.Quantity)))
		if err != nil {
			return err
		}
	}

	// Delete stock logs within transaction
	err = s.stockRepo.DeleteLogsTx(tx, "outbound", id)
	if err != nil {
		return err
	}

	// Delete the outbound order (items will be cascade deleted)
	err = s.outboundRepo.DeleteTx(tx, id)
	if err != nil {
		return err
	}

	// Commit transaction
	if err = tx.Commit(); err != nil {
		return err
	}

	return nil
}

func (s *OutboundService) Update(id int64, req *model.UpdateOutboundRequest, operator string) (*model.OutboundOrder, error) {
	// Get old order data
	oldOrder, err := s.outboundRepo.GetByID(id)
	if err != nil {
		return nil, err
	}

	// Validate all new items first (outside transaction)
	for _, item := range req.Items {
		exists, err := s.materialSvc.Exists(item.MaterialID)
		if err != nil {
			return nil, err
		}
		if !exists {
			return nil, ErrMaterialNotFound
		}
		active, err := s.materialSvc.IsActive(item.MaterialID)
		if err != nil {
			return nil, err
		}
		if !active {
			return nil, ErrMaterialObsolete
		}

		currentStock, err := s.stockRepo.GetStock(item.MaterialID)
		if err != nil {
			return nil, err
		}
		// Calculate effective stock: current + old outbound quantity - new outbound quantity
		oldQty := 0
		for _, oldItem := range oldOrder.Items {
			if oldItem.MaterialID == item.MaterialID {
				oldQty = oldItem.Quantity
				break
			}
		}
		effectiveStock := currentStock.Add(decimal.NewFromInt(int64(oldQty)))
		if effectiveStock.LessThan(decimal.NewFromInt(int64(item.Quantity))) {
			return nil, ErrInsufficientStock
		}
	}

	// Start transaction
	tx, err := repository.BeginTx()
	if err != nil {
		return nil, err
	}
	defer func() {
		if err != nil {
			tx.Rollback()
		}
	}()

	// Reverse stock for old items (add back what was previously subtracted)
	for _, item := range oldOrder.Items {
		err = s.stockRepo.UpdateStockTx(tx, item.MaterialID, decimal.NewFromInt(int64(item.Quantity)))
		if err != nil {
			return nil, err
		}
	}

	// Re-check stock with row lock (SELECT FOR UPDATE) to prevent overselling
	for _, item := range req.Items {
		lockedStock, err := s.stockRepo.GetStockForUpdateTx(tx, item.MaterialID)
		if err != nil {
			return nil, err
		}
		oldQty := 0
		for _, oldItem := range oldOrder.Items {
			if oldItem.MaterialID == item.MaterialID {
				oldQty = oldItem.Quantity
				break
			}
		}
		effectiveStock := lockedStock.Add(decimal.NewFromInt(int64(oldQty)))
		if effectiveStock.LessThan(decimal.NewFromInt(int64(item.Quantity))) {
			err = ErrInsufficientStock
			return nil, err
		}
	}

	// Delete old stock logs
	err = s.stockRepo.DeleteLogsTx(tx, "outbound", id)
	if err != nil {
		return nil, err
	}

	// Update order in repository
	// 客户端不能指定操作人；编辑也由当前登录用户接管操作人和兼容字段 handler。
	req.Handler = operator
	req.Operator = operator
	err = s.outboundRepo.UpdateTx(tx, id, req)
	if err != nil {
		return nil, err
	}

	// Deduct stock for new items and create logs
	for _, item := range req.Items {
		err = s.stockRepo.UpdateStockTx(tx, item.MaterialID, decimal.NewFromInt(int64(-item.Quantity)))
		if err != nil {
			return nil, err
		}

		stockLog := &model.StockLog{
			MaterialID:       item.MaterialID,
			Type:             "out",
			Quantity:         item.Quantity,
			RelatedOrderType: "outbound",
			RelatedOrderID:   id,
		}
		err = s.stockRepo.CreateLogTx(tx, stockLog)
		if err != nil {
			return nil, err
		}
	}

	// Commit transaction
	if err = tx.Commit(); err != nil {
		return nil, err
	}

	// Get updated order with material details
	updatedOrder, err := s.outboundRepo.GetByID(id)
	if err != nil {
		return nil, err
	}
	updatedOrder.Status = "completed"

	return updatedOrder, nil
}