package services

import (
	"context"
	"fmt"
	"log/slog"

	"git.mchus.pro/mchus/priceforge/internal/lotmatch"
	"git.mchus.pro/mchus/priceforge/internal/repository"
	"gorm.io/gorm"
)

// PartsLogBackfillService resolves lot_name for unresolved parts_log rows.
// Runs daily via the embedded scheduler and can be triggered manually via API.
// The only permitted mutation on parts_log is filling lot_name/lot_category.
type PartsLogBackfillService struct {
	db          *gorm.DB
	partsLogRepo *repository.PartsLogRepository
}

func NewPartsLogBackfillService(db *gorm.DB) *PartsLogBackfillService {
	return &PartsLogBackfillService{
		db:          db,
		partsLogRepo: repository.NewPartsLogRepository(db),
	}
}

// RunBatch resolves up to limit unresolved parts_log rows.
// Returns the number of rows resolved in this run.
func (s *PartsLogBackfillService) RunBatch(ctx context.Context, limit int) (int, error) {
	if limit <= 0 {
		limit = 1000
	}

	rows, err := s.partsLogRepo.FindUnresolved(limit)
	if err != nil {
		return 0, fmt.Errorf("backfill: find unresolved: %w", err)
	}
	if len(rows) == 0 {
		return 0, nil
	}

	// Load lot names for direct-match check (partnumber == lot_name)
	lotNames, err := s.loadAllLotNames()
	if err != nil {
		return 0, fmt.Errorf("backfill: load lot names: %w", err)
	}
	lotCategoryByName, err := s.loadLotCategories(lotNames)
	if err != nil {
		return 0, fmt.Errorf("backfill: load lot categories: %w", err)
	}

	// Load the partnumber→lot matcher from qt_partnumber_book_items
	matcher, err := lotmatch.NewMappingMatcherFromDB(s.db)
	if err != nil {
		return 0, fmt.Errorf("backfill: load matcher: %w", err)
	}

	var updates []repository.LotResolutionUpdate
	for _, row := range updates {
		_ = row // avoid unused warning — handled below
	}
	updates = updates[:0]

	for _, pl := range rows {
		if ctx.Err() != nil {
			break
		}

		var resolvedLot, resolvedCat string

		// Rule 1: if partnumber matches a known lot_name directly (lot_log pattern)
		if _, ok := lotCategoryByName[pl.Partnumber]; ok {
			resolvedLot = pl.Partnumber
			resolvedCat = lotCategoryByName[pl.Partnumber]
		} else {
			// Rule 2: resolve through qt_partnumber_book_items
			lots := matcher.MatchLotsWithVendor(pl.Partnumber, pl.Vendor)
			if len(lots) > 0 {
				resolvedLot = lots[0]
				resolvedCat = lotCategoryByName[resolvedLot]
			}
		}

		if resolvedLot != "" {
			updates = append(updates, repository.LotResolutionUpdate{
				ID:          pl.ID,
				LotName:     resolvedLot,
				LotCategory: resolvedCat,
			})
		}
	}

	if len(updates) == 0 {
		return 0, nil
	}

	if err := s.partsLogRepo.UpdateLotResolutionBatch(updates); err != nil {
		return 0, fmt.Errorf("backfill: update batch: %w", err)
	}

	slog.Info("parts_log backfill completed", "resolved", len(updates), "scanned", len(rows))
	return len(updates), nil
}

func (s *PartsLogBackfillService) loadAllLotNames() ([]string, error) {
	var names []string
	err := s.db.Table("lot").Select("lot_name").Pluck("lot_name", &names).Error
	return names, err
}

func (s *PartsLogBackfillService) loadLotCategories(lotNames []string) (map[string]string, error) {
	if len(lotNames) == 0 {
		return map[string]string{}, nil
	}
	type row struct {
		LotName     string  `gorm:"column:lot_name"`
		LotCategory *string `gorm:"column:lot_category"`
	}
	var rows []row
	err := s.db.Table("lot").Select("lot_name, lot_category").
		Where("lot_name IN ?", lotNames).Scan(&rows).Error
	if err != nil {
		return nil, err
	}
	result := make(map[string]string, len(rows))
	for _, r := range rows {
		cat := ""
		if r.LotCategory != nil {
			cat = *r.LotCategory
		}
		result[r.LotName] = cat
	}
	return result, nil
}