package services

import (
	"errors"
	"fmt"
	"log/slog"
	"sort"
	"strconv"
	"strings"
	"time"

	"git.mchus.pro/mchus/priceforge/internal/models"
	"gorm.io/gorm"
)

// Retention policy: how many snapshots to keep per tier.
const (
	retainDaily   = 7
	retainWeekly  = 5
	retainMonthly = 12
	retainYearly  = 10
)

// PartnumberBookService creates versioned snapshots of the partnumber→LOT mapping
// for consumption by QuoteForge via qt_partnumber_books / qt_partnumber_book_items.
type PartnumberBookService struct {
	db *gorm.DB
}

func NewPartnumberBookService(db *gorm.DB) *PartnumberBookService {
	return &PartnumberBookService{db: db}
}

type PartnumberBookProgress struct {
	Current int
	Total   int
	Status  string
	Message string
}

// PartnumberBookSummary is returned by ListBooks.
type PartnumberBookSummary struct {
	ID        uint64    `json:"id"`
	Version   string    `json:"version"`
	CreatedAt time.Time `json:"created_at"`
	CreatedBy string    `json:"created_by"`
	IsActive  bool      `json:"is_active"`
	ItemCount int       `json:"item_count"`
}

// ListBooks returns all partnumber books ordered newest-first with item counts.
func (s *PartnumberBookService) ListBooks() ([]PartnumberBookSummary, error) {
	if s.db == nil {
		return nil, fmt.Errorf("offline mode")
	}

	type row struct {
		models.PartnumberBook
		ItemCount int `gorm:"column:item_count"`
	}

	var rows []row
	if err := s.db.Model(&models.PartnumberBook{}).
		Select("qt_partnumber_books.*, COUNT(qt_partnumber_book_items.id) AS item_count").
		Joins("LEFT JOIN qt_partnumber_book_items ON qt_partnumber_book_items.book_id = qt_partnumber_books.id").
		Group("qt_partnumber_books.id").
		Order("qt_partnumber_books.created_at DESC").
		Find(&rows).Error; err != nil {
		return nil, fmt.Errorf("listing partnumber books: %w", err)
	}

	result := make([]PartnumberBookSummary, len(rows))
	for i, r := range rows {
		result[i] = PartnumberBookSummary{
			ID:        r.PartnumberBook.ID,
			Version:   r.PartnumberBook.Version,
			CreatedAt: r.PartnumberBook.CreatedAt,
			CreatedBy: r.PartnumberBook.CreatedBy,
			IsActive:  r.PartnumberBook.IsActive,
			ItemCount: r.ItemCount,
		}
	}
	return result, nil
}

// CreateSnapshot takes a snapshot of all active partnumber→LOT mappings,
// expands bundles, writes qt_partnumber_book_items, activates the new book,
// deactivates all previous books, then applies the retention policy.
func (s *PartnumberBookService) CreateSnapshot(createdBy string, onProgress func(PartnumberBookProgress)) (*models.PartnumberBook, error) {
	if s.db == nil {
		return nil, fmt.Errorf("offline mode: cannot create partnumber book")
	}

	report := func(p PartnumberBookProgress) {
		if onProgress != nil {
			onProgress(p)
		}
	}
	report(PartnumberBookProgress{Current: 0, Total: 100, Status: "starting", Message: "Подготовка"})

	// 1. Load all partnumber mappings.
	var mappings []models.LotPartnumber
	if err := s.db.Find(&mappings).Error; err != nil {
		return nil, fmt.Errorf("loading lot_partnumbers: %w", err)
	}
	report(PartnumberBookProgress{Current: 10, Total: 100, Status: "running", Message: fmt.Sprintf("Загружено маппингов: %d", len(mappings))})

	// 2. Identify bundle LOT names.
	bundleSet, err := s.loadBundleSet()
	if err != nil {
		return nil, err
	}

	// 3. Expand bundles into book items.
	items, err := s.expandMappings(mappings, bundleSet)
	if err != nil {
		return nil, err
	}
	report(PartnumberBookProgress{Current: 40, Total: 100, Status: "running", Message: fmt.Sprintf("Строк в снимке: %d", len(items))})

	// 4. Generate version string (format: PNBOOK-YYYY-MM-DD-NNN).
	version, err := s.generateVersion()
	if err != nil {
		return nil, err
	}

	// 5. Persist inside a transaction.
	var book models.PartnumberBook
	err = s.db.Transaction(func(tx *gorm.DB) error {
		// Deactivate all existing books.
		if err := tx.Model(&models.PartnumberBook{}).
			Where("is_active = ?", true).
			Update("is_active", false).Error; err != nil {
			return fmt.Errorf("deactivating old books: %w", err)
		}

		// Create header.
		book = models.PartnumberBook{
			Version:   version,
			CreatedBy: createdBy,
			IsActive:  true,
		}
		if err := tx.Create(&book).Error; err != nil {
			return fmt.Errorf("creating partnumber book: %w", err)
		}

		// Attach book_id and bulk-insert items.
		for i := range items {
			items[i].BookID = book.ID
		}

		const batchSize = 500
		for i := 0; i < len(items); i += batchSize {
			end := i + batchSize
			if end > len(items) {
				end = len(items)
			}
			if err := tx.Create(items[i:end]).Error; err != nil {
				return fmt.Errorf("inserting partnumber book items (batch %d): %w", i/batchSize, err)
			}
		}

		return nil
	})
	if err != nil {
		return nil, err
	}

	report(PartnumberBookProgress{Current: 80, Total: 100, Status: "running", Message: "Применение политики хранения..."})

	// 6. Apply retention policy (non-fatal: log errors but don't fail the snapshot).
	if deleted, retErr := s.applyRetention(); retErr != nil {
		slog.Warn("partnumber book retention cleanup failed", "error", retErr)
	} else if deleted > 0 {
		slog.Info("partnumber book retention: deleted old snapshots", "count", deleted)
	}

	report(PartnumberBookProgress{Current: 100, Total: 100, Status: "completed", Message: fmt.Sprintf("Снимок %s создан (%d строк)", version, len(items))})
	slog.Info("partnumber book snapshot created", "version", version, "items", len(items), "book_id", book.ID)
	return &book, nil
}

// applyRetention implements GFS (Grandfather-Father-Son) retention:
//
//	7 daily  (most recent snapshot per calendar day, last 7 days)
//	5 weekly (most recent per ISO week, beyond daily window)
//
// 12 monthly (most recent per month, beyond weekly window)
// 10 yearly  (most recent per year,  beyond monthly window)
//
// Everything outside these windows is deleted.
// The active book is never deleted.
func (s *PartnumberBookService) applyRetention() (int, error) {
	var all []models.PartnumberBook
	if err := s.db.Order("created_at DESC").Find(&all).Error; err != nil {
		return 0, fmt.Errorf("loading all books for retention: %w", err)
	}

	keep := retentionKeepSet(all)

	var toDelete []uint64
	for _, b := range all {
		if b.IsActive {
			continue // never delete the active book
		}
		if !keep[b.ID] {
			toDelete = append(toDelete, b.ID)
		}
	}

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

	return len(toDelete), s.db.Transaction(func(tx *gorm.DB) error {
		// Delete items explicitly — do not rely on FK CASCADE.
		if err := tx.Where("book_id IN ?", toDelete).Delete(&models.PartnumberBookItem{}).Error; err != nil {
			return fmt.Errorf("deleting book items: %w", err)
		}
		if err := tx.Where("id IN ?", toDelete).Delete(&models.PartnumberBook{}).Error; err != nil {
			return fmt.Errorf("deleting old books: %w", err)
		}
		return nil
	})
}

// retentionKeepSet returns the set of book IDs to keep according to GFS policy.
// Books are expected to be sorted newest-first.
func retentionKeepSet(books []models.PartnumberBook) map[uint64]bool {
	keep := make(map[uint64]bool)

	// Sort newest first (should already be, but be defensive).
	sorted := make([]models.PartnumberBook, len(books))
	copy(sorted, books)
	sort.Slice(sorted, func(i, j int) bool {
		return sorted[i].CreatedAt.After(sorted[j].CreatedAt)
	})

	dailySeen := make(map[string]int)   // "YYYY-MM-DD" → count kept
	weeklySeen := make(map[string]int)  // "YYYY-WW" → count kept
	monthlySeen := make(map[string]int) // "YYYY-MM" → count kept
	yearlySeen := make(map[string]int)  // "YYYY" → count kept

	for _, b := range sorted {
		t := b.CreatedAt
		dayKey := t.Format("2006-01-02")
		year, week := t.ISOWeek()
		weekKey := fmt.Sprintf("%d-%02d", year, week)
		monthKey := t.Format("2006-01")
		yearKey := t.Format("2006")

		if dailySeen[dayKey] < retainDaily {
			keep[b.ID] = true
			dailySeen[dayKey]++
			continue
		}
		if weeklySeen[weekKey] < retainWeekly {
			keep[b.ID] = true
			weeklySeen[weekKey]++
			continue
		}
		if monthlySeen[monthKey] < retainMonthly {
			keep[b.ID] = true
			monthlySeen[monthKey]++
			continue
		}
		if yearlySeen[yearKey] < retainYearly {
			keep[b.ID] = true
			yearlySeen[yearKey]++
			continue
		}
		// Falls outside all retention windows → will be deleted.
	}

	return keep
}

// loadBundleSet returns a set of all bundle_lot_name values.
func (s *PartnumberBookService) loadBundleSet() (map[string]bool, error) {
	var bundleNames []string
	if err := s.db.Model(&models.LotBundle{}).Pluck("bundle_lot_name", &bundleNames).Error; err != nil {
		return nil, fmt.Errorf("loading bundle names: %w", err)
	}
	set := make(map[string]bool, len(bundleNames))
	for _, n := range bundleNames {
		set[n] = true
	}
	return set, nil
}

// expandMappings converts lot_partnumbers rows into book items, expanding bundles.
// Rows with empty lot_name and ignored partnumbers are excluded.
func (s *PartnumberBookService) expandMappings(mappings []models.LotPartnumber, bundleSet map[string]bool) ([]models.PartnumberBookItem, error) {
	// Pre-load all bundle items keyed by bundle_lot_name.
	var rawItems []models.LotBundleItem
	if err := s.db.Find(&rawItems).Error; err != nil {
		return nil, fmt.Errorf("loading bundle items: %w", err)
	}
	bundleItems := make(map[string][]models.LotBundleItem, len(rawItems))
	for _, bi := range rawItems {
		bundleItems[bi.BundleLotName] = append(bundleItems[bi.BundleLotName], bi)
	}

	// Build ignored partnumber set from qt_vendor_partnumber_seen.
	var ignoredPNs []string
	if err := s.db.Model(&models.VendorPartnumberSeen{}).
		Where("is_ignored = ?", true).
		Pluck("partnumber", &ignoredPNs).Error; err != nil {
		return nil, fmt.Errorf("loading ignored partnumbers: %w", err)
	}
	ignoredSet := make(map[string]bool, len(ignoredPNs))
	for _, pn := range ignoredPNs {
		ignoredSet[pn] = true
	}

	var result []models.PartnumberBookItem
	for _, m := range mappings {
		// Skip ignored partnumbers.
		if ignoredSet[m.Partnumber] {
			continue
		}
		// Skip mappings without a resolved lot_name.
		if strings.TrimSpace(m.LotName) == "" {
			continue
		}

		if bundleSet[m.LotName] {
			// Expand bundle: emit one item per component LOT.
			// Description from lot_partnumbers is carried to all expanded rows.
			components := bundleItems[m.LotName]
			if len(components) == 0 {
				// Bundle with no items — skip silently.
				continue
			}
			for _, c := range components {
				result = append(result, models.PartnumberBookItem{
					Partnumber:  m.Partnumber,
					LotName:     c.LotName,
					IsPrimaryPN: m.IsPrimaryPN,
					Description: m.Description,
				})
			}
		} else {
			// Direct mapping.
			result = append(result, models.PartnumberBookItem{
				Partnumber:  m.Partnumber,
				LotName:     m.LotName,
				IsPrimaryPN: m.IsPrimaryPN,
				Description: m.Description,
			})
		}
	}
	return result, nil
}

// generateVersion produces a version string in format PNBOOK-YYYY-MM-DD-NNN.
func (s *PartnumberBookService) generateVersion() (string, error) {
	today := time.Now().Format("2006-01-02")
	prefix := "PNBOOK-" + today

	var last models.PartnumberBook
	err := s.db.Model(&models.PartnumberBook{}).
		Select("version").
		Where("version LIKE ?", prefix+"-%").
		Order("version DESC").
		Limit(1).
		Take(&last).Error
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return prefix + "-001", nil
		}
		return "", fmt.Errorf("loading latest today's book version: %w", err)
	}

	parts := strings.Split(last.Version, "-")
	n, err := strconv.Atoi(parts[len(parts)-1])
	if err != nil {
		return "", fmt.Errorf("invalid book version format: %s", last.Version)
	}
	return fmt.Sprintf("%s-%03d", prefix, n+1), nil
}