package services

import (
	"encoding/json"
	"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
	}

	var rows []row
	if err := s.db.Model(&models.PartnumberBook{}).
		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 {
		var pns []string
		if strings.TrimSpace(r.PartnumbersJSON) != "" {
			if err := json.Unmarshal([]byte(r.PartnumbersJSON), &pns); err != nil {
				return nil, fmt.Errorf("decode partnumbers_json for book %d: %w", r.ID, err)
			}
		}
		result[i] = PartnumberBookSummary{
			ID:        r.PartnumberBook.ID,
			Version:   r.PartnumberBook.Version,
			CreatedAt: r.PartnumberBook.CreatedAt,
			CreatedBy: r.PartnumberBook.CreatedBy,
			IsActive:  r.PartnumberBook.IsActive,
			ItemCount: len(pns),
		}
	}
	return result, nil
}

// CreateSnapshot takes a snapshot of all active partnumber→LOT mappings,
// serializes resolved LOT composition into qt_partnumber_book_items.lots_json,
// 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. Build current canonical PN catalog.
	items, err := s.buildSnapshotItems()
	if err != nil {
		return nil, err
	}
	report(PartnumberBookProgress{Current: 10, Total: 100, Status: "running", Message: fmt.Sprintf("Строк в каталоге: %d", len(items))})

	// 2. Filter to the current snapshot payload.
	report(PartnumberBookProgress{Current: 40, Total: 100, Status: "running", Message: fmt.Sprintf("Строк в снимке: %d", len(items))})

	// 3. Generate version string (format: PNBOOK-YYYY-MM-DD-NNN).
	report(PartnumberBookProgress{Current: 50, Total: 100, Status: "running", Message: "Подготовка версии снимка..."})
	version, err := s.generateVersion()
	if err != nil {
		return nil, err
	}

	partnumbersJSON, err := collectPartnumbersJSON(items)
	if err != nil {
		return nil, err
	}

	// 4. Persist inside a transaction.
	report(PartnumberBookProgress{Current: 60, Total: 100, Status: "running", Message: "Запись снимка в базу..."})
	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,
			PartnumbersJSON: partnumbersJSON,
		}
		if err := tx.Create(&book).Error; err != nil {
			return fmt.Errorf("creating partnumber book: %w", err)
		}

		report(PartnumberBookProgress{Current: 75, Total: 100, Status: "running", Message: "Обновление каталога PN..."})
		if err := s.upsertCatalogItems(tx, items); err != nil {
			return err
		}

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

	report(PartnumberBookProgress{Current: 90, 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 {
		if err := tx.Where("id IN ?", toDelete).Delete(&models.PartnumberBook{}).Error; err != nil {
			return fmt.Errorf("deleting old books: %w", err)
		}
		return nil
	})
}

func (s *PartnumberBookService) upsertCatalogItems(tx *gorm.DB, items []models.PartnumberBookItem) error {
	if len(items) == 0 {
		return nil
	}

	partnumbers := make([]string, 0, len(items))
	byPN := make(map[string]models.PartnumberBookItem)
	for _, item := range items {
		existing, ok := byPN[item.Partnumber]
		if ok {
			if existing.LotsJSON != item.LotsJSON || normalizeDescription(existing.Description) != normalizeDescription(item.Description) {
				return fmt.Errorf("conflicting snapshot items for partnumber %s", item.Partnumber)
			}
			continue
		}
		byPN[item.Partnumber] = item
		partnumbers = append(partnumbers, item.Partnumber)
	}

	var existing []models.PartnumberBookItem
	if err := tx.Where("partnumber IN ?", partnumbers).Find(&existing).Error; err != nil {
		return fmt.Errorf("loading existing partnumber book items: %w", err)
	}
	existingByPN := make(map[string]models.PartnumberBookItem, len(existing))
	for _, item := range existing {
		existingByPN[item.Partnumber] = item
	}

	toCreate := make([]models.PartnumberBookItem, 0, len(byPN))
	for _, pn := range partnumbers {
		if _, ok := existingByPN[pn]; ok {
			continue
		}
		toCreate = append(toCreate, byPN[pn])
	}
	if len(toCreate) > 0 {
		const batchSize = 500
		for i := 0; i < len(toCreate); i += batchSize {
			end := i + batchSize
			if end > len(toCreate) {
				end = len(toCreate)
			}
			if err := tx.Create(toCreate[i:end]).Error; err != nil {
				return fmt.Errorf("inserting partnumber book items (batch %d): %w", i/batchSize, err)
			}
		}
	}

	for _, item := range items {
		existingItem, ok := existingByPN[item.Partnumber]
		if !ok {
			continue
		}
		if existingItem.LotsJSON == item.LotsJSON &&
			normalizeDescription(existingItem.Description) == normalizeDescription(item.Description) {
			continue
		}
		updates := map[string]any{
			"lots_json":   item.LotsJSON,
			"description": item.Description,
		}
		if err := tx.Model(&models.PartnumberBookItem{}).
			Where("id = ?", existingItem.ID).
			Updates(updates).Error; err != nil {
			return fmt.Errorf("updating partnumber book item for %s: %w", item.Partnumber, 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
}

// buildSnapshotItems returns the canonical PN catalog for snapshotting.
// Source of truth is qt_partnumber_book_items.
func (s *PartnumberBookService) buildSnapshotItems() ([]models.PartnumberBookItem, error) {
	// 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 catalog []models.PartnumberBookItem
	if err := s.db.Order("partnumber ASC").Find(&catalog).Error; err != nil {
		return nil, fmt.Errorf("loading partnumber catalog: %w", err)
	}

	byPN := make(map[string]models.PartnumberBookItem, len(catalog))
	result := make([]models.PartnumberBookItem, 0, len(catalog))

	for _, item := range catalog {
		pn := strings.TrimSpace(item.Partnumber)
		if pn == "" || ignoredSet[pn] {
			continue
		}
		lots := parseSnapshotLots(item.LotsJSON)
		if len(lots) == 0 {
			continue
		}
		normalizedJSON, err := marshalSnapshotLots(lots)
		if err != nil {
			return nil, fmt.Errorf("normalize lots_json for partnumber %s: %w", pn, err)
		}
		item.Partnumber = pn
		item.LotsJSON = normalizedJSON
		if prev, ok := byPN[pn]; ok {
			if prev.LotsJSON != item.LotsJSON || normalizeDescription(prev.Description) != normalizeDescription(item.Description) {
				return nil, fmt.Errorf("multiple distinct mappings for partnumber %s in partnumber book snapshot", pn)
			}
			continue
		}
		byPN[pn] = item
		result = append(result, item)
	}

	return result, nil
}

func parseSnapshotLots(lotsJSON string) []models.PartnumberBookLot {
	var lots []models.PartnumberBookLot
	if err := json.Unmarshal([]byte(strings.TrimSpace(lotsJSON)), &lots); err != nil {
		return nil
	}
	out := make([]models.PartnumberBookLot, 0, len(lots))
	for _, lot := range lots {
		name := strings.TrimSpace(lot.LotName)
		if name == "" || lot.Qty <= 0 {
			continue
		}
		out = append(out, models.PartnumberBookLot{LotName: name, Qty: lot.Qty})
	}
	sort.Slice(out, func(i, j int) bool { return out[i].LotName < out[j].LotName })
	return out
}

func marshalSnapshotLots(lots []models.PartnumberBookLot) (string, error) {
	sort.Slice(lots, func(i, j int) bool { return lots[i].LotName < lots[j].LotName })
	b, err := json.Marshal(lots)
	if err != nil {
		return "", err
	}
	return string(b), nil
}

func collectPartnumbersJSON(items []models.PartnumberBookItem) (string, error) {
	partnumbers := make([]string, 0, len(items))
	for _, item := range items {
		if strings.TrimSpace(item.Partnumber) == "" {
			continue
		}
		partnumbers = append(partnumbers, item.Partnumber)
	}
	sort.Strings(partnumbers)
	b, err := json.Marshal(partnumbers)
	if err != nil {
		return "", fmt.Errorf("marshal partnumbers_json: %w", err)
	}
	return string(b), nil
}

func normalizeDescription(v *string) string {
	if v == nil {
		return ""
	}
	return strings.TrimSpace(*v)
}

// 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
}