package sync

import (
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"sort"
	"strings"
	"time"

	"git.mchus.pro/mchus/quoteforge/internal/appmeta"
	"git.mchus.pro/mchus/quoteforge/internal/db"
	"git.mchus.pro/mchus/quoteforge/internal/localdb"
	"git.mchus.pro/mchus/quoteforge/internal/models"
	"git.mchus.pro/mchus/quoteforge/internal/repository"
	"github.com/google/uuid"
	"gorm.io/gorm"
)

var ErrOffline = errors.New("database is offline")

// Service handles synchronization between MariaDB and local SQLite
type Service struct {
	connMgr  *db.ConnectionManager
	localDB  *localdb.LocalDB
	directDB *gorm.DB
}

// NewService creates a new sync service
func NewService(connMgr *db.ConnectionManager, localDB *localdb.LocalDB) *Service {
	return &Service{
		connMgr: connMgr,
		localDB: localDB,
	}
}

// NewServiceWithDB creates sync service that uses a direct DB handle (used in tests).
func NewServiceWithDB(mariaDB *gorm.DB, localDB *localdb.LocalDB) *Service {
	return &Service{
		localDB:  localDB,
		directDB: mariaDB,
	}
}

// SyncStatus represents the current sync status
type SyncStatus struct {
	LastSyncAt       *time.Time `json:"last_sync_at"`
	ServerPricelists int        `json:"server_pricelists"`
	LocalPricelists  int        `json:"local_pricelists"`
	NeedsSync        bool       `json:"needs_sync"`
}

type UserSyncStatus struct {
	Username   string    `json:"username"`
	LastSyncAt time.Time `json:"last_sync_at"`
	AppVersion string    `json:"app_version,omitempty"`
	IsOnline   bool      `json:"is_online"`
}

// ConfigImportResult represents server->local configuration import stats.
type ConfigImportResult struct {
	Imported int `json:"imported"`
	Updated  int `json:"updated"`
	Skipped  int `json:"skipped"`
}

// ProjectImportResult represents server->local project import stats.
type ProjectImportResult struct {
	Imported int `json:"imported"`
	Updated  int `json:"updated"`
	Skipped  int `json:"skipped"`
}

// ConfigurationChangePayload is stored in pending_changes.payload for configuration events.
// It carries version metadata so sync can push the latest snapshot and prepare for conflict resolution.
type ConfigurationChangePayload struct {
	EventID           string               `json:"event_id"`
	IdempotencyKey    string               `json:"idempotency_key"`
	ConfigurationUUID string               `json:"configuration_uuid"`
	ProjectUUID       *string              `json:"project_uuid,omitempty"`
	PricelistID       *uint                `json:"pricelist_id,omitempty"`
	Operation         string               `json:"operation"` // create/update/rollback/deactivate/reactivate/delete
	CurrentVersionID  string               `json:"current_version_id,omitempty"`
	CurrentVersionNo  int                  `json:"current_version_no,omitempty"`
	ConflictPolicy    string               `json:"conflict_policy,omitempty"` // currently: last_write_wins
	Snapshot          models.Configuration `json:"snapshot"`
	CreatedAt         time.Time            `json:"created_at"`
	CreatedBy         *string              `json:"created_by,omitempty"`
}

type ProjectChangePayload struct {
	EventID        string         `json:"event_id"`
	IdempotencyKey string         `json:"idempotency_key"`
	ProjectUUID    string         `json:"project_uuid"`
	Operation      string         `json:"operation"`
	Snapshot       models.Project `json:"snapshot"`
	CreatedAt      time.Time      `json:"created_at"`
}

// ImportConfigurationsToLocal imports configurations from MariaDB into local SQLite.
// Existing local configs with pending local changes are skipped to avoid data loss.
func (s *Service) ImportConfigurationsToLocal() (*ConfigImportResult, error) {
	mariaDB, err := s.getDB()
	if err != nil {
		return nil, ErrOffline
	}

	configRepo := repository.NewConfigurationRepository(mariaDB)
	result := &ConfigImportResult{}

	offset := 0
	const limit = 200
	for {
		serverConfigs, _, err := configRepo.ListAll(offset, limit)
		if err != nil {
			return nil, fmt.Errorf("listing server configurations: %w", err)
		}
		if len(serverConfigs) == 0 {
			break
		}

		for i := range serverConfigs {
			cfg := serverConfigs[i]
			existing, err := s.localDB.GetConfigurationByUUID(cfg.UUID)
			if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
				return nil, fmt.Errorf("getting local configuration %s: %w", cfg.UUID, err)
			}

			if existing != nil && err == nil && existing.SyncStatus == "pending" {
				result.Skipped++
				continue
			}
			if existing != nil && err == nil && !existing.IsActive {
				// Keep local deactivation sticky: do not resurrect hidden entries from server pull.
				result.Skipped++
				continue
			}

			localCfg := localdb.ConfigurationToLocal(&cfg)
			now := time.Now()
			localCfg.SyncedAt = &now
			localCfg.SyncStatus = "synced"
			localCfg.UpdatedAt = now

			if existing != nil && err == nil {
				localCfg.ID = existing.ID
				if localCfg.Line <= 0 && existing.Line > 0 {
					localCfg.Line = existing.Line
				}
				result.Updated++
			} else {
				result.Imported++
			}

			if err := s.localDB.SaveConfiguration(localCfg); err != nil {
				return nil, fmt.Errorf("saving local configuration %s: %w", cfg.UUID, err)
			}
		}

		offset += len(serverConfigs)
	}

	return result, nil
}

// ImportProjectsToLocal imports projects from MariaDB into local SQLite.
// Existing local projects with pending local changes are skipped to avoid data loss.
func (s *Service) ImportProjectsToLocal() (*ProjectImportResult, error) {
	mariaDB, err := s.getDB()
	if err != nil {
		return nil, ErrOffline
	}

	projectRepo := repository.NewProjectRepository(mariaDB)
	result := &ProjectImportResult{}

	offset := 0
	const limit = 200
	for {
		serverProjects, _, err := projectRepo.List(offset, limit, true)
		if err != nil {
			return nil, fmt.Errorf("listing server projects: %w", err)
		}
		if len(serverProjects) == 0 {
			break
		}

		now := time.Now()
		for i := range serverProjects {
			project := serverProjects[i]

			existing, getErr := s.localDB.GetProjectByUUID(project.UUID)
			if getErr != nil && !errors.Is(getErr, gorm.ErrRecordNotFound) {
				return nil, fmt.Errorf("getting local project %s: %w", project.UUID, getErr)
			}

			if existing != nil && getErr == nil {
				// Keep unsynced local changes intact.
				if existing.SyncStatus == "pending" {
					result.Skipped++
					continue
				}

				existing.OwnerUsername = project.OwnerUsername
				existing.Code = project.Code
				existing.Name = project.Name
				existing.TrackerURL = project.TrackerURL
				existing.IsActive = project.IsActive
				existing.IsSystem = project.IsSystem
				existing.CreatedAt = project.CreatedAt
				existing.UpdatedAt = project.UpdatedAt
				serverID := project.ID
				existing.ServerID = &serverID
				existing.SyncStatus = "synced"
				existing.SyncedAt = &now

				if err := s.localDB.SaveProject(existing); err != nil {
					return nil, fmt.Errorf("saving local project %s: %w", project.UUID, err)
				}
				result.Updated++
				continue
			}

			localProject := localdb.ProjectToLocal(&project)
			localProject.SyncStatus = "synced"
			localProject.SyncedAt = &now
			if err := s.localDB.SaveProject(localProject); err != nil {
				return nil, fmt.Errorf("saving local project %s: %w", project.UUID, err)
			}
			result.Imported++
		}

		offset += len(serverProjects)
	}

	return result, nil
}

// GetStatus returns the current sync status
func (s *Service) GetStatus() (*SyncStatus, error) {
	lastSync := s.localDB.GetLastSyncTime()

	// Count server pricelists (only if already connected, don't reconnect)
	serverCount := 0
	connStatus := s.getConnectionStatus()
	if connStatus.IsConnected {
		if mariaDB, err := s.getDB(); err == nil && mariaDB != nil {
			pricelistRepo := repository.NewPricelistRepository(mariaDB)
			activeCount, err := pricelistRepo.CountActive()
			if err == nil {
				serverCount = int(activeCount)
			}
		}
	}

	// Count local pricelists
	localCount := s.localDB.CountLocalPricelists()

	needsSync, _ := s.NeedSync()

	return &SyncStatus{
		LastSyncAt:       lastSync,
		ServerPricelists: serverCount,
		LocalPricelists:  int(localCount),
		NeedsSync:        needsSync,
	}, nil
}

// NeedSync checks if synchronization is needed
// Returns true if there are new pricelists on server or last sync was >1 hour ago
func (s *Service) NeedSync() (bool, error) {
	lastSync := s.localDB.GetLastSyncTime()

	// If never synced, need sync
	if lastSync == nil {
		return true, nil
	}

	// If last sync was more than 1 hour ago, suggest sync
	if time.Since(*lastSync) > time.Hour {
		return true, nil
	}

	// Check if there are new pricelists on server (only if already connected)
	connStatus := s.getConnectionStatus()
	if !connStatus.IsConnected {
		// If offline, can't check server, no need to sync
		return false, nil
	}

	mariaDB, err := s.getDB()
	if err != nil {
		// If offline, can't check server, no need to sync
		return false, nil
	}

	pricelistRepo := repository.NewPricelistRepository(mariaDB)
	sources := []models.PricelistSource{
		models.PricelistSourceEstimate,
		models.PricelistSourceWarehouse,
		models.PricelistSourceCompetitor,
	}
	for _, source := range sources {
		latestServer, err := pricelistRepo.GetLatestActiveBySource(string(source))
		if err != nil {
			// No active pricelist for this source yet.
			continue
		}

		latestLocal, err := s.localDB.GetLatestLocalPricelistBySource(string(source))
		if err != nil {
			// No local pricelist for an existing source on server.
			return true, nil
		}

		// If server has newer pricelist for this source, need sync.
		if latestServer.ID != latestLocal.ServerID {
			return true, nil
		}
	}

	return false, nil
}

// SyncPricelists synchronizes all active pricelists from server to local SQLite
func (s *Service) SyncPricelists() (int, error) {
	slog.Info("starting pricelist sync")
	if _, err := s.EnsureReadinessForSync(); err != nil {
		return 0, err
	}

	// Get database connection
	mariaDB, err := s.getDB()
	if err != nil {
		return 0, fmt.Errorf("database not available: %w", err)
	}

	// Create repository
	pricelistRepo := repository.NewPricelistRepository(mariaDB)

	// Get active pricelists from server (up to 100)
	serverPricelists, _, err := pricelistRepo.ListActive(0, 100)
	if err != nil {
		return 0, fmt.Errorf("getting active server pricelists: %w", err)
	}
	serverPricelistIDs := make([]uint, 0, len(serverPricelists))
	for i := range serverPricelists {
		serverPricelistIDs = append(serverPricelistIDs, serverPricelists[i].ID)
	}

	synced := 0
	for _, pl := range serverPricelists {
		// Check if pricelist already exists locally
		existing, _ := s.localDB.GetLocalPricelistByServerID(pl.ID)
		if existing != nil {
			continue
		}

		// Create local pricelist
		localPL := &localdb.LocalPricelist{
			ServerID:  pl.ID,
			Source:    pl.Source,
			Version:   pl.Version,
			Name:      pl.Notification, // Using notification as name
			CreatedAt: pl.CreatedAt,
			SyncedAt:  time.Now(),
			IsUsed:    false,
		}

		if err := s.localDB.SaveLocalPricelist(localPL); err != nil {
			slog.Warn("failed to save local pricelist", "version", pl.Version, "error", err)
			continue
		}

		// Sync items for the newly created pricelist
		itemCount, err := s.SyncPricelistItems(localPL.ID)
		if err != nil {
			slog.Warn("failed to sync pricelist items", "version", pl.Version, "error", err)
			// Continue even if items sync fails - we have the pricelist metadata
		} else {
			slog.Debug("synced pricelist with items", "version", pl.Version, "items", itemCount)
		}

		synced++
	}

	removed, err := s.localDB.DeleteUnusedLocalPricelistsMissingOnServer(serverPricelistIDs)
	if err != nil {
		slog.Warn("failed to cleanup stale local pricelists", "error", err)
	} else if removed > 0 {
		slog.Info("deleted stale local pricelists", "deleted", removed)
	}

	// Backfill lot_category for used pricelists (older local caches may miss the column values).
	s.backfillUsedPricelistItemCategories(pricelistRepo, serverPricelistIDs)

	// Update last sync time
	s.localDB.SetLastSyncTime(time.Now())
	s.RecordSyncHeartbeat()

	slog.Info("pricelist sync completed", "synced", synced, "total", len(serverPricelists))
	return synced, nil
}

func (s *Service) backfillUsedPricelistItemCategories(pricelistRepo *repository.PricelistRepository, activeServerPricelistIDs []uint) {
	if s.localDB == nil || pricelistRepo == nil {
		return
	}

	activeSet := make(map[uint]struct{}, len(activeServerPricelistIDs))
	for _, id := range activeServerPricelistIDs {
		activeSet[id] = struct{}{}
	}

	type row struct {
		ID uint `gorm:"column:id"`
	}
	var usedRows []row
	if err := s.localDB.DB().Raw(`
		SELECT DISTINCT pricelist_id AS id
		FROM local_configurations
		WHERE is_active = 1 AND pricelist_id IS NOT NULL
		UNION
		SELECT DISTINCT warehouse_pricelist_id AS id
		FROM local_configurations
		WHERE is_active = 1 AND warehouse_pricelist_id IS NOT NULL
		UNION
		SELECT DISTINCT competitor_pricelist_id AS id
		FROM local_configurations
		WHERE is_active = 1 AND competitor_pricelist_id IS NOT NULL
	`).Scan(&usedRows).Error; err != nil {
		slog.Warn("pricelist category backfill: failed to list used pricelists", "error", err)
		return
	}

	for _, r := range usedRows {
		serverID := r.ID
		if serverID == 0 {
			continue
		}
		if _, ok := activeSet[serverID]; !ok {
			// Not present on server (or not active) - cannot backfill from remote.
			continue
		}

		localPL, err := s.localDB.GetLocalPricelistByServerID(serverID)
		if err != nil || localPL == nil {
			continue
		}

		if s.localDB.CountLocalPricelistItems(localPL.ID) == 0 {
			continue
		}

		missing, err := s.localDB.CountLocalPricelistItemsWithEmptyCategory(localPL.ID)
		if err != nil {
			slog.Warn("pricelist category backfill: failed to check local items", "server_id", serverID, "error", err)
			continue
		}
		if missing == 0 {
			continue
		}

		serverItems, _, err := pricelistRepo.GetItems(serverID, 0, 10000, "")
		if err != nil {
			slog.Warn("pricelist category backfill: failed to load server items", "server_id", serverID, "error", err)
			continue
		}
		localItems := make([]localdb.LocalPricelistItem, len(serverItems))
		for i := range serverItems {
			localItems[i] = *localdb.PricelistItemToLocal(&serverItems[i], localPL.ID)
		}

		if err := s.localDB.ReplaceLocalPricelistItems(localPL.ID, localItems); err != nil {
			slog.Warn("pricelist category backfill: failed to replace local items", "server_id", serverID, "error", err)
			continue
		}
		slog.Info("pricelist category backfill: refreshed local items", "server_id", serverID, "items", len(localItems))
	}
}

// RecordSyncHeartbeat updates shared sync heartbeat for current DB user.
// Only users with write rights are expected to be able to update this table.
func (s *Service) RecordSyncHeartbeat() {
	username := strings.TrimSpace(s.localDB.GetDBUser())
	if username == "" {
		return
	}

	mariaDB, err := s.getDB()
	if err != nil || mariaDB == nil {
		return
	}

	if err := ensureUserSyncStatusTable(mariaDB); err != nil {
		slog.Warn("sync heartbeat: failed to ensure table", "error", err)
		return
	}

	now := time.Now().UTC()
	if err := mariaDB.Exec(`
		INSERT INTO qt_pricelist_sync_status (username, last_sync_at, updated_at, app_version)
		VALUES (?, ?, ?, ?)
		ON DUPLICATE KEY UPDATE
			last_sync_at = VALUES(last_sync_at),
			updated_at = VALUES(updated_at),
			app_version = VALUES(app_version)
	`, username, now, now, appmeta.Version()).Error; err != nil {
		slog.Debug("sync heartbeat: skipped", "username", username, "error", err)
	}
}

// ListUserSyncStatuses returns users who have recorded sync heartbeat.
func (s *Service) ListUserSyncStatuses(onlineThreshold time.Duration) ([]UserSyncStatus, error) {
	mariaDB, err := s.getDB()
	if err != nil || mariaDB == nil {
		return nil, ErrOffline
	}

	if err := ensureUserSyncStatusTable(mariaDB); err != nil {
		return nil, fmt.Errorf("ensure sync status table: %w", err)
	}

	type row struct {
		Username   string    `gorm:"column:username"`
		LastSyncAt time.Time `gorm:"column:last_sync_at"`
		AppVersion string    `gorm:"column:app_version"`
	}
	var rows []row
	if err := mariaDB.Raw(`
		SELECT username, last_sync_at, COALESCE(app_version, '') AS app_version
		FROM qt_pricelist_sync_status
		ORDER BY last_sync_at DESC, username ASC
	`).Scan(&rows).Error; err != nil {
		return nil, fmt.Errorf("load sync status rows: %w", err)
	}

	activeUsers, err := s.listConnectedDBUsers(mariaDB)
	if err != nil {
		slog.Debug("sync status: failed to load connected DB users", "error", err)
		activeUsers = map[string]struct{}{}
	}

	now := time.Now().UTC()
	result := make([]UserSyncStatus, 0, len(rows)+len(activeUsers))
	for i := range rows {
		r := rows[i]
		username := strings.TrimSpace(r.Username)
		if username == "" {
			continue
		}

		isOnline := now.Sub(r.LastSyncAt) <= onlineThreshold
		if _, connected := activeUsers[username]; connected {
			isOnline = true
			delete(activeUsers, username)
		}

		appVersion := strings.TrimSpace(r.AppVersion)

		result = append(result, UserSyncStatus{
			Username:   username,
			LastSyncAt: r.LastSyncAt,
			AppVersion: appVersion,
			IsOnline:   isOnline,
		})
	}

	for username := range activeUsers {
		result = append(result, UserSyncStatus{
			Username:   username,
			LastSyncAt: now,
			AppVersion: "",
			IsOnline:   true,
		})
	}

	sort.SliceStable(result, func(i, j int) bool {
		if result[i].IsOnline != result[j].IsOnline {
			return result[i].IsOnline
		}
		if result[i].LastSyncAt.Equal(result[j].LastSyncAt) {
			return strings.ToLower(result[i].Username) < strings.ToLower(result[j].Username)
		}
		return result[i].LastSyncAt.After(result[j].LastSyncAt)
	})

	return result, nil
}

func (s *Service) listConnectedDBUsers(mariaDB *gorm.DB) (map[string]struct{}, error) {
	type processUserRow struct {
		Username string `gorm:"column:username"`
	}

	var rows []processUserRow
	if err := mariaDB.Raw(`
		SELECT DISTINCT TRIM(USER) AS username
		FROM information_schema.PROCESSLIST
		WHERE COALESCE(TRIM(USER), '') <> ''
		  AND DB = DATABASE()
	`).Scan(&rows).Error; err != nil {
		return nil, err
	}

	users := make(map[string]struct{}, len(rows))
	for i := range rows {
		username := strings.TrimSpace(rows[i].Username)
		if username == "" {
			continue
		}
		users[username] = struct{}{}
	}
	return users, nil
}

func ensureUserSyncStatusTable(db *gorm.DB) error {
	// Check if table exists instead of trying to create (avoids permission issues)
	if !tableExists(db, "qt_pricelist_sync_status") {
		if err := db.Exec(`
			CREATE TABLE IF NOT EXISTS qt_pricelist_sync_status (
				username VARCHAR(100) NOT NULL,
				last_sync_at DATETIME NOT NULL,
				updated_at DATETIME NOT NULL,
				app_version VARCHAR(64) NULL,
				PRIMARY KEY (username),
				INDEX idx_qt_pricelist_sync_status_last_sync (last_sync_at)
			)
		`).Error; err != nil {
			return fmt.Errorf("create qt_pricelist_sync_status table: %w", err)
		}
	}

	// Backward compatibility for environments where table was created without app_version.
	// Only try to add column if table exists.
	if tableExists(db, "qt_pricelist_sync_status") {
		if err := db.Exec(`
			ALTER TABLE qt_pricelist_sync_status
			ADD COLUMN IF NOT EXISTS app_version VARCHAR(64) NULL
		`).Error; err != nil {
			// Log but don't fail if alter fails (column might already exist)
			slog.Debug("failed to add app_version column", "error", err)
		}
	}
	return nil
}

// SyncPricelistItems synchronizes items for a specific pricelist
func (s *Service) SyncPricelistItems(localPricelistID uint) (int, error) {
	// Get local pricelist
	localPL, err := s.localDB.GetLocalPricelistByID(localPricelistID)
	if err != nil {
		return 0, fmt.Errorf("getting local pricelist: %w", err)
	}

	// Check if items already exist
	existingCount := s.localDB.CountLocalPricelistItems(localPricelistID)
	if existingCount > 0 {
		slog.Debug("pricelist items already synced", "pricelist_id", localPricelistID, "count", existingCount)
		return int(existingCount), nil
	}

	// Get database connection
	mariaDB, err := s.getDB()
	if err != nil {
		return 0, fmt.Errorf("database not available: %w", err)
	}

	// Create repository
	pricelistRepo := repository.NewPricelistRepository(mariaDB)

	// Get items from server
	serverItems, _, err := pricelistRepo.GetItems(localPL.ServerID, 0, 10000, "")
	if err != nil {
		return 0, fmt.Errorf("getting server pricelist items: %w", err)
	}

	// Convert and save locally
	localItems := make([]localdb.LocalPricelistItem, len(serverItems))
	for i, item := range serverItems {
		localItems[i] = *localdb.PricelistItemToLocal(&item, localPricelistID)
	}

	if err := s.localDB.SaveLocalPricelistItems(localItems); err != nil {
		return 0, fmt.Errorf("saving local pricelist items: %w", err)
	}

	slog.Info("synced pricelist items", "pricelist_id", localPricelistID, "items", len(localItems))
	return len(localItems), nil
}

// SyncPricelistItemsByServerID syncs items for a pricelist by its server ID
func (s *Service) SyncPricelistItemsByServerID(serverPricelistID uint) (int, error) {
	localPL, err := s.localDB.GetLocalPricelistByServerID(serverPricelistID)
	if err != nil {
		return 0, fmt.Errorf("local pricelist not found for server ID %d", serverPricelistID)
	}
	return s.SyncPricelistItems(localPL.ID)
}

// GetLocalPriceForLot returns the price for a lot from a local pricelist
func (s *Service) GetLocalPriceForLot(localPricelistID uint, lotName string) (float64, error) {
	return s.localDB.GetLocalPriceForLot(localPricelistID, lotName)
}

// GetPricelistForOffline returns a pricelist suitable for offline use
// If items are not synced, it will sync them first
func (s *Service) GetPricelistForOffline(serverPricelistID uint) (*localdb.LocalPricelist, error) {
	// Ensure pricelist is synced
	localPL, err := s.localDB.GetLocalPricelistByServerID(serverPricelistID)
	if err != nil {
		// Try to sync pricelists first
		if _, err := s.SyncPricelists(); err != nil {
			return nil, fmt.Errorf("syncing pricelists: %w", err)
		}

		// Try again
		localPL, err = s.localDB.GetLocalPricelistByServerID(serverPricelistID)
		if err != nil {
			return nil, fmt.Errorf("pricelist not found on server: %w", err)
		}
	}

	// Ensure items are synced
	if _, err := s.SyncPricelistItems(localPL.ID); err != nil {
		return nil, fmt.Errorf("syncing pricelist items: %w", err)
	}

	return localPL, nil
}

// SyncPricelistsIfNeeded checks for new pricelists and syncs if needed
// This should be called before creating a new configuration when online
func (s *Service) SyncPricelistsIfNeeded() error {
	needSync, err := s.NeedSync()
	if err != nil {
		slog.Warn("failed to check if sync needed", "error", err)
		return nil // Don't fail on check error
	}

	if !needSync {
		slog.Debug("pricelists are up to date, no sync needed")
		return nil
	}

	slog.Info("new pricelists detected, syncing...")
	_, err = s.SyncPricelists()
	if err != nil {
		return fmt.Errorf("syncing pricelists: %w", err)
	}

	return nil
}

// PushPendingChanges pushes all pending changes to the server
func (s *Service) PushPendingChanges() (int, error) {
	if _, err := s.EnsureReadinessForSync(); err != nil {
		return 0, err
	}

	removed, err := s.localDB.PurgeOrphanConfigurationPendingChanges()
	if err != nil {
		slog.Warn("failed to purge orphan configuration pending changes", "error", err)
	} else if removed > 0 {
		slog.Info("purged orphan configuration pending changes", "removed", removed)
	}

	changes, err := s.localDB.GetPendingChanges()
	if err != nil {
		return 0, fmt.Errorf("getting pending changes: %w", err)
	}

	if len(changes) == 0 {
		slog.Debug("no pending changes to push")
		return 0, nil
	}

	slog.Info("pushing pending changes", "count", len(changes))
	pushed := 0
	var syncedIDs []int64
	sortedChanges := prioritizeProjectChanges(changes)

	for _, change := range sortedChanges {
		err := s.pushSingleChange(&change)
		if err != nil {
			slog.Warn("failed to push change", "id", change.ID, "type", change.EntityType, "operation", change.Operation, "error", err)
			// Increment attempts
			s.localDB.IncrementPendingChangeAttempts(change.ID, err.Error())
			continue
		}

		syncedIDs = append(syncedIDs, change.ID)
		pushed++
	}

	// Mark synced changes as complete by deleting them
	if len(syncedIDs) > 0 {
		if err := s.localDB.MarkChangesSynced(syncedIDs); err != nil {
			slog.Error("failed to mark changes as synced", "error", err)
		}
	}

	slog.Info("pending changes pushed", "pushed", pushed, "failed", len(changes)-pushed)
	return pushed, nil
}

// pushSingleChange pushes a single pending change to the server
func (s *Service) pushSingleChange(change *localdb.PendingChange) error {
	switch change.EntityType {
	case "project":
		return s.pushProjectChange(change)
	case "configuration":
		return s.pushConfigurationChange(change)
	default:
		return fmt.Errorf("unknown entity type: %s", change.EntityType)
	}
}

func prioritizeProjectChanges(changes []localdb.PendingChange) []localdb.PendingChange {
	if len(changes) < 2 {
		return changes
	}

	projectChanges := make([]localdb.PendingChange, 0, len(changes))
	otherChanges := make([]localdb.PendingChange, 0, len(changes))
	for _, change := range changes {
		if change.EntityType == "project" {
			projectChanges = append(projectChanges, change)
			continue
		}
		otherChanges = append(otherChanges, change)
	}

	sorted := make([]localdb.PendingChange, 0, len(changes))
	sorted = append(sorted, projectChanges...)
	sorted = append(sorted, otherChanges...)
	return sorted
}

func (s *Service) pushProjectChange(change *localdb.PendingChange) error {
	payload, err := decodeProjectChangePayload(change)
	if err != nil {
		return fmt.Errorf("decode project payload: %w", err)
	}

	mariaDB, err := s.getDB()
	if err != nil {
		return fmt.Errorf("database not available: %w", err)
	}

	projectRepo := repository.NewProjectRepository(mariaDB)
	project := payload.Snapshot
	project.UUID = payload.ProjectUUID
	if strings.TrimSpace(project.Code) == "" {
		project.Code = strings.TrimSpace(derefString(project.Name))
		if project.Code == "" {
			project.Code = project.UUID
		}
	}

	// Try upsert by UUID first
	err = projectRepo.UpsertByUUID(&project)
	if err != nil {
		// Check if it's a duplicate (code, variant) constraint violation
		// In this case, find existing project with same (code, variant) and link to it
		var existing models.Project
		lookupErr := mariaDB.Where("code = ? AND variant = ?", project.Code, project.Variant).First(&existing).Error
		if lookupErr == nil {
			// Found duplicate - link local project to existing server project
			slog.Info("project duplicate found, linking to existing",
				"local_uuid", project.UUID,
				"server_uuid", existing.UUID,
				"server_id", existing.ID,
				"code", project.Code,
				"variant", project.Variant)
			project.ID = existing.ID
		} else {
			// Not a duplicate issue, return original error
			return fmt.Errorf("upsert project on server: %w", err)
		}
	}

	// Update local project with server ID
	localProject, localErr := s.localDB.GetProjectByUUID(project.UUID)
	if localErr == nil {
		if project.ID > 0 {
			serverID := project.ID
			localProject.ServerID = &serverID
		}
		localProject.SyncStatus = "synced"
		now := time.Now()
		localProject.SyncedAt = &now
		_ = s.localDB.SaveProject(localProject)
	}

	return nil
}

func derefString(value *string) string {
	if value == nil {
		return ""
	}
	return *value
}

func ptrString(value string) *string {
	return &value
}

func decodeProjectChangePayload(change *localdb.PendingChange) (ProjectChangePayload, error) {
	var payload ProjectChangePayload
	if err := json.Unmarshal([]byte(change.Payload), &payload); err == nil && payload.ProjectUUID != "" {
		if payload.Operation == "" {
			payload.Operation = change.Operation
		}
		return payload, nil
	}

	var project models.Project
	if err := json.Unmarshal([]byte(change.Payload), &project); err != nil {
		return ProjectChangePayload{}, fmt.Errorf("unmarshal legacy project payload: %w", err)
	}

	return ProjectChangePayload{
		ProjectUUID:    project.UUID,
		Operation:      change.Operation,
		IdempotencyKey: fmt.Sprintf("%s:%s:legacy", project.UUID, change.Operation),
		Snapshot:       project,
	}, nil
}

// pushConfigurationChange pushes a configuration change to the server
func (s *Service) pushConfigurationChange(change *localdb.PendingChange) error {
	switch change.Operation {
	case "create":
		return s.pushConfigurationCreate(change)
	case "update":
		return s.pushConfigurationUpdate(change)
	case "rollback":
		return s.pushConfigurationRollback(change)
	case "deactivate":
		return s.pushConfigurationDeactivate(change)
	case "reactivate":
		return s.pushConfigurationReactivate(change)
	case "delete":
		return s.pushConfigurationDelete(change)
	default:
		return fmt.Errorf("unknown operation: %s", change.Operation)
	}
}

// pushConfigurationCreate creates a configuration on the server
func (s *Service) pushConfigurationCreate(change *localdb.PendingChange) error {
	payload, cfg, isStale, err := s.resolveConfigurationPayloadForPush(change)
	if err != nil {
		return err
	}
	if isStale {
		slog.Debug("skipping stale create event, newer version exists", "uuid", payload.ConfigurationUUID, "idempotency_key", payload.IdempotencyKey)
		return nil
	}

	// Get database connection
	mariaDB, err := s.getDB()
	if err != nil {
		return fmt.Errorf("database not available: %w", err)
	}

	// Create repository
	configRepo := repository.NewConfigurationRepository(mariaDB)
	if err := s.ensureConfigurationOwner(mariaDB, &cfg); err != nil {
		return fmt.Errorf("resolve configuration owner: %w", err)
	}
	if err := s.ensureConfigurationProject(mariaDB, &cfg); err != nil {
		return fmt.Errorf("resolve configuration project: %w", err)
	}
	if err := s.ensureConfigurationPricelist(mariaDB, &cfg); err != nil {
		return fmt.Errorf("resolve configuration pricelist: %w", err)
	}

	// Create on server
	if err := configRepo.Create(&cfg); err != nil {
		// Idempotency fallback: configuration may already be created remotely.
		serverCfg, getErr := configRepo.GetByUUID(cfg.UUID)
		if getErr != nil {
			return fmt.Errorf("creating configuration on server: %w", err)
		}
		cfg.ID = serverCfg.ID
		if updateErr := configRepo.Update(&cfg); updateErr != nil {
			return fmt.Errorf("create fallback update on server: %w", updateErr)
		}
	}

	// Update local configuration with server ID
	localCfg, err := s.localDB.GetConfigurationByUUID(cfg.UUID)
	if err == nil {
		serverID := cfg.ID
		localCfg.ServerID = &serverID
		localCfg.SyncStatus = "synced"
		s.localDB.SaveConfiguration(localCfg)
	}

	slog.Info("configuration created on server",
		"uuid", cfg.UUID,
		"server_id", cfg.ID,
		"version_no", payload.CurrentVersionNo,
		"version_id", payload.CurrentVersionID,
		"idempotency_key", payload.IdempotencyKey,
	)
	return nil
}

// pushConfigurationUpdate updates a configuration on the server
func (s *Service) pushConfigurationUpdate(change *localdb.PendingChange) error {
	payload, cfg, isStale, err := s.resolveConfigurationPayloadForPush(change)
	if err != nil {
		return err
	}
	if isStale {
		slog.Debug("skipping stale update event, newer version exists", "uuid", payload.ConfigurationUUID, "idempotency_key", payload.IdempotencyKey)
		return nil
	}

	// Get database connection
	mariaDB, err := s.getDB()
	if err != nil {
		return fmt.Errorf("database not available: %w", err)
	}

	// Create repository
	configRepo := repository.NewConfigurationRepository(mariaDB)
	if err := s.ensureConfigurationOwner(mariaDB, &cfg); err != nil {
		return fmt.Errorf("resolve configuration owner: %w", err)
	}
	if err := s.ensureConfigurationProject(mariaDB, &cfg); err != nil {
		return fmt.Errorf("resolve configuration project: %w", err)
	}
	if err := s.ensureConfigurationPricelist(mariaDB, &cfg); err != nil {
		return fmt.Errorf("resolve configuration pricelist: %w", err)
	}

	// Ensure we have a server ID before updating
	// If the payload doesn't have ID, get it from local configuration
	if cfg.ID == 0 {
		localCfg, err := s.localDB.GetConfigurationByUUID(cfg.UUID)
		if err != nil {
			return fmt.Errorf("getting local configuration: %w", err)
		}

		if localCfg.ServerID == nil {
			// Configuration hasn't been synced yet, try to find it on server by UUID.
			// If not found (e.g. stale create was skipped), create it from current snapshot.
			serverCfg, getErr := configRepo.GetByUUID(cfg.UUID)
			if getErr != nil {
				if !errors.Is(getErr, gorm.ErrRecordNotFound) {
					return fmt.Errorf("loading configuration from server: %w", getErr)
				}
				if createErr := configRepo.Create(&cfg); createErr != nil {
					// Idempotency fallback: configuration may have been created concurrently.
					existing, existingErr := configRepo.GetByUUID(cfg.UUID)
					if existingErr != nil {
						return fmt.Errorf("creating missing configuration on server: %w", createErr)
					}
					cfg.ID = existing.ID
				}
				if cfg.ID == 0 {
					existing, existingErr := configRepo.GetByUUID(cfg.UUID)
					if existingErr != nil {
						return fmt.Errorf("loading created configuration from server: %w", existingErr)
					}
					cfg.ID = existing.ID
				}
			} else {
				cfg.ID = serverCfg.ID
			}

			// Update local with server ID
			serverID := cfg.ID
			localCfg.ServerID = &serverID
			s.localDB.SaveConfiguration(localCfg)
		} else {
			cfg.ID = *localCfg.ServerID
		}
	}

	// Update on server
	if err := configRepo.Update(&cfg); err != nil {
		return fmt.Errorf("updating configuration on server: %w", err)
	}

	// Update local sync status
	localCfg, err := s.localDB.GetConfigurationByUUID(cfg.UUID)
	if err == nil {
		localCfg.SyncStatus = "synced"
		s.localDB.SaveConfiguration(localCfg)
	}

	slog.Info("configuration updated on server",
		"uuid", cfg.UUID,
		"version_no", payload.CurrentVersionNo,
		"version_id", payload.CurrentVersionID,
		"idempotency_key", payload.IdempotencyKey,
		"operation", payload.Operation,
		"conflict_policy", payload.ConflictPolicy,
	)
	return nil
}

func (s *Service) ensureConfigurationOwner(mariaDB *gorm.DB, cfg *models.Configuration) error {
	if cfg == nil {
		return fmt.Errorf("configuration is nil")
	}

	ownerUsername := cfg.OwnerUsername
	if ownerUsername == "" {
		ownerUsername = s.localDB.GetDBUser()
		cfg.OwnerUsername = ownerUsername
	}
	if ownerUsername == "" {
		return fmt.Errorf("owner username is empty")
	}

	// user_id is legacy and no longer used for ownership in local-first mode.
	// Keep it NULL on writes; ownership is represented by owner_username.
	cfg.UserID = nil
	cfg.AppVersion = appmeta.Version()
	return nil
}

func (s *Service) ensureConfigurationProject(mariaDB *gorm.DB, cfg *models.Configuration) error {
	if cfg == nil {
		return fmt.Errorf("configuration is nil")
	}

	projectRepo := repository.NewProjectRepository(mariaDB)

	if cfg.ProjectUUID != nil && *cfg.ProjectUUID != "" {
		_, err := projectRepo.GetByUUID(*cfg.ProjectUUID)
		if err == nil {
			return nil
		}
		if !errors.Is(err, gorm.ErrRecordNotFound) {
			return err
		}

		localProject, localErr := s.localDB.GetProjectByUUID(*cfg.ProjectUUID)
		if localErr != nil {
			return err
		}
		modelProject := localdb.LocalToProject(localProject)
		if modelProject.OwnerUsername == "" {
			modelProject.OwnerUsername = cfg.OwnerUsername
		}
		if createErr := projectRepo.UpsertByUUID(modelProject); createErr != nil {
			return createErr
		}
		if modelProject.ID > 0 {
			serverID := modelProject.ID
			localProject.ServerID = &serverID
			localProject.SyncStatus = "synced"
			now := time.Now()
			localProject.SyncedAt = &now
			_ = s.localDB.SaveProject(localProject)
		}
		return nil
	}

	systemProject := &models.Project{}
	err := mariaDB.
		Where("LOWER(TRIM(COALESCE(name, ''))) = LOWER(?) AND is_system = ?", "Без проекта", true).
		Order("CASE WHEN TRIM(COALESCE(owner_username, '')) = '' THEN 0 ELSE 1 END, created_at ASC, id ASC").
		First(systemProject).Error
	if err != nil {
		if !errors.Is(err, gorm.ErrRecordNotFound) {
			return err
		}
		systemProject = &models.Project{
			UUID:          uuid.NewString(),
			OwnerUsername: "",
			Code:          "Без проекта",
			Name:          ptrString("Без проекта"),
			IsActive:      true,
			IsSystem:      true,
		}
		if createErr := projectRepo.Create(systemProject); createErr != nil {
			return createErr
		}
	}

	cfg.ProjectUUID = &systemProject.UUID
	return nil
}

func (s *Service) ensureConfigurationPricelist(mariaDB *gorm.DB, cfg *models.Configuration) error {
	if cfg == nil {
		return fmt.Errorf("configuration is nil")
	}

	pricelistRepo := repository.NewPricelistRepository(mariaDB)

	if cfg.PricelistID != nil && *cfg.PricelistID > 0 {
		if _, err := pricelistRepo.GetByID(*cfg.PricelistID); err == nil {
			return nil
		}
	}

	latest, err := pricelistRepo.GetLatestActive()
	if err != nil {
		cfg.PricelistID = nil
		return nil
	}

	cfg.PricelistID = &latest.ID
	return nil
}

func (s *Service) pushConfigurationRollback(change *localdb.PendingChange) error {
	// Last-write-wins for now: rollback is pushed as an update with rollback metadata.
	return s.pushConfigurationUpdate(change)
}

func (s *Service) pushConfigurationDeactivate(change *localdb.PendingChange) error {
	// Local deactivate is represented as the latest snapshot push.
	return s.pushConfigurationUpdate(change)
}

func (s *Service) pushConfigurationReactivate(change *localdb.PendingChange) error {
	// Local reactivate is represented as the latest snapshot push.
	return s.pushConfigurationUpdate(change)
}

func (s *Service) resolveConfigurationPayloadForPush(change *localdb.PendingChange) (ConfigurationChangePayload, models.Configuration, bool, error) {
	payload, err := decodeConfigurationChangePayload(change)
	if err != nil {
		return ConfigurationChangePayload{}, models.Configuration{}, false, fmt.Errorf("decode configuration payload: %w", err)
	}
	eventVersionNo := payload.CurrentVersionNo

	currentCfg, currentVersionID, currentVersionNo, err := s.loadCurrentConfigurationState(payload.ConfigurationUUID)
	if err != nil {
		// Local config may be gone (e.g. stale queue item after delete/cleanup). Treat as no-op.
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return payload, payload.Snapshot, true, nil
		}
		// create->deactivate race: config may no longer be active/visible locally, skip stale create.
		if change.Operation == "create" {
			return payload, payload.Snapshot, true, nil
		}
		return ConfigurationChangePayload{}, models.Configuration{}, false, fmt.Errorf("load current local configuration state: %w", err)
	}

	if payload.ConflictPolicy == "" {
		payload.ConflictPolicy = "last_write_wins"
	}

	if currentCfg.UUID != "" {
		payload.Snapshot = currentCfg
		if currentVersionID != "" {
			payload.CurrentVersionID = currentVersionID
		}
		if currentVersionNo > 0 {
			payload.CurrentVersionNo = currentVersionNo
		}
		payload.PricelistID = currentCfg.PricelistID
	}

	isStale := false
	if eventVersionNo > 0 && currentVersionNo > eventVersionNo {
		// Keep only latest intent in queue; older versions become no-op.
		isStale = true
	}
	if !isStale && change.Operation == "create" {
		localCfg, getErr := s.localDB.GetConfigurationByUUID(payload.ConfigurationUUID)
		if getErr == nil && !localCfg.IsActive {
			isStale = true
		}
	}

	return payload, payload.Snapshot, isStale, nil
}

func decodeConfigurationChangePayload(change *localdb.PendingChange) (ConfigurationChangePayload, error) {
	var payload ConfigurationChangePayload
	if err := json.Unmarshal([]byte(change.Payload), &payload); err == nil && payload.ConfigurationUUID != "" && payload.Snapshot.UUID != "" {
		if payload.Operation == "" {
			payload.Operation = change.Operation
		}
		return payload, nil
	}

	// Backward compatibility: legacy queue stored raw models.Configuration JSON.
	var cfg models.Configuration
	if err := json.Unmarshal([]byte(change.Payload), &cfg); err != nil {
		return ConfigurationChangePayload{}, fmt.Errorf("unmarshal legacy configuration payload: %w", err)
	}

	return ConfigurationChangePayload{
		EventID:           "",
		IdempotencyKey:    fmt.Sprintf("%s:%s:legacy", cfg.UUID, change.Operation),
		ConfigurationUUID: cfg.UUID,
		ProjectUUID:       cfg.ProjectUUID,
		PricelistID:       cfg.PricelistID,
		Operation:         change.Operation,
		ConflictPolicy:    "last_write_wins",
		Snapshot:          cfg,
	}, nil
}

func (s *Service) loadCurrentConfigurationState(configurationUUID string) (models.Configuration, string, int, error) {
	localCfg, err := s.localDB.GetConfigurationByUUID(configurationUUID)
	if err != nil {
		return models.Configuration{}, "", 0, fmt.Errorf("get local configuration by uuid: %w", err)
	}

	cfg := *localdb.LocalToConfiguration(localCfg)

	currentVersionID := ""
	if localCfg.CurrentVersionID != nil {
		currentVersionID = *localCfg.CurrentVersionID
	}

	currentVersionNo := 0
	if currentVersionID != "" {
		var version localdb.LocalConfigurationVersion
		err = s.localDB.DB().
			Where("id = ? AND configuration_uuid = ?", currentVersionID, configurationUUID).
			First(&version).Error
		if err == nil {
			currentVersionNo = version.VersionNo
		}
	}

	if currentVersionNo == 0 {
		var latest localdb.LocalConfigurationVersion
		err = s.localDB.DB().
			Where("configuration_uuid = ?", configurationUUID).
			Order("version_no DESC").
			First(&latest).Error
		if err == nil {
			currentVersionNo = latest.VersionNo
			currentVersionID = latest.ID
		}
	}

	if currentVersionNo == 0 {
		if err := s.repairMissingConfigurationVersion(localCfg); err != nil {
			return models.Configuration{}, "", 0, fmt.Errorf("repair missing configuration version: %w", err)
		}
		var latest localdb.LocalConfigurationVersion
		err = s.localDB.DB().
			Where("configuration_uuid = ?", configurationUUID).
			Order("version_no DESC").
			First(&latest).Error
		if err == nil {
			currentVersionNo = latest.VersionNo
			currentVersionID = latest.ID
		}
	}

	if currentVersionNo == 0 {
		return models.Configuration{}, "", 0, fmt.Errorf("no local configuration version found for %s", configurationUUID)
	}

	return cfg, currentVersionID, currentVersionNo, nil
}

func (s *Service) repairMissingConfigurationVersion(localCfg *localdb.LocalConfiguration) error {
	if localCfg == nil {
		return fmt.Errorf("local configuration is nil")
	}

	return s.localDB.DB().Transaction(func(tx *gorm.DB) error {
		var cfg localdb.LocalConfiguration
		if err := tx.Where("uuid = ?", localCfg.UUID).First(&cfg).Error; err != nil {
			return fmt.Errorf("load local configuration: %w", err)
		}

		// If versions exist, just make sure current_version_id is set.
		var latest localdb.LocalConfigurationVersion
		if err := tx.Where("configuration_uuid = ?", cfg.UUID).
			Order("version_no DESC").
			First(&latest).Error; err == nil {
			if cfg.CurrentVersionID == nil || *cfg.CurrentVersionID == "" {
				if err := tx.Model(&localdb.LocalConfiguration{}).
					Where("uuid = ?", cfg.UUID).
					Update("current_version_id", latest.ID).Error; err != nil {
					return fmt.Errorf("set current version id: %w", err)
				}
			}
			return nil
		} else if !errors.Is(err, gorm.ErrRecordNotFound) {
			return fmt.Errorf("load latest version: %w", err)
		}

		snapshot, err := localdb.BuildConfigurationSnapshot(&cfg)
		if err != nil {
			return fmt.Errorf("build configuration snapshot: %w", err)
		}

		note := "Auto-repaired missing local version"
		version := localdb.LocalConfigurationVersion{
			ID:                uuid.NewString(),
			ConfigurationUUID: cfg.UUID,
			VersionNo:         1,
			Data:              snapshot,
			ChangeNote:        &note,
			AppVersion:        appmeta.Version(),
			CreatedAt:         time.Now(),
		}

		if err := tx.Create(&version).Error; err != nil {
			return fmt.Errorf("create initial version: %w", err)
		}
		if err := tx.Model(&localdb.LocalConfiguration{}).
			Where("uuid = ?", cfg.UUID).
			Update("current_version_id", version.ID).Error; err != nil {
			return fmt.Errorf("set current version id: %w", err)
		}

		slog.Warn("repaired missing local configuration version", "uuid", cfg.UUID, "version_no", version.VersionNo)
		return nil
	})
}

// NOTE: prepared for future conflict resolution:
// when server starts storing version metadata, we can compare payload.CurrentVersionNo
// against remote version and branch into custom strategies. For now use last-write-wins.

// pushConfigurationDelete deletes a configuration from the server
func (s *Service) pushConfigurationDelete(change *localdb.PendingChange) error {
	// Get database connection
	mariaDB, err := s.getDB()
	if err != nil {
		return fmt.Errorf("database not available: %w", err)
	}

	// Create repository
	configRepo := repository.NewConfigurationRepository(mariaDB)

	// Get the configuration from server by UUID to get the ID
	cfg, err := configRepo.GetByUUID(change.EntityUUID)
	if err != nil {
		// Already deleted or not found, consider it successful
		slog.Warn("configuration not found on server, considering delete successful", "uuid", change.EntityUUID)
		return nil
	}

	// Delete from server
	if err := configRepo.Delete(cfg.ID); err != nil {
		return fmt.Errorf("deleting configuration from server: %w", err)
	}

	slog.Info("configuration deleted on server", "uuid", change.EntityUUID)
	return nil
}

func (s *Service) getDB() (*gorm.DB, error) {
	if s.directDB != nil {
		return s.directDB, nil
	}
	if s.connMgr == nil {
		return nil, ErrOffline
	}
	return s.connMgr.GetDB()
}

func (s *Service) getConnectionStatus() db.ConnectionStatus {
	if s.directDB != nil {
		return db.ConnectionStatus{IsConnected: true}
	}
	if s.connMgr == nil {
		return db.ConnectionStatus{IsConnected: false}
	}
	return s.connMgr.GetStatus()
}