package sync

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

	"git.mchus.pro/mchus/priceforge/internal/appmeta"
	"git.mchus.pro/mchus/priceforge/internal/db"
	"git.mchus.pro/mchus/priceforge/internal/localdb"
	"git.mchus.pro/mchus/priceforge/internal/models"
	"git.mchus.pro/mchus/priceforge/internal/repository"
	"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"`
}

// 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
}

// 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 {
	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 err
	}

	// Backward compatibility for environments where table was created without app_version.
	return db.Exec(`
		ALTER TABLE qt_pricelist_sync_status
		ADD COLUMN IF NOT EXISTS app_version VARCHAR(64) NULL
	`).Error
}

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()
}