package services

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"strings"
	"sync"
	"time"

	"github.com/emersion/go-ical"
	"github.com/emersion/go-webdav"
	"github.com/emersion/go-webdav/caldav"
	"github.com/google/uuid"
	"github.com/jmoiron/sqlx"

	"mgit.msbls.de/m/KanzlAI-mGMT/internal/models"
)

const (
	calDAVDomain   = "kanzlai.msbls.de"
	calDAVProdID   = "-//KanzlAI//KanzlAI-mGMT//EN"
	defaultSyncMin = 15
)

// CalDAVConfig holds per-tenant CalDAV configuration from tenants.settings.
type CalDAVConfig struct {
	URL                 string `json:"url"`
	Username            string `json:"username"`
	Password            string `json:"password"`
	CalendarPath        string `json:"calendar_path"`
	SyncEnabled         bool   `json:"sync_enabled"`
	SyncIntervalMinutes int    `json:"sync_interval_minutes"`
}

// SyncStatus holds the last sync result for a tenant.
type SyncStatus struct {
	TenantID     uuid.UUID `json:"tenant_id"`
	LastSyncAt   time.Time `json:"last_sync_at"`
	ItemsPushed  int       `json:"items_pushed"`
	ItemsPulled  int       `json:"items_pulled"`
	Errors       []string  `json:"errors,omitempty"`
	SyncDuration string    `json:"sync_duration"`
}

// CalDAVService handles bidirectional CalDAV synchronization.
type CalDAVService struct {
	db *sqlx.DB

	mu       sync.RWMutex
	statuses map[uuid.UUID]*SyncStatus // per-tenant sync status

	stopCh chan struct{}
	wg     sync.WaitGroup
}

// NewCalDAVService creates a new CalDAV sync service.
func NewCalDAVService(db *sqlx.DB) *CalDAVService {
	return &CalDAVService{
		db:       db,
		statuses: make(map[uuid.UUID]*SyncStatus),
		stopCh:   make(chan struct{}),
	}
}

// GetStatus returns the last sync status for a tenant.
func (s *CalDAVService) GetStatus(tenantID uuid.UUID) *SyncStatus {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.statuses[tenantID]
}

// setStatus stores the sync status for a tenant.
func (s *CalDAVService) setStatus(status *SyncStatus) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.statuses[status.TenantID] = status
}

// Start begins the background sync goroutine that polls per-tenant.
func (s *CalDAVService) Start() {
	s.wg.Go(func() {
		s.backgroundLoop()
	})
	slog.Info("CalDAV sync service started")
}

// Stop gracefully stops the background sync.
func (s *CalDAVService) Stop() {
	close(s.stopCh)
	s.wg.Wait()
	slog.Info("CalDAV sync service stopped")
}

// backgroundLoop polls tenants at their configured interval.
func (s *CalDAVService) backgroundLoop() {
	// Check every minute, but only sync tenants whose interval has elapsed.
	ticker := time.NewTicker(1 * time.Minute)
	defer ticker.Stop()

	for {
		select {
		case <-s.stopCh:
			return
		case <-ticker.C:
			s.syncAllTenants()
		}
	}
}

// syncAllTenants checks all tenants and syncs those due for a sync.
func (s *CalDAVService) syncAllTenants() {
	configs, err := s.loadAllTenantConfigs()
	if err != nil {
		slog.Error("CalDAV: failed to load tenant configs", "error", err)
		return
	}

	for tenantID, cfg := range configs {
		if !cfg.SyncEnabled {
			continue
		}

		interval := cfg.SyncIntervalMinutes
		if interval <= 0 {
			interval = defaultSyncMin
		}

		// Check if enough time has passed since last sync
		status := s.GetStatus(tenantID)
		if status != nil && time.Since(status.LastSyncAt) < time.Duration(interval)*time.Minute {
			continue
		}

		go func(tid uuid.UUID, c CalDAVConfig) {
			ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
			defer cancel()
			if _, err := s.SyncTenant(ctx, tid, c); err != nil {
				slog.Error("CalDAV: sync failed", "tenant_id", tid, "error", err)
			}
		}(tenantID, cfg)
	}
}

// loadAllTenantConfigs reads CalDAV configs from all tenants.
func (s *CalDAVService) loadAllTenantConfigs() (map[uuid.UUID]CalDAVConfig, error) {
	type row struct {
		ID       uuid.UUID       `db:"id"`
		Settings json.RawMessage `db:"settings"`
	}
	var rows []row
	if err := s.db.Select(&rows, "SELECT id, settings FROM tenants"); err != nil {
		return nil, fmt.Errorf("querying tenants: %w", err)
	}

	result := make(map[uuid.UUID]CalDAVConfig)
	for _, r := range rows {
		cfg, err := parseCalDAVConfig(r.Settings)
		if err != nil || cfg.URL == "" {
			continue
		}
		result[r.ID] = cfg
	}
	return result, nil
}

// LoadTenantConfig reads CalDAV config for a single tenant.
func (s *CalDAVService) LoadTenantConfig(tenantID uuid.UUID) (*CalDAVConfig, error) {
	var settings json.RawMessage
	if err := s.db.Get(&settings, "SELECT settings FROM tenants WHERE id = $1", tenantID); err != nil {
		return nil, fmt.Errorf("loading tenant settings: %w", err)
	}
	cfg, err := parseCalDAVConfig(settings)
	if err != nil {
		return nil, err
	}
	if cfg.URL == "" {
		return nil, fmt.Errorf("no CalDAV configuration for tenant")
	}
	return &cfg, nil
}

func parseCalDAVConfig(settings json.RawMessage) (CalDAVConfig, error) {
	if len(settings) == 0 {
		return CalDAVConfig{}, nil
	}
	var wrapper struct {
		CalDAV CalDAVConfig `json:"caldav"`
	}
	if err := json.Unmarshal(settings, &wrapper); err != nil {
		return CalDAVConfig{}, fmt.Errorf("parsing CalDAV settings: %w", err)
	}
	return wrapper.CalDAV, nil
}

// newCalDAVClient creates a caldav.Client from config.
func newCalDAVClient(cfg CalDAVConfig) (*caldav.Client, error) {
	httpClient := webdav.HTTPClientWithBasicAuth(nil, cfg.Username, cfg.Password)
	return caldav.NewClient(httpClient, cfg.URL)
}

// SyncTenant performs a full bidirectional sync for a tenant.
func (s *CalDAVService) SyncTenant(ctx context.Context, tenantID uuid.UUID, cfg CalDAVConfig) (*SyncStatus, error) {
	start := time.Now()
	status := &SyncStatus{
		TenantID: tenantID,
	}

	client, err := newCalDAVClient(cfg)
	if err != nil {
		status.Errors = append(status.Errors, fmt.Sprintf("creating client: %v", err))
		status.LastSyncAt = time.Now()
		s.setStatus(status)
		return status, err
	}

	// Push local changes to CalDAV
	pushed, pushErrs := s.pushAll(ctx, client, tenantID, cfg)
	status.ItemsPushed = pushed
	status.Errors = append(status.Errors, pushErrs...)

	// Pull remote changes from CalDAV
	pulled, pullErrs := s.pullAll(ctx, client, tenantID, cfg)
	status.ItemsPulled = pulled
	status.Errors = append(status.Errors, pullErrs...)

	status.LastSyncAt = time.Now()
	status.SyncDuration = time.Since(start).String()
	s.setStatus(status)

	if len(status.Errors) > 0 {
		return status, fmt.Errorf("sync completed with %d errors", len(status.Errors))
	}
	return status, nil
}

// --- Push: Local -> CalDAV ---

// pushAll pushes all deadlines and appointments to CalDAV.
func (s *CalDAVService) pushAll(ctx context.Context, client *caldav.Client, tenantID uuid.UUID, cfg CalDAVConfig) (int, []string) {
	var pushed int
	var errs []string

	// Push deadlines as VTODO
	deadlines, err := s.loadDeadlines(tenantID)
	if err != nil {
		return 0, []string{fmt.Sprintf("loading deadlines: %v", err)}
	}
	for _, d := range deadlines {
		if err := s.pushDeadline(ctx, client, cfg, &d); err != nil {
			errs = append(errs, fmt.Sprintf("push deadline %s: %v", d.ID, err))
		} else {
			pushed++
		}
	}

	// Push appointments as VEVENT
	appointments, err := s.loadAppointments(ctx, tenantID)
	if err != nil {
		errs = append(errs, fmt.Sprintf("loading appointments: %v", err))
		return pushed, errs
	}
	for _, a := range appointments {
		if err := s.pushAppointment(ctx, client, cfg, &a); err != nil {
			errs = append(errs, fmt.Sprintf("push appointment %s: %v", a.ID, err))
		} else {
			pushed++
		}
	}

	return pushed, errs
}

// PushDeadline pushes a single deadline to CalDAV (called on create/update).
func (s *CalDAVService) PushDeadline(ctx context.Context, tenantID uuid.UUID, deadline *models.Deadline) error {
	cfg, err := s.LoadTenantConfig(tenantID)
	if err != nil || !cfg.SyncEnabled {
		return nil // CalDAV not configured or disabled — silently skip
	}
	client, err := newCalDAVClient(*cfg)
	if err != nil {
		return fmt.Errorf("creating CalDAV client: %w", err)
	}
	return s.pushDeadline(ctx, client, *cfg, deadline)
}

func (s *CalDAVService) pushDeadline(ctx context.Context, client *caldav.Client, cfg CalDAVConfig, d *models.Deadline) error {
	uid := deadlineUID(d.ID)

	cal := ical.NewCalendar()
	cal.Props.SetText(ical.PropProductID, calDAVProdID)
	cal.Props.SetText(ical.PropVersion, "2.0")

	todo := ical.NewComponent(ical.CompToDo)
	todo.Props.SetText(ical.PropUID, uid)
	todo.Props.SetText(ical.PropSummary, d.Title)
	todo.Props.SetDateTime(ical.PropDateTimeStamp, time.Now().UTC())

	if d.Description != nil {
		todo.Props.SetText(ical.PropDescription, *d.Description)
	}
	if d.Notes != nil {
		desc := ""
		if d.Description != nil {
			desc = *d.Description + "\n\n"
		}
		todo.Props.SetText(ical.PropDescription, desc+*d.Notes)
	}

	// Parse due_date (stored as string "YYYY-MM-DD")
	if due, err := time.Parse("2006-01-02", d.DueDate); err == nil {
		todo.Props.SetDate(ical.PropDue, due)
	}

	// Map status
	switch d.Status {
	case "completed":
		todo.Props.SetText(ical.PropStatus, "COMPLETED")
		if d.CompletedAt != nil {
			todo.Props.SetDateTime(ical.PropCompleted, d.CompletedAt.UTC())
		}
	case "pending":
		todo.Props.SetText(ical.PropStatus, "NEEDS-ACTION")
	default:
		todo.Props.SetText(ical.PropStatus, "IN-PROCESS")
	}

	cal.Children = append(cal.Children, todo)

	path := calendarObjectPath(cfg.CalendarPath, uid)
	obj, err := client.PutCalendarObject(ctx, path, cal)
	if err != nil {
		return fmt.Errorf("putting VTODO: %w", err)
	}

	// Update caldav_uid and etag in DB
	return s.updateDeadlineCalDAV(d.ID, uid, obj.ETag)
}

// PushAppointment pushes a single appointment to CalDAV (called on create/update).
func (s *CalDAVService) PushAppointment(ctx context.Context, tenantID uuid.UUID, appointment *models.Appointment) error {
	cfg, err := s.LoadTenantConfig(tenantID)
	if err != nil || !cfg.SyncEnabled {
		return nil
	}
	client, err := newCalDAVClient(*cfg)
	if err != nil {
		return fmt.Errorf("creating CalDAV client: %w", err)
	}
	return s.pushAppointment(ctx, client, *cfg, appointment)
}

func (s *CalDAVService) pushAppointment(ctx context.Context, client *caldav.Client, cfg CalDAVConfig, a *models.Appointment) error {
	uid := appointmentUID(a.ID)

	cal := ical.NewCalendar()
	cal.Props.SetText(ical.PropProductID, calDAVProdID)
	cal.Props.SetText(ical.PropVersion, "2.0")

	event := ical.NewEvent()
	event.Props.SetText(ical.PropUID, uid)
	event.Props.SetText(ical.PropSummary, a.Title)
	event.Props.SetDateTime(ical.PropDateTimeStamp, time.Now().UTC())
	event.Props.SetDateTime(ical.PropDateTimeStart, a.StartAt.UTC())

	if a.EndAt != nil {
		event.Props.SetDateTime(ical.PropDateTimeEnd, a.EndAt.UTC())
	}
	if a.Description != nil {
		event.Props.SetText(ical.PropDescription, *a.Description)
	}
	if a.Location != nil {
		event.Props.SetText(ical.PropLocation, *a.Location)
	}

	cal.Children = append(cal.Children, event.Component)

	path := calendarObjectPath(cfg.CalendarPath, uid)
	obj, err := client.PutCalendarObject(ctx, path, cal)
	if err != nil {
		return fmt.Errorf("putting VEVENT: %w", err)
	}

	return s.updateAppointmentCalDAV(a.ID, uid, obj.ETag)
}

// DeleteDeadlineCalDAV removes a deadline's VTODO from CalDAV.
func (s *CalDAVService) DeleteDeadlineCalDAV(ctx context.Context, tenantID uuid.UUID, deadline *models.Deadline) error {
	if deadline.CalDAVUID == nil || *deadline.CalDAVUID == "" {
		return nil
	}
	cfg, err := s.LoadTenantConfig(tenantID)
	if err != nil || !cfg.SyncEnabled {
		return nil
	}
	client, err := newCalDAVClient(*cfg)
	if err != nil {
		return fmt.Errorf("creating CalDAV client: %w", err)
	}
	path := calendarObjectPath(cfg.CalendarPath, *deadline.CalDAVUID)
	return client.RemoveAll(ctx, path)
}

// DeleteAppointmentCalDAV removes an appointment's VEVENT from CalDAV.
func (s *CalDAVService) DeleteAppointmentCalDAV(ctx context.Context, tenantID uuid.UUID, appointment *models.Appointment) error {
	if appointment.CalDAVUID == nil || *appointment.CalDAVUID == "" {
		return nil
	}
	cfg, err := s.LoadTenantConfig(tenantID)
	if err != nil || !cfg.SyncEnabled {
		return nil
	}
	client, err := newCalDAVClient(*cfg)
	if err != nil {
		return fmt.Errorf("creating CalDAV client: %w", err)
	}
	path := calendarObjectPath(cfg.CalendarPath, *appointment.CalDAVUID)
	return client.RemoveAll(ctx, path)
}

// --- Pull: CalDAV -> Local ---

// pullAll fetches all calendar objects from CalDAV and reconciles with local DB.
func (s *CalDAVService) pullAll(ctx context.Context, client *caldav.Client, tenantID uuid.UUID, cfg CalDAVConfig) (int, []string) {
	var pulled int
	var errs []string

	query := &caldav.CalendarQuery{
		CompFilter: caldav.CompFilter{
			Name: ical.CompCalendar,
		},
	}

	objects, err := client.QueryCalendar(ctx, cfg.CalendarPath, query)
	if err != nil {
		return 0, []string{fmt.Sprintf("querying calendar: %v", err)}
	}

	for _, obj := range objects {
		if obj.Data == nil {
			continue
		}

		for _, child := range obj.Data.Children {
			switch child.Name {
			case ical.CompToDo:
				uid, _ := child.Props.Text(ical.PropUID)
				if uid == "" || !isKanzlAIUID(uid, "deadline") {
					continue
				}
				if err := s.reconcileDeadline(ctx, tenantID, child, obj.ETag); err != nil {
					errs = append(errs, fmt.Sprintf("reconcile deadline %s: %v", uid, err))
				} else {
					pulled++
				}
			case ical.CompEvent:
				uid, _ := child.Props.Text(ical.PropUID)
				if uid == "" || !isKanzlAIUID(uid, "appointment") {
					continue
				}
				if err := s.reconcileAppointment(ctx, tenantID, child, obj.ETag); err != nil {
					errs = append(errs, fmt.Sprintf("reconcile appointment %s: %v", uid, err))
				} else {
					pulled++
				}
			}
		}
	}

	return pulled, errs
}

// reconcileDeadline handles conflict resolution for a pulled VTODO.
// KanzlAI wins for dates/status, CalDAV wins for notes/description.
func (s *CalDAVService) reconcileDeadline(ctx context.Context, tenantID uuid.UUID, comp *ical.Component, remoteEtag string) error {
	uid, _ := comp.Props.Text(ical.PropUID)
	deadlineID := extractIDFromUID(uid, "deadline")
	if deadlineID == uuid.Nil {
		return fmt.Errorf("invalid UID: %s", uid)
	}

	// Load existing deadline
	var d models.Deadline
	err := s.db.Get(&d, `SELECT id, tenant_id, case_id, title, description, due_date, original_due_date,
		warning_date, source, rule_id, status, completed_at,
		caldav_uid, caldav_etag, notes, created_at, updated_at
		FROM deadlines WHERE id = $1 AND tenant_id = $2`, deadlineID, tenantID)
	if err != nil {
		return fmt.Errorf("loading deadline: %w", err)
	}

	// Check if remote changed (etag mismatch)
	if d.CalDAVEtag != nil && *d.CalDAVEtag == remoteEtag {
		return nil // No change
	}

	// CalDAV wins for description/notes
	description, _ := comp.Props.Text(ical.PropDescription)
	hasConflict := false

	if description != "" {
		existingDesc := ""
		if d.Description != nil {
			existingDesc = *d.Description
		}
		existingNotes := ""
		if d.Notes != nil {
			existingNotes = *d.Notes
		}
		// CalDAV wins for notes/description
		if description != existingDesc && description != existingNotes {
			hasConflict = true
			_, err = s.db.Exec(`UPDATE deadlines SET notes = $1, caldav_etag = $2, updated_at = NOW()
				WHERE id = $3 AND tenant_id = $4`, description, remoteEtag, deadlineID, tenantID)
			if err != nil {
				return fmt.Errorf("updating deadline notes: %w", err)
			}
		}
	}

	if !hasConflict {
		// Just update etag
		_, err = s.db.Exec(`UPDATE deadlines SET caldav_etag = $1, updated_at = NOW()
			WHERE id = $2 AND tenant_id = $3`, remoteEtag, deadlineID, tenantID)
		if err != nil {
			return fmt.Errorf("updating deadline etag: %w", err)
		}
	}

	// Log conflict in case_events if detected
	if hasConflict {
		s.logConflictEvent(ctx, tenantID, d.CaseID, "deadline", deadlineID, "CalDAV description updated from remote")
	}

	return nil
}

// reconcileAppointment handles conflict resolution for a pulled VEVENT.
func (s *CalDAVService) reconcileAppointment(ctx context.Context, tenantID uuid.UUID, comp *ical.Component, remoteEtag string) error {
	uid, _ := comp.Props.Text(ical.PropUID)
	appointmentID := extractIDFromUID(uid, "appointment")
	if appointmentID == uuid.Nil {
		return fmt.Errorf("invalid UID: %s", uid)
	}

	var a models.Appointment
	err := s.db.GetContext(ctx, &a, `SELECT * FROM appointments WHERE id = $1 AND tenant_id = $2`, appointmentID, tenantID)
	if err != nil {
		return fmt.Errorf("loading appointment: %w", err)
	}

	if a.CalDAVEtag != nil && *a.CalDAVEtag == remoteEtag {
		return nil
	}

	// CalDAV wins for description
	description, _ := comp.Props.Text(ical.PropDescription)
	location, _ := comp.Props.Text(ical.PropLocation)
	hasConflict := false

	updates := []string{"caldav_etag = $1", "updated_at = NOW()"}
	args := []any{remoteEtag}
	argN := 2

	if description != "" {
		existingDesc := ""
		if a.Description != nil {
			existingDesc = *a.Description
		}
		if description != existingDesc {
			hasConflict = true
			updates = append(updates, fmt.Sprintf("description = $%d", argN))
			args = append(args, description)
			argN++
		}
	}
	if location != "" {
		existingLoc := ""
		if a.Location != nil {
			existingLoc = *a.Location
		}
		if location != existingLoc {
			hasConflict = true
			updates = append(updates, fmt.Sprintf("location = $%d", argN))
			args = append(args, location)
			argN++
		}
	}

	args = append(args, appointmentID, tenantID)
	query := fmt.Sprintf("UPDATE appointments SET %s WHERE id = $%d AND tenant_id = $%d",
		strings.Join(updates, ", "), argN, argN+1)

	if _, err := s.db.ExecContext(ctx, query, args...); err != nil {
		return fmt.Errorf("updating appointment: %w", err)
	}

	if hasConflict {
		caseID := uuid.Nil
		if a.CaseID != nil {
			caseID = *a.CaseID
		}
		s.logConflictEvent(ctx, tenantID, caseID, "appointment", appointmentID, "CalDAV description/location updated from remote")
	}

	return nil
}

// --- DB helpers ---

func (s *CalDAVService) loadDeadlines(tenantID uuid.UUID) ([]models.Deadline, error) {
	var deadlines []models.Deadline
	err := s.db.Select(&deadlines, `SELECT id, tenant_id, case_id, title, description, due_date,
		original_due_date, warning_date, source, rule_id, status, completed_at,
		caldav_uid, caldav_etag, notes, created_at, updated_at
		FROM deadlines WHERE tenant_id = $1`, tenantID)
	return deadlines, err
}

func (s *CalDAVService) loadAppointments(ctx context.Context, tenantID uuid.UUID) ([]models.Appointment, error) {
	var appointments []models.Appointment
	err := s.db.SelectContext(ctx, &appointments, "SELECT * FROM appointments WHERE tenant_id = $1", tenantID)
	return appointments, err
}

func (s *CalDAVService) updateDeadlineCalDAV(id uuid.UUID, calDAVUID, etag string) error {
	_, err := s.db.Exec(`UPDATE deadlines SET caldav_uid = $1, caldav_etag = $2, updated_at = NOW()
		WHERE id = $3`, calDAVUID, etag, id)
	return err
}

func (s *CalDAVService) updateAppointmentCalDAV(id uuid.UUID, calDAVUID, etag string) error {
	_, err := s.db.Exec(`UPDATE appointments SET caldav_uid = $1, caldav_etag = $2, updated_at = NOW()
		WHERE id = $3`, calDAVUID, etag, id)
	return err
}

func (s *CalDAVService) logConflictEvent(ctx context.Context, tenantID, caseID uuid.UUID, objectType string, objectID uuid.UUID, msg string) {
	if caseID == uuid.Nil {
		return
	}
	metadata, _ := json.Marshal(map[string]string{
		"object_type": objectType,
		"object_id":   objectID.String(),
		"source":      "caldav_sync",
	})
	_, err := s.db.ExecContext(ctx, `INSERT INTO case_events (id, tenant_id, case_id, event_type, title, description, metadata, created_at, updated_at)
		VALUES ($1, $2, $3, 'caldav_conflict', $4, $5, $6, NOW(), NOW())`,
		uuid.New(), tenantID, caseID, "CalDAV sync conflict", msg, metadata)
	if err != nil {
		slog.Error("CalDAV: failed to log conflict event", "error", err)
	}
}

// --- UID helpers ---

func deadlineUID(id uuid.UUID) string {
	return fmt.Sprintf("kanzlai-deadline-%s@%s", id, calDAVDomain)
}

func appointmentUID(id uuid.UUID) string {
	return fmt.Sprintf("kanzlai-appointment-%s@%s", id, calDAVDomain)
}

func isKanzlAIUID(uid, objectType string) bool {
	return strings.HasPrefix(uid, "kanzlai-"+objectType+"-") && strings.HasSuffix(uid, "@"+calDAVDomain)
}

func extractIDFromUID(uid, objectType string) uuid.UUID {
	prefix := "kanzlai-" + objectType + "-"
	suffix := "@" + calDAVDomain
	if !strings.HasPrefix(uid, prefix) || !strings.HasSuffix(uid, suffix) {
		return uuid.Nil
	}
	idStr := uid[len(prefix) : len(uid)-len(suffix)]
	id, err := uuid.Parse(idStr)
	if err != nil {
		return uuid.Nil
	}
	return id
}

func calendarObjectPath(calendarPath, uid string) string {
	path := strings.TrimSuffix(calendarPath, "/")
	return path + "/" + uid + ".ics"
}