package bookings

import (
	"context"
	"crypto/subtle"
	"errors"
	"fmt"
	"strings"
	"time"

	"bookra/apps/backend/internal/db"
	"bookra/apps/backend/internal/domain"
	"bookra/apps/backend/internal/notifications"
)

var (
	ErrInvalidReschedule = errors.New("invalid reschedule request")
	ErrBookingCancelled  = errors.New("booking already cancelled")
	ErrUnauthorized      = errors.New("unauthorized access")
)

type CustomerService struct {
	repo        db.Repository
	notifier    CustomerNotifier
	frontendURL string
}

type CustomerNotifier interface {
	SendBookingConfirmation(ctx context.Context, data notifications.BookingEmailData) error
	SendBookingReschedule(ctx context.Context, data notifications.BookingEmailData) error
	SendBookingCancellation(ctx context.Context, data notifications.BookingEmailData) error
}

func NewCustomerService(repo db.Repository, notifier CustomerNotifier, frontendURL string) *CustomerService {
	if notifier == nil {
		notifier = &customerNoopNotifier{}
	}
	if frontendURL == "" {
		frontendURL = "http://localhost:3000"
	}
	return &CustomerService{repo: repo, notifier: notifier, frontendURL: strings.TrimRight(frontendURL, "/")}
}

type customerNoopNotifier struct{}

func (n *customerNoopNotifier) SendBookingConfirmation(ctx context.Context, data notifications.BookingEmailData) error {
	return nil
}

func (n *customerNoopNotifier) SendBookingReschedule(ctx context.Context, data notifications.BookingEmailData) error {
	return nil
}

func (n *customerNoopNotifier) SendBookingCancellation(ctx context.Context, data notifications.BookingEmailData) error {
	return nil
}

// authorize compares the caller-supplied management token against the stored
// per-booking token in constant time. Bookings without a token (created before
// the feature) cannot be managed through the public endpoints.
func authorize(booking db.BookingRecord, token string) error {
	if booking.ManageToken == "" || token == "" {
		return ErrUnauthorized
	}
	if subtle.ConstantTimeCompare([]byte(token), []byte(booking.ManageToken)) != 1 {
		return ErrUnauthorized
	}
	return nil
}

func (s *CustomerService) managementURL(booking db.BookingRecord) string {
	return fmt.Sprintf("%s/manage/%s?token=%s", s.frontendURL, booking.Reference, booking.ManageToken)
}

func (s *CustomerService) descriptors(ctx context.Context, booking db.BookingRecord) (serviceName string, locationName string) {
	if booking.ServiceID == nil && booking.ClassSessionID != nil {
		// Class bookings carry no service; the session title is the label.
		if session, err := s.repo.GetClassSessionByID(ctx, *booking.ClassSessionID); err == nil {
			serviceName = session.Title
		}
	}
	if booking.ServiceID != nil {
		if services, err := s.repo.ListServicesByTenant(ctx, booking.TenantID); err == nil {
			for _, service := range services {
				if service.ID == *booking.ServiceID {
					serviceName = service.Name
					break
				}
			}
		}
	}
	if booking.LocationID != nil {
		if location, err := s.repo.GetLocationByID(ctx, *booking.LocationID); err == nil {
			locationName = location.Name
		}
	}
	return serviceName, locationName
}

// GetBookingByReference returns booking details for customer management link
func (s *CustomerService) GetBookingByReference(ctx context.Context, reference string, token string) (domain.CustomerBookingView, error) {
	booking, err := s.repo.GetBookingByReference(ctx, reference)
	if err != nil {
		return domain.CustomerBookingView{}, ErrBookingNotFound
	}
	if err := authorize(booking, token); err != nil {
		return domain.CustomerBookingView{}, err
	}

	tenant, err := s.repo.GetTenantByID(ctx, booking.TenantID)
	if err != nil {
		return domain.CustomerBookingView{}, err
	}

	serviceName, locationName := s.descriptors(ctx, booking)

	position := 0
	if booking.Status == "waitlisted" && booking.ClassSessionID != nil {
		position, _ = s.repo.GetWaitlistPosition(ctx, *booking.ClassSessionID, booking.ID)
	}

	return domain.CustomerBookingView{
		Reference:        booking.Reference,
		CustomerName:     booking.CustomerName,
		CustomerEmail:    booking.CustomerEmail,
		Service:          serviceName,
		BusinessName:     tenant.Name,
		TenantSlug:       tenant.Slug,
		ServiceID:        booking.ServiceID,
		StaffID:          booking.StaffID,
		ClassSessionID:   booking.ClassSessionID,
		StartsAt:         booking.StartsAt,
		EndsAt:           booking.EndsAt,
		Location:         locationName,
		Status:           booking.Status,
		Notes:            booking.Notes,
		WaitlistPosition: position,
	}, nil
}

// RescheduleBooking allows customers to reschedule their booking
func (s *CustomerService) RescheduleBooking(ctx context.Context, reference string, req domain.RescheduleBookingRequest, token string) error {
	booking, err := s.repo.GetBookingByReference(ctx, reference)
	if err != nil {
		return ErrBookingNotFound
	}
	if err := authorize(booking, token); err != nil {
		return err
	}

	if booking.Status == "cancelled" {
		return ErrBookingCancelled
	}

	// Only live bookings may move: waitlisted entries sit in a queue tied to
	// their session, and completed bookings are history.
	if booking.Status == "waitlisted" || booking.Status == "completed" {
		return ErrInvalidReschedule
	}

	// Class bookings are bound to their session window; moving to another
	// session means cancelling and booking again.
	if booking.ClassSessionID != nil {
		return ErrInvalidReschedule
	}

	newStartsAt, err := time.Parse(time.RFC3339, req.NewStartsAt)
	if err != nil {
		return ErrInvalidReschedule
	}

	newEndsAt, err := time.Parse(time.RFC3339, req.NewEndsAt)
	if err != nil {
		return ErrInvalidReschedule
	}

	if !newEndsAt.After(newStartsAt) {
		return ErrInvalidReschedule
	}

	if newStartsAt.Before(time.Now().UTC()) {
		return ErrInvalidReschedule
	}

	// Re-check resource conflicts at the requested window, excluding self.
	existing, err := s.repo.ListBookingsByTenantBetween(ctx, booking.TenantID, newStartsAt, newEndsAt)
	if err != nil {
		return err
	}
	for _, other := range existing {
		if other.ID == booking.ID || other.Status == "cancelled" || other.Status == "waitlisted" {
			continue
		}
		if resourcesCollide(other, booking.StaffID, booking.LocationID) {
			return ErrBookingConflict
		}
	}

	// Appointments must land inside bookable hours and off blocked days.
	// Class bookings never reach this point — rejected above.
	tenant, err := s.repo.GetTenantByID(ctx, booking.TenantID)
	if err != nil {
		return err
	}
	if err := validateAppointmentTarget(ctx, s.repo, tenant, booking.StaffID, booking.LocationID, newStartsAt, newEndsAt); err != nil {
		return ErrInvalidReschedule
	}

	if err := s.repo.RescheduleBooking(ctx, booking.ID, newStartsAt, newEndsAt); err != nil {
		if db.IsExclusionViolation(err) {
			return ErrBookingConflict
		}
		return err
	}

	// Re-arm the reminder for the new time; a booking moved inside the
	// no-reminder horizon simply gets none.
	if err := s.repo.DeletePendingReminderJobsForBooking(ctx, booking.ID); err == nil {
		if scheduledFor, ok := reminderSchedule(newStartsAt); ok {
			_ = s.repo.CreateReminderJob(ctx, db.ReminderJobParams{
				TenantID:     booking.TenantID,
				BookingID:    booking.ID,
				Channel:      "email",
				ScheduledFor: scheduledFor,
			})
		}
	}

	serviceName, _ := s.descriptors(ctx, booking)
	_ = s.repo.AppendActivityEvent(ctx, db.ActivityEventParams{
		TenantID:   booking.TenantID,
		ActorKind:  "customer",
		ActorName:  booking.CustomerName,
		Action:     "booking.rescheduled",
		EntityType: "booking",
		EntityID:   &booking.ID,
		Summary:    booking.CustomerName + " — " + serviceName,
	})

	// Send reschedule email (async)
	go s.sendRescheduleEmail(booking, newStartsAt, newEndsAt)

	return nil
}

// CancelBooking allows customers to cancel their booking
func (s *CustomerService) CancelBooking(ctx context.Context, reference string, token string) error {
	booking, err := s.repo.GetBookingByReference(ctx, reference)
	if err != nil {
		return ErrBookingNotFound
	}
	if err := authorize(booking, token); err != nil {
		return err
	}

	if booking.Status == "cancelled" {
		return ErrBookingCancelled
	}

	if err := s.repo.UpdateBookingStatus(ctx, booking.ID, "cancelled"); err != nil {
		return err
	}
	_ = s.repo.CancelPendingReminderJobsForBooking(ctx, booking.ID)
	serviceName, _ := s.descriptors(ctx, booking)
	_ = s.repo.AppendActivityEvent(ctx, db.ActivityEventParams{
		TenantID:   booking.TenantID,
		ActorKind:  "customer",
		ActorName:  booking.CustomerName,
		Action:     "booking.cancelled",
		EntityType: "booking",
		EntityID:   &booking.ID,
		Summary:    booking.CustomerName + " — " + serviceName,
	})

	// Send cancellation email (async)
	go s.sendCancellationEmail(booking)

	// A freed class seat promotes the earliest waitlisted booking.
	if booking.ClassSessionID != nil {
		if promoted, err := PromoteWaitlist(ctx, s.repo, booking.TenantID, *booking.ClassSessionID); err == nil {
			for _, promotedBooking := range promoted {
				go s.sendPromotionEmail(promotedBooking)
			}
		}
	}

	return nil
}

func (s *CustomerService) sendRescheduleEmail(booking db.BookingRecord, newStartsAt, newEndsAt time.Time) {
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	tenant, err := s.repo.GetTenantByID(ctx, booking.TenantID)
	if err != nil {
		return
	}

	brand, _ := s.repo.GetBrandProfile(ctx, tenant.ID)
	brandColor := brand.PrimaryColor
	if brandColor == "" {
		brandColor = "#a65c3e"
	}

	serviceName, locationName := s.descriptors(ctx, booking)

	emailData := notifications.BookingEmailData{
		TenantID:      tenant.ID,
		TenantName:    tenant.Name,
		TenantSlug:    tenant.Slug,
		BrandColor:    brandColor,
		CustomerName:  booking.CustomerName,
		CustomerEmail: booking.CustomerEmail,
		Service:       serviceName,
		Location:      locationName,
		Reference:     booking.Reference,
		StartsAt:      newStartsAt,
		EndsAt:        newEndsAt,
		Timezone:      tenant.Timezone,
		Locale:        tenant.Locale,
		ManagementURL: s.managementURL(booking),
	}

	s.notifier.SendBookingReschedule(ctx, emailData)
}

func (s *CustomerService) sendCancellationEmail(booking db.BookingRecord) {
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	tenant, err := s.repo.GetTenantByID(ctx, booking.TenantID)
	if err != nil {
		return
	}

	brand, _ := s.repo.GetBrandProfile(ctx, tenant.ID)
	brandColor := brand.PrimaryColor
	if brandColor == "" {
		brandColor = "#a65c3e"
	}

	serviceName, locationName := s.descriptors(ctx, booking)

	emailData := notifications.BookingEmailData{
		TenantID:      tenant.ID,
		TenantName:    tenant.Name,
		TenantSlug:    tenant.Slug,
		BrandColor:    brandColor,
		CustomerName:  booking.CustomerName,
		CustomerEmail: booking.CustomerEmail,
		Service:       serviceName,
		Location:      locationName,
		Reference:     booking.Reference,
		StartsAt:      booking.StartsAt,
		EndsAt:        booking.EndsAt,
		Timezone:      tenant.Timezone,
		Locale:        tenant.Locale,
		ManagementURL: "",
	}

	s.notifier.SendBookingCancellation(ctx, emailData)
}

// sendPromotionEmail confirms a booking that moved off the class waitlist.
func (s *CustomerService) sendPromotionEmail(booking db.BookingRecord) {
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	tenant, err := s.repo.GetTenantByID(ctx, booking.TenantID)
	if err != nil {
		return
	}
	brand, _ := s.repo.GetBrandProfile(ctx, tenant.ID)
	brandColor := brand.PrimaryColor
	if brandColor == "" {
		brandColor = "#a65c3e"
	}
	serviceName, locationName := s.descriptors(ctx, booking)

	s.notifier.SendBookingConfirmation(ctx, notifications.BookingEmailData{
		TenantID:      tenant.ID,
		TenantName:    tenant.Name,
		TenantSlug:    tenant.Slug,
		BrandColor:    brandColor,
		CustomerName:  booking.CustomerName,
		CustomerEmail: booking.CustomerEmail,
		Service:       serviceName,
		Location:      locationName,
		Reference:     booking.Reference,
		StartsAt:      booking.StartsAt,
		EndsAt:        booking.EndsAt,
		Timezone:      tenant.Timezone,
		Locale:        tenant.Locale,
		ManagementURL: s.managementURL(booking),
	})
}

// classBookingForMove returns the booking and its current session when the
// record is a live class booking, or an error explaining why it cannot move.
func (s *CustomerService) classBookingForMove(ctx context.Context, reference string, token string) (db.BookingRecord, db.ClassSessionRecord, error) {
	booking, err := s.repo.GetBookingByReference(ctx, reference)
	if err != nil {
		return db.BookingRecord{}, db.ClassSessionRecord{}, ErrBookingNotFound
	}
	if err := authorize(booking, token); err != nil {
		return db.BookingRecord{}, db.ClassSessionRecord{}, err
	}
	if booking.Status == "cancelled" {
		return db.BookingRecord{}, db.ClassSessionRecord{}, ErrBookingCancelled
	}
	if booking.ClassSessionID == nil || (booking.Status != "confirmed" && booking.Status != "waitlisted") {
		return db.BookingRecord{}, db.ClassSessionRecord{}, ErrInvalidReschedule
	}
	session, err := s.repo.GetClassSessionByID(ctx, *booking.ClassSessionID)
	if err != nil {
		return db.BookingRecord{}, db.ClassSessionRecord{}, ErrInvalidReschedule
	}
	return booking, session, nil
}

// ListSessionMoveTargets returns upcoming sessions of the same class template
// the customer could move to, with live capacity info for the picker.
func (s *CustomerService) ListSessionMoveTargets(ctx context.Context, reference string, token string) ([]domain.SessionMoveTarget, error) {
	booking, session, err := s.classBookingForMove(ctx, reference, token)
	if err != nil {
		return nil, err
	}

	now := time.Now().UTC()
	sessions, err := s.repo.ListClassSessionsByTenant(ctx, booking.TenantID, now, 50)
	if err != nil {
		return nil, err
	}
	locations, _ := s.repo.ListLocationsByTenant(ctx, booking.TenantID)
	locationNames := map[string]string{}
	for _, location := range locations {
		locationNames[location.ID] = location.Name
	}

	var targets []domain.SessionMoveTarget
	for _, candidate := range sessions {
		if candidate.ID == session.ID || candidate.TemplateID != session.TemplateID {
			continue
		}
		if !candidate.StartsAt.After(now) {
			continue
		}
		bookings, err := s.repo.ListBookingsBySession(ctx, candidate.ID)
		if err != nil {
			return nil, err
		}
		confirmed, waitlisted := 0, 0
		for _, other := range bookings {
			switch other.Status {
			case "confirmed":
				confirmed++
			case "waitlisted":
				waitlisted++
			}
		}
		location := ""
		if candidate.LocationID != nil {
			location = locationNames[*candidate.LocationID]
		}
		targets = append(targets, domain.SessionMoveTarget{
			SessionID:      candidate.ID,
			Title:          candidate.Title,
			StartsAt:       candidate.StartsAt,
			EndsAt:         candidate.EndsAt,
			Location:       location,
			Capacity:       candidate.Capacity,
			ConfirmedCount: confirmed,
			WaitlistCount:  waitlisted,
			Remaining:      int(candidate.Capacity) - confirmed,
		})
	}
	return targets, nil
}

// MoveBookingToSession retargets a class booking to another session of the
// same template. The freed spot (confirmed or queue position) is released on
// the old session — a confirmed move also drains its waitlist — and the
// booking is re-seated or re-queued on the target.
func (s *CustomerService) MoveBookingToSession(ctx context.Context, reference string, token string, targetSessionID string) (domain.MoveBookingResponse, error) {
	booking, currentSession, err := s.classBookingForMove(ctx, reference, token)
	if err != nil {
		return domain.MoveBookingResponse{}, err
	}

	target, err := s.repo.GetClassSessionByID(ctx, targetSessionID)
	if err != nil {
		return domain.MoveBookingResponse{}, ErrInvalidReschedule
	}
	if target.TenantID != booking.TenantID || target.TemplateID != currentSession.TemplateID || target.ID == currentSession.ID {
		return domain.MoveBookingResponse{}, ErrInvalidReschedule
	}
	if !target.StartsAt.After(time.Now().UTC()) {
		return domain.MoveBookingResponse{}, ErrInvalidReschedule
	}

	targetBookings, err := s.repo.ListBookingsBySession(ctx, target.ID)
	if err != nil {
		return domain.MoveBookingResponse{}, err
	}
	confirmed, waitlisted := 0, 0
	for _, other := range targetBookings {
		switch other.Status {
		case "confirmed":
			confirmed++
		case "waitlisted":
			waitlisted++
		}
	}

	wasConfirmed := booking.Status == "confirmed"
	newStatus := "confirmed"
	if target.Capacity > 0 && confirmed >= int(target.Capacity) {
		newStatus = "waitlisted"
	}

	// Release the old spot first so the seat/queue position is free before
	// the retarget lands.
	if booking.Status == "waitlisted" {
		_ = s.repo.ResolveWaitlistEntry(ctx, booking.TenantID, currentSession.ID, booking.CustomerEmail)
	}
	if err := s.repo.UpdateBookingSession(ctx, booking.ID, target.ID, target.StartsAt, target.EndsAt, newStatus); err != nil {
		return domain.MoveBookingResponse{}, err
	}
	if newStatus == "waitlisted" {
		if err := s.repo.AppendWaitlistEntry(ctx, db.WaitlistEntryParams{
			TenantID:       booking.TenantID,
			ClassSessionID: target.ID,
			CustomerName:   booking.CustomerName,
			CustomerEmail:  booking.CustomerEmail,
			Position:       waitlisted + 1,
		}); err != nil {
			return domain.MoveBookingResponse{}, err
		}
	}

	// Re-arm reminders for the new window (confirmed only; a queue spot
	// re-arms on promotion through the shared confirm path).
	if err := s.repo.DeletePendingReminderJobsForBooking(ctx, booking.ID); err == nil && newStatus == "confirmed" {
		_ = armReminderJobs(ctx, s.repo, booking.TenantID, booking.ID, target.StartsAt, booking.CustomerPhone)
	}

	// A confirmed move frees a seat on the old session — drain its queue.
	if wasConfirmed {
		if promoted, err := PromoteWaitlist(ctx, s.repo, booking.TenantID, currentSession.ID); err == nil {
			for _, promotedBooking := range promoted {
				go s.sendPromotionEmail(promotedBooking)
			}
		}
	}

	updated := booking
	updated.ClassSessionID = &target.ID
	_ = s.repo.AppendActivityEvent(ctx, db.ActivityEventParams{
		TenantID:   booking.TenantID,
		ActorKind:  "customer",
		ActorName:  booking.CustomerName,
		Action:     "booking.moved",
		EntityType: "booking",
		EntityID:   &booking.ID,
		Summary:    booking.CustomerName + " — " + target.Title,
	})
	go s.sendRescheduleEmail(updated, target.StartsAt, target.EndsAt)

	return domain.MoveBookingResponse{Status: newStatus}, nil
}