package export

import (
	"context"
	"encoding/csv"
	"errors"
	"io"
	"strconv"
	"time"

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

var ErrTenantMembership = errors.New("tenant membership not found")

// utf8BOM lets Excel detect the encoding for Czech diacritics.
var utf8BOM = []byte{0xEF, 0xBB, 0xBF}

const customerPageSize = 500

type Service struct {
	repo     db.Repository
	bookings *bookings.Service
}

func NewService(repo db.Repository, bookingsService *bookings.Service) *Service {
	return &Service{repo: repo, bookings: bookingsService}
}

func (s *Service) tenantFor(ctx context.Context, principal domain.Principal) (db.TenantRecord, error) {
	membership, err := s.repo.GetTenantMembershipBySubject(ctx, principal.Subject)
	if err != nil {
		return db.TenantRecord{}, ErrTenantMembership
	}
	return membership.Tenant, nil
}

// WriteBookingsCSV streams every tenant booking in [from, to) as CSV rows.
// Service labels resolve to service names for appointments and session titles
// for classes, matching how the rest of the app labels them.
func (s *Service) WriteBookingsCSV(ctx context.Context, principal domain.Principal, w io.Writer, from, to time.Time) error {
	tenant, err := s.tenantFor(ctx, principal)
	if err != nil {
		return err
	}

	bookings, err := s.repo.ListBookingsByTenantBetween(ctx, tenant.ID, from, to)
	if err != nil {
		return err
	}
	services, err := s.repo.ListServicesByTenant(ctx, tenant.ID)
	if err != nil {
		return err
	}
	sessions, err := s.repo.ListClassSessionsByTenant(ctx, tenant.ID, from, 10000)
	if err != nil {
		return err
	}
	staff, err := s.repo.ListStaffByTenant(ctx, tenant.ID)
	if err != nil {
		return err
	}
	locations, err := s.repo.ListLocationsByTenant(ctx, tenant.ID)
	if err != nil {
		return err
	}

	serviceNames := make(map[string]string, len(services))
	for _, service := range services {
		serviceNames[service.ID] = service.Name
	}
	sessionTitles := make(map[string]string, len(sessions))
	for _, session := range sessions {
		sessionTitles[session.ID] = session.Title
	}
	staffNames := make(map[string]string, len(staff))
	for _, member := range staff {
		staffNames[member.ID] = member.DisplayName
	}
	locationNames := make(map[string]string, len(locations))
	for _, location := range locations {
		locationNames[location.ID] = location.Name
	}

	if _, err := w.Write(utf8BOM); err != nil {
		return err
	}
	out := csv.NewWriter(w)
	defer out.Flush()

	if err := out.Write([]string{
		"reference", "status", "customer_name", "customer_email", "customer_phone",
		"service", "staff", "location", "starts_at", "ends_at", "created_at", "notes",
	}); err != nil {
		return err
	}
	for _, booking := range bookings {
		label := ""
		if booking.ServiceID != nil {
			label = serviceNames[*booking.ServiceID]
		}
		if booking.ClassSessionID != nil {
			label = sessionTitles[*booking.ClassSessionID]
		}
		staffName := ""
		if booking.StaffID != nil {
			staffName = staffNames[*booking.StaffID]
		}
		locationName := ""
		if booking.LocationID != nil {
			locationName = locationNames[*booking.LocationID]
		}
		if err := out.Write([]string{
			booking.Reference,
			booking.Status,
			booking.CustomerName,
			booking.CustomerEmail,
			booking.CustomerPhone,
			label,
			staffName,
			locationName,
			booking.StartsAt.UTC().Format(time.RFC3339),
			booking.EndsAt.UTC().Format(time.RFC3339),
			booking.CreatedAt.UTC().Format(time.RFC3339),
			booking.Notes,
		}); err != nil {
			return err
		}
	}
	return out.Error()
}

// WriteCustomersCSV streams the tenant's full customer list, paging through
// the repository in bounded chunks.
func (s *Service) WriteCustomersCSV(ctx context.Context, principal domain.Principal, w io.Writer) error {
	tenant, err := s.tenantFor(ctx, principal)
	if err != nil {
		return err
	}

	if _, err := w.Write(utf8BOM); err != nil {
		return err
	}
	out := csv.NewWriter(w)
	defer out.Flush()

	if err := out.Write([]string{"name", "email", "phone", "status", "created_at"}); err != nil {
		return err
	}
	for offset := 0; ; offset += customerPageSize {
		page, err := s.repo.ListCustomersByTenant(ctx, tenant.ID, customerPageSize, offset)
		if err != nil {
			return err
		}
		for _, customer := range page {
			phone := ""
			if customer.Phone != nil {
				phone = *customer.Phone
			}
			if err := out.Write([]string{
				customer.Name,
				customer.Email,
				phone,
				customer.Status,
				customer.CreatedAt.UTC().Format(time.RFC3339),
			}); err != nil {
				return err
			}
		}
		if len(page) < customerPageSize {
			break
		}
	}
	return out.Error()
}

// WriteStaffReportCSV exports the per-staff performance metrics over a
// trailing window — the same numbers the dashboard performance panel shows.
func (s *Service) WriteStaffReportCSV(ctx context.Context, principal domain.Principal, w io.Writer, days int) error {
	metrics, err := s.bookings.StaffMetrics(ctx, principal, days)
	if err != nil {
		if errors.Is(err, bookings.ErrTenantMembership) {
			return ErrTenantMembership
		}
		return err
	}

	if _, err := w.Write(utf8BOM); err != nil {
		return err
	}
	out := csv.NewWriter(w)
	defer out.Flush()

	if err := out.Write([]string{
		"staff", "bookings", "completed", "cancelled",
		"booked_minutes", "capacity_minutes", "utilization_percent", "revenue_cents",
	}); err != nil {
		return err
	}
	for _, m := range metrics.Staff {
		if err := out.Write([]string{
			m.DisplayName,
			strconv.Itoa(m.Bookings),
			strconv.Itoa(m.Completed),
			strconv.Itoa(m.Cancelled),
			strconv.Itoa(m.BookedMinutes),
			strconv.Itoa(m.CapacityMinutes),
			strconv.Itoa(m.UtilizationPercent),
			strconv.FormatInt(m.RevenueCents, 10),
		}); err != nil {
			return err
		}
	}
	return out.Error()
}

// WriteServiceReportCSV exports the per-service performance metrics over a
// trailing window — the same aggregation the dashboard services panel shows.
func (s *Service) WriteServiceReportCSV(ctx context.Context, principal domain.Principal, w io.Writer, days int) error {
	metrics, err := s.bookings.ServiceMetrics(ctx, principal, days)
	if err != nil {
		if errors.Is(err, bookings.ErrTenantMembership) {
			return ErrTenantMembership
		}
		return err
	}

	if _, err := w.Write(utf8BOM); err != nil {
		return err
	}
	out := csv.NewWriter(w)
	defer out.Flush()

	if err := out.Write([]string{"service", "bookings", "completed", "cancelled", "revenue_cents"}); err != nil {
		return err
	}
	for _, m := range metrics.Services {
		if err := out.Write([]string{
			m.Name,
			strconv.Itoa(m.Bookings),
			strconv.Itoa(m.Completed),
			strconv.Itoa(m.Cancelled),
			strconv.FormatInt(m.RevenueCents, 10),
		}); err != nil {
			return err
		}
	}
	if metrics.ClassBookings > 0 {
		if err := out.Write([]string{"class sessions", strconv.Itoa(metrics.ClassBookings), "0", "0", "0"}); err != nil {
			return err
		}
	}
	return out.Error()
}