import { format, parseISO, differenceInCalendarDays, isValid } from 'date-fns';
import { de } from 'date-fns/locale';
import type { ExpirationWarningStatus } from '@/types/domain';

export function formatDateGerman(dateStr: string | Date | null | undefined): string {
  if (!dateStr) return '-';
  const date = typeof dateStr === 'string' ? parseISO(dateStr) : dateStr;
  if (!isValid(date)) return '-';
  return format(date, 'dd.MM.yyyy', { locale: de });
}

export function formatDateTimeGerman(dateStr: string | Date | null | undefined): string {
  if (!dateStr) return '-';
  const date = typeof dateStr === 'string' ? parseISO(dateStr) : dateStr;
  if (!isValid(date)) return '-';
  return format(date, 'dd.MM.yyyy HH:mm', { locale: de });
}

export function getExpirationStatus(expirationDateStr: string | null | undefined): ExpirationWarningStatus {
  if (!expirationDateStr) {
    return { status: 'OK', label: 'Kein Ablaufdatum', daysRemaining: null };
  }

  const expDate = parseISO(expirationDateStr);
  if (!isValid(expDate)) {
    return { status: 'OK', label: 'Kein Ablaufdatum', daysRemaining: null };
  }

  const today = new Date();
  const daysDiff = differenceInCalendarDays(expDate, today);

  if (daysDiff < 0) {
    return {
      status: 'EXPIRED',
      label: `Abgelaufen (${Math.abs(daysDiff)} Tag${Math.abs(daysDiff) === 1 ? '' : 'e'})`,
      daysRemaining: daysDiff,
    };
  }
  if (daysDiff === 0) {
    return { status: 'TODAY', label: 'Läuft heute ab', daysRemaining: 0 };
  }
  if (daysDiff <= 3) {
    return { status: 'IN_3_DAYS', label: `Läuft in ${daysDiff} Tagen ab`, daysRemaining: daysDiff };
  }
  if (daysDiff <= 7) {
    return { status: 'IN_7_DAYS', label: `Läuft in ${daysDiff} Tagen ab`, daysRemaining: daysDiff };
  }
  if (daysDiff <= 14) {
    return { status: 'IN_14_DAYS', label: `Läuft in ${daysDiff} Tagen ab`, daysRemaining: daysDiff };
  }

  return { status: 'OK', label: `Haltbar bis ${formatDateGerman(expDate)}`, daysRemaining: daysDiff };
}