export interface SystemTimezoneOption {
  value: string;
}

const PRIMARY_SYSTEM_TIMEZONE_OPTIONS: SystemTimezoneOption[] = [
  { value: 'Asia/Shanghai' },
  { value: 'Europe/London' },
  { value: 'Europe/Berlin' },
  { value: 'America/New_York' },
  { value: 'America/Los_Angeles' },
  { value: 'Asia/Tokyo' },
];

export function getSystemTimezoneOptions(currentValue?: string): SystemTimezoneOption[] {
  const normalized = String(currentValue || '').trim();
  if (!normalized) {
    return [...PRIMARY_SYSTEM_TIMEZONE_OPTIONS];
  }
  if (PRIMARY_SYSTEM_TIMEZONE_OPTIONS.some((option) => option.value === normalized)) {
    return [...PRIMARY_SYSTEM_TIMEZONE_OPTIONS];
  }
  return [
    {
      value: normalized,
    },
    ...PRIMARY_SYSTEM_TIMEZONE_OPTIONS,
  ];
}