export function parseStoredDate(value: string) {
  const trimmed = value.trim();
  const normalized = /^\d{4}-\d{2}-\d{2}$/.test(trimmed)
    ? `${trimmed}T00:00:00+08:00`
    : /^\d{4}-\d{2}-\d{2}[ T]\d{2}:\d{2}(?::\d{2}(?:\.\d+)?)?$/.test(
          trimmed,
        )
      ? `${trimmed.replace(" ", "T")}Z`
      : trimmed;
  return new Date(normalized);
}

export function formatShanghaiDate(
  value: string | null | undefined,
  withTime = false,
) {
  if (!value) return "—";
  const date = parseStoredDate(value);
  if (Number.isNaN(date.getTime())) return value;
  return new Intl.DateTimeFormat("zh-CN", {
    timeZone: "Asia/Shanghai",
    month: "2-digit",
    day: "2-digit",
    ...(withTime ? { hour: "2-digit", minute: "2-digit" } : {}),
  }).format(date);
}

export function formatShanghaiToday(value: Date | number = Date.now()) {
  const date = value instanceof Date ? value : new Date(value);
  const parts = new Intl.DateTimeFormat("zh-CN", {
    timeZone: "Asia/Shanghai",
    month: "numeric",
    day: "numeric",
  }).formatToParts(date);
  const calendar = Object.fromEntries(
    parts.map((part) => [part.type, part.value]),
  );
  return `${calendar.month}月${calendar.day}日`;
}