/** 格式化为 Asia/Shanghai：2026-08-03 15:14:30（不依赖 Intl，兼容微信小程序） */
export function formatShanghaiDateTime(input?: string | Date | null): string {
  if (input == null || input === '') return '—';
  if (typeof input === 'string') {
    const s = input.trim();
    if (/^\d{4}-\d{2}-\d{2}[ T]\d{2}:\d{2}/.test(s)) {
      return s.slice(0, 19).replace('T', ' ');
    }
  }
  const d = input instanceof Date ? input : new Date(input);
  if (Number.isNaN(d.getTime())) return '—';
  // 用 UTC 读数 + 固定东八区偏移，避免依赖 Intl / 设备时区 API 差异
  const sh = new Date(d.getTime() + 8 * 60 * 60 * 1000);
  const p = (n: number) => String(n).padStart(2, '0');
  return `${sh.getUTCFullYear()}-${p(sh.getUTCMonth() + 1)}-${p(sh.getUTCDate())} ${p(sh.getUTCHours())}:${p(sh.getUTCMinutes())}:${p(sh.getUTCSeconds())}`;
}