// 后端按北京时间存储(无时区标记)，此处显式按 Asia/Shanghai 渲染，
// 避免浏览器本地时区导致时间显示错乱。
export function formatBjTime(t?: string | null): string {
  if (!t) return '-';
  const iso = /[Z+]/.test(t) ? t : t + '+08:00';
  const d = new Date(iso);
  if (isNaN(d.getTime())) return t;
  return d.toLocaleString('zh-CN', { timeZone: 'Asia/Shanghai', hour12: false });
}

// 仅日期（北京时间）
export function formatBjDate(t?: string | null): string {
  if (!t) return '-';
  const iso = /[Z+]/.test(t) ? t : t + '+08:00';
  const d = new Date(iso);
  if (isNaN(d.getTime())) return t;
  return d.toLocaleDateString('zh-CN', { timeZone: 'Asia/Shanghai' });
}

// 将任意 Date 换算为「北京墙钟」对应的 UTC 视图，便于按北京日历日比较
function toBjView(d: Date): Date {
  return new Date(d.getTime() + (d.getTimezoneOffset() + 480) * 60000);
}

// 聊天消息时间：今天 HH:MM / 昨天 HH:MM / MM-DD HH:MM / YYYY-MM-DD HH:MM（北京时间）
export function formatChatTime(iso?: string | null): string {
  if (!iso) return '';
  const s = /[Z+]/.test(iso) ? iso : iso + '+08:00';
  const d = new Date(s);
  if (isNaN(d.getTime())) return '';
  const bj = toBjView(d);
  const nowBj = toBjView(new Date());
  const dayDiff = Math.floor(nowBj.getTime() / 86400000) - Math.floor(bj.getTime() / 86400000);
  const hhmm = d.toLocaleTimeString('zh-CN', { timeZone: 'Asia/Shanghai', hour: '2-digit', minute: '2-digit' });
  if (dayDiff <= 0) return hhmm;
  if (dayDiff === 1) return '昨天 ' + hhmm;
  const md = d.toLocaleDateString('zh-CN', { timeZone: 'Asia/Shanghai', month: '2-digit', day: '2-digit' });
  if (bj.getUTCFullYear() === nowBj.getUTCFullYear()) return md + ' ' + hhmm;
  return d.toLocaleDateString('zh-CN', { timeZone: 'Asia/Shanghai', year: 'numeric', month: '2-digit', day: '2-digit' }) + ' ' + hhmm;
}