/** 纯数字 @qq.com（大小写不敏感）→ QQ 号码，用于与后端一致的展示逻辑 */

export function qqUinFromEmail(email) {
  if (!email || typeof email !== "string") return "";
  const e = email.trim().toLowerCase();
  const at = e.lastIndexOf("@");
  if (at <= 0 || at >= e.length - 1) return "";
  const local = e.slice(0, at);
  const domain = e.slice(at + 1);
  if (domain !== "qq.com" || !local) return "";
  if (!/^\d+$/.test(local)) return "";
  return local;
}

export function qqUinFromUser(user) {
  if (!user || typeof user !== "object") return "";
  const primary = qqUinFromEmail(user.email);
  if (primary) return primary;
  for (const em of user.secondaryEmails || []) {
    const u = qqUinFromEmail(em);
    if (u) return u;
  }
  return "";
}

/** 与后端 ResolvedAvatarURL 一致的三档 QQ CDN（依次作为 img onError 回退） */
export function qqAvatarUrlCandidates(uin) {
  if (!uin) return [];
  return [
    `https://q.qlogo.cn/headimg_dl?dst_uin=${encodeURIComponent(uin)}&spec=640&img_type=jpg`,
    `https://q1.qlogo.cn/g?b=qq&nk=${encodeURIComponent(uin)}&s=100`,
    `https://q2.qlogo.cn/headimg_dl?dst_uin=${encodeURIComponent(uin)}&spec=100`
  ];
}

export function placeholderAvatarUrl(size) {
  return `https://dummyimage.com/${size}x${size}/ddd/fff&text=Avatar`;
}

/** 用于 <img src>：自选链接优先，否则 QQ 邮箱推断的多 CDN，否则 API 下发的 avatarUrl，最后占位图 */
export function avatarImageCandidates(user, placeholderSize = 120) {
  const custom = (user?.customAvatarUrl != null && String(user.customAvatarUrl).trim()) || "";
  if (custom) return [custom];
  const uin = qqUinFromUser(user);
  if (uin) return qqAvatarUrlCandidates(uin);
  const resolved = (user?.avatarUrl != null && String(user.avatarUrl).trim()) || "";
  if (resolved) return [resolved];
  return [placeholderAvatarUrl(placeholderSize)];
}

export function resolveDisplayAvatarUrl(user, placeholderSize = 120) {
  const c = avatarImageCandidates(user, placeholderSize);
  return c[0] || placeholderAvatarUrl(placeholderSize);
}

export function avatarStatusLabel(user) {
  const custom = (user?.customAvatarUrl != null && String(user.customAvatarUrl).trim()) || "";
  if (custom) return "已设置";
  if (qqUinFromUser(user)) return "QQ 邮箱头像";
  return "未填写";
}