/**
 * 账号选择器（顶栏下拉）：像邮箱 app 的账号切换。
 *
 * 列表：`全部邮箱`（≥2 个可用账号时才出现——只有一个账号时它是噪声）、
 * 每个账号（带未选中点/选中勾）、`管理账号…`。
 *
 * # 为什么"全部邮箱"在只有一个可用账号时不显示
 *
 * 聚合的语义是"合并多个账号的收件箱"。只有一个账号时它与该账号等价，
 * 留着只会让人以为漏了谁。少于两个可用账号时选择器直接退化成静态标题。
 */

import { useEffect, useRef, useState } from 'react';
import { AGGREGATE_ID, isUsableAccount } from '../lib/accounts';
import { useAccountStore } from '../stores/accountStore';
import { useMailStore } from '../stores/mailStore';
import { useUIStore } from '../stores/uiStore';
import { ChevronRightIcon } from './icons';

export default function AccountSwitcher() {
  const accounts = useAccountStore(s => s.accounts);
  const activeId = useAccountStore(s => s.activeId);
  const setActive = useAccountStore(s => s.setActive);
  const fetchInbox = useMailStore(s => s.fetchInbox);
  const setViewMode = useUIStore(s => s.setViewMode);
  const [open, setOpen] = useState(false);
  const boxRef = useRef<HTMLDivElement>(null);

  const usable = accounts.filter(isUsableAccount);
  const active = usable.find(a => a.id === activeId) ?? null;
  const aggregateAvailable = usable.length >= 2;

  // 点外面 / 按 Esc 关下拉：不关的话它会盖住列表且没有明显出口
  useEffect(() => {
    if (!open) return;
    const onDown = (e: MouseEvent) => {
      if (boxRef.current && !boxRef.current.contains(e.target as Node)) setOpen(false);
    };
    const onKey = (e: KeyboardEvent) => {
      if (e.key === 'Escape') setOpen(false);
    };
    document.addEventListener('mousedown', onDown);
    document.addEventListener('keydown', onKey);
    return () => {
      document.removeEventListener('mousedown', onDown);
      document.removeEventListener('keydown', onKey);
    };
  }, [open]);

  // 没有账号（首次运行 / 全被删掉）时不渲染：那时界面该显示登录，
  // 由 LoginPage 负责，这里画一个"未命名账号"的下拉只会添乱
  if (usable.length === 0) return null;

  const label = activeId === AGGREGATE_ID && aggregateAvailable ? '全部邮箱' : (active?.displayName ?? '全部邮箱');

  const pick = async (id: string) => {
    setOpen(false);
    await setActive(id);
    // 切账号后**必须重取**：收件箱是按账号返回的，不重取就会看到上一个账号的信。
    // 这条在聚合⇄单账号之间同样成立（聚合要并发问多个账号）。
    await fetchInbox('all');
  };

  const title = aggregateAvailable ? label : active?.displayName;

  return (
    <div className="relative ml-auto" ref={boxRef}>
      <button
        type="button"
        data-testid="account-switcher"
        aria-haspopup="listbox"
        aria-expanded={open}
        onClick={() => aggregateAvailable && setOpen(o => !o)}
        className={`flex items-center gap-1 max-w-[150px] text-xs rounded-md px-2 py-1 border ${
          aggregateAvailable
            ? 'border-gray-200 text-gray-600 hover:bg-gray-50 cursor-pointer'
            : 'border-transparent text-gray-400 cursor-default'
        }`}
      >
        <span className="truncate" title={title ?? ''}>
          {title}
        </span>
        {aggregateAvailable && (
          <ChevronRightIcon className={`w-3 h-3 shrink-0 transition-transform ${open ? 'rotate-90' : ''}`} />
        )}
      </button>

      {open && (
        <div
          role="listbox"
          data-testid="account-menu"
          className="absolute right-0 top-full mt-1 z-20 w-56 bg-white border border-gray-200 rounded-lg shadow-lg py-1"
        >
          {aggregateAvailable && (
            <button
              type="button"
              role="option"
              aria-selected={activeId === AGGREGATE_ID}
              data-testid="account-option-all"
              onClick={() => pick(AGGREGATE_ID)}
              className="w-full text-left px-3 py-2 text-sm hover:bg-gray-50 flex items-center gap-2"
            >
              <span className="flex-1">全部邮箱</span>
              <span className="text-[11px] text-gray-400">{usable.length} 个账号</span>
            </button>
          )}
          <div className="my-1 border-t border-gray-100" />
          {usable.map(a => (
            <button
              key={a.id}
              type="button"
              role="option"
              aria-selected={a.id === activeId}
              data-testid={`account-option-${a.id}`}
              onClick={() => pick(a.id)}
              className="w-full text-left px-3 py-2 text-sm hover:bg-gray-50"
            >
              <span className="block truncate">{a.displayName}</span>
              <span className="block text-[11px] text-gray-400 truncate">{a.gateway}</span>
            </button>
          ))}
          <div className="my-1 border-t border-gray-100" />
          <button
            type="button"
            data-testid="account-manage"
            onClick={() => {
              setOpen(false);
              setViewMode('account');
            }}
            className="w-full text-left px-3 py-2 text-sm text-gray-600 hover:bg-gray-50"
          >
            管理账号…
          </button>
        </div>
      )}
    </div>
  );
}