const BASE = import.meta.env.VITE_API_BASE_URL || '';

// 동시 401 발생 시 refresh를 한 번만 실행하기 위한 Promise 공유
let refreshingPromise = null;

async function tryRefresh() {
  if (refreshingPromise) return refreshingPromise;

  refreshingPromise = (async () => {
    const rt = localStorage.getItem('refreshToken');
    if (!rt) throw new Error('no_refresh_token');

    const res = await fetch(BASE + '/api/auth/refresh', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ refreshToken: rt }),
    });

    if (!res.ok) throw new Error('refresh_failed');

    const data = await res.json();
    localStorage.setItem('token', data.token);
    localStorage.setItem('refreshToken', data.refreshToken);
    return data.token;
  })().finally(() => {
    refreshingPromise = null;
  });

  return refreshingPromise;
}

async function doFetch(path, options, token) {
  const headers = { 'Content-Type': 'application/json', ...options.headers };
  if (token) headers['Authorization'] = `Bearer ${token}`;
  return fetch(BASE + path, { ...options, headers });
}

async function parseError(res) {
  let message = res.statusText;
  try {
    const body = await res.json();
    if (body.error) message = body.error;
  } catch {}
  const err = new Error(message);
  err.status = res.status;
  return err;
}

// 204 No Content는 null 반환, 나머지는 JSON 파싱
async function parseResponse(res) {
  if (res.status === 204) return null;
  return res.json();
}

export async function apiFetch(path, options = {}) {
  const token = localStorage.getItem('token');
  const res = await doFetch(path, options, token);

  if (res.status === 401) {
    try {
      const newToken = await tryRefresh();
      // 새 토큰으로 원래 요청 재시도
      const retryRes = await doFetch(path, options, newToken);
      if (retryRes.status === 401) {
        window.dispatchEvent(new Event('auth:unauthorized'));
        throw await parseError(retryRes);
      }
      if (!retryRes.ok) throw await parseError(retryRes);
      return parseResponse(retryRes);
    } catch (e) {
      // refresh 자체 실패 → 로그아웃
      if (e.message === 'no_refresh_token' || e.message === 'refresh_failed') {
        window.dispatchEvent(new Event('auth:unauthorized'));
        const err = new Error('인증이 필요합니다');
        err.status = 401;
        throw err;
      }
      throw e;
    }
  }

  if (!res.ok) throw await parseError(res);
  return parseResponse(res);
}