/* 唯一的网络出口。页面代码里不出现 fetch，所有接口怪癖都在这一层消化掉。
   前端和后端不同源（前端在 static 目录下单独用 python -m http.server 起），
   所以这里必须写全后端地址；后端 main.py 里配了 CORS 中间件放行。 */

const API_BASE = 'http://127.0.0.1:8001';

class ApiError extends Error {
  constructor(message, status, body) {
    super(message);
    this.name = 'ApiError';
    this.status = status;
    this.body = body;
  }
}

// FastAPI 的错误统一放在 {"detail": ...}；422 的 detail 是数组，拼成一句中文
function detailOf(data) {
  if (!data || data.detail === undefined || data.detail === null) return null;
  const d = data.detail;
  if (typeof d === 'string') return d;
  if (Array.isArray(d)) {
    return d.map(x => {
      const where = (x.loc || []).slice(1).join('.') || '参数';
      return `${where}：${x.msg}`;
    }).join('；');
  }
  return JSON.stringify(d);
}

/**
 * @param {string} method
 * @param {string} path   必须写成后端的规范路径（尾斜杠与否由这里一处决定，
 *                        写错会吃 307 重定向，所以每个方法里都写死）
 * @param {object} opts   { query: 查询参数对象, body: JSON 请求体 }
 *                        body 不传就不带请求体（成绩模块那几个接口全靠这个）
 */
async function request(method, path, opts = {}) {
  let url = API_BASE + path;

  if (opts.query) {
    const usp = new URLSearchParams();
    Object.entries(opts.query).forEach(([k, v]) => {
      if (v !== undefined && v !== null && v !== '') usp.append(k, v);
    });
    const qs = usp.toString();
    if (qs) url += '?' + qs;
  }

  const init = { method, headers: {} };
  if (opts.body !== undefined) {
    init.headers['Content-Type'] = 'application/json';
    init.body = JSON.stringify(opts.body);
  }

  let res;
  try {
    res = await fetch(url, init);
  } catch (e) {
    throw new ApiError('无法连接后端服务，请确认 python main.py 已启动', 0, null);
  }

  const text = await res.text();
  let data = null;
  if (text) {
    try { data = JSON.parse(text); } catch (e) {
      // 正常走不到这里：路径写错时后端返回的是 JSON 404。多半是 API_BASE 配错了，
      // 请求打到前端自己的 8080 上，拿回 http.server 的一页 HTML。
      throw new ApiError('接口返回了非 JSON 内容，请检查 API_BASE 是否指向后端（HTTP ' + res.status + '）', res.status, null);
    }
  }

  if (!res.ok) throw new ApiError(detailOf(data) || `请求失败（HTTP ${res.status}）`, res.status, data);
  return data;
}

/* ---------- 学生 ---------- 注意：路径是 ""，所以没有尾斜杠 */
const StudentApi = {
  list:   (q)      => request('GET', '/students', { query: q }),
  create: (b)      => request('POST', '/students', { body: b }),      // 200（不是 201）
  update: (no, b)  => request('PUT', `/students/${encodeURIComponent(no)}`, { body: b }),
  remove: (no)     => request('DELETE', `/students/${encodeURIComponent(no)}`),
};

/* ---------- 班级 ---------- 集合路径带尾斜杠 */
const ClassApi = {
  // 只有这个列表接口会带上 head_teacher_name / course_teacher_names
  list:   (q)      => request('GET', '/classes/', { query: q }),
  create: (b)      => request('POST', '/classes/', { body: b }),
  detail: (id)     => request('GET', `/classes/${id}`),   // 别用它取班主任名，永远是"暂无"
  update: (id, b)  => request('PUT', `/classes/${id}`, { body: b }),
  async remove(id) {
    // 这个接口删除失败也返回 HTTP 200，只是 body 里 code=404，必须看 body 而不是状态码
    const r = await request('DELETE', `/classes/${id}`);
    if (r && typeof r.code === 'number' && r.code !== 200) {
      throw new ApiError(r.msg || '删除失败', 200, r);
    }
    return r;
  },
};

/* ---------- 老师 ---------- 单数前缀 */
const TeacherApi = {
  list:       ()   => request('GET', '/teacher/'),
  generateNo: ()   => request('GET', '/teacher/generate-no'),   // -> { t_no }
  create:     (b)  => request('POST', '/teacher/', { body: b }),  // 201
  update: (id, b)  => request('PUT', `/teacher/${id}`, { body: b }),
  async remove(id) {
    // 老师不存在时返回 HTTP 200 + body 为 null，不抛 404，得自己判
    const r = await request('DELETE', `/teacher/${id}`);
    if (r === null) throw new ApiError('老师不存在', 200, null);
    return r;
  },
};

/* ---------- 顾问 ---------- */
const AdvisorApi = {
  list:   (q)      => request('GET', '/advisor/', { query: q }),
  create: (b)      => request('POST', '/advisor/', { body: b }),  // 201
  update: (id, b)  => request('PUT', `/advisor/${id}`, { body: b }),
  remove: (id)     => request('DELETE', `/advisor/${id}`),
};

/* ---------- 就业 ---------- 按学号定位 */
const EmpApi = {
  list:   (q)      => request('GET', '/emp/', { query: q }),
  create: (b)      => request('POST', '/emp/', { body: b }),    // 201，学号重复会 400
  update: (no, b)  => request('PUT', `/emp/${encodeURIComponent(no)}`, { body: b }),
  async remove(no) {
    const r = await request('DELETE', `/emp/${encodeURIComponent(no)}`);
    if (r === null) throw new ApiError('就业信息不存在', 200, null);
    return r;
  },
};

/* ---------- 成绩 ----------
   五个接口的标量参数都走 query string，没有 JSON body；
   对外一律用业务学号 stu_no，不是内部主键 stu_id。 */
const ScoreApi = {
  listByStuNo: (no)                 => request('GET', `/score/list/${encodeURIComponent(no)}`),
  add:    (no, order, score)        => request('POST', '/score/add', { query: { stu_no: no, exam_order: order, score } }),
  update: (no, order, newScore)     => request('PUT', '/score/update', { query: { stu_no: no, exam_order: order, new_score: newScore } }),
  del:    (no, order)               => request('DELETE', '/score/del', { query: { stu_no: no, exam_order: order } }),
};

/* ---------- 统计 ---------- */
const StatsApi = {
  studentsByAge: (op, value, value2) => request('GET', '/statistics/students/age', { query: { op, value, value2 } }),
  classCount:    ()                  => request('GET', '/statistics/classes/count'),
  outScoreLine:  (line)              => request('GET', `/statistics/scores/out_score_line/${line}`),
  failScore:     (n)                 => request('GET', `/statistics/scores/fail_score/${n}`),
  classAvgScore: (sortOrder)         => request('GET', '/statistics/scores/get_class_avg_score', { query: { sort_order: sortOrder } }),
  topRank:       (rank)              => request('GET', `/statistics/emp/top_rank/${rank}`),
  empTime:       ()                  => request('GET', '/statistics/emp/emp_time'),
  classAvgEmpTime: (sortOrder)       => request('GET', '/statistics/emp/class_avg_emp_time', { query: { sort_order: sortOrder } }),
};