import express from "express";
import compression from "compression";
import { fileURLToPath } from "node:url";
import { resolve } from "node:path";
import multer from "multer";
import { parseWord, PARSER_VERSION } from "./parser.js";
import { scheduleFor } from "./schedules.js";
import { rateLimit, semaphore } from "./limits.js";
import { apiError, describe } from "./errors.js";
import { createHash } from "node:crypto";
import { timetable } from "./timetable.js";
import { catalogDiagnostics } from "./diagnostics.js";
import {
  getIndex,
  indexStatus,
  search,
  dayOf,
  freeRooms,
  examsOf,
  findGroups,
  readyIndex,
  sessionEntriesOf,
  directoryCalendar,
  todayIso,
} from "./directory.js";
import {
  getCatalog,
  getCalendar,
  documentFor,
  request,
  sourceStatus,
} from "./source.js";
const app = express();
app.disable("x-powered-by");
// Behind Caddy or a tunnel on this host, the client's address comes from X-Forwarded-For;
// only proxies on private networks are believed, so a client cannot forge its own.
app.set("trust proxy", "loopback, linklocal, uniquelocal");
// gzip or brotli: a semester of lessons is about 200 KB of JSON and shrinks tenfold.
app.use(compression());
app.use("/api", (_req, res, next) => {
  // Clients may keep a response but must ask again each time; Express's ETag turns an
  // unchanged answer into an empty 304, so a phone re-downloads a timetable only when it changed.
  res.set("Cache-Control", "no-cache");
  next();
});
// Raised whenever an endpoint is added or changed, so a deployment is easy to verify:
// 2 — /api/timetable for the Android client; 3 — its range=semester;
// 4 — compression, ETag revalidation, throttled refresh and import limits;
// 5 — error codes (`code` beside `error`, see server/errors.js), timetable 304 before any work;
// 6 — the timetable carries the group's exams and credits from other catalog documents;
// 7 — /api/diagnostics, cells the parser could not read with confidence;
// 8 — /api/ready, and `ready` in /api/health.
const API_VERSION = 8;

/**
 * What the server still waits for before it answers from memory: the catalog, the week table
 * and the directory index. A first start without a cache crawls and parses every document.
 */
const waitingFor = (sources, directory) =>
  [!sources.catalog && "catalog", !sources.calendar && "calendar", !directory.builtAt && "index"].filter(Boolean);
// Liveness plus what the server currently reads from the university, without network calls.
app.get("/api/health", async (_req, res) => {
  const sources = await sourceStatus().catch((e) => ({ error: e.message }));
  res.json({
    ok: true,
    ready: waitingFor(sources, indexStatus()).length === 0,
    apiVersion: API_VERSION,
    parserVersion: PARSER_VERSION,
    ...sources,
    directory: indexStatus(),
  });
});
// Readiness for Docker and a proxy: 503 until the catalog, the week table and the index are
// loaded, so traffic does not reach a server whose first requests would wait half a minute.
app.get("/api/ready", async (_req, res) => {
  const sources = await sourceStatus().catch(() => ({}));
  const directory = indexStatus();
  const waiting = waitingFor(sources, directory);
  if (waiting.length)
    return res.status(503).json({
      ready: false,
      waiting,
      error: "Сервер ещё загружает каталог расписаний. Попробуйте через минуту.",
      code: "not_ready",
    });
  res.json({ ready: true, documents: directory.documents, builtAt: directory.builtAt });
});
const isDate = (s) => /^\d{4}-\d{2}-\d{2}$/.test(s || "");
const badRequest = (res, error) => res.status(400).json({ error, code: "bad_request" });
// University-wide lookups over every catalog document.
app.get("/api/directory/search", async (req, res, next) => {
  try {
    res.json(search(await getIndex(), String(req.query.q || "").slice(0, 60)));
  } catch (e) {
    next(e);
  }
});
app.get("/api/directory/day", async (req, res, next) => {
  try {
    const date = req.query.date || todayIso();
    const teacher = String(req.query.teacher || "").slice(0, 80),
      room = String(req.query.room || "").slice(0, 20);
    if (!isDate(date)) return badRequest(res, "Дата должна быть в формате ГГГГ-ММ-ДД.");
    if (!teacher && !room) return badRequest(res, "Укажите преподавателя или аудиторию.");
    res.json(dayOf(await getIndex(), await directoryCalendar(), { teacher, room }, date));
  } catch (e) {
    next(e);
  }
});
app.get("/api/directory/free", async (req, res, next) => {
  try {
    const date = req.query.date || todayIso(),
      pair = Number(req.query.pair);
    if (!isDate(date)) return badRequest(res, "Дата должна быть в формате ГГГГ-ММ-ДД.");
    const calendar = await directoryCalendar();
    const result = freeRooms(await getIndex(), calendar, date, pair);
    if (!result) return badRequest(res, "Нет такой пары в расписании звонков.");
    res.json(result);
  } catch (e) {
    next(e);
  }
});
app.get("/api/groups", async (req, res, next) => {
  try {
    const text = (name) => String(req.query[name] || "").slice(0, 120);
    res.json(
      findGroups(await getIndex(), {
        q: text("q"),
        faculty: text("faculty"),
        course: text("course"),
        form: text("form"),
      }),
    );
  } catch (e) {
    next(e);
  }
});
// A group's lessons by date with weeks applied: for native and other clients.
app.get("/api/timetable", async (req, res, next) => {
  try {
    const doc = String(req.query.doc || ""),
      group = String(req.query.group || "").slice(0, 40),
      from = req.query.from || todayIso();
    if (!doc || !group) return badRequest(res, "Укажите документ (doc) и группу (group).");
    if (!isDate(from)) return badRequest(res, "Дата должна быть в формате ГГГГ-ММ-ДД.");
    const file = await documentFor(doc);
    const calendar = await directoryCalendar();
    const range = req.query.range === "semester" ? "semester" : undefined;
    const today = todayIso();
    // The group's exams and credits from other documents ("Расписание зачетов"); a server
    // still building its first index answers without them rather than wait.
    const idx = readyIndex();
    // The answer follows only from these: the document's version, the parser and the server
    // that read it, the week table, the request and the date. An unchanged one comes back
    // as an empty 304 before the document is opened or a single day is computed.
    const etag = 'W/"tt-' + createHash("sha1")
      .update([API_VERSION, PARSER_VERSION, file.id, file.modified, calendar?.updatedAt, idx?.builtAt, group, from, req.query.days, range, today].join("|"))
      .digest("base64url")
      .slice(0, 22) + '"';
    res.set("ETag", etag);
    if (req.fresh) return res.status(304).end();
    const schedule = await scheduleFor(file);
    res.json(
      timetable({
        file,
        schedule,
        calendar,
        group,
        from,
        days: req.query.days,
        range,
        today,
        session: sessionEntriesOf(idx, group, file.faculty || schedule.source.faculty, file.id),
      }),
    );
  } catch (e) {
    next(e);
  }
});
app.get("/api/exams", async (req, res, next) => {
  try {
    const group = String(req.query.group || "").slice(0, 40);
    if (!group) return badRequest(res, "Укажите группу.");
    res.json({
      group,
      exams: examsOf(await getIndex(), group, String(req.query.faculty || "") || null),
    });
  } catch (e) {
    next(e);
  }
});
// Cells of catalog documents that look misread: a new layout or a typo in Word, with the
// original text, so they can be checked against the document and the parser taught.
app.get("/api/diagnostics", async (req, res, next) => {
  try {
    const text = (name) => String(req.query[name] || "").slice(0, 60);
    res.json(catalogDiagnostics(await getIndex(), { group: text("group"), doc: text("doc"), code: text("code") }));
  } catch (e) {
    next(e);
  }
});
app.get("/api/catalog", async (req, res, next) => {
  try {
    res.json(await getCatalog(req.query.refresh === "1"));
  } catch (e) {
    next(e);
  }
});
app.get("/api/calendar", async (req, res, next) => {
  try {
    res.json(await getCalendar(req.query.refresh === "1"));
  } catch (e) {
    next(e);
  }
});
app.get("/api/schedule/:id", async (req, res, next) => {
  try {
    const file = await documentFor(req.params.id);
    res.json(await scheduleFor(file, { refresh: req.query.refresh === "1" }));
  } catch (e) {
    next(e);
  }
});
app.get("/api/original/:id", async (req, res, next) => {
  try {
    const file = await documentFor(req.params.id);
    res.set("Content-Type", "application/octet-stream");
    res.set(
      "Content-Disposition",
      `attachment; filename*=UTF-8''${encodeURIComponent(file.name)}`,
    );
    res.send(await request(file.path));
  } catch (e) {
    next(e);
  }
});
// Parsing runs a LibreOffice conversion for old .doc files: two at a time, a few more wait,
// and each address may import ten files in ten minutes.
const importLimit = rateLimit({
  max: 10,
  windowMs: 10 * 60 * 1000,
  message: "Слишком много файлов подряд. Попробуйте через несколько минут.",
});
const parsing = semaphore({
  limit: 2,
  queue: 4,
  message: "Сервер занят разбором других файлов. Попробуйте через минуту.",
});
const upload = multer({
  storage: multer.memoryStorage(),
  limits: { fileSize: 10 * 1024 * 1024, files: 1, fields: 0 },
});
app.post("/api/import", importLimit, upload.single("file"), async (req, res, next) => {
  try {
    if (!req.file)
      return badRequest(res, "Выберите файл Word.");
    // Multer decodes multipart names as latin1 by default.
    const name = Buffer.from(req.file.originalname, "latin1").toString("utf8");
    if (!/\.docx?$/i.test(name))
      return badRequest(res, "Поддерживаются файлы .docx и .doc.");
    res.json(await parsing(() => parseWord(req.file.buffer, { name, uploaded: true })));
  } catch (e) {
    // A file that cannot be read is the client's problem; a busy server keeps its 429.
    next(e.status || e.code === "LIMIT_FILE_SIZE" ? e : apiError(422, "unreadable_file", e.message));
  }
});
const dist = fileURLToPath(new URL("../dist/", import.meta.url));
app.use(express.static(dist, { maxAge: 0 }));
app.get("/{*path}", (req, res, next) =>
  req.path.startsWith("/api/")
    ? res.status(404).json({ error: "Адрес не найден.", code: "unknown_endpoint" })
    : res.sendFile(dist + "index.html", (err) => err && next(err)),
);
app.use((error, req, res, _next) => {
  const { status, code, message } = describe(error);
  // Faults of the server keep their stack; expected errors need a line.
  if (status >= 500 && code === "internal") console.error(req.method, req.originalUrl, error);
  else console.error(`${req.method} ${req.originalUrl} → ${status} ${code}: ${error.message}`);
  res.status(status).json({ error: message, code });
});
export { app };

/** Starts listening and loads the week table and the whole catalog in the background. */
export function start(port = Number(process.env.PORT || 3001), host = process.env.HOST || "127.0.0.1") {
  return app.listen(port, host, () => {
    console.log(`API и PWA: http://127.0.0.1:${port}`);
    // So the first visit and the first search do not wait for the university.
    getCalendar().catch((e) => console.error(`Таблица недель: ${e.message}`));
    getIndex().catch((e) => console.error(`Индекс: ${e.message}`));
  });
}
// `node server/index.js` serves; tests import the app without listening.
if (process.argv[1] && fileURLToPath(import.meta.url) === resolve(process.argv[1])) start();