import { readFile, writeFile, mkdir } from "node:fs/promises";
import { parseWord, PARSER_VERSION } from "./parser.js";
import { request, MIN_REFRESH } from "./source.js";
import { DATA } from "./paths.js";

const data = DATA + "parsed/";
// The downloaded Word files: a new parser reads them again without asking the university.
const originals = DATA + "documents/";
// When each document was last downloaded, and the downloads under way: a forced refresh
// downloads a document at most once per MIN_REFRESH, and simultaneous ones share a download.
const fetchedAt = new Map(),
  loading = new Map();

/** A parsed catalog document, from the disk cache while the file and parser are unchanged. */
export async function scheduleFor(file, { refresh = false } = {}) {
  const cache = data + file.id + ".json";
  if (refresh && Date.now() - (fetchedAt.get(file.id) || 0) < MIN_REFRESH) refresh = false;
  if (!refresh)
    try {
      const cached = JSON.parse(await readFile(cache, "utf8"));
      if (cached.source.modified === file.modified) {
        if (cached.schemaVersion === PARSER_VERSION) return cached;
        // The same file read by an older parser: parse the saved copy again.
        const saved = await readFile(originals + file.id).catch(() => null);
        if (saved) return parse(file, saved, cache);
      }
    } catch {}
  if (!loading.has(file.id))
    loading.set(
      file.id,
      download(file, cache).finally(() => loading.delete(file.id)),
    );
  return loading.get(file.id);
}

async function download(file, cache) {
  const buffer = await request(file.path);
  fetchedAt.set(file.id, Date.now());
  await mkdir(originals, { recursive: true });
  await writeFile(originals + file.id, buffer);
  return parse(file, buffer, cache);
}

async function parse(file, buffer, cache) {
  const parsed = await parseWord(buffer, {
    name: file.name,
    url: file.url,
    faculty: file.faculty,
    modified: file.modified,
    fileId: file.id,
    form: file.form,
    course: file.course,
    year: file.year,
  });
  await mkdir(data, { recursive: true });
  await writeFile(cache, JSON.stringify(parsed));
  return parsed;
}