import { promises as fs } from "fs";
import path from "path";
import { STATIC_DIR, SUBJECTS } from "./constants.js";

export const cache = new Map();

async function populateResources() {
  const filenamesRaw = await fs.readdir(STATIC_DIR);
  const filenames = filenamesRaw
    .filter((file) => file.endsWith(".md"))
    .map((file) => file.replace(".md", ""));

  const topicResources = {};
  filenames.forEach((resourceId) => {
    const parts = resourceId.split("_");

    const subjectPart = parts[1];
    const topicPart = parts[2];

    const topicId = `${subjectPart}_${topicPart}`;
    topicResources[topicId] ||= [];
    topicResources[topicId].push({
      id: resourceId,
      version: parseInt(parts[3].substring(2)),
    });
  });
  Object.values(topicResources).forEach((resources) => {
    resources.sort((a, b) => a.version - b.version);
  });

  Object.values(SUBJECTS).forEach((subject) => {
    Object.values(subject.topics).forEach((topic) => {
      if (topic.id in topicResources) {
        topic.resources = topicResources[topic.id];
      }
    });
  });
}

export async function getStructure({ refresh = false } = {}) {
  const structureKey = "structure";

  if (refresh) {
    cache.delete(structureKey);
  }

  if (!cache.has(structureKey)) {
    await populateResources();
    cache.set(structureKey, SUBJECTS);
  }

  return cache.get(structureKey);
}