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

export const cache = new Map();

function getObjectWithMaxTimestamp(array) {
  if (!array || array.length === 0) {
    return null;
  }

  return array.reduce((max, current) => {
    return current.timestamp > max.timestamp ? current : max;
  });
}

async function populateResources() {
  const filenamesRaw = await fs.readdir(STATIC_DIR);
  const filenames = filenamesRaw
    .filter((filename) => FILENAME_REGEX.test(filename))
    .map((filename) => {
      const parts = filename.replace(".md", "").split("_");
      if (parts.length !== 4 || parts[0] !== "F") {
        console.warn(`File not following format: ${filename}`);
        return;
      }

      const topicSeq = Number(parts[1].substring(1));
      const resourceSeq = Number(parts[2].substring(1));
      const timestamp = Number(parts[3]);
      return { topicSeq, resourceSeq, timestamp, filename };
    });

  const topicsBySeq = Object.groupBy(filenames, ({ topicSeq }) => topicSeq);

  TOPICS.forEach((topic) => {
    if (topic.seq in topicsBySeq) {
      const resourcesBySeq = Object.groupBy(
        topicsBySeq[topic.seq],
        ({ resourceSeq }) => resourceSeq,
      );

      topic.resources.forEach((resource) => {
        if (resource.seq in resourcesBySeq) {
          const latestResource = getObjectWithMaxTimestamp(
            resourcesBySeq[resource.seq],
          );
          resource.filename = latestResource.filename;
        }
      });
    }
  });
}

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

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

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

  return cache.get(structureKey);
}