import fs from "fs";
import fetch from "node-fetch";
import unionBy from "lodash-es/unionBy.js";
import domain from "./metadata.js";

// Load .env variables with dotenv
import "dotenv/config.js";

// Configuration Parameters
const CACHE_DIR = '_cache';
const API_ORIGIN = 'https://webmention.io/api/mentions.jf2';
const TOKEN = process.env.WEBMENTION_IO_TOKEN;

async function fetchWebmentions(since, perPage = 10000) {
  // If we don't have a domain name or token, abort
  if (!domain || !TOKEN) {
	console.warn('>>> unable to fetch webmentions: missing domain or token');
	return false;
  }

  let url = `${API_ORIGIN}?domain=${domain}&token=${TOKEN}&per-page=${perPage}`;
  if (since) url += `&since=${since}`; // only fetch new mentions

  const response = await fetch(url);
  if (response.ok) {
	const feed = await response.json();
	console.log(`>>> ${feed.children.length} new webmentions fetched from ${API_ORIGIN}`);
	return feed;
  }

  return null;
}

// Merge fresh webmentions with cached entries, unique per id
function mergeWebmentions(a, b) {
  return unionBy(a.children, b.children, 'wm-id');
}

// save combined webmentions in cache file
function writeToCache(data) {
  const filePath = `${CACHE_DIR}/webmentions.json`;
  const fileContent = JSON.stringify(data, null, 2);

  // create cache folder if it doesnt exist already
  if (!fs.existsSync(CACHE_DIR)) {
	fs.mkdirSync(CACHE_DIR);
  }
  // write data to cache json file
  fs.writeFile(filePath, fileContent, err => {
	if (err) throw err;
	console.log(`>>> webmentions cached to ${filePath}`);
  });
}

// get cache contents from json file
function readFromCache() {
  const filePath = `${CACHE_DIR}/webmentions.json`;

  if (fs.existsSync(filePath)) {
	const cacheFile = fs.readFileSync(filePath);
	return JSON.parse(cacheFile);
  };
  // no cache found
  return {
	lastFetched: null,
	children: []
  };
}

export default async function() {
  console.log('>>> Reading webmentions from cache...');

  const cache = readFromCache();

  if (cache.children.length) {
    console.log(`>>> ${cache.children.length} webmentions loaded from cache`);
  };

  // Only fetch new mentions in production
  if (process.env.ELEVENTY_ENV === 'production') {
    console.log('>>> Checking for new webmentions...');
	const feed = await fetchWebmentions(cache.lastFetched);

	if (feed) {
	  const webmentions = {
		lastFetched: new Date().toISOString(),
		children: mergeWebmentions(cache, feed)
	  }

	  writeToCache(webmentions);
	  return webmentions;
	}
  }

  return cache;
}