'use strict';
const http = require('node:http');
const fs = require('node:fs');
const path = require('node:path');
const { buildOverview } = require('./days.js');

const PORT = process.env.PORT || 3000;
const TAGS_PATH = path.join(__dirname, 'tags.json');
const INDEX_PATH = path.join(__dirname, 'public', 'index.html');

function readTags() {
  return JSON.parse(fs.readFileSync(TAGS_PATH, 'utf8'));
}

function sendJSON(res, status, body) {
  res.writeHead(status, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify(body));
}

async function handleOverview(res, query) {
  const icsUrl = query.get('url');
  if (!icsUrl) return sendJSON(res, 400, { error: 'missing url parameter' });

  let parsedUrl;
  try {
    parsedUrl = new URL(icsUrl);
  } catch {
    return sendJSON(res, 400, { error: 'invalid url' });
  }
  if (parsedUrl.protocol !== 'http:' && parsedUrl.protocol !== 'https:') {
    return sendJSON(res, 400, { error: 'url must be http or https' });
  }

  let icsText;
  try {
    const fetchRes = await fetch(icsUrl);
    if (!fetchRes.ok) throw new Error(`HTTP ${fetchRes.status}`);
    icsText = await fetchRes.text();
  } catch (err) {
    return sendJSON(res, 502, { error: `could not fetch calendar: ${err.message}` });
  }

  const now = new Date();
  const rangeStart = `${now.getFullYear()}-01-01`;
  const rangeEnd = `${now.getFullYear() + 1}-12-31`;

  let overview;
  try {
    overview = buildOverview(icsText, readTags(), rangeStart, rangeEnd);
  } catch (err) {
    return sendJSON(res, 500, { error: `could not parse calendar: ${err.message}` });
  }

  sendJSON(res, 200, { rangeStart, rangeEnd, days: overview });
}

const server = http.createServer(async (req, res) => {
  const url = new URL(req.url, `http://localhost:${PORT}`);

  if (req.method === 'GET' && url.pathname === '/') {
    res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
    res.end(fs.readFileSync(INDEX_PATH));
    return;
  }

  if (req.method === 'GET' && url.pathname === '/tags.json') {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(fs.readFileSync(TAGS_PATH));
    return;
  }

  if (req.method === 'GET' && url.pathname === '/api/default-url') {
    return sendJSON(res, 200, { url: process.env.CALURL || null });
  }

  if (req.method === 'GET' && url.pathname === '/api/overview') {
    await handleOverview(res, url.searchParams);
    return;
  }

  res.writeHead(404, { 'Content-Type': 'text/plain' });
  res.end('not found');
});

server.listen(PORT, () => {
  console.log(`http://localhost:${PORT}`);
});