// 21:13
// Given urls ['url1', 'url2', 'url2', 'url3'...], limit
// Function `process` should `get` all urls, respecting limit and return when finished.
// Limit means that at the same time there should be N (limit) requests in progress, at least and at most
// Duplicate urls shouldn't be processed again, but the final order should be the same
// Get is used to mock requests
function get(url) {
  return Promise.resolve("result" + url);
}

// Checkpoint 21:22
// Checkpoint 21:34

function process(urls, limit) {
  async function _process() {
    const urlMap = {};
    const first10urls = urls.slice(0, limit);
    const restUrls = urls.slice(limit);
    const res = [];

    function processNext(url, resolve) {
      if (!urlMap[url]) {
        urlMap[url] = get(url).then(res => {
          if (restUrls.length) {
            nextUrl = restUrls.pop();
            processNext(nextUrl, resolve);
          } else {
            resolve();
          }
          return res;
        });
      }
    }

    function wait() {
      return new Promise(resolve => {
        first10urls.forEach(url => {
          processNext(url, resolve);
        });
      });
    }

    await wait();
    // urlMap should be full by that time

    for (let url of urls) {
      const data = await urlMap[url];
      res.push(data);
    }

    return res;
  }

  return _process();
}

// 21:39
// Handle wait for all promies
// Done 21:45

console.log(
  process(["url1", "url2", "url3", "url4", "url5", "url6", "url7", "url2"], 2)
);