import URLToolkit from 'url-toolkit';
import window from 'global/window';

const DEFAULT_LOCATION = 'http://example.com';

const resolveUrl = (baseUrl, relativeUrl) => {
  // return early if we don't need to resolve
  if ((/^[a-z]+:/i).test(relativeUrl)) {
    return relativeUrl;
  }

  // if baseUrl is a data URI, ignore it and resolve everything relative to window.location
  if ((/^data:/).test(baseUrl)) {
    baseUrl = window.location && window.location.href || '';
  }

  // IE11 supports URL but not the URL constructor
  // feature detect the behavior we want
  const nativeURL = typeof window.URL === 'function';

  const protocolLess = (/^\/\//.test(baseUrl));
  // remove location if window.location isn't available (i.e. we're in node)
  // and if baseUrl isn't an absolute url
  const removeLocation = !window.location && !(/\/\//i).test(baseUrl);

  // if the base URL is relative then combine with the current location
  if (nativeURL) {
    baseUrl = new window.URL(baseUrl, window.location || DEFAULT_LOCATION);
  } else if (!(/\/\//i).test(baseUrl)) {
    baseUrl = URLToolkit.buildAbsoluteURL(window.location && window.location.href || '', baseUrl);
  }

  if (nativeURL) {
    const newUrl = new URL(relativeUrl, baseUrl);

    // if we're a protocol-less url, remove the protocol
    // and if we're location-less, remove the location
    // otherwise, return the url unmodified
    if (removeLocation) {
      return newUrl.href.slice(DEFAULT_LOCATION.length);
    } else if (protocolLess) {
      return newUrl.href.slice(newUrl.protocol.length);
    }

    return newUrl.href;
  }
  return URLToolkit.buildAbsoluteURL(baseUrl, relativeUrl);

};

export default resolveUrl;
