"use strict";
  const whatwgURL = require("whatwg-url");
  
  exports.documentBaseURL = document => {
    // https://html.spec.whatwg.org/multipage/infrastructure.html#document-base-url
  
    const firstBase = document.querySelector("base[href]");
    const fallbackBaseURL = exports.fallbackBaseURL(document);
  
    if (firstBase === null) {
      return fallbackBaseURL;
    }
  
    return frozenBaseURL(firstBase, fallbackBaseURL);
  };
  
  exports.documentBaseURLSerialized = document => {
    return whatwgURL.serializeURL(exports.documentBaseURL(document));
  };
  
  exports.fallbackBaseURL = document => {
    // https://html.spec.whatwg.org/multipage/infrastructure.html#fallback-base-url
  
    // Unimplemented: <iframe srcdoc>
  
    if (document.URL === "about:blank" && document._defaultView &&
        document._defaultView._parent !== document._defaultView) {
      return exports.documentBaseURL(document._defaultView._parent._document);
    }
  
    return document._URL;
  };
  
  exports.parseURLToResultingURLRecord = (url, document) => {
    // https://html.spec.whatwg.org/#resolve-a-url
  
    // Encoding stuff ignored; always UTF-8 for us, for now.
  
    const baseURL = exports.documentBaseURL(document);
  
    return whatwgURL.parseURL(url, { baseURL });
    // This returns the resulting URL record; to get the resulting URL string, just serialize it.
  };
  
  function frozenBaseURL(baseElement, fallbackBaseURL) {
    // https://html.spec.whatwg.org/multipage/semantics.html#frozen-base-url
    // The spec is eager (setting the frozen base URL when things change); we are lazy (getting it when we need to)
  
    const baseHrefAttribute = baseElement.getAttributeNS(null, "href");
    const result = whatwgURL.parseURL(baseHrefAttribute, { baseURL: fallbackBaseURL });
    return result === null ? fallbackBaseURL : result;
  }