import * as R from "ramda";

 function wrapEvent(target, name, obj) {

   target.addEventListener(name, obj);
 }
 

 function runOnceFor(object, flag, cb) {

   if (!object[flag]) {
     object[flag] = true;
     cb();
   }
 }
 
 let MISSING_CHANGE_URL = Symbol("missing_change_url");
 export default function addChangeUrlEvent(window) {

   runOnceFor(window, MISSING_CHANGE_URL, () => {

     const changeUrlEventCreator = {

       lastLocation: null,

       handleEvent(_) {

         // interface for EventListener

         let { hash, host, hostname, origin, href, pathname, port, protocol } =
           window.location || {};

         // store in object for comparison

         const pushedLocation = {
           hash,
           host,
           hostname,
           origin,
           href,
           pathname,
           port,
           protocol
         };

 
         // only dispatch action when url has actually changed so same link can be clicked repeatedly.
         if (!R.equals(pushedLocation, this.lastLocation)) {

           var urlChangeEvent = new CustomEvent("urlchanged", {
             detail: pushedLocation
           });

           window.dispatchEvent(urlChangeEvent);
           this.lastLocation = pushedLocation;
         }
       }

     };

     // / make sure we fire urlchanged for these

     wrapEvent(window, "popstate", changeUrlEventCreator);
     wrapEvent(window, "pushstate", changeUrlEventCreator);
     wrapEvent(window, "replacestate", changeUrlEventCreator);

   });
 }