var setupCache = function() {
  let newWorker; // When sw.js is changed, this is the new service worker generated.
  
  // Toggle a CSS class to display a popup prompting the user to fetch a new version.
  function showUpdateModal() {
    $('#update-prompt-modal').addClass('show');
  }

  /**
  * When a new service worker has been loaded, the button in the update prompt
  * modal should trigger the skipWaiting event to replace the current
  * service worker with the new one.
  */
  $('#reload').on('click', function() {
    newWorker.postMessage({ action: 'skipWaiting' });
  });

  if ('serviceWorker' in navigator) {
    // Register the service worker.
    navigator.serviceWorker.register('sw.js', { scope: '/examples/' })
      .then(function(registration) {

          return new Promise(function(resolve,reject){

            registration.addEventListener('updatefound', () => {
              // When sw.js has been changed, get a reference to the new service worker.
              newWorker = registration.installing;

              if(!newWorker){
                return reject(new Error('error in installing service worker'));
              }

            newWorker.addEventListener('statechange', () => {
              // Check if service worker state has changed.
              switch(newWorker.state) {
                case 'installed':
                  if(navigator.serviceWorker.controller) {
                    // New service worker available; prompt the user to update.
                    showUpdateModal();
                    $('#reload').on('click',(e) => {
                      e.preventDefault();
                      console.log('New Service Worker Installed Successfully');
                      location.reload();
                      return resolve();
                    })
                  }
                  // No updates available; do nothing.
                  break;

                case 'redundant':
                  return reject(new Error('installing new service worker now became redundant'));
              }
            })
          })
        })
      }).catch(err => {
        console.log('Failed In Registering Service Worker: ',err);
      });

      /**
      * This is the event listener for when the service worker updates.
      * When the service worker updates, reload the page.
      */
      let refreshing;
      navigator.serviceWorker.addEventListener('controllerchange', function() {
        if(refreshing) return;
        window.location.reload();
        refreshing = true;
      });
  }

  if ('serviceWorker' in navigator) {
    caches.keys().then(function(cacheNames) {
      cacheNames.forEach(function(cacheName) {
        $('#clear-cache').append(' ' + cacheName);
      });
    });
  }

  const clearCache = () => {
    if ('serviceWorker' in navigator) {
      return caches.keys()
        .then(function(cache) {
          return Promise.all(cache.map(function(cacheItem) {
            return caches.delete(cacheItem);
        }));
      });
    }
  }

  $('#clear-cache').click(function() {
    clearCache();
    location.reload();
  });

};

module.exports = setupCache;