Use a specialized new tab page in TOUCH_UI builds

chrome/browser/resources/touch_ntp/newtab.js

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview Touch-based new tab page
+ * This is the main code for the new tab page used by touch-enabled Chrome
+ * browsers.  For now this is still a prototype.
+ */
+
+// Use an anonymous function to enable strict mode just for this file (which
+// will be concatenated with other files when embedded in Chrome
+var ntp = (function() {
+  'use strict';
+
+  /**
+   * The Slider object to use for changing app pages.
+   * @type {Slider|undefined}
+   */
+  var slider;
+
+  /**
+   * Template to use for creating new 'apps-page' elements
+   * @type {!Element|undefined}
+   */
+  var appsPageTemplate;
+
+  /**
+   * Template to use for creating new 'app-container' elements
+   * @type {!Element|undefined}
+   */
+  var appTemplate;
+
+  /**
+   * Template to use for creating new 'dot' elements
+   * @type {!Element|undefined}
+   */
+  var dotTemplate;
+
+  /**
+   * The 'apps-page-list' element.
+   * @type {!Element}
+   */
+  var appsPageList = getRequiredElement('apps-page-list');
+
+  /**
+   * A list of all 'apps-page' elements.
+   * @type {!NodeList|undefined}
+   */
+  var appsPages;
+
+  /**
+   * The 'dots-list' element.
+   * @type {!Element}
+   */
+  var dotList = getRequiredElement('dot-list');
+
+  /**
+   * A list of all 'dots' elements.
+   * @type {!NodeList|undefined}
+   */
+  var dots;
+
+  /**
+   * The 'trash' element.  Note that technically this is unnecessary,
+   * JavaScript creates the object for us based on the id.  But I don't want
+   * to rely on the ID being the same, and JSCompiler doesn't know about it.
+   * @type {!Element}
+   */
+  var trash = getRequiredElement('trash');
+
+  /**
+   * The time in milliseconds for most transitions.  This should match what's
+   * in newtab.css.  Unfortunately there's no better way to try to time
+   * something to occur until after a transition has completed.
+   * @type {number}
+   * @const
+   */
+  var DEFAULT_TRANSITION_TIME = 500;
+
+  /**
+   * All the Grabber objects currently in use on the page
+   * @type {Array.<Grabber>}
+   */
+  var grabbers = [];
+
+  /**
+   * Holds all event handlers tied to apps (and so subject to removal when the
+   * app list is refreshed)
+   * @type {!EventTracker}
+   */
+  var appEvents = new EventTracker();
+
+  /**
+   * Invoked at startup once the DOM is available to initialize the app.
+   */
+  function initializeNtp() {
+    // Request data on the apps so we can fill them in.
+    // Note that this is kicked off asynchronously.  'getAppsCallback' will be
+    // invoked at some point after this function returns.
+    chrome.send('getApps');
+
+    // Prevent touch events from triggering any sort of native scrolling
+    document.addEventListener('touchmove', function(e) {
+      e.preventDefault();
+    }, true);
+
+    // Get the template elements and remove them from the DOM.  Things are
+    // simpler if we start with 0 pages and 0 apps and don't leave hidden
+    // template elements behind in the DOM.
+    appTemplate = getRequiredElement('app-template');
+    appTemplate.id = null;
+
+    appsPages = appsPageList.getElementsByClassName('apps-page');
+    assert(appsPages.length == 1,
+           'Expected exactly one apps-page in the apps-page-list.');
+    appsPageTemplate = appsPages[0];
+    appsPageList.removeChild(appsPages[0]);
+
+    dots = dotList.getElementsByClassName('dot');
+    assert(dots.length == 1,
+           'Expected exactly one dot in the dots-list.');
+    dotTemplate = dots[0];
+    dotList.removeChild(dots[0]);
+
+    // Initialize the slider without any cards at the moment
+    var appsFrame = getRequiredElement('apps-frame');
+    slider = new Slider(appsFrame, appsPageList, [], 0, appsFrame.offsetWidth);
+    slider.initialize();
+
+    // Ensure the slider is resized appropriately with the window
+    window.addEventListener('resize', function() {
+      slider.resize(appsFrame.offsetWidth);
+    });
+
+    // Handle the page being changed
+    appsPageList.addEventListener(
+        Slider.EventType.CARD_CHANGED,
+        function(e) {
+          // Update the active dot
+          var curDot = dotList.getElementsByClassName('selected')[0];
+          if (curDot)
+            curDot.classList.remove('selected');
+          var newPageIndex = e.slider.currentCard;
+          dots[newPageIndex].classList.add('selected');
+          // If an app was being dragged, move it to the end of the new page
+          if (draggingAppContainer)
+            appsPages[newPageIndex].appendChild(draggingAppContainer);
+        });
+
+    // Add a drag handler to the body (for drags that don't land on an existing
+    // app)
+    document.addEventListener(Grabber.EventType.DRAG_ENTER, appDragEnter);
+
+    // Handle dropping an app anywhere other than on the trash
+    document.addEventListener(Grabber.EventType.DROP, appDrop);
+
+    // Add handles to manage the transition into/out-of rearrange mode
+    // Note that we assume here that we only use a Grabber for moving apps,
+    // so ANY GRAB event means we're enterring rearrange mode.
+    appsFrame.addEventListener(Grabber.EventType.GRAB, enterRearrangeMode);
+    appsFrame.addEventListener(Grabber.EventType.RELEASE, leaveRearrangeMode);
+
+    // Add handlers for the tash can
+    trash.addEventListener(Grabber.EventType.DRAG_ENTER, function(e) {
+      trash.classList.add('hover');
+      e.grabbedElement.classList.add('trashing');
+      e.stopPropagation();
+    });
+    trash.addEventListener(Grabber.EventType.DRAG_LEAVE, function(e) {
+      e.grabbedElement.classList.remove('trashing');
+      trash.classList.remove('hover');
+    });
+    trash.addEventListener(Grabber.EventType.DROP, appTrash);
+  }
+
+  /**
+   * Simple common assertion API
+   * @param {*} condition The condition to test.  Note that this may be used to
+   *     test whether a value is defined or not, and we don't want to force a
+   *     cast to Boolean.
+   * @param {string=} opt_message A message to use in any error.
+   */
+  function assert(condition, opt_message) {
+    'use strict';
+    if (!condition) {
+      var msg = 'Assertion failed';
+      if (opt_message)
+        msg = msg + ': ' + opt_message;
+      throw new Error(msg);
+    }
+  }
+
+  /**
+   * Get an element that's known to exist by its ID. We use this instead of just
+   * calling getElementById and not checking the result because this lets us
+   * satisfy the JSCompiler type system.
+   * @param {string} id The identifier name.
+   * @return {!Element} the Element.
+   */
+  function getRequiredElement(id) {
+    var element = document.getElementById(id);
+    assert(element, 'Missing required element: ' + id);
+    return element;
+  }
+
+  /**
+   * Remove all children of an element which have a given class in
+   * their classList.
+   * @param {!Element} element The parent element to examine.
+   * @param {string} className The class to look for.
+   */
+  function removeChildrenByClassName(element, className) {
+    for (var child = element.firstElementChild; child;) {
+      var prev = child;
+      child = child.nextElementSibling;
+      if (prev.classList.contains(className))
+        element.removeChild(prev);
+    }
+  }
+
+  /**
+   * Callback invoked by chrome with the apps available.
+   *
+   * Note that calls to this function can occur at any time, not just in
+   * response to a getApps request. For example, when a user installs/uninstalls
+   * an app on another synchronized devices.
+   * @param {Object} data An object with all the data on available
+   *        applications.
+   */
+  function getAppsCallback(data)
+  {
+    // Clean up any existing grabber objects - cancelling any outstanding drag.
+    // Ideally an async app update wouldn't disrupt an active drag but
+    // that would require us to re-use existing elements and detect how the apps
+    // have changed, which would be a lot of work.
+    // Note that we have to explicitly clean up the grabber objects so they stop
+    // listening to events and break the DOM<->JS cycles necessary to enable
+    // collection of all these objects.
+    grabbers.forEach(function(g) {
+      // Note that this may raise DRAG_END/RELEASE events to clean up an
+      // oustanding drag.
+      g.dispose();
+    });
+    assert(!draggingAppContainer && !draggingAppOriginalPosition &&
+           !draggingAppOriginalPage);
+    grabbers = [];
+    appEvents.removeAll();
+
+    // Clear any existing apps pages and dots.
+    // TODO(rbyers): It might be nice to preserve animation of dots after an
+    // uninstall. Could we re-use the existing page and dot elements?  It seems
+    // unfortunate to have Chrome send us the entire apps list after an
+    // uninstall.
+    removeChildrenByClassName(appsPageList, 'apps-page');
+    removeChildrenByClassName(dotList, 'dot');
+
+    // Get the array of apps and add any special synthesized entries
+    var apps = data.apps;
+    apps.push(makeWebstoreApp());
+
+    // Sort by launch index
+    apps.sort(function(a, b) {
+      return a.app_launch_index - b.app_launch_index;
+    });
+
+    // Add the apps, creating pages as necessary
+    for (var i = 0; i < apps.length; i++) {
+      var app = apps[i];
+      var pageIndex = (app.page_index || 0);
+      while (pageIndex >= appsPages.length) {
+        var origPageCount = appsPages.length;
+        createAppPage();
+        // Confirm that appsPages is a live object, updated when a new page is
+        // added (otherwise we'd have an infinite loop)
+        assert(appsPages.length == origPageCount + 1, 'expected new page');
+      }
+      appendApp(appsPages[pageIndex], app);
+    }
+
+    // Tell the slider about the pages
+    updateSliderCards();
+
+    // Mark the current page
+    dots[slider.currentCard].classList.add('selected');
+  }
+
+  /**
+   * Make a synthesized app object representing the chrome web store.  It seems
+   * like this could just as easily come from the back-end, and then would
+   * support being rearranged, etc.
+   * @return {Object} The app object as would be sent from the webui back-end.
+   */
+  function makeWebstoreApp() {
+    return {
+      id: '',   // Empty ID signifies this is a special synthesized app
+      page_index: 0,
+      app_launch_index: -1,   // always first
+      name: templateData.web_store_title,
+      launch_url: templateData.web_store_url,
+      icon_big: getThemeUrl('IDR_WEBSTORE_ICON')
+    };
+  }
+
+  /**
+   * Given a theme resource name, construct a URL for it.
+   * @param {string} resourceName The name of the resource.
+   * @return {string} A url which can be used to load the resource.
+   */
+  function getThemeUrl(resourceName) {
+    // Allow standalone_hack.js to hook this mapping (since chrome:// URLs
+    // won't work for a standalone page)
+    if (typeof themeUrlMapper == 'function') {
+      var u = themeUrlMapper(resourceName);
+      if (u)
+        return u;
+    }
+    return 'chrome://theme/' + resourceName;
+  }
+
+  /**
+   * Callback invoked by chrome whenever an app preference changes.
+   * The normal NTP uses this to keep track of the current launch-type of an
+   * app, updating the choices in the context menu.  We don't have such a menu
+   * so don't use this at all (but it still needs to be here for chrome to
+   * call).
+   * @param {Object} data An object with all the data on available
+   *        applications.
+   */
+  function appsPrefChangeCallback(data) {
+  }
+
+  /**
+   * Invoked whenever the pages in apps-page-list have changed so that
+   * the Slider knows about the new elements.
+   */
+  function updateSliderCards() {
+    var pageNo = slider.currentCard;
+    if (pageNo >= appsPages.length)
+      pageNo = appsPages.length - 1;
+    var pageArray = [];
+    for (var i = 0; i < appsPages.length; i++)
+      pageArray[i] = appsPages[i];
+    slider.setCards(pageArray, pageNo);
+  }
+
+  /**
+   * Create a new app element and attach it to the end of the specified app
+   * page.
+   * @param {!Element} parent The element where the app should be inserted.
+   * @param {!Object} app The application object to create an app for.
+   */
+  function appendApp(parent, app) {
+    // Make a deep copy of the template and clear its ID
+    var containerElement = appTemplate.cloneNode(true);
+    var appElement = containerElement.getElementsByClassName('app')[0];
+    assert(appElement, 'Expected app-template to have an app child');
+    assert(typeof(app.id) == 'string',
+           'Expected every app to have an ID or empty string');
+    appElement.setAttribute('app-id', app.id);
+
+    // Find the span element (if any) and fill it in with the app name
+    var span = appElement.querySelector('span');
+    if (span)
+      span.textContent = app.name;
+
+    // Fill in the image
+    // We use a mask of the same image so CSS rules can highlight just the image
+    // when it's touched.
+    var appImg = appElement.querySelector('img');
+    if (appImg) {
+      appImg.src = app.icon_big;
+      appImg.style.webkitMaskImage = url(app.icon_big);
+      // We put a click handler just on the app image - so clicking on the
+      // margins between apps doesn't do anything
+      if (app.id) {
+        appEvents.add(appImg, 'click', appClick, false);
+      } else {
+        // Special case of synthesized apps - can't launch directly so just
+        // change the URL as if we clicked a link.  We may want to eventually
+        // support tracking clicks with ping messages, but really it seems it
+        // would be better for the back-end to just create virtual apps for such
+        // cases.
+        appEvents.add(appImg, 'click', function(e) {
+          window.location = app.launch_url;
+        }, false);
+      }
+    }
+
+    // Only real apps with back-end storage (for their launch index, etc.) can
+    // be rearranged.
+    if (app.id) {
+      // Create a grabber to support moving apps around
+      // Note that we move the app rather than the container. This is so that an
+      // element remains in the original position so we can detect when an app
+      // is dropped in its starting location.
+      var grabber = new Grabber(appElement);
+      grabbers.push(grabber);
+
+      // Register to be made aware of when we are dragged
+      appEvents.add(appElement, Grabber.EventType.DRAG_START, appDragStart,
+                    false);
+      appEvents.add(appElement, Grabber.EventType.DRAG_END, appDragEnd,
+                    false);
+
+      // Register to be made aware of any app drags on top of our container
+      appEvents.add(containerElement, Grabber.EventType.DRAG_ENTER,
+          appDragEnter, false);
+    } else {
+      // Prevent any built-in drag-and-drop support from activating for the
+      // element.
+      appEvents.add(appElement, 'dragstart', function(e) {
+        e.preventDefault();
+      }, true);
+    }
+
+    // Insert at the end of the provided page
+    parent.appendChild(containerElement);
+  }
+
+  /**
+   * Creates a new page for apps
+   *
+   * @return {!Element} The apps-page element created.
+   * @param {boolean=} opt_animate If true, add the class 'new' to the created
+   *        dot.
+   */
+  function createAppPage(opt_animate)
+  {
+    // Make a shallow copy of the app page template.
+    var newPage = appsPageTemplate.cloneNode(false);
+    appsPageList.appendChild(newPage);
+
+    // Make a deep copy of the dot template to add a new one.
+    var dotCount = dots.length;
+    var newDot = dotTemplate.cloneNode(true);
+    if (opt_animate)
+      newDot.classList.add('new');
+    dotList.appendChild(newDot);
+
+    // Add click handler to the dot to change the page.
+    // TODO(rbyers): Perhaps this should be TouchHandler.START_EVENT_ (so we
+    // don't rely on synthesized click events, and the change takes effect
+    // before releasing). However, click events seems to be synthesized for a
+    // region outside the border, and a 10px box is too small to require touch
+    // events to fall inside of. We could get around this by adding a box around
+    // the dot for accepting the touch events.
+    function switchPage(e) {
+      slider.selectCard(dotCount, true);
+      e.stopPropagation();
+    }
+    appEvents.add(newDot, 'click', switchPage, false);
+
+    // Change pages whenever an app is dragged over a dot.
+    appEvents.add(newDot, Grabber.EventType.DRAG_ENTER, switchPage, false);
+
+    return newPage;
+  }
+
+  /**
+   * Invoked when an app is clicked
+   * @param {Event} e The click event.
+   */
+  function appClick(e) {
+    var target = e.currentTarget;
+    var app = getParentByClassName(target, 'app');
+    assert(app, 'appClick should have been on a descendant of an app');
+
+    var appId = app.getAttribute('app-id');
+    assert(appId, 'unexpected app without appId');
+
+    // Tell chrome to launch the app.
+    var NTP_APPS_MAXIMIZED = 0;
+    chrome.send('launchApp', [appId, NTP_APPS_MAXIMIZED]);
+
+    // Don't allow the click to trigger a link or anything
+    e.preventDefault();
+  }
+
+  /**
+   * Search an elements ancestor chain for the nearest element that is a member
+   * of the specified class.
+   * @param {!Element} element The element to start searching from.
+   * @param {string} className The name of the class to locate.
+   * @return {Element} The first ancestor of the specified class or null.
+   */
+  function getParentByClassName(element, className)
+  {
+    for (var e = element; e; e = e.parentElement) {
+      if (e.classList.contains(className))
+        return e;
+    }
+    return null;
+  }
+
+  /**
+   * The container where the app currently being dragged came from.
+   * @type {!Element|undefined}
+   */
+  var draggingAppContainer;
+
+  /**
+   * The apps-page that the app currently being dragged camed from.
+   * @type {!Element|undefined}
+   */
+  var draggingAppOriginalPage;
+
+  /**
+   * The element that was originally after the app currently being dragged (or
+   * null if it was the last on the page).
+   * @type {!Element|undefined}
+   */
+  var draggingAppOriginalPosition;
+
+  /**
+   * Invoked when app dragging begins.
+   * @param {Grabber.Event} e The event from the Grabber indicating the drag.
+   */
+  function appDragStart(e) {
+    // Pull the element out to the appsFrame using fixed positioning. This
+    // ensures that the app is not affected (remains under the finger) if the
+    // slider changes cards and is translated.  An alternate approach would be
+    // to use fixed positioning for the slider (so that changes to its position
+    // don't affect children that aren't positioned relative to it), but we
+    // don't yet have GPU acceleration for this.  Note that we use the appsFrame
+    var element = e.grabbedElement;
+
+    var pos = element.getBoundingClientRect();
+    element.style.webkitTransform = '';
+
+    element.style.position = 'fixed';
+    // Don't want to zoom around the middle since the left/top co-ordinates
+    // are post-transform values.
+    element.style.webkitTransformOrigin = 'left top';
+    element.style.left = pos.left + 'px';
+    element.style.top = pos.top + 'px';
+
+    // Keep track of what app is being dragged and where it came from
+    assert(!draggingAppContainer, 'got DRAG_START without DRAG_END');
+    draggingAppContainer = element.parentNode;
+    assert(draggingAppContainer.classList.contains('app-container'));
+    draggingAppOriginalPosition = draggingAppContainer.nextSibling;
+    draggingAppOriginalPage = draggingAppContainer.parentNode;
+
+    // Move the app out of the container
+    // Note that appendChild also removes the element from its current parent.
+    getRequiredElement('apps-frame').appendChild(element);
+  }
+
+  /**
+   * Invoked when app dragging terminates (either successfully or not)
+   * @param {Grabber.Event} e The event from the Grabber.
+   */
+  function appDragEnd(e) {
+    // Stop floating the app
+    var appBeingDragged = e.grabbedElement;
+    assert(appBeingDragged.classList.contains('app'));
+    appBeingDragged.style.position = '';
+    appBeingDragged.style.webkitTransformOrigin = '';
+    appBeingDragged.style.left = '';
+    appBeingDragged.style.top = '';
+
+    // Ensure the trash can is not active (we won't necessarily get a DRAG_LEAVE
+    // for it - eg. if we drop on it, or the drag is cancelled)
+    trash.classList.remove('hover');
+    appBeingDragged.classList.remove('trashing');
+
+    // If we have an active drag (i.e. it wasn't aborted by an app update)
+    if (draggingAppContainer) {
+      // Put the app back into it's container
+      if (appBeingDragged.parentNode != draggingAppContainer)
+        draggingAppContainer.appendChild(appBeingDragged);
+
+      // If we care about the container's original position
+      if (draggingAppOriginalPage)
+      {
+        // Then put the container back where it came from
+        if (draggingAppOriginalPosition) {
+          draggingAppOriginalPage.insertBefore(draggingAppContainer,
+                                               draggingAppOriginalPosition);
+        } else {
+          draggingAppOriginalPage.appendChild(draggingAppContainer);
+        }
+      }
+    }
+
+    draggingAppContainer = undefined;
+    draggingAppOriginalPage = undefined;
+    draggingAppOriginalPosition = undefined;
+  }
+
+  /**
+   * Invoked when an app is dragged over another app.  Updates the DOM to affect
+   * the rearrangement (but doesn't commit the change until the app is dropped).
+   * @param {Grabber.Event} e The event from the Grabber indicating the drag.
+   */
+  function appDragEnter(e)
+  {
+    assert(draggingAppContainer, 'expected stored container');
+    var sourceContainer = draggingAppContainer;
+
+    // Ensure enter events delivered to an app-container don't also get
+    // delivered to the document.
+    e.stopPropagation();
+
+    var curPage = appsPages[slider.currentCard];
+    var followingContainer = null;
+
+    // If we dragged over a specific app, determine which one to insert before
+    if (e.currentTarget != document) {
+
+      // Start by assuming we'll insert the app before the one dragged over
+      followingContainer = e.currentTarget;
+      assert(followingContainer.classList.contains('app-container'),
+             'expected drag over container');
+      assert(followingContainer.parentNode == curPage);
+      if (followingContainer == draggingAppContainer)
+        return;
+
+      // But if it's after the current container position then we'll need to
+      // move ahead by one to account for the container being removed.
+      if (curPage == draggingAppContainer.parentNode) {
+        for (var c = draggingAppContainer; c; c = c.nextElementSibling) {
+          if (c == followingContainer) {
+            followingContainer = followingContainer.nextElementSibling;
+            break;
+          }
+        }
+      }
+    }
+
+    // Move the container to the appropriate place on the page
+    curPage.insertBefore(draggingAppContainer, followingContainer);
+  }
+
+  /**
+   * Invoked when an app is dropped on the trash
+   * @param {Grabber.Event} e The event from the Grabber indicating the drop.
+   */
+  function appTrash(e) {
+    var appElement = e.grabbedElement;
+    assert(appElement.classList.contains('app'));
+    var appId = appElement.getAttribute('app-id');
+    assert(appId);
+
+    // Mark this drop as handled so that the catch-all drop handler
+    // on the document doesn't see this event.
+    e.stopPropagation();
+
+    // Tell chrome to uninstall the app (prompting the user)
+    chrome.send('uninstallApp', [appId]);
+  }
+
+  /**
+   * Called when an app is dropped anywhere other than the trash can.  Commits
+   * any movement that has occurred.
+   * @param {Grabber.Event} e The event from the Grabber indicating the drop.
+   */
+  function appDrop(e) {
+    if (!draggingAppContainer)
+      // Drag was aborted (eg. due to an app update) - do nothing
+      return;
+
+    // If the app is dropped back into it's original position then do nothing
+    assert(draggingAppOriginalPage);
+    if (draggingAppContainer.parentNode == draggingAppOriginalPage &&
+        draggingAppContainer.nextSibling == draggingAppOriginalPosition)
+      return;
+
+    // Determine which app was being dragged
+    var appElement = e.grabbedElement;
+    assert(appElement.classList.contains('app'));
+    var appId = appElement.getAttribute('app-id');
+    assert(appId);
+
+    // Update the page index for the app if it's changed.  This doesn't trigger
+    // a call to getAppsCallback so we want to do it before reorderApps
+    var pageIndex = slider.currentCard;
+    assert(pageIndex >= 0 && pageIndex < appsPages.length,
+           'page number out of range');
+    if (appsPages[pageIndex] != draggingAppOriginalPage)
+      chrome.send('setPageIndex', [appId, pageIndex]);
+
+    // Put the app being dragged back into it's container
+    draggingAppContainer.appendChild(appElement);
+
+    // Create a list of all appIds in the order now present in the DOM
+    var appIds = [];
+    for (var page = 0; page < appsPages.length; page++) {
+      var appsOnPage = appsPages[page].getElementsByClassName('app');
+      for (var i = 0; i < appsOnPage.length; i++) {
+        var id = appsOnPage[i].getAttribute('app-id');
+        if (id)
+          appIds.push(id);
+      }
+    }
+
+    // We are going to commit this repositioning - clear the original position
+    draggingAppOriginalPage = undefined;
+    draggingAppOriginalPosition = undefined;
+
+    // Tell chrome to update its database to persist this new order of apps This
+    // will cause getAppsCallback to be invoked and the apps to be redrawn.
+    chrome.send('reorderApps', [appId, appIds]);
+    appMoved = true;
+  }
+
+  /**
+   * Set to true if we're currently in rearrange mode and an app has
+   * been successfully dropped to a new location.  This indicates that
+   * a getAppsCallback call is pending and we can rely on the DOM being
+   * updated by that.
+   * @type {boolean}
+   */
+  var appMoved = false;
+
+  /**
+   * Invoked whenever some app is grabbed
+   * @param {Grabber.Event} e The Grabber Grab event.
+   */
+  function enterRearrangeMode(e)
+  {
+    // Stop the slider from sliding for this touch
+    slider.cancelTouch();
+
+    // Add an extra blank page in case the user wants to create a new page
+    createAppPage(true);
+    var pageAdded = appsPages.length - 1;
+    window.setTimeout(function() {
+      dots[pageAdded].classList.remove('new');
+    }, 0);
+
+    updateSliderCards();
+
+    // Cause the dot-list to grow
+    getRequiredElement('footer').classList.add('rearrange-mode');
+
+    assert(!appMoved, 'appMoved should not be set yet');
+  }
+
+  /**
+   * Invoked whenever some app is released
+   * @param {Grabber.Event} e The Grabber RELEASE event.
+   */
+  function leaveRearrangeMode(e)
+  {
+    // Return the dot-list to normal
+    getRequiredElement('footer').classList.remove('rearrange-mode');
+
+    // If we didn't successfully re-arrange an app, then we won't be
+    // refreshing the app view in getAppCallback and need to explicitly remove
+    // the extra empty page we added.  We don't want to do this in the normal
+    // case because if we did actually drop an app there, we want to retain that
+    // page as our current page number.
+    if (!appMoved) {
+      assert(appsPages[appsPages.length - 1].
+             getElementsByClassName('app-container').length == 0,
+             'Last app page should be empty');
+      removePage(appsPages.length - 1);
+    }
+    appMoved = false;
+  }
+
+  /**
+   * Remove the page with the specified index and update the slider.
+   * @param {number} pageNo The index of the page to remove.
+   */
+  function removePage(pageNo)
+  {
+    var page = appsPages[pageNo];
+
+    // Remove the page from the DOM
+    page.parentNode.removeChild(page);
+
+    // Remove the corresponding dot
+    // Need to give it a chance to animate though
+    var dot = dots[pageNo];
+    dot.classList.add('new');
+    window.setTimeout(function() {
+      // If we've re-created the apps (eg. because an app was uninstalled) then
+      // we will have removed the old dots from the document already, so skip.
+      if (dot.parentNode)
+        dot.parentNode.removeChild(dot);
+    }, DEFAULT_TRANSITION_TIME);
+
+    updateSliderCards();
+  }
+
+  // Return an object with all the exports
+  return {
+    assert: assert,
+    appsPrefChangeCallback: appsPrefChangeCallback,
+    getAppsCallback: getAppsCallback,
+    initialize: initializeNtp
+  };
+})();
+
+// publish ntp globals
+var assert = ntp.assert;
+var getAppsCallback = ntp.getAppsCallback;
+var appsPrefChangeCallback = ntp.appsPrefChangeCallback;
+
+// Initialize immediately once globals are published (there doesn't seem to be
+// any need to wait for DOMContentLoaded)
+ntp.initialize();