// Copyright (c) 2012 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.

cr.define('ntp', function() {
  'use strict';

  var APP_LAUNCH = {
    // The histogram buckets (keep in sync with extension_constants.h).
    NTP_APPS_MAXIMIZED: 0,
    NTP_APPS_COLLAPSED: 1,
    NTP_APPS_MENU: 2,
    NTP_MOST_VISITED: 3,
    NTP_APP_RE_ENABLE: 16,
    NTP_WEBSTORE_FOOTER: 18,
    NTP_WEBSTORE_PLUS_ICON: 19,
  };

  // Histogram buckets for UMA tracking of where a DnD drop came from.
  var DRAG_SOURCE = {
    SAME_APPS_PANE: 0,
    OTHER_APPS_PANE: 1,
    MOST_VISITED_PANE: 2,  // Deprecated.
    BOOKMARKS_PANE: 3,  // Deprecated.
    OUTSIDE_NTP: 4
  };
  var DRAG_SOURCE_LIMIT = DRAG_SOURCE.OUTSIDE_NTP + 1;

  /**
   * App context menu. The class is designed to be used as a singleton with
   * the app that is currently showing a context menu stored in this.app_.
   * @constructor
   */
  function AppContextMenu() {
    this.__proto__ = AppContextMenu.prototype;
    this.initialize();
  }
  cr.addSingletonGetter(AppContextMenu);

  AppContextMenu.prototype = {
    initialize: function() {
      var menu = new cr.ui.Menu;
      cr.ui.decorate(menu, cr.ui.Menu);
      menu.classList.add('app-context-menu');
      this.menu = menu;

      this.launch_ = this.appendMenuItem_();
      this.launch_.addEventListener('activate', this.onLaunch_.bind(this));

      menu.appendChild(cr.ui.MenuItem.createSeparator());
      this.launchRegularTab_ = this.appendMenuItem_('applaunchtyperegular');
      this.launchPinnedTab_ = this.appendMenuItem_('applaunchtypepinned');
      if (loadTimeData.getBoolean('enableNewBookmarkApps') || !cr.isMac)
        this.launchNewWindow_ = this.appendMenuItem_('applaunchtypewindow');
      this.launchFullscreen_ = this.appendMenuItem_('applaunchtypefullscreen');

      var self = this;
      this.forAllLaunchTypes_(function(launchTypeButton, id) {
        launchTypeButton.addEventListener('activate',
            self.onLaunchTypeChanged_.bind(self));
      });

      this.launchTypeMenuSeparator_ = cr.ui.MenuItem.createSeparator();
      menu.appendChild(this.launchTypeMenuSeparator_);
      this.options_ = this.appendMenuItem_('appoptions');
      this.uninstall_ = this.appendMenuItem_('appuninstall');

      if (loadTimeData.getBoolean('canShowAppInfoDialog')) {
        this.appinfo_ = this.appendMenuItem_('appinfodialog');
        this.appinfo_.addEventListener('activate',
                                       this.onShowAppInfo_.bind(this));
      } else {
        this.details_ = this.appendMenuItem_('appdetails');
        this.details_.addEventListener('activate',
                                       this.onShowDetails_.bind(this));
      }

      this.options_.addEventListener('activate',
                                     this.onShowOptions_.bind(this));
      this.uninstall_.addEventListener('activate',
                                       this.onUninstall_.bind(this));

      if (!cr.isChromeOS) {
        this.createShortcutSeparator_ =
            menu.appendChild(cr.ui.MenuItem.createSeparator());
        this.createShortcut_ = this.appendMenuItem_('appcreateshortcut');
        this.createShortcut_.addEventListener(
            'activate', this.onCreateShortcut_.bind(this));
      }

      document.body.appendChild(menu);
    },

    /**
     * Appends a menu item to |this.menu|.
     * @param {string=} opt_textId If defined, the ID for the localized string
     *     that acts as the item's label.
     */
    appendMenuItem_: function(opt_textId) {
      var button = cr.doc.createElement('button');
      this.menu.appendChild(button);
      cr.ui.decorate(button, cr.ui.MenuItem);
      if (opt_textId)
        button.textContent = loadTimeData.getString(opt_textId);
      return button;
    },

    /**
     * Iterates over all the launch type menu items.
     * @param {function(cr.ui.MenuItem, number)} f The function to call for each
     *     menu item. The parameters to the function include the menu item and
     *     the associated launch ID.
     */
    forAllLaunchTypes_: function(f) {
      // Order matters: index matches launchType id.
      var launchTypes = [this.launchPinnedTab_,
                         this.launchRegularTab_,
                         this.launchFullscreen_,
                         this.launchNewWindow_];

      for (var i = 0; i < launchTypes.length; ++i) {
        if (!launchTypes[i])
          continue;

        f(launchTypes[i], i);
      }
    },

    /**
     * Does all the necessary setup to show the menu for the given app.
     * @param {App} app The App object that will be showing a context menu.
     */
    setupForApp: function(app) {
      this.app_ = app;

      this.launch_.textContent = app.appData.title;

      var launchTypeWindow = this.launchNewWindow_;
      this.forAllLaunchTypes_(function(launchTypeButton, id) {
        launchTypeButton.disabled = false;
        launchTypeButton.checked = app.appData.launch_type == id;
        // If bookmark apps are enabled, only show the "Open as window" button.
        launchTypeButton.hidden = app.appData.packagedApp ||
            (loadTimeData.getBoolean('enableNewBookmarkApps') &&
             launchTypeButton != launchTypeWindow);
      });

      this.launchTypeMenuSeparator_.hidden = app.appData.packagedApp;

      this.options_.disabled = !app.appData.optionsUrl || !app.appData.enabled;
      if (this.details_)
        this.details_.disabled = !app.appData.detailsUrl;
      this.uninstall_.disabled = !app.appData.mayDisable;

      if (cr.isMac) {
        // On Windows and Linux, these should always be visible. On ChromeOS,
        // they are never created. On Mac, shortcuts can only be created for
        // new-style packaged apps, so hide the menu item.
        this.createShortcutSeparator_.hidden = this.createShortcut_.hidden =
            !app.appData.packagedApp;
      }
    },

    /**
     * Handlers for menu item activation.
     * @param {Event} e The activation event.
     * @private
     */
    onLaunch_: function(e) {
      chrome.send('launchApp', [this.app_.appId, APP_LAUNCH.NTP_APPS_MENU]);
    },
    onLaunchTypeChanged_: function(e) {
      var pressed = e.currentTarget;
      var app = this.app_;
      var targetLaunchType = pressed;
      // When bookmark apps are enabled, hosted apps can only toggle between
      // open as window and open as tab.
      if (loadTimeData.getBoolean('enableNewBookmarkApps')) {
        targetLaunchType = this.launchNewWindow_.checked ?
            this.launchRegularTab_ : this.launchNewWindow_;
      }
      this.forAllLaunchTypes_(function(launchTypeButton, id) {
        if (launchTypeButton == targetLaunchType) {
          chrome.send('setLaunchType', [app.appId, id]);
          // Manually update the launch type. We will only get
          // appsPrefChangeCallback calls after changes to other NTP instances.
          app.appData.launch_type = id;
        }
      });
    },
    onShowOptions_: function(e) {
      window.location = this.app_.appData.optionsUrl;
    },
    onShowDetails_: function(e) {
      var url = this.app_.appData.detailsUrl;
      url = appendParam(url, 'utm_source', 'chrome-ntp-launcher');
      window.location = url;
    },
    onUninstall_: function(e) {
      chrome.send('uninstallApp', [this.app_.appData.id]);
    },
    onCreateShortcut_: function(e) {
      chrome.send('createAppShortcut', [this.app_.appData.id]);
    },
    onShowAppInfo_: function(e) {
      chrome.send('showAppInfo', [this.app_.appData.id]);
    }
  };

  /**
   * Creates a new App object.
   * @param {Object} appData The data object that describes the app.
   * @constructor
   * @extends {HTMLDivElement}
   */
  function App(appData) {
    var el = cr.doc.createElement('div');
    el.__proto__ = App.prototype;
    el.initialize(appData);

    return el;
  }

  App.prototype = {
    __proto__: HTMLDivElement.prototype,

    /**
     * Initialize the app object.
     * @param {Object} appData The data object that describes the app.
     */
    initialize: function(appData) {
      this.appData = appData;
      assert(this.appData_.id, 'Got an app without an ID');
      this.id = this.appData_.id;
      this.setAttribute('role', 'menuitem');

      this.className = 'app focusable';

      if (!this.appData_.icon_big_exists && this.appData_.icon_small_exists)
        this.useSmallIcon_ = true;

      this.appContents_ = this.useSmallIcon_ ?
          $('app-small-icon-template').cloneNode(true) :
          $('app-large-icon-template').cloneNode(true);
      this.appContents_.id = '';
      this.appendChild(this.appContents_);

      this.appImgContainer_ = /** @type {HTMLElement} */(
          this.querySelector('.app-img-container'));
      this.appImg_ = this.appImgContainer_.querySelector('img');
      this.setIcon();

      if (this.useSmallIcon_) {
        this.imgDiv_ = /** @type {HTMLElement} */(
            this.querySelector('.app-icon-div'));
        this.addLaunchClickTarget_(this.imgDiv_);
        this.imgDiv_.title = this.appData_.full_name;
        chrome.send('getAppIconDominantColor', [this.id]);
      } else {
        this.addLaunchClickTarget_(this.appImgContainer_);
        this.appImgContainer_.title = this.appData_.full_name;
      }

      // The app's full name is shown in the tooltip, whereas the short name
      // is used for the label.
      var appSpan = /** @type {HTMLElement} */(
          this.appContents_.querySelector('.title'));
      appSpan.textContent = this.appData_.title;
      appSpan.title = this.appData_.full_name;
      this.addLaunchClickTarget_(appSpan);

      this.addEventListener('keydown', cr.ui.contextMenuHandler);
      this.addEventListener('keyup', cr.ui.contextMenuHandler);

      // This hack is here so that appContents.contextMenu will be the same as
      // this.contextMenu.
      var self = this;
      this.appContents_.__defineGetter__('contextMenu', function() {
        return self.contextMenu;
      });

      if (!this.appData_.kioskMode) {
        this.appContents_.addEventListener('contextmenu',
                                           cr.ui.contextMenuHandler);
      }

      this.addEventListener('mousedown', this.onMousedown_, true);
      this.addEventListener('keydown', this.onKeydown_);
      this.addEventListener('keyup', this.onKeyup_);
    },

    /**
     * Sets the color of the favicon dominant color bar.
     * @param {string} color The css-parsable value for the color.
     */
    set stripeColor(color) {
      this.querySelector('.color-stripe').style.backgroundColor = color;
    },

    /**
     * Removes the app tile from the page. Should be called after the app has
     * been uninstalled.
     */
    remove: function(opt_animate) {
      // Unset the ID immediately, because the app is already gone. But leave
      // the tile on the page as it animates out.
      this.id = '';
      this.tile.doRemove(opt_animate);
    },

    /**
     * Set the URL of the icon from |appData_|. This won't actually show the
     * icon until loadIcon() is called (for performance reasons; we don't want
     * to load icons until we have to).
     */
    setIcon: function() {
      var src = this.useSmallIcon_ ? this.appData_.icon_small :
                                     this.appData_.icon_big;
      if (!this.appData_.enabled ||
          (!this.appData_.offlineEnabled && !navigator.onLine)) {
        src += '?grayscale=true';
      }

      this.appImgSrc_ = src;
      this.classList.add('icon-loading');
    },

    /**
     * Shows the icon for the app. That is, it causes chrome to load the app
     * icon resource.
     */
    loadIcon: function() {
      if (this.appImgSrc_) {
        this.appImg_.src = this.appImgSrc_;
        this.appImg_.classList.remove('invisible');
        this.appImgSrc_ = null;
      }

      this.classList.remove('icon-loading');
    },

    /**
     * Set the size and position of the app tile.
     * @param {number} size The total size of |this|.
     * @param {number} x The x-position.
     * @param {number} y The y-position.
     *     animate.
     */
    setBounds: function(size, x, y) {
      var imgSize = size * APP_IMG_SIZE_FRACTION;
      this.appImgContainer_.style.width = this.appImgContainer_.style.height =
          toCssPx(this.useSmallIcon_ ? 16 : imgSize);
      if (this.useSmallIcon_) {
        // 3/4 is the ratio of 96px to 128px (the used height and full height
        // of icons in apps).
        var iconSize = imgSize * 3 / 4;
        // The -2 is for the div border to improve the visual alignment for the
        // icon div.
        this.imgDiv_.style.width = this.imgDiv_.style.height =
            toCssPx(iconSize - 2);
        // Margins set to get the icon placement right and the text to line up.
        this.imgDiv_.style.marginTop = this.imgDiv_.style.marginBottom =
            toCssPx((imgSize - iconSize) / 2);
      }

      this.style.width = this.style.height = toCssPx(size);
      this.style.left = toCssPx(x);
      this.style.right = toCssPx(x);
      this.style.top = toCssPx(y);
    },

    /**
     * Invoked when an app is clicked.
     * @param {Event} e The click event.
     * @private
     */
    onClick_: function(e) {
      var url = !this.appData_.is_webstore ? '' :
          appendParam(this.appData_.url,
                      'utm_source',
                      'chrome-ntp-icon');

      chrome.send('launchApp',
                  [this.appId, APP_LAUNCH.NTP_APPS_MAXIMIZED, url,
                   e.button, e.altKey, e.ctrlKey, e.metaKey, e.shiftKey]);

      // Don't allow the click to trigger a link or anything
      e.preventDefault();
    },

    /**
     * Invoked when the user presses a key while the app is focused.
     * @param {Event} e The key event.
     * @private
     */
    onKeydown_: function(e) {
      if (e.keyIdentifier == 'Enter') {
        chrome.send('launchApp',
                    [this.appId, APP_LAUNCH.NTP_APPS_MAXIMIZED, '',
                     0, e.altKey, e.ctrlKey, e.metaKey, e.shiftKey]);
        e.preventDefault();
        e.stopPropagation();
      }
      this.onKeyboardUsed_(e.keyCode);
    },

    /**
     * Invoked when the user releases a key while the app is focused.
     * @param {Event} e The key event.
     * @private
     */
    onKeyup_: function(e) {
      this.onKeyboardUsed_(e.keyCode);
    },

    /**
     * Called when the keyboard has been used (key down or up). The .click-focus
     * hack is removed if the user presses a key that can change focus.
     * @param {number} keyCode The key code of the keyboard event.
     * @private
     */
    onKeyboardUsed_: function(keyCode) {
      switch (keyCode) {
        case 9:  // Tab.
        case 37:  // Left arrow.
        case 38:  // Up arrow.
        case 39:  // Right arrow.
        case 40:  // Down arrow.
          this.classList.remove('click-focus');
      }
    },

    /**
     * Adds a node to the list of targets that will launch the app. This list
     * is also used in onMousedown to determine whether the app contents should
     * be shown as active (if we don't do this, then clicking anywhere in
     * appContents, even a part that is outside the ideally clickable region,
     * will cause the app icon to look active).
     * @param {HTMLElement} node The node that should be clickable.
     */
    addLaunchClickTarget_: function(node) {
      node.classList.add('launch-click-target');
      node.addEventListener('click', this.onClick_.bind(this));
    },

    /**
     * Handler for mousedown on the App. Adds a class that allows us to
     * not display as :active for right clicks (specifically, don't pulse on
     * these occasions). Also, we don't pulse for clicks that aren't within the
     * clickable regions.
     * @param {Event} e The mousedown event.
     */
    onMousedown_: function(e) {
      // If the current platform uses middle click to autoscroll and this
      // mousedown isn't handled, onClick_() will never fire. crbug.com/142939
      if (e.button == 1)
        e.preventDefault();

      if (e.button == 2 ||
          !findAncestorByClass(/** @type {Element} */(e.target),
                               'launch-click-target')) {
        this.appContents_.classList.add('suppress-active');
      } else {
        this.appContents_.classList.remove('suppress-active');
      }

      // This class is here so we don't show the focus state for apps that
      // gain keyboard focus via mouse clicking.
      this.classList.add('click-focus');
    },

    /**
     * Change the appData and update the appearance of the app.
     * @param {AppInfo} appData The new data object that describes the app.
     */
    replaceAppData: function(appData) {
      this.appData_ = appData;
      this.setIcon();
      this.loadIcon();
    },

    /**
     * The data and preferences for this app.
     * @type {Object}
     */
    set appData(data) {
      this.appData_ = data;
    },
    get appData() {
      return this.appData_;
    },

    get appId() {
      return this.appData_.id;
    },

    /**
     * Returns a pointer to the context menu for this app. All apps share the
     * singleton AppContextMenu. This function is called by the
     * ContextMenuHandler in response to the 'contextmenu' event.
     * @type {cr.ui.Menu}
     */
    get contextMenu() {
      var menu = AppContextMenu.getInstance();
      menu.setupForApp(this);
      return menu.menu;
    },

    /**
     * Returns whether this element can be 'removed' from chrome (i.e. whether
     * the user can drag it onto the trash and expect something to happen).
     * @return {boolean} True if the app can be uninstalled.
     */
    canBeRemoved: function() {
      return this.appData_.mayDisable;
    },

    /**
     * Uninstalls the app after it's been dropped on the trash.
     */
    removeFromChrome: function() {
      chrome.send('uninstallApp', [this.appData_.id, true]);
      this.tile.tilePage.removeTile(this.tile, true);
    },

    /**
     * Called when a drag is starting on the tile. Updates dataTransfer with
     * data for this tile.
     */
    setDragData: function(dataTransfer) {
      dataTransfer.setData('Text', this.appData_.title);
      dataTransfer.setData('URL', this.appData_.url);
    },
  };

  var TilePage = ntp.TilePage;

  // The fraction of the app tile size that the icon uses.
  var APP_IMG_SIZE_FRACTION = 4 / 5;

  var appsPageGridValues = {
    // The fewest tiles we will show in a row.
    minColCount: 3,
    // The most tiles we will show in a row.
    maxColCount: 6,

    // The smallest a tile can be.
    minTileWidth: 64 / APP_IMG_SIZE_FRACTION,
    // The biggest a tile can be.
    maxTileWidth: 128 / APP_IMG_SIZE_FRACTION,

    // The padding between tiles, as a fraction of the tile width.
    tileSpacingFraction: 1 / 8,
  };
  TilePage.initGridValues(appsPageGridValues);

  /**
   * Creates a new AppsPage object.
   * @constructor
   * @extends {TilePage}
   */
  function AppsPage() {
    var el = new TilePage(appsPageGridValues);
    el.__proto__ = AppsPage.prototype;
    el.initialize();

    return el;
  }

  AppsPage.prototype = {
    __proto__: TilePage.prototype,

    initialize: function() {
      this.classList.add('apps-page');

      this.addEventListener('cardselected', this.onCardSelected_);

      this.addEventListener('tilePage:tile_added', this.onTileAdded_);

      this.content_.addEventListener('scroll', this.onScroll_.bind(this));
    },

    /**
     * Highlight a newly installed app as it's added to the NTP.
     * @param {AppInfo} appData The data object that describes the app.
     */
    insertAndHighlightApp: function(appData) {
      ntp.getCardSlider().selectCardByValue(this);
      this.content_.scrollTop = this.content_.scrollHeight;
      this.insertApp(appData, true);
    },

    /**
     * Similar to appendApp, but it respects the app_launch_ordinal field of
     * |appData|.
     * @param {Object} appData The data that describes the app.
     * @param {boolean} animate Whether to animate the insertion.
     */
    insertApp: function(appData, animate) {
      var index = this.tileElements_.length;
      for (var i = 0; i < this.tileElements_.length; i++) {
        if (appData.app_launch_ordinal <
            this.tileElements_[i].firstChild.appData.app_launch_ordinal) {
          index = i;
          break;
        }
      }

      this.addTileAt(new App(appData), index, animate);
    },

    /**
     * Handler for 'cardselected' event, fired when |this| is selected. The
     * first time this is called, we load all the app icons.
     * @private
     */
    onCardSelected_: function(e) {
      var apps = this.querySelectorAll('.app.icon-loading');
      for (var i = 0; i < apps.length; i++) {
        apps[i].loadIcon();
      }
    },

    /**
     * Handler for tile additions to this page.
     * @param {Event} e The tilePage:tile_added event.
     */
    onTileAdded_: function(e) {
      assert(e.currentTarget == this);
      assert(e.addedTile.firstChild instanceof App);
      if (this.classList.contains('selected-card'))
        e.addedTile.firstChild.loadIcon();
    },

    /**
     * A handler for when the apps page is scrolled (then we need to reposition
     * the bubbles.
     * @private
     */
    onScroll_: function(e) {
      if (!this.selected)
        return;
      for (var i = 0; i < this.tileElements_.length; i++) {
        var app = this.tileElements_[i].firstChild;
        assert(app instanceof App);
      }
    },

    /** @override */
    doDragOver: function(e) {
      // Only animatedly re-arrange if the user is currently dragging an app.
      var tile = ntp.getCurrentlyDraggingTile();
      if (tile && tile.querySelector('.app')) {
        TilePage.prototype.doDragOver.call(this, e);
      } else {
        e.preventDefault();
        this.setDropEffect(e.dataTransfer);
      }
    },

    /** @override */
    shouldAcceptDrag: function(e) {
      if (ntp.getCurrentlyDraggingTile())
        return true;
      if (!e.dataTransfer || !e.dataTransfer.types)
        return false;
      return Array.prototype.indexOf.call(e.dataTransfer.types,
                                          'text/uri-list') != -1;
    },

    /** @override */
    addDragData: function(dataTransfer, index) {
      var sourceId = -1;
      var currentlyDraggingTile = ntp.getCurrentlyDraggingTile();
      if (currentlyDraggingTile) {
        var tileContents = currentlyDraggingTile.firstChild;
        if (tileContents.classList.contains('app')) {
          var originalPage = currentlyDraggingTile.tilePage;
          var samePageDrag = originalPage == this;
          sourceId = samePageDrag ? DRAG_SOURCE.SAME_APPS_PANE :
                                    DRAG_SOURCE.OTHER_APPS_PANE;
          this.tileGrid_.insertBefore(currentlyDraggingTile,
                                      this.tileElements_[index]);
          this.tileMoved(currentlyDraggingTile);
          if (!samePageDrag) {
            originalPage.fireRemovedEvent(currentlyDraggingTile, index, true);
            this.fireAddedEvent(currentlyDraggingTile, index, true);
          }
        }
      } else {
        this.addOutsideData_(dataTransfer);
        sourceId = DRAG_SOURCE.OUTSIDE_NTP;
      }

      assert(sourceId != -1);
      chrome.send('metricsHandler:recordInHistogram',
          ['NewTabPage.AppsPageDragSource', sourceId, DRAG_SOURCE_LIMIT]);
    },

    /**
     * Adds drag data that has been dropped from a source that is not a tile.
     * @param {Object} dataTransfer The data transfer object that holds drop
     *     data.
     * @private
     */
    addOutsideData_: function(dataTransfer) {
      var url = dataTransfer.getData('url');
      assert(url);

      // If the dataTransfer has html data, use that html's text contents as the
      // title of the new link.
      var html = dataTransfer.getData('text/html');
      var title;
      if (html) {
        // It's important that we don't attach this node to the document
        // because it might contain scripts.
        var node = this.ownerDocument.createElement('div');
        node.innerHTML = html;
        title = node.textContent;
      }

      // Make sure title is >=1 and <=45 characters for Chrome app limits.
      if (!title)
        title = url;
      if (title.length > 45)
        title = title.substring(0, 45);
      var data = {url: url, title: title};

      // Synthesize an app.
      this.generateAppForLink(data);
    },

    /**
     * Creates a new crx-less app manifest and installs it.
     * @param {Object} data The data object describing the link. Must have |url|
     *     and |title| members.
     */
    generateAppForLink: function(data) {
      assert(data.url != undefined);
      assert(data.title != undefined);
      var pageIndex = ntp.getAppsPageIndex(this);
      chrome.send('generateAppForLink', [data.url, data.title, pageIndex]);
    },

    /** @override */
    tileMoved: function(draggedTile) {
      if (!(draggedTile.firstChild instanceof App))
        return;

      var pageIndex = ntp.getAppsPageIndex(this);
      chrome.send('setPageIndex', [draggedTile.firstChild.appId, pageIndex]);

      var appIds = [];
      for (var i = 0; i < this.tileElements_.length; i++) {
        var tileContents = this.tileElements_[i].firstChild;
        if (tileContents instanceof App)
          appIds.push(tileContents.appId);
      }

      chrome.send('reorderApps', [draggedTile.firstChild.appId, appIds]);
    },

    /** @override */
    setDropEffect: function(dataTransfer) {
      var tile = ntp.getCurrentlyDraggingTile();
      if (tile && tile.querySelector('.app'))
        ntp.setCurrentDropEffect(dataTransfer, 'move');
      else
        ntp.setCurrentDropEffect(dataTransfer, 'copy');
    },
  };

  /**
   * Launches the specified app using the APP_LAUNCH_NTP_APP_RE_ENABLE
   * histogram. This should only be invoked from the AppLauncherHandler.
   * @param {string} appId The ID of the app.
   */
  function launchAppAfterEnable(appId) {
    chrome.send('launchApp', [appId, APP_LAUNCH.NTP_APP_RE_ENABLE]);
  }

  return {
    APP_LAUNCH: APP_LAUNCH,
    AppsPage: AppsPage,
    launchAppAfterEnable: launchAppAfterEnable,
  };
});