/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * Handles the Downloads panel user interface for each browser window.
 *
 * This file includes the following constructors and global objects:
 *
 * DownloadsPanel
 * Main entry point for the downloads panel interface.
 *
 * DownloadsOverlayLoader
 * Allows loading the downloads panel and the status indicator interfaces on
 * demand, to improve startup performance.
 *
 * DownloadsView
 * Builds and updates the downloads list widget, responding to changes in the
 * download state and real-time data.  In addition, handles part of the user
 * interaction events raised by the downloads list widget.
 *
 * DownloadsViewItem
 * Builds and updates a single item in the downloads list widget, responding to
 * changes in the download state and real-time data.
 *
 * DownloadsViewController
 * Handles part of the user interaction events raised by the downloads list
 * widget, in particular the "commands" that apply to multiple items, and
 * dispatches the commands that apply to individual items.
 *
 * DownloadsViewItemController
 * Handles all the user interaction events, in particular the "commands",
 * related to a single item in the downloads list widgets.
 */

/**
 * A few words on focus and focusrings
 *
 * We do quite a few hacks in the Downloads Panel for focusrings. In fact, we
 * basically suppress most if not all XUL-level focusrings, and style/draw
 * them ourselves (using :focus instead of -moz-focusring). There are a few
 * reasons for this:
 *
 * 1) Richlists on OSX don't have focusrings; instead, they are shown as
 *    selected. This makes for some ambiguity when we have a focused/selected
 *    item in the list, and the mouse is hovering a completed download (which
 *    highlights).
 * 2) Windows doesn't show focusrings until after the first time that tab is
 *    pressed (and by then you're focusing the second item in the panel).
 * 3) Richlistbox sets -moz-focusring even when we select it with a mouse.
 *
 * In general, the desired behaviour is to focus the first item after pressing
 * tab/down, and show that focus with a ring. Then, if the mouse moves over
 * the panel, to hide that focus ring; essentially resetting us to the state
 * before pressing the key.
 *
 * We end up capturing the tab/down key events, and preventing their default
 * behaviour. We then set a "keyfocus" attribute on the panel, which allows
 * us to draw a ring around the currently focused element. If the panel is
 * closed or the mouse moves over the panel, we remove the attribute.
 */

"use strict";

////////////////////////////////////////////////////////////////////////////////
//// Globals

XPCOMUtils.defineLazyModuleGetter(this, "DownloadUtils",
                                  "resource://gre/modules/DownloadUtils.jsm");
XPCOMUtils.defineLazyModuleGetter(this, "DownloadsCommon",
                                  "resource:///modules/DownloadsCommon.jsm");
XPCOMUtils.defineLazyModuleGetter(this, "OS",
                                  "resource://gre/modules/osfile.jsm");
XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
                                  "resource://gre/modules/PrivateBrowsingUtils.jsm");
XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
                                  "resource://gre/modules/PlacesUtils.jsm");
XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
                                  "resource://gre/modules/NetUtil.jsm");

////////////////////////////////////////////////////////////////////////////////
//// DownloadsPanel

/**
 * Main entry point for the downloads panel interface.
 */
const DownloadsPanel = {
  //////////////////////////////////////////////////////////////////////////////
  //// Initialization and termination

  /**
   * Internal state of the downloads panel, based on one of the kState
   * constants.  This is not the same state as the XUL panel element.
   */
  _state: 0,

  /** The panel is not linked to downloads data yet. */
  get kStateUninitialized() 0,
  /** This object is linked to data, but the panel is invisible. */
  get kStateHidden() 1,
  /** The panel will be shown as soon as possible. */
  get kStateWaitingData() 2,
  /** The panel is almost shown - we're just waiting to get a handle on the
      anchor. */
  get kStateWaitingAnchor() 3,
  /** The panel is open. */
  get kStateShown() 4,

  /**
   * Location of the panel overlay.
   */
  get kDownloadsOverlay()
      "chrome://browser/content/downloads/downloadsOverlay.xul",

  /**
   * Starts loading the download data in background, without opening the panel.
   * Use showPanel instead to load the data and open the panel at the same time.
   *
   * @param aCallback
   *        Called when initialization is complete.
   */
  initialize: function DP_initialize(aCallback)
  {
    DownloadsCommon.log("Attempting to initialize DownloadsPanel for a window.");
    if (this._state != this.kStateUninitialized) {
      DownloadsCommon.log("DownloadsPanel is already initialized.");
      DownloadsOverlayLoader.ensureOverlayLoaded(this.kDownloadsOverlay,
                                                 aCallback);
      return;
    }
    this._state = this.kStateHidden;

    window.addEventListener("unload", this.onWindowUnload, false);

    // Load and resume active downloads if required.  If there are downloads to
    // be shown in the panel, they will be loaded asynchronously.
    DownloadsCommon.initializeAllDataLinks();

    // Now that data loading has eventually started, load the required XUL
    // elements and initialize our views.
    DownloadsCommon.log("Ensuring DownloadsPanel overlay loaded.");
    DownloadsOverlayLoader.ensureOverlayLoaded(this.kDownloadsOverlay,
                                               function DP_I_callback() {
      DownloadsViewController.initialize();
      DownloadsCommon.log("Attaching DownloadsView...");
      DownloadsCommon.getData(window).addView(DownloadsView);
      DownloadsCommon.getSummary(window, DownloadsView.kItemCountLimit)
                     .addView(DownloadsSummary);
      DownloadsCommon.log("DownloadsView attached - the panel for this window",
                          "should now see download items come in.");
      DownloadsPanel._attachEventListeners();
      DownloadsCommon.log("DownloadsPanel initialized.");
      aCallback();
    });
  },

  /**
   * Closes the downloads panel and frees the internal resources related to the
   * downloads.  The downloads panel can be reopened later, even after this
   * function has been called.
   */
  terminate: function DP_terminate()
  {
    DownloadsCommon.log("Attempting to terminate DownloadsPanel for a window.");
    if (this._state == this.kStateUninitialized) {
      DownloadsCommon.log("DownloadsPanel was never initialized. Nothing to do.");
      return;
    }

    window.removeEventListener("unload", this.onWindowUnload, false);

    // Ensure that the panel is closed before shutting down.
    this.hidePanel();

    DownloadsViewController.terminate();
    DownloadsCommon.getData(window).removeView(DownloadsView);
    DownloadsCommon.getSummary(window, DownloadsView.kItemCountLimit)
                   .removeView(DownloadsSummary);
    this._unattachEventListeners();

    this._state = this.kStateUninitialized;

    DownloadsSummary.active = false;
    DownloadsCommon.log("DownloadsPanel terminated.");
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Panel interface

  /**
   * Main panel element in the browser window, or null if the panel overlay
   * hasn't been loaded yet.
   */
  get panel()
  {
    // If the downloads panel overlay hasn't loaded yet, just return null
    // without reseting this.panel.
    let downloadsPanel = document.getElementById("downloadsPanel");
    if (!downloadsPanel)
      return null;

    delete this.panel;
    return this.panel = downloadsPanel;
  },

  /**
   * Starts opening the downloads panel interface, anchored to the downloads
   * button of the browser window.  The list of downloads to display is
   * initialized the first time this method is called, and the panel is shown
   * only when data is ready.
   */
  showPanel: function DP_showPanel()
  {
    DownloadsCommon.log("Opening the downloads panel.");

    if (this.isPanelShowing) {
      DownloadsCommon.log("Panel is already showing - focusing instead.");
      this._focusPanel();
      return;
    }

    this.initialize(function DP_SP_callback() {
      // Delay displaying the panel because this function will sometimes be
      // called while another window is closing (like the window for selecting
      // whether to save or open the file), and that would cause the panel to
      // close immediately.
      setTimeout(function () DownloadsPanel._openPopupIfDataReady(), 0);
    }.bind(this));

    DownloadsCommon.log("Waiting for the downloads panel to appear.");
    this._state = this.kStateWaitingData;
  },

  /**
   * Hides the downloads panel, if visible, but keeps the internal state so that
   * the panel can be reopened quickly if required.
   */
  hidePanel: function DP_hidePanel()
  {
    DownloadsCommon.log("Closing the downloads panel.");

    if (!this.isPanelShowing) {
      DownloadsCommon.log("Downloads panel is not showing - nothing to do.");
      return;
    }

    this.panel.hidePopup();

    // Ensure that we allow the panel to be reopened.  Note that, if the popup
    // was open, then the onPopupHidden event handler has already updated the
    // current state, otherwise we must update the state ourselves.
    this._state = this.kStateHidden;
    DownloadsCommon.log("Downloads panel is now closed.");
  },

  /**
   * Indicates whether the panel is shown or will be shown.
   */
  get isPanelShowing()
  {
    return this._state == this.kStateWaitingData ||
           this._state == this.kStateWaitingAnchor ||
           this._state == this.kStateShown;
  },

  /**
   * Returns whether the user has started keyboard navigation.
   */
  get keyFocusing()
  {
    return this.panel.hasAttribute("keyfocus");
  },

  /**
   * Set to true if the user has started keyboard navigation, and we should be
   * showing focusrings in the panel. Also adds a mousemove event handler to
   * the panel which disables keyFocusing.
   */
  set keyFocusing(aValue)
  {
    if (aValue) {
      this.panel.setAttribute("keyfocus", "true");
      this.panel.addEventListener("mousemove", this);
    } else {
      this.panel.removeAttribute("keyfocus");
      this.panel.removeEventListener("mousemove", this);
    }
    return aValue;
  },

  /**
   * Handles the mousemove event for the panel, which disables focusring
   * visualization.
   */
  handleEvent: function DP_handleEvent(aEvent)
  {
    if (aEvent.type == "mousemove") {
      this.keyFocusing = false;
    }
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Callback functions from DownloadsView

  /**
   * Called after data loading finished.
   */
  onViewLoadCompleted: function DP_onViewLoadCompleted()
  {
    this._openPopupIfDataReady();
  },

  //////////////////////////////////////////////////////////////////////////////
  //// User interface event functions

  onWindowUnload: function DP_onWindowUnload()
  {
    // This function is registered as an event listener, we can't use "this".
    DownloadsPanel.terminate();
  },

  onPopupShown: function DP_onPopupShown(aEvent)
  {
    // Ignore events raised by nested popups.
    if (aEvent.target != aEvent.currentTarget) {
      return;
    }

    DownloadsCommon.log("Downloads panel has shown.");
    this._state = this.kStateShown;

    // Since at most one popup is open at any given time, we can set globally.
    DownloadsCommon.getIndicatorData(window).attentionSuppressed = true;

    // Ensure that the first item is selected when the panel is focused.
    if (DownloadsView.richListBox.itemCount > 0 &&
        DownloadsView.richListBox.selectedIndex == -1) {
      DownloadsView.richListBox.selectedIndex = 0;
    }

    this._focusPanel();
  },

  onPopupHidden: function DP_onPopupHidden(aEvent)
  {
    // Ignore events raised by nested popups.
    if (aEvent.target != aEvent.currentTarget) {
      return;
    }

    DownloadsCommon.log("Downloads panel has hidden.");

    // Removes the keyfocus attribute so that we stop handling keyboard
    // navigation.
    this.keyFocusing = false;

    // Since at most one popup is open at any given time, we can set globally.
    DownloadsCommon.getIndicatorData(window).attentionSuppressed = false;

    // Allow the anchor to be hidden.
    DownloadsButton.releaseAnchor();

    // Allow the panel to be reopened.
    this._state = this.kStateHidden;
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Related operations

  /**
   * Shows or focuses the user interface dedicated to downloads history.
   */
  showDownloadsHistory: function DP_showDownloadsHistory()
  {
    DownloadsCommon.log("Showing download history.");
    // Hide the panel before showing another window, otherwise focus will return
    // to the browser window when the panel closes automatically.
    this.hidePanel();

    BrowserDownloadsUI();
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Internal functions

  /**
   * Attach event listeners to a panel element. These listeners should be
   * removed in _unattachEventListeners. This is called automatically after the
   * panel has successfully loaded.
   */
  _attachEventListeners: function DP__attachEventListeners()
  {
    // Handle keydown to support accel-V.
    this.panel.addEventListener("keydown", this._onKeyDown.bind(this), false);
    // Handle keypress to be able to preventDefault() events before they reach
    // the richlistbox, for keyboard navigation.
    this.panel.addEventListener("keypress", this._onKeyPress.bind(this), false);
  },

  /**
   * Unattach event listeners that were added in _attachEventListeners. This
   * is called automatically on panel termination.
   */
  _unattachEventListeners: function DP__unattachEventListeners()
  {
    this.panel.removeEventListener("keydown", this._onKeyDown.bind(this),
                                   false);
    this.panel.removeEventListener("keypress", this._onKeyPress.bind(this),
                                   false);
  },

  _onKeyPress: function DP__onKeyPress(aEvent)
  {
    // Handle unmodified keys only.
    if (aEvent.altKey || aEvent.ctrlKey || aEvent.shiftKey || aEvent.metaKey) {
      return;
    }

    let richListBox = DownloadsView.richListBox;

    // If the user has pressed the tab, up, or down cursor key, start keyboard
    // navigation, thus enabling focusrings in the panel.  Keyboard navigation
    // is automatically disabled if the user moves the mouse on the panel, or
    // if the panel is closed.
    if ((aEvent.keyCode == Ci.nsIDOMKeyEvent.DOM_VK_TAB ||
        aEvent.keyCode == Ci.nsIDOMKeyEvent.DOM_VK_UP ||
        aEvent.keyCode == Ci.nsIDOMKeyEvent.DOM_VK_DOWN) &&
        !this.keyFocusing) {
      this.keyFocusing = true;
      // Ensure there's a selection, we will show the focus ring around it and
      // prevent the richlistbox from changing the selection.
      if (DownloadsView.richListBox.selectedIndex == -1)
        DownloadsView.richListBox.selectedIndex = 0;
      aEvent.preventDefault();
      return;
    }

    if (aEvent.keyCode == Ci.nsIDOMKeyEvent.DOM_VK_DOWN) {
      // If the last element in the list is selected, or the footer is already
      // focused, focus the footer.
      if (richListBox.selectedItem === richListBox.lastChild ||
          document.activeElement.parentNode.id === "downloadsFooter") {
        DownloadsFooter.focus();
        aEvent.preventDefault();
        return;
      }
    }

    // Pass keypress events to the richlistbox view when it's focused.
    if (document.activeElement === richListBox) {
      DownloadsView.onDownloadKeyPress(aEvent);
    }
  },

  /**
   * Keydown listener that listens for the keys to start key focusing, as well
   * as the the accel-V "paste" event, which initiates a file download if the
   * pasted item can be resolved to a URI.
   */
  _onKeyDown: function DP__onKeyDown(aEvent)
  {
    // If the footer is focused and the downloads list has at least 1 element
    // in it, focus the last element in the list when going up.
    if (aEvent.keyCode == Ci.nsIDOMKeyEvent.DOM_VK_UP &&
        document.activeElement.parentNode.id === "downloadsFooter" &&
        DownloadsView.richListBox.firstChild) {
      DownloadsView.richListBox.focus();
      DownloadsView.richListBox.selectedItem = DownloadsView.richListBox.lastChild;
      aEvent.preventDefault();
      return;
    }

    let pasting = aEvent.keyCode == Ci.nsIDOMKeyEvent.DOM_VK_V &&
#ifdef XP_MACOSX
                  aEvent.metaKey;
#else
                  aEvent.ctrlKey;
#endif

    if (!pasting) {
      return;
    }

    DownloadsCommon.log("Received a paste event.");

    let trans = Cc["@mozilla.org/widget/transferable;1"]
                  .createInstance(Ci.nsITransferable);
    trans.init(null);
    let flavors = ["text/x-moz-url", "text/unicode"];
    flavors.forEach(trans.addDataFlavor);
    Services.clipboard.getData(trans, Services.clipboard.kGlobalClipboard);
    // Getting the data or creating the nsIURI might fail
    try {
      let data = {};
      trans.getAnyTransferData({}, data, {});
      let [url, name] = data.value
                            .QueryInterface(Ci.nsISupportsString)
                            .data
                            .split("\n");
      if (!url) {
        return;
      }

      let uri = NetUtil.newURI(url);
      DownloadsCommon.log("Pasted URL seems valid. Starting download.");
      DownloadURL(uri.spec, name, document);
    } catch (ex) {}
  },

  /**
   * Move focus to the main element in the downloads panel, unless another
   * element in the panel is already focused.
   */
  _focusPanel: function DP_focusPanel()
  {
    // We may be invoked while the panel is still waiting to be shown.
    if (this._state != this.kStateShown) {
      return;
    }

    let element = document.commandDispatcher.focusedElement;
    while (element && element != this.panel) {
      element = element.parentNode;
    }
    if (!element) {
      if (DownloadsView.richListBox.itemCount > 0) {
        DownloadsView.richListBox.focus();
      } else {
        DownloadsFooter.focus();
      }
    }
  },

  /**
   * Opens the downloads panel when data is ready to be displayed.
   */
  _openPopupIfDataReady: function DP_openPopupIfDataReady()
  {
    // We don't want to open the popup if we already displayed it, or if we are
    // still loading data.
    if (this._state != this.kStateWaitingData || DownloadsView.loading) {
      return;
    }

    this._state = this.kStateWaitingAnchor;

    // Ensure the anchor is visible.  If that is not possible, show the panel
    // anchored to the top area of the window, near the default anchor position.
    DownloadsButton.getAnchor(function DP_OPIDR_callback(aAnchor) {
      // If somehow we've switched states already (by getting a panel hiding
      // event before an overlay is loaded, for example), bail out.
      if (this._state != this.kStateWaitingAnchor)
        return;

      // At this point, if the window is minimized, opening the panel could fail
      // without any notification, and there would be no way to either open or
      // close the panel anymore.  To prevent this, check if the window is
      // minimized and in that case force the panel to the closed state.
      if (window.windowState == Ci.nsIDOMChromeWindow.STATE_MINIMIZED) {
        DownloadsButton.releaseAnchor();
        this._state = this.kStateHidden;
        return;
      }

      // When the panel is opened, we check if the target files of visible items
      // still exist, and update the allowed items interactions accordingly.  We
      // do these checks on a background thread, and don't prevent the panel to
      // be displayed while these checks are being performed.
      for each (let viewItem in DownloadsView._viewItems) {
        viewItem.verifyTargetExists();
      }

      if (aAnchor) {
        DownloadsCommon.log("Opening downloads panel popup.");
        this.panel.openPopup(aAnchor, "bottomcenter topright", 0, 0, false,
                             null);
      } else {
        DownloadsCommon.error("We can't find the anchor! Failure case - opening",
                              "downloads panel on TabsToolbar. We should never",
                              "get here!");
        Components.utils.reportError(
          "Downloads button cannot be found");
      }
    }.bind(this));
  }
};

////////////////////////////////////////////////////////////////////////////////
//// DownloadsOverlayLoader

/**
 * Allows loading the downloads panel and the status indicator interfaces on
 * demand, to improve startup performance.
 */
const DownloadsOverlayLoader = {
  /**
   * We cannot load two overlays at the same time, thus we use a queue of
   * pending load requests.
   */
  _loadRequests: [],

  /**
   * True while we are waiting for an overlay to be loaded.
   */
  _overlayLoading: false,

  /**
   * This object has a key for each overlay URI that is already loaded.
   */
  _loadedOverlays: {},

  /**
   * Loads the specified overlay and invokes the given callback when finished.
   *
   * @param aOverlay
   *        String containing the URI of the overlay to load in the current
   *        window.  If this overlay has already been loaded using this
   *        function, then the overlay is not loaded again.
   * @param aCallback
   *        Invoked when loading is completed.  If the overlay is already
   *        loaded, the function is called immediately.
   */
  ensureOverlayLoaded: function DOL_ensureOverlayLoaded(aOverlay, aCallback)
  {
    // The overlay is already loaded, invoke the callback immediately.
    if (aOverlay in this._loadedOverlays) {
      aCallback();
      return;
    }

    // The callback will be invoked when loading is finished.
    this._loadRequests.push({ overlay: aOverlay, callback: aCallback });
    if (this._overlayLoading) {
      return;
    }

    function DOL_EOL_loadCallback() {
      this._overlayLoading = false;
      this._loadedOverlays[aOverlay] = true;

      this.processPendingRequests();
    }

    this._overlayLoading = true;
    DownloadsCommon.log("Loading overlay ", aOverlay);
    document.loadOverlay(aOverlay, DOL_EOL_loadCallback.bind(this));
  },

  /**
   * Re-processes all the currently pending requests, invoking the callbacks
   * and/or loading more overlays as needed.  In most cases, there will be a
   * single request for one overlay, that will be processed immediately.
   */
  processPendingRequests: function DOL_processPendingRequests()
  {
    // Re-process all the currently pending requests, yet allow more requests
    // to be appended at the end of the array if we're not ready for them.
    let currentLength = this._loadRequests.length;
    for (let i = 0; i < currentLength; i++) {
      let request = this._loadRequests.shift();

      // We must call ensureOverlayLoaded again for each request, to check if
      // the associated callback can be invoked now, or if we must still wait
      // for the associated overlay to load.
      this.ensureOverlayLoaded(request.overlay, request.callback);
    }
  }
};

////////////////////////////////////////////////////////////////////////////////
//// DownloadsView

/**
 * Builds and updates the downloads list widget, responding to changes in the
 * download state and real-time data.  In addition, handles part of the user
 * interaction events raised by the downloads list widget.
 */
const DownloadsView = {
  //////////////////////////////////////////////////////////////////////////////
  //// Functions handling download items in the list

  /**
   * Maximum number of items shown by the list at any given time.
   */
  kItemCountLimit: 3,

  /**
   * Indicates whether we are still loading downloads data asynchronously.
   */
  loading: false,

  /**
   * Ordered array of all DownloadsDataItem objects.  We need to keep this array
   * because only a limited number of items are shown at once, and if an item
   * that is currently visible is removed from the list, we might need to take
   * another item from the array and make it appear at the bottom.
   */
  _dataItems: [],

  /**
   * Object containing the available DownloadsViewItem objects, indexed by their
   * numeric download identifier.  There is a limited number of view items in
   * the panel at any given time.
   */
  _viewItems: {},

  /**
   * Called when the number of items in the list changes.
   */
  _itemCountChanged: function DV_itemCountChanged()
  {
    DownloadsCommon.log("The downloads item count has changed - we are tracking",
                        this._dataItems.length, "downloads in total.");
    let count = this._dataItems.length;
    let hiddenCount = count - this.kItemCountLimit;

    if (count > 0) {
      DownloadsCommon.log("Setting the panel's hasdownloads attribute to true.");
      DownloadsPanel.panel.setAttribute("hasdownloads", "true");
    } else {
      DownloadsCommon.log("Removing the panel's hasdownloads attribute.");
      DownloadsPanel.panel.removeAttribute("hasdownloads");
    }

    // If we've got some hidden downloads, we should activate the
    // DownloadsSummary. The DownloadsSummary will determine whether or not
    // it's appropriate to actually display the summary.
    DownloadsSummary.active = hiddenCount > 0;
  },

  /**
   * Element corresponding to the list of downloads.
   */
  get richListBox()
  {
    delete this.richListBox;
    return this.richListBox = document.getElementById("downloadsListBox");
  },

  /**
   * Element corresponding to the button for showing more downloads.
   */
  get downloadsHistory()
  {
    delete this.downloadsHistory;
    return this.downloadsHistory = document.getElementById("downloadsHistory");
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Callback functions from DownloadsData

  /**
   * Called before multiple downloads are about to be loaded.
   */
  onDataLoadStarting: function DV_onDataLoadStarting()
  {
    DownloadsCommon.log("onDataLoadStarting called for DownloadsView.");
    this.loading = true;
  },

  /**
   * Called after data loading finished.
   */
  onDataLoadCompleted: function DV_onDataLoadCompleted()
  {
    DownloadsCommon.log("onDataLoadCompleted called for DownloadsView.");

    this.loading = false;

    // We suppressed item count change notifications during the batch load, at
    // this point we should just call the function once.
    this._itemCountChanged();

    // Notify the panel that all the initially available downloads have been
    // loaded.  This ensures that the interface is visible, if still required.
    DownloadsPanel.onViewLoadCompleted();
  },

  /**
   * Called when a new download data item is available, either during the
   * asynchronous data load or when a new download is started.
   *
   * @param aDataItem
   *        DownloadsDataItem object that was just added.
   * @param aNewest
   *        When true, indicates that this item is the most recent and should be
   *        added in the topmost position.  This happens when a new download is
   *        started.  When false, indicates that the item is the least recent
   *        and should be appended.  The latter generally happens during the
   *        asynchronous data load.
   */
  onDataItemAdded: function DV_onDataItemAdded(aDataItem, aNewest)
  {
    DownloadsCommon.log("A new download data item was added - aNewest =",
                        aNewest);

    if (aNewest) {
      this._dataItems.unshift(aDataItem);
    } else {
      this._dataItems.push(aDataItem);
    }

    let itemsNowOverflow = this._dataItems.length > this.kItemCountLimit;
    if (aNewest || !itemsNowOverflow) {
      // The newly added item is visible in the panel and we must add the
      // corresponding element.  This is either because it is the first item, or
      // because it was added at the bottom but the list still doesn't overflow.
      this._addViewItem(aDataItem, aNewest);
    }
    if (aNewest && itemsNowOverflow) {
      // If the list overflows, remove the last item from the panel to make room
      // for the new one that we just added at the top.
      this._removeViewItem(this._dataItems[this.kItemCountLimit]);
    }

    // For better performance during batch loads, don't update the count for
    // every item, because the interface won't be visible until load finishes.
    if (!this.loading) {
      this._itemCountChanged();
    }
  },

  /**
   * Called when a data item is removed.  Ensures that the widget associated
   * with the view item is removed from the user interface.
   *
   * @param aDataItem
   *        DownloadsDataItem object that is being removed.
   */
  onDataItemRemoved: function DV_onDataItemRemoved(aDataItem)
  {
    DownloadsCommon.log("A download data item was removed.");

    let itemIndex = this._dataItems.indexOf(aDataItem);
    this._dataItems.splice(itemIndex, 1);

    if (itemIndex < this.kItemCountLimit) {
      // The item to remove is visible in the panel.
      this._removeViewItem(aDataItem);
      if (this._dataItems.length >= this.kItemCountLimit) {
        // Reinsert the next item into the panel.
        this._addViewItem(this._dataItems[this.kItemCountLimit - 1], false);
      }
    }

    this._itemCountChanged();
  },

  /**
   * Returns the view item associated with the provided data item for this view.
   *
   * @param aDataItem
   *        DownloadsDataItem object for which the view item is requested.
   *
   * @return Object that can be used to notify item status events.
   */
  getViewItem: function DV_getViewItem(aDataItem)
  {
    // If the item is visible, just return it, otherwise return a mock object
    // that doesn't react to notifications.
    if (aDataItem.downloadGuid in this._viewItems) {
      return this._viewItems[aDataItem.downloadGuid];
    }
    return this._invisibleViewItem;
  },

  /**
   * Mock DownloadsDataItem object that doesn't react to notifications.
   */
  _invisibleViewItem: Object.freeze({
    onStateChange: function () { },
    onProgressChange: function () { }
  }),

  /**
   * Creates a new view item associated with the specified data item, and adds
   * it to the top or the bottom of the list.
   */
  _addViewItem: function DV_addViewItem(aDataItem, aNewest)
  {
    DownloadsCommon.log("Adding a new DownloadsViewItem to the downloads list.",
                        "aNewest =", aNewest);

    let element = document.createElement("richlistitem");
    let viewItem = new DownloadsViewItem(aDataItem, element);
    this._viewItems[aDataItem.downloadGuid] = viewItem;
    if (aNewest) {
      this.richListBox.insertBefore(element, this.richListBox.firstChild);
    } else {
      this.richListBox.appendChild(element);
    }
  },

  /**
   * Removes the view item associated with the specified data item.
   */
  _removeViewItem: function DV_removeViewItem(aDataItem)
  {
    DownloadsCommon.log("Removing a DownloadsViewItem from the downloads list.");
    let element = this.getViewItem(aDataItem)._element;
    let previousSelectedIndex = this.richListBox.selectedIndex;
    this.richListBox.removeChild(element);
    if (previousSelectedIndex != -1) {
      this.richListBox.selectedIndex = Math.min(previousSelectedIndex,
                                                this.richListBox.itemCount - 1);
    }
    delete this._viewItems[aDataItem.downloadGuid];
  },

  //////////////////////////////////////////////////////////////////////////////
  //// User interface event functions

  /**
   * Helper function to do commands on a specific download item.
   *
   * @param aEvent
   *        Event object for the event being handled.  If the event target is
   *        not a richlistitem that represents a download, this function will
   *        walk up the parent nodes until it finds a DOM node that is.
   * @param aCommand
   *        The command to be performed.
   */
  onDownloadCommand: function DV_onDownloadCommand(aEvent, aCommand)
  {
    let target = aEvent.target;
    while (target.nodeName != "richlistitem") {
      target = target.parentNode;
    }
    new DownloadsViewItemController(target).doCommand(aCommand);
  },

  onDownloadClick: function DV_onDownloadClick(aEvent)
  {
    // Handle primary clicks only, and exclude the action button.
    if (aEvent.button == 0 &&
        !aEvent.originalTarget.hasAttribute("oncommand")) {
      goDoCommand("downloadsCmd_open");
    }
  },

  /**
   * Handles keypress events on a download item.
   */
  onDownloadKeyPress: function DV_onDownloadKeyPress(aEvent)
  {
    // Pressing the key on buttons should not invoke the action because the
    // event has already been handled by the button itself.
    if (aEvent.originalTarget.hasAttribute("command") ||
        aEvent.originalTarget.hasAttribute("oncommand")) {
      return;
    }

    if (aEvent.charCode == " ".charCodeAt(0)) {
      goDoCommand("downloadsCmd_pauseResume");
      return;
    }

    if (aEvent.keyCode == KeyEvent.DOM_VK_RETURN) {
      goDoCommand("downloadsCmd_doDefault");
    }
  },


  /**
   * Mouse listeners to handle selection on hover.
   */
  onDownloadMouseOver: function DV_onDownloadMouseOver(aEvent)
  {
    if (aEvent.originalTarget.parentNode == this.richListBox)
      this.richListBox.selectedItem = aEvent.originalTarget;
  },
  onDownloadMouseOut: function DV_onDownloadMouseOut(aEvent)
  {
    if (aEvent.originalTarget.parentNode == this.richListBox) {
      // If the destination element is outside of the richlistitem, clear the
      // selection.
      let element = aEvent.relatedTarget;
      while (element && element != aEvent.originalTarget) {
        element = element.parentNode;
      }
      if (!element)
        this.richListBox.selectedIndex = -1;
    }
  },

  onDownloadContextMenu: function DV_onDownloadContextMenu(aEvent)
  {
    let element = this.richListBox.selectedItem;
    if (!element) {
      return;
    }

    DownloadsViewController.updateCommands();

    // Set the state attribute so that only the appropriate items are displayed.
    let contextMenu = document.getElementById("downloadsContextMenu");
    contextMenu.setAttribute("state", element.getAttribute("state"));
  },

  onDownloadDragStart: function DV_onDownloadDragStart(aEvent)
  {
    let element = this.richListBox.selectedItem;
    if (!element) {
      return;
    }

    let controller = new DownloadsViewItemController(element);
    let localFile = controller.dataItem.localFile;
    if (!localFile.exists()) {
      return;
    }

    let dataTransfer = aEvent.dataTransfer;
    dataTransfer.mozSetDataAt("application/x-moz-file", localFile, 0);
    dataTransfer.effectAllowed = "copyMove";
    var url = Services.io.newFileURI(localFile).spec;
    dataTransfer.setData("text/uri-list", url);
    dataTransfer.setData("text/plain", url);
    dataTransfer.addElement(element);

    aEvent.stopPropagation();
  }
}

////////////////////////////////////////////////////////////////////////////////
//// DownloadsViewItem

/**
 * Builds and updates a single item in the downloads list widget, responding to
 * changes in the download state and real-time data.
 *
 * @param aDataItem
 *        DownloadsDataItem to be associated with the view item.
 * @param aElement
 *        XUL element corresponding to the single download item in the view.
 */
function DownloadsViewItem(aDataItem, aElement)
{
  this._element = aElement;
  this.dataItem = aDataItem;

  this.lastEstimatedSecondsLeft = Infinity;

  // Set the URI that represents the correct icon for the target file.  As soon
  // as bug 239948 comment 12 is handled, the "file" property will be always a
  // file URL rather than a file name.  At that point we should remove the "//"
  // (double slash) from the icon URI specification (see test_moz_icon_uri.js).
  this.image = "moz-icon://" + this.dataItem.file + "?size=32";

  let attributes = {
    "type": "download",
    "class": "download-state",
    "id": "downloadsItem_" + this.dataItem.downloadGuid,
    "downloadGuid": this.dataItem.downloadGuid,
    "state": this.dataItem.state,
    "progress": this.dataItem.inProgress ? this.dataItem.percentComplete : 100,
    "target": this.dataItem.target,
    "image": this.image
  };

  for (let attributeName in attributes) {
    this._element.setAttribute(attributeName, attributes[attributeName]);
  }

  // Initialize more complex attributes.
  this._updateProgress();
  this._updateStatusLine();
  this.verifyTargetExists();
}

DownloadsViewItem.prototype = {
  /**
   * The DownloadDataItem associated with this view item.
   */
  dataItem: null,

  /**
   * The XUL element corresponding to the associated richlistbox item.
   */
  _element: null,

  /**
   * The inner XUL element for the progress bar, or null if not available.
   */
  _progressElement: null,

  //////////////////////////////////////////////////////////////////////////////
  //// Callback functions from DownloadsData

  /**
   * Called when the download state might have changed.  Sometimes the state of
   * the download might be the same as before, if the data layer received
   * multiple events for the same download.
   */
  onStateChange: function DVI_onStateChange(aOldState)
  {
    // If a download just finished successfully, it means that the target file
    // now exists and we can extract its specific icon.  To ensure that the icon
    // is reloaded, we must change the URI used by the XUL image element, for
    // example by adding a query parameter.  Since this URI has a "moz-icon"
    // scheme, this only works if we add one of the parameters explicitly
    // supported by the nsIMozIconURI interface.
    if (aOldState != Ci.nsIDownloadManager.DOWNLOAD_FINISHED &&
        aOldState != this.dataItem.state) {
      this._element.setAttribute("image", this.image + "&state=normal");

      // We assume the existence of the target of a download that just completed
      // successfully, without checking the condition in the background.  If the
      // panel is already open, this will take effect immediately.  If the panel
      // is opened later, a new background existence check will be performed.
      this._element.setAttribute("exists", "true");
    }

    // Update the user interface after switching states.
    this._element.setAttribute("state", this.dataItem.state);
    this._updateProgress();
    this._updateStatusLine();
  },

  /**
   * Called when the download progress has changed.
   */
  onProgressChange: function DVI_onProgressChange() {
    this._updateProgress();
    this._updateStatusLine();
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Functions for updating the user interface

  /**
   * Updates the progress bar.
   */
  _updateProgress: function DVI_updateProgress() {
    if (this.dataItem.starting) {
      // Before the download starts, the progress meter has its initial value.
      this._element.setAttribute("progressmode", "normal");
      this._element.setAttribute("progress", "0");
    } else if (this.dataItem.state == Ci.nsIDownloadManager.DOWNLOAD_SCANNING ||
               this.dataItem.percentComplete == -1) {
      // We might not know the progress of a running download, and we don't know
      // the remaining time during the malware scanning phase.
      this._element.setAttribute("progressmode", "undetermined");
    } else {
      // This is a running download of which we know the progress.
      this._element.setAttribute("progressmode", "normal");
      this._element.setAttribute("progress", this.dataItem.percentComplete);
    }

    // Find the progress element as soon as the download binding is accessible.
    if (!this._progressElement) {
      this._progressElement =
           document.getAnonymousElementByAttribute(this._element, "anonid",
                                                   "progressmeter");
    }

    // Dispatch the ValueChange event for accessibility, if possible.
    if (this._progressElement) {
      let event = document.createEvent("Events");
      event.initEvent("ValueChange", true, true);
      this._progressElement.dispatchEvent(event);
    }
  },

  /**
   * Updates the main status line, including bytes transferred, bytes total,
   * download rate, and time remaining.
   */
  _updateStatusLine: function DVI_updateStatusLine() {
    const nsIDM = Ci.nsIDownloadManager;

    let status = "";
    let statusTip = "";

    if (this.dataItem.paused) {
      let transfer = DownloadUtils.getTransferTotal(this.dataItem.currBytes,
                                                    this.dataItem.maxBytes);

      // We use the same XUL label to display both the state and the amount
      // transferred, for example "Paused -  1.1 MB".
      status = DownloadsCommon.strings.statusSeparatorBeforeNumber(
                                            DownloadsCommon.strings.statePaused,
                                            transfer);
    } else if (this.dataItem.state == nsIDM.DOWNLOAD_DOWNLOADING) {
      // We don't show the rate for each download in order to reduce clutter.
      // The remaining time per download is likely enough information for the
      // panel.
      [status] =
        DownloadUtils.getDownloadStatusNoRate(this.dataItem.currBytes,
                                              this.dataItem.maxBytes,
                                              this.dataItem.speed,
                                              this.lastEstimatedSecondsLeft);

      // We are, however, OK with displaying the rate in the tooltip.
      let newEstimatedSecondsLeft;
      [statusTip, newEstimatedSecondsLeft] =
        DownloadUtils.getDownloadStatus(this.dataItem.currBytes,
                                        this.dataItem.maxBytes,
                                        this.dataItem.speed,
                                        this.lastEstimatedSecondsLeft);
      this.lastEstimatedSecondsLeft = newEstimatedSecondsLeft;
    } else if (this.dataItem.starting) {
      status = DownloadsCommon.strings.stateStarting;
    } else if (this.dataItem.state == nsIDM.DOWNLOAD_SCANNING) {
      status = DownloadsCommon.strings.stateScanning;
    } else if (!this.dataItem.inProgress) {
      let stateLabel = function () {
        let s = DownloadsCommon.strings;
        switch (this.dataItem.state) {
          case nsIDM.DOWNLOAD_FAILED:           return s.stateFailed;
          case nsIDM.DOWNLOAD_CANCELED:         return s.stateCanceled;
          case nsIDM.DOWNLOAD_BLOCKED_PARENTAL: return s.stateBlockedParentalControls;
          case nsIDM.DOWNLOAD_BLOCKED_POLICY:   return s.stateBlockedPolicy;
          case nsIDM.DOWNLOAD_DIRTY:            return s.stateDirty;
          case nsIDM.DOWNLOAD_FINISHED:         return this._fileSizeText;
        }
        return null;
      }.apply(this);

      let [displayHost, fullHost] =
        DownloadUtils.getURIHost(this.dataItem.referrer || this.dataItem.uri);

      let end = new Date(this.dataItem.endTime);
      let [displayDate, fullDate] = DownloadUtils.getReadableDates(end);

      // We use the same XUL label to display the state, the host name, and the
      // end time, for example "Canceled - 222.net - 11:15" or "1.1 MB -
      // website2.com - Yesterday".  We show the full host and the complete date
      // in the tooltip.
      let firstPart = DownloadsCommon.strings.statusSeparator(stateLabel,
                                                              displayHost);
      status = DownloadsCommon.strings.statusSeparator(firstPart, displayDate);
      statusTip = DownloadsCommon.strings.statusSeparator(fullHost, fullDate);
    }

    this._element.setAttribute("status", status);
    this._element.setAttribute("statusTip", statusTip || status);
  },

  /**
   * Localized string representing the total size of completed downloads, for
   * example "1.5 MB" or "Unknown size".
   */
  get _fileSizeText()
  {
    // Display the file size, but show "Unknown" for negative sizes.
    let fileSize = this.dataItem.maxBytes;
    if (fileSize < 0) {
      return DownloadsCommon.strings.sizeUnknown;
    }
    let [size, unit] = DownloadUtils.convertByteUnits(fileSize);
    return DownloadsCommon.strings.sizeWithUnits(size, unit);
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Functions called by the panel

  /**
   * Starts checking whether the target file of a finished download is still
   * available on disk, and sets an attribute that controls how the item is
   * presented visually.
   *
   * The existence check is executed on a background thread.
   */
  verifyTargetExists: function DVI_verifyTargetExists() {
    // We don't need to check if the download is not finished successfully.
    if (!this.dataItem.openable) {
      return;
    }

    OS.File.exists(this.dataItem.localFile.path).then(
      function DVI_RTE_onSuccess(aExists) {
        if (aExists) {
          this._element.setAttribute("exists", "true");
        } else {
          this._element.removeAttribute("exists");
        }
      }.bind(this), Cu.reportError);
  },
};

////////////////////////////////////////////////////////////////////////////////
//// DownloadsViewController

/**
 * Handles part of the user interaction events raised by the downloads list
 * widget, in particular the "commands" that apply to multiple items, and
 * dispatches the commands that apply to individual items.
 */
const DownloadsViewController = {
  //////////////////////////////////////////////////////////////////////////////
  //// Initialization and termination

  initialize: function DVC_initialize()
  {
    window.controllers.insertControllerAt(0, this);
  },

  terminate: function DVC_terminate()
  {
    window.controllers.removeController(this);
  },

  //////////////////////////////////////////////////////////////////////////////
  //// nsIController

  supportsCommand: function DVC_supportsCommand(aCommand)
  {
    // Firstly, determine if this is a command that we can handle.
    if (!(aCommand in this.commands) &&
        !(aCommand in DownloadsViewItemController.prototype.commands)) {
      return false;
    }
    // Secondly, determine if focus is on a control in the downloads list.
    let element = document.commandDispatcher.focusedElement;
    while (element && element != DownloadsView.richListBox) {
      element = element.parentNode;
    }
    // We should handle the command only if the downloads list is among the
    // ancestors of the focused element.
    return !!element;
  },

  isCommandEnabled: function DVC_isCommandEnabled(aCommand)
  {
    // Handle commands that are not selection-specific.
    if (aCommand == "downloadsCmd_clearList") {
      return DownloadsCommon.getData(window).canRemoveFinished;
    }

    // Other commands are selection-specific.
    let element = DownloadsView.richListBox.selectedItem;
    return element &&
           new DownloadsViewItemController(element).isCommandEnabled(aCommand);
  },

  doCommand: function DVC_doCommand(aCommand)
  {
    // If this command is not selection-specific, execute it.
    if (aCommand in this.commands) {
      this.commands[aCommand].apply(this);
      return;
    }

    // Other commands are selection-specific.
    let element = DownloadsView.richListBox.selectedItem;
    if (element) {
      // The doCommand function also checks if the command is enabled.
      new DownloadsViewItemController(element).doCommand(aCommand);
    }
  },

  onEvent: function () { },

  //////////////////////////////////////////////////////////////////////////////
  //// Other functions

  updateCommands: function DVC_updateCommands()
  {
    Object.keys(this.commands).forEach(goUpdateCommand);
    Object.keys(DownloadsViewItemController.prototype.commands)
          .forEach(goUpdateCommand);
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Selection-independent commands

  /**
   * This object contains one key for each command that operates regardless of
   * the currently selected item in the list.
   */
  commands: {
    downloadsCmd_clearList: function DVC_downloadsCmd_clearList()
    {
      DownloadsCommon.getData(window).removeFinished();
    }
  }
};

////////////////////////////////////////////////////////////////////////////////
//// DownloadsViewItemController

/**
 * Handles all the user interaction events, in particular the "commands",
 * related to a single item in the downloads list widgets.
 */
function DownloadsViewItemController(aElement) {
  let downloadGuid = aElement.getAttribute("downloadGuid");
  this.dataItem = DownloadsCommon.getData(window).dataItems[downloadGuid];
}

DownloadsViewItemController.prototype = {
  //////////////////////////////////////////////////////////////////////////////
  //// Command dispatching

  /**
   * The DownloadDataItem controlled by this object.
   */
  dataItem: null,

  isCommandEnabled: function DVIC_isCommandEnabled(aCommand)
  {
    switch (aCommand) {
      case "downloadsCmd_open": {
        return this.dataItem.openable && this.dataItem.localFile.exists();
      }
      case "downloadsCmd_show": {
        return this.dataItem.localFile.exists() ||
               this.dataItem.partFile.exists();
      }
      case "downloadsCmd_pauseResume":
        return this.dataItem.inProgress && this.dataItem.resumable;
      case "downloadsCmd_retry":
        return this.dataItem.canRetry;
      case "downloadsCmd_openReferrer":
        return !!this.dataItem.referrer;
      case "cmd_delete":
      case "downloadsCmd_cancel":
      case "downloadsCmd_copyLocation":
      case "downloadsCmd_doDefault":
        return true;
    }
    return false;
  },

  doCommand: function DVIC_doCommand(aCommand)
  {
    if (this.isCommandEnabled(aCommand)) {
      this.commands[aCommand].apply(this);
    }
  },

  //////////////////////////////////////////////////////////////////////////////
  //// Item commands

  /**
   * This object contains one key for each command that operates on this item.
   *
   * In commands, the "this" identifier points to the controller item.
   */
  commands: {
    cmd_delete: function DVIC_cmd_delete()
    {
      this.dataItem.remove();
      PlacesUtils.bhistory.removePage(NetUtil.newURI(this.dataItem.uri));
    },

    downloadsCmd_cancel: function DVIC_downloadsCmd_cancel()
    {
      this.dataItem.cancel();
    },

    downloadsCmd_open: function DVIC_downloadsCmd_open()
    {
      this.dataItem.openLocalFile();

      // We explicitly close the panel here to give the user the feedback that
      // their click has been received, and we're handling the action.
      // Otherwise, we'd have to wait for the file-type handler to execute
      // before the panel would close. This also helps to prevent the user from
      // accidentally opening a file several times.
      DownloadsPanel.hidePanel();
    },

    downloadsCmd_show: function DVIC_downloadsCmd_show()
    {
      this.dataItem.showLocalFile();

      // We explicitly close the panel here to give the user the feedback that
      // their click has been received, and we're handling the action.
      // Otherwise, we'd have to wait for the operating system file manager
      // window to open before the panel closed. This also helps to prevent the
      // user from opening the containing folder several times.
      DownloadsPanel.hidePanel();
    },

    downloadsCmd_pauseResume: function DVIC_downloadsCmd_pauseResume()
    {
      this.dataItem.togglePauseResume();
    },

    downloadsCmd_retry: function DVIC_downloadsCmd_retry()
    {
      this.dataItem.retry();
    },

    downloadsCmd_openReferrer: function DVIC_downloadsCmd_openReferrer()
    {
      openURL(this.dataItem.referrer);
    },

    downloadsCmd_copyLocation: function DVIC_downloadsCmd_copyLocation()
    {
      let clipboard = Cc["@mozilla.org/widget/clipboardhelper;1"]
                      .getService(Ci.nsIClipboardHelper);
      clipboard.copyString(this.dataItem.uri, document);
    },

    downloadsCmd_doDefault: function DVIC_downloadsCmd_doDefault()
    {
      const nsIDM = Ci.nsIDownloadManager;

      // Determine the default command for the current item.
      let defaultCommand = function () {
        switch (this.dataItem.state) {
          case nsIDM.DOWNLOAD_NOTSTARTED:       return "downloadsCmd_cancel";
          case nsIDM.DOWNLOAD_FINISHED:         return "downloadsCmd_open";
          case nsIDM.DOWNLOAD_FAILED:           return "downloadsCmd_retry";
          case nsIDM.DOWNLOAD_CANCELED:         return "downloadsCmd_retry";
          case nsIDM.DOWNLOAD_PAUSED:           return "downloadsCmd_pauseResume";
          case nsIDM.DOWNLOAD_QUEUED:           return "downloadsCmd_cancel";
          case nsIDM.DOWNLOAD_BLOCKED_PARENTAL: return "downloadsCmd_openReferrer";
          case nsIDM.DOWNLOAD_SCANNING:         return "downloadsCmd_show";
          case nsIDM.DOWNLOAD_DIRTY:            return "downloadsCmd_openReferrer";
          case nsIDM.DOWNLOAD_BLOCKED_POLICY:   return "downloadsCmd_openReferrer";
        }
        return "";
      }.apply(this);
      if (defaultCommand && this.isCommandEnabled(defaultCommand))
        this.doCommand(defaultCommand);
    }
  }
};


////////////////////////////////////////////////////////////////////////////////
//// DownloadsSummary

/**
 * Manages the summary at the bottom of the downloads panel list if the number
 * of items in the list exceeds the panels limit.
 */
const DownloadsSummary = {

  /**
   * Sets the active state of the summary. When active, the summary subscribes
   * to the DownloadsCommon DownloadsSummaryData singleton.
   *
   * @param aActive
   *        Set to true to activate the summary.
   */
  set active(aActive)
  {
    if (aActive == this._active || !this._summaryNode) {
      return this._active;
    }
    if (aActive) {
      DownloadsCommon.getSummary(window, DownloadsView.kItemCountLimit)
                     .refreshView(this);
    } else {
      DownloadsFooter.showingSummary = false;
    }

    return this._active = aActive;
  },

  /**
   * Returns the active state of the downloads summary.
   */
  get active() this._active,

  _active: false,

  /**
   * Sets whether or not we show the progress bar.
   *
   * @param aShowingProgress
   *        True if we should show the progress bar.
   */
  set showingProgress(aShowingProgress)
  {
    if (aShowingProgress) {
      this._summaryNode.setAttribute("inprogress", "true");
    } else {
      this._summaryNode.removeAttribute("inprogress");
    }
    // If progress isn't being shown, then we simply do not show the summary.
    return DownloadsFooter.showingSummary = aShowingProgress;
  },

  /**
   * Sets the amount of progress that is visible in the progress bar.
   *
   * @param aValue
   *        A value between 0 and 100 to represent the progress of the
   *        summarized downloads.
   */
  set percentComplete(aValue)
  {
    if (this._progressNode) {
      this._progressNode.setAttribute("value", aValue);
    }
    return aValue;
  },

  /**
   * Sets the description for the download summary.
   *
   * @param aValue
   *        A string representing the description of the summarized
   *        downloads.
   */
  set description(aValue)
  {
    if (this._descriptionNode) {
      this._descriptionNode.setAttribute("value", aValue);
      this._descriptionNode.setAttribute("tooltiptext", aValue);
    }
    return aValue;
  },

  /**
   * Sets the details for the download summary, such as the time remaining,
   * the amount of bytes transferred, etc.
   *
   * @param aValue
   *        A string representing the details of the summarized
   *        downloads.
   */
  set details(aValue)
  {
    if (this._detailsNode) {
      this._detailsNode.setAttribute("value", aValue);
      this._detailsNode.setAttribute("tooltiptext", aValue);
    }
    return aValue;
  },

  /**
   * Focuses the root element of the summary.
   */
  focus: function()
  {
    if (this._summaryNode) {
      this._summaryNode.focus();
    }
  },

  /**
   * Respond to keydown events on the Downloads Summary node.
   *
   * @param aEvent
   *        The keydown event being handled.
   */
  onKeyDown: function DS_onKeyDown(aEvent)
  {
    if (aEvent.charCode == " ".charCodeAt(0) ||
        aEvent.keyCode == KeyEvent.DOM_VK_RETURN) {
      DownloadsPanel.showDownloadsHistory();
    }
  },

  /**
   * Respond to click events on the Downloads Summary node.
   *
   * @param aEvent
   *        The click event being handled.
   */
  onClick: function DS_onClick(aEvent)
  {
    DownloadsPanel.showDownloadsHistory();
  },

  /**
   * Element corresponding to the root of the downloads summary.
   */
  get _summaryNode()
  {
    let node = document.getElementById("downloadsSummary");
    if (!node) {
      return null;
    }
    delete this._summaryNode;
    return this._summaryNode = node;
  },

  /**
   * Element corresponding to the progress bar in the downloads summary.
   */
  get _progressNode()
  {
    let node = document.getElementById("downloadsSummaryProgress");
    if (!node) {
      return null;
    }
    delete this._progressNode;
    return this._progressNode = node;
  },

  /**
   * Element corresponding to the main description of the downloads
   * summary.
   */
  get _descriptionNode()
  {
    let node = document.getElementById("downloadsSummaryDescription");
    if (!node) {
      return null;
    }
    delete this._descriptionNode;
    return this._descriptionNode = node;
  },

  /**
   * Element corresponding to the secondary description of the downloads
   * summary.
   */
  get _detailsNode()
  {
    let node = document.getElementById("downloadsSummaryDetails");
    if (!node) {
      return null;
    }
    delete this._detailsNode;
    return this._detailsNode = node;
  }
}

////////////////////////////////////////////////////////////////////////////////
//// DownloadsFooter

/**
 * Manages events sent to to the footer vbox, which contains both the
 * DownloadsSummary as well as the "Show All Downloads" button.
 */
const DownloadsFooter = {

  /**
   * Focuses the appropriate element within the footer. If the summary
   * is visible, focus it. If not, focus the "Show All Downloads"
   * button.
   */
  focus: function DF_focus()
  {
    if (this._showingSummary) {
      DownloadsSummary.focus();
    } else {
      DownloadsView.downloadsHistory.focus();
    }
  },

  _showingSummary: false,

  /**
   * Sets whether or not the Downloads Summary should be displayed in the
   * footer. If not, the "Show All Downloads" button is shown instead.
   */
  set showingSummary(aValue)
  {
    if (this._footerNode) {
      if (aValue) {
        this._footerNode.setAttribute("showingsummary", "true");
      } else {
        this._footerNode.removeAttribute("showingsummary");
      }
      this._showingSummary = aValue;
    }
    return aValue;
  },

  /**
   * Element corresponding to the footer of the downloads panel.
   */
  get _footerNode()
  {
    let node = document.getElementById("downloadsFooter");
    if (!node) {
      return null;
    }
    delete this._footerNode;
    return this._footerNode = node;
  }
};
