[MD Bookmarks] Add a drag and drop indicator to bookmarks.

chrome/browser/resources/md_bookmarks/dnd_manager.js

Index: chrome/browser/resources/md_bookmarks/dnd_manager.js
diff --git a/chrome/browser/resources/md_bookmarks/dnd_manager.js b/chrome/browser/resources/md_bookmarks/dnd_manager.js
new file mode 100644
index 0000000000000000000000000000000000000000..cda4c8cad756423f5b60c3913d2df179c0b979d1
--- /dev/null
+++ b/chrome/browser/resources/md_bookmarks/dnd_manager.js
@@ -0,0 +1,522 @@
+// Copyright 2017 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.
+
+/**
+ * Enumeration of valid drop locations relative to an element. These are
+ * bit masks to allow combining multiple locations in a single value.
+ * @enum {number}
+ * @const
+ */
+var DropPosition = {
+  NONE: 0,
+  ABOVE: 1,
+  ON: 2,
+  BELOW: 4,
+};
+
+/** @typedef {{element: BookmarkElement, position: DropPosition}} */
+var DropDestination;
+
+cr.define('bookmarks', function() {
+  /**
+   * @param {BookmarkElement} element
+   * @return {boolean}
+   */
+  function isBookmarkItem(element) {
+    return element.tagName == 'BOOKMARKS-ITEM';
+  }
+
+  /**
+   * @param {BookmarkElement} element
+   * @return {boolean}
+   */
+  function isBookmarkFolderNode(element) {
+    return element.tagName == 'BOOKMARKS-FOLDER-NODE';
+  }
+
+  /**
+   * @param {Array<!Element>|undefined} path
+   * @return {BookmarkElement}
+   */
+  function getBookmarkElement(path) {
+    if (!path)
+      return null;
+
+    for (var i = 0; i < path.length; i++) {
+      if (isBookmarkItem(path[i]) || isBookmarkFolderNode(path[i]))
+        return path[i];
+    }
+    return null;
+  }
+
+  /**
+   * @param {BookmarkElement} bookmarkElement
+   * @return {BookmarkNode}
+   */
+  function getBookmarkNode(bookmarkElement) {
+    return bookmarks.Store.getInstance().data.nodes[bookmarkElement.itemId];
+  }
+
+  /**
+   * Contains and provides utility methods for drag data sent by the
+   * bookmarkManagerPrivate API.
+   * @constructor
+   */
+  function DragInfo() {
+    /** @type {DragData} */
+    this.dragData = null;
+  }
+
+  DragInfo.prototype = {
+    /** @param {DragData} newDragData */
+    handleChromeDragEnter: function(newDragData) {
+      this.dragData = newDragData;
+    },
+
+    clearDragData: function() {
+      this.dragData = null;
+    },
+
+    /** @return {boolean} */
+    isDragValid: function() {
+      return !!this.dragData;
+    },
+
+    /** @return {boolean} */
+    isSameProfile: function() {
+      return !!this.dragData && this.dragData.sameProfile;
+    },
+
+    /** @return {boolean} */
+    isDraggingFolders: function() {
+      return !!this.dragData && this.dragData.elements.some(function(node) {
+        return !node.url;
+      });
+    },
+
+    /** @return {boolean} */
+    isDraggingBookmark: function(bookmarkId) {
+      return !!this.dragData && this.isSameProfile() &&
+          this.dragData.elements.some(function(node) {
+            return node.id == bookmarkId;
+          });
+    },
+
+    /** @return {boolean} */
+    isDraggingChildBookmark: function(folderId) {
+      return !!this.dragData && this.isSameProfile() &&
+          this.dragData.elements.some(function(node) {
+            return node.parentId == folderId;
+          });
+    },
+
+    /** @return {boolean} */
+    isDraggingFolderToDescendant: function(itemId, nodes) {
+      if (!this.isSameProfile())
+        return false;
+
+      var parentId = nodes[itemId].parentId;
+      var parents = {};
+      while (parentId) {
+        parents[parentId] = true;
+        parentId = nodes[parentId].parentId;
+      }
+
+      return !!this.dragData && this.dragData.elements.some(function(node) {
+        return parents[node.id];
+      });
+    },
+  };
+
+  /**
+   * Encapsulates the behavior of the drag and drop indicator which puts a line
+   * between items or highlights folders which are valid drop targets.
+   * @constructor
+   */
+  function DropIndicator() {
+    /**
+     * @type {number|null} Timer id used to help minimize flicker.
+     */
+    this.removeDropIndicatorTimer = null;
+
+    /**
+     * The element that had a style applied it to indicate the drop location.
+     * This is used to easily remove the style when necessary.
+     * @type {BookmarkElement|null}
+     */
+    this.lastIndicatorElement = null;
+
+    /**
+     * The style that was applied to indicate the drop location.
+     * @type {?string|null}
+     */
+    this.lastIndicatorClassName = null;
+
+    /**
+     * Used to instantly remove the indicator style in tests.
+     * @type {function((Function|null|string), number)}

[tsergeant, 2017/03/27 06:49:24]

Nit: @private

[calamity, 2017/03/28 04:15:03]

Done. Also privated the rest of the things here.

+     */
+    this.setTimeout_ = window.setTimeout.bind(window);
+  }
+
+  DropIndicator.prototype = {
+    /**
+     * Applies the drop indicator style on the target element and stores that
+     * information to easily remove the style in the future.
+     * @param {HTMLElement} indicatorElement
+     * @param {DropPosition} position
+     */
+    addDropIndicatorStyle: function(indicatorElement, position) {
+      var indicatorStyleName = position == DropPosition.ABOVE ?
+          'drag-above' :
+          position == DropPosition.BELOW ? 'drag-below' : 'drag-on';
+
+      this.lastIndicatorElement = indicatorElement;
+      this.lastIndicatorClassName = indicatorStyleName;
+
+      indicatorElement.classList.add(indicatorStyleName);
+    },
+
+    /**
+     * Clears the drop indicator style from the last element was the drop target

[tsergeant, 2017/03/27 06:49:24]

nit: this sentence doesn't quite grammar

maybe just "Clears the drop indicator style from the last drop target"

[calamity, 2017/03/28 04:15:03]

Uhhhhh. Done.

+     * so the drop indicator is no longer for that element.
+     */
+    removeDropIndicatorStyle: function() {
+      if (!this.lastIndicatorElement || !this.lastIndicatorClassName)
+        return;
+
+      this.lastIndicatorElement.classList.remove(this.lastIndicatorClassName);
+      this.lastIndicatorElement = null;
+      this.lastIndicatorClassName = null;
+    },
+
+    /**
+     * Displays the drop indicator on the current drop target to give the
+     * user feedback on where the drop will occur.
+     * @param {DropDestination} dropDest
+     */
+    update: function(dropDest) {
+      window.clearTimeout(this.removeDropIndicatorTimer);
+
+      var indicatorElement = dropDest.element.getDropTarget();
+      var position = dropDest.position;
+
+      this.removeDropIndicatorStyle();
+      this.addDropIndicatorStyle(indicatorElement, position);
+    },
+
+    /**
+     * Stop displaying the drop indicator.
+     */
+    finish: function() {
+      // The use of a timeout is in order to reduce flickering as we move
+      // between valid drop targets.
+      window.clearTimeout(this.removeDropIndicatorTimer);
+      this.removeDropIndicatorTimer = this.setTimeout_(function() {
+        this.removeDropIndicatorStyle();
+      }.bind(this), 100);
+    },
+
+    disableTimeoutForTesting: function() {
+      this.setTimeout_ = function(fn, timeout) {
+        fn();
+      };
+    },
+  };
+
+  /**
+   * Manages drag and drop events for the bookmarks-app.
+   * @constructor
+   */
+  function DNDManager() {
+    /** @private {bookmarks.DragInfo} */
+    this.dragInfo_ = null;
+
+    /** @private {?DropDestination} */
+    this.dropDestination_ = null;
+
+    /** @private {bookmarks.DropIndicator} */
+    this.dropIndicator_ = null;
+
+    /** @private {Object<string, function(!Event)>} */
+    this.documentListeners_ = null;
+  }
+
+  DNDManager.prototype = {
+    init: function() {
+      this.dragInfo_ = new DragInfo();
+      this.dropIndicator_ = new DropIndicator();
+
+      this.documentListeners_ = {
+        'dragstart': this.onDragStart_.bind(this),
+        'dragenter': this.onDragEnter_.bind(this),
+        'dragover': this.onDragOver_.bind(this),
+        'dragleave': this.onDragLeave_.bind(this),
+        'drop': this.onDrop_.bind(this),
+        'dragend': this.clearDragData_.bind(this),
+        'mouseup': this.clearDragData_.bind(this),
+        // TODO(calamity): Add touch support.
+      };
+      for (var event in this.documentListeners_)
+        document.addEventListener(event, this.documentListeners_[event]);
+
+      chrome.bookmarkManagerPrivate.onDragEnter.addListener(
+          this.dragInfo_.handleChromeDragEnter.bind(this.dragInfo_));
+      chrome.bookmarkManagerPrivate.onDragLeave.addListener(
+          this.clearDragData_.bind(this));
+      chrome.bookmarkManagerPrivate.onDrop.addListener(
+          this.clearDragData_.bind(this));
+    },
+
+    destroy: function() {
+      for (var event in this.documentListeners_)
+        document.removeEventListener(event, this.documentListeners_[event]);
+    },
+
+    /** @private */
+    onDragLeave_: function() {
+      this.dropIndicator_.finish();
+    },
+
+    /**
+     * @private
+     * @param {!Event} e
+     */
+    onDrop_: function(e) {
+      if (this.dropDestination_) {

[tsergeant, 2017/03/27 06:49:23]

Nit: {}

[calamity, 2017/03/28 04:15:03]

Done.

+        e.preventDefault();
+      }
+      this.dropDestination_ = null;
+      this.dropIndicator_.finish();
+    },
+
+    /** @private */
+    clearDragData_: function() {
+      this.dragInfo_.clearDragData();
+      this.dropDestination_ = null;
+      this.dropIndicator_.finish();
+    },
+
+    /**
+     * @private
+     * @param {Event} e
+     */
+    onDragStart_: function(e) {
+      var dragElement = getBookmarkElement(e.path);
+      if (!dragElement)
+        return;
+
+      // Determine the selected bookmarks.
+      var state = bookmarks.Store.getInstance().data;
+      var draggedNodes = Object.keys(state.selection.items);

[tsergeant, 2017/03/27 06:49:24]

Hrmm, at the moment we don't really guarantee from the store side that
everything in the `selection.items` map has the value `true`. It's possible
right now for a reducer to set `selection.items[id] = false` and everything else
will work.

I think it's fine to make the assumption that everything in the items map is
true, but we should probably document it somewhere. Maybe in types.js? That's
not a super visible place, but I'm not sure there's anywhere better.

[calamity, 2017/03/28 04:15:03]

Done.

Remind me why we didn't use a Set again?

[tsergeant, 2017/03/28 23:52:22]

Yeah, we could probably give it a go with a Set.

+
+      if (isBookmarkFolderNode(dragElement) ||
+          draggedNodes.indexOf(dragElement.itemId) == -1) {
+        // TODO(calamity): clear current selection.
+        draggedNodes = [dragElement.itemId];
+      }
+
+      e.preventDefault();
+
+      // If we are dragging a single link, we can do the *Link* effect.
+      // Otherwise, we only allow copy and move.
+      if (e.dataTransfer) {
+        e.dataTransfer.effectAllowed =
+            draggedNodes.length == 1 && state.nodes[draggedNodes[0]].url ?
+            'copyLink' :
+            'copyMove';
+      }
+
+      // TODO(calamity): account for touch.
+      chrome.bookmarkManagerPrivate.startDrag(draggedNodes, false);
+    },
+
+    /**
+     * @private
+     * @param {Event} e
+     */
+    onDragEnter_: function(e) {
+      e.preventDefault();
+    },
+
+    /**
+     * @private
+     * @param {Event} e
+     */
+    onDragOver_: function(e) {
+      this.dropDestination_ = null;
+
+      // This is necessary to actually trigger the 'none' effect, even though
+      // the event will have this set to 'none' already.

[tsergeant, 2017/03/27 06:49:24]

😕

[calamity, 2017/03/28 04:15:03]

Mate, you have no idea.

+      if (e.dataTransfer)
+        e.dataTransfer.dropEffect = 'none';
+
+      // Allow normal DND on text inputs.
+      if (e.path[0].tagName == 'INPUT')
+        return;
+
+      // The default operation is to allow dropping links etc to do
+      // navigation. We never want to do that for the bookmark manager.
+      e.preventDefault();
+
+      if (!this.dragInfo_.isDragValid())
+        return;
+
+      var overElement = getBookmarkElement(e.path);
+      if (!overElement)
+        return;
+
+      // TODO(calamity): open folders on hover.
+
+      // Now we know that we can drop. Determine if we will drop above, on or
+      // below based on mouse position etc.
+      this.dropDestination_ =
+          this.calculateDropDestination_(e.clientY, overElement);
+      if (!this.dropDestination_)
+        return;
+
+      if (e.dataTransfer) {
+        e.dataTransfer.dropEffect =
+            this.dragInfo_.isSameProfile() ? 'move' : 'copy';
+      }
+
+      this.dropIndicator_.update(this.dropDestination_);
+    },
+
+    /**
+     * This function determines where the drop will occur.
+     * @private
+     * @param {number} elementClientY
+     * @param {!BookmarkElement} overElement
+     * @return {?DropDestination} If no valid drop position is found, null,
+     *   otherwise:
+     *       element - The target element that will receive the drop.
+     *       position - A |DropPosition| relative to the |element|.
+     */
+    calculateDropDestination_: function(elementClientY, overElement) {
+      var validDropPositions = this.calculateValidDropPositions_(overElement);
+      if (validDropPositions == DropPosition.NONE)
+        return null;
+
+      var above = validDropPositions & DropPosition.ABOVE;
+      var below = validDropPositions & DropPosition.BELOW;
+      var on = validDropPositions & DropPosition.ON;
+      var rect = overElement.getDropTarget().getBoundingClientRect();
+      var yRatio = (elementClientY - rect.top) / rect.height;
+
+      if (above && (yRatio <= .25 || yRatio <= .5 && (!below || !on)))
+        return {element: overElement, position: DropPosition.ABOVE};
+
+      if (below && (yRatio > .75 || yRatio > .5 && (!above || !on)))
+        return {element: overElement, position: DropPosition.BELOW};
+
+      if (on)
+        return {element: overElement, position: DropPosition.ON};
+
+      return null;
+    },
+
+    /**
+     * Determines the valid drop positions for the given target element.
+     * @private
+     * @param {!BookmarkElement} overElement The element that we are currently
+     *     dragging over.
+     * @return {DropPosition} An bit field enumeration of valid drop locations.
+     */
+    calculateValidDropPositions_: function(overElement) {
+      var dragInfo = this.dragInfo_;
+      var state = bookmarks.Store.getInstance().data;
+
+      // Drags aren't allowed onto the search result list.
+      if (isBookmarkItem(overElement) &&
+          bookmarks.util.isShowingSearch(state)) {
+        return DropPosition.NONE;
+      }
+
+      // Drags of a bookmark onto itself or of a folder into its children aren't
+      // allowed.
+      if (dragInfo.isDraggingBookmark(overElement.itemId) ||
+          dragInfo.isDraggingFolderToDescendant(
+              overElement.itemId, state.nodes)) {
+        return DropPosition.NONE;
+      }
+
+      var validDropPositions = this.calculateDropAboveBelow_(overElement);
+      if (this.canDropOn_(overElement))
+        validDropPositions |= DropPosition.ON;
+
+      return validDropPositions;
+    },
+
+    /**
+     * @private
+     * @param {BookmarkElement} overElement
+     * @return {DropPosition}
+     */
+    calculateDropAboveBelow_: function(overElement) {
+      var dragInfo = this.dragInfo_;
+      var state = bookmarks.Store.getInstance().data;
+
+      // We cannot drop between Bookmarks bar and Other bookmarks.
+      if (getBookmarkNode(overElement).parentId == bookmarks.util.ROOT_NODE_ID)
+        return DropPosition.NONE;
+
+      var isOverFolderNode = isBookmarkFolderNode(overElement);
+
+      // We can only drop between items in the tree if we have any folders.
+      if (isOverFolderNode && !dragInfo.isDraggingFolders())
+        return DropPosition.NONE;
+
+      var validDropPositions = DropPosition.NONE;
+
+      // Cannot drop above if the item above is already in the drag source.
+      var previousElem = overElement.previousElementSibling;
+      if (!previousElem || !dragInfo.isDraggingBookmark(previousElem.itemId)) {

[tsergeant, 2017/03/27 06:49:24]

Nit: {}

[calamity, 2017/03/28 04:15:03]

Done.

+        validDropPositions |= DropPosition.ABOVE;
+      }
+
+      // Don't allow dropping below an expanded sidebar folder item since it is
+      // confusing to the user anyway.
+      if (isOverFolderNode && !state.closedFolders[overElement.itemId] &&
+          bookmarks.util.hasChildFolders(overElement.itemId, state.nodes)) {
+        return validDropPositions;
+      }
+
+      // Cannot drop below if the item below is already in the drag source.

[tsergeant, 2017/03/27 06:49:23]

Does this comment belong on the if statement on line 493?

[calamity, 2017/03/28 04:15:03]

Ugh, I never know what to do with comments like these. I want to comment the
entire block below here, but I guess the conditional will do.

+      var nextElement = overElement.nextElementSibling;
+
+      // The template element sits past the end of the last bookmark element.
+      if (!isBookmarkItem(nextElement) && !isBookmarkFolderNode(nextElement))
+        nextElement = null;
+
+      if (!nextElement || !dragInfo.isDraggingBookmark(nextElement.itemId)) {

[tsergeant, 2017/03/27 06:49:23]

{} here too

[calamity, 2017/03/28 04:15:03]

Done.

+        validDropPositions |= DropPosition.BELOW;
+      }
+
+      return validDropPositions;
+    },
+
+    /**
+     * Determine whether we can drop the dragged items on the drop target.
+     * @private
+     * @param {!BookmarkElement} overElement The element that we are currently
+     *     dragging over.
+     * @return {boolean} Whether we can drop the dragged items on the drop
+     *     target.
+     */
+    canDropOn_: function(overElement) {
+      // We can only drop on a folder.
+      if (getBookmarkNode(overElement).url)
+        return false;
+
+      return !this.dragInfo_.isDraggingChildBookmark(overElement.itemId)
+    },
+  };
+
+  return {
+    DNDManager: DNDManager,
+    DragInfo: DragInfo,
+    DropIndicator: DropIndicator,
+  };
+});