Replace TagPanel react-dnd with react-beautiful-dnd

This new library handles the simple case of an ordered vertical
(or horizontal) list of items that can be reordered.

It provides animations, handles positioning of items mid-drag
and exposes a much simpler API to react-dnd (with a slight loss
of potential function, but we don't need this flexibility here
anyway).

Apart from this, TagOrderStore had to be changed in a highly
coupled way, but arguably for the better. Instead of being
updated incrementally every time an item is dragged over
another and having a separate "commit" action, the
asyncronous action `moveTag` is used to reposition the tag in
the list and both dispatch an optimistic update and carry out
the request as before. (The MatrixActions.accountData is still
used to indicate a successful reordering of tags).

The view is updated instantly, in an animated way, and this
is handled at the layer "above" React by the DND library.

src/components/structures/TagPanel.js

@@ -25,6 +25,8 @@ import TagOrderActions from '../../actions/TagOrderActions';
 import sdk from '../../index';
 import dis from '../../dispatcher';
 
+import { DragDropContext, Droppable } from 'react-beautiful-dnd';
+
 const TagPanel = React.createClass({
     displayName: 'TagPanel',
 
@@ -69,7 +71,9 @@ const TagPanel = React.createClass({
         dis.dispatch(GroupActions.fetchJoinedGroups(this.context.matrixClient));
     },
 
-    onClick() {
+    onClick(e) {
+        // Ignore clicks on children
+        if (e.target !== e.currentTarget) return;
         dis.dispatch({action: 'deselect_tags'});
     },
 
@@ -78,8 +82,20 @@ const TagPanel = React.createClass({
         dis.dispatch({action: 'view_create_group'});
     },
 
-    onTagTileEndDrag() {
-        dis.dispatch(TagOrderActions.commitTagOrdering(this.context.matrixClient));
+    onTagTileEndDrag(result) {
+        // Dragged to an invalid destination, not onto a droppable
+        if (!result.destination) {
+            return;
+        }
+
+        // Dispatch synchronously so that the TagPanel receives an
+        // optimistic update from TagOrderStore before the previous
+        // state is shown.
+        dis.dispatch(TagOrderActions.moveTag(
+            this.context.matrixClient,
+            result.draggableId,
+            result.destination.index,
+        ), true);
     },
 
     render() {
@@ -89,16 +105,26 @@ const TagPanel = React.createClass({
 
         const tags = this.state.orderedTags.map((tag, index) => {
             return <DNDTagTile
-                key={tag + '_' + index}
+                key={tag}
                 tag={tag}
+                index={index}
                 selected={this.state.selectedTags.includes(tag)}
-                onEndDrag={this.onTagTileEndDrag}
             />;
         });
         return <div className="mx_TagPanel" onClick={this.onClick}>
-            <div className="mx_TagPanel_tagTileContainer">
-                { tags }
-            </div>
+            <DragDropContext onDragEnd={this.onTagTileEndDrag}>
+                <Droppable droppableId="tag-panel-droppable">
+                    { (provided, snapshot) => (
+                        <div
+                            className="mx_TagPanel_tagTileContainer"
+                            ref={provided.innerRef}
+                        >
+                            { tags }
+                            { provided.placeholder }
+                        </div>
+                    ) }
+                </Droppable>
+            </DragDropContext>
             <AccessibleButton className="mx_TagPanel_createGroupButton" onClick={this.onCreateGroupClick}>
                 <TintableSvg src="img/icons-create-room.svg" width="25" height="25" />
             </AccessibleButton>

src/components/views/elements/DNDTagTile.js

@@ -15,71 +15,29 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { DragSource, DropTarget } from 'react-dnd';
-
 import TagTile from './TagTile';
-import dis from '../../../dispatcher';
-import { findDOMNode } from 'react-dom';
 
-const tagTileSource = {
-    canDrag: function(props, monitor) {
-        return true;
-    },
+import { Draggable } from 'react-beautiful-dnd';
 
-    beginDrag: function(props) {
-        // Return the data describing the dragged item
-        return {
-            tag: props.tag,
-        };
-    },
-
-    endDrag: function(props, monitor, component) {
-        const dropResult = monitor.getDropResult();
-        if (!monitor.didDrop() || !dropResult) {
-            return;
-        }
-        props.onEndDrag();
-    },
-};
-
-const tagTileTarget = {
-    canDrop(props, monitor) {
-        return true;
-    },
-
-    hover(props, monitor, component) {
-        if (!monitor.canDrop()) return;
-        const draggedY = monitor.getClientOffset().y;
-        const {top, bottom} = findDOMNode(component).getBoundingClientRect();
-        const targetY = (top + bottom) / 2;
-        dis.dispatch({
-            action: 'order_tag',
-            tag: monitor.getItem().tag,
-            targetTag: props.tag,
-            // Note: we indicate that the tag should be after the target when
-            // it's being dragged over the top half of the target.
-            after: draggedY < targetY,
-        });
-    },
-
-    drop(props) {
-        // Return the data to be returned by getDropResult
-        return {
-            tag: props.tag,
-        };
-    },
-};
-
-export default
-    DropTarget('TagTile', tagTileTarget, (connect, monitor) => ({
-        connectDropTarget: connect.dropTarget(),
-    }))(DragSource('TagTile', tagTileSource, (connect, monitor) => ({
-        connectDragSource: connect.dragSource(),
-    }))((props) => {
-        const { connectDropTarget, connectDragSource, ...otherProps } = props;
-        return connectDropTarget(connectDragSource(
-            <div>
-                <TagTile {...otherProps} />
-            </div>,
-        ));
-    }));
+export default function DNDTagTile(props) {
+    return <div>
+        <Draggable
+            key={props.tag}
+            draggableId={props.tag}
+            index={props.index}
+        >
+            { (provided, snapshot) => (
+                <div>
+                    <div
+                        ref={provided.innerRef}
+                        {...provided.draggableProps}
+                        {...provided.dragHandleProps}
+                    >
+                        <TagTile {...props} />
+                    </div>
+                    { provided.placeholder }
+                </div>
+            ) }
+        </Draggable>
+    </div>;
+}