get drag impact refactor

src/state/action-creators.js

@@ -69,7 +69,6 @@ export type CompleteLiftAction = {|
     id: DraggableId,
     type: TypeId,
     client: InitialDragLocation,
-    page: InitialDragLocation,
     windowScroll: Position,
     isScrollAllowed: boolean,
   |}
@@ -78,7 +77,6 @@ export type CompleteLiftAction = {|
 const completeLift = (id: DraggableId,
   type: TypeId,
   client: InitialDragLocation,
-  page: InitialDragLocation,
   windowScroll: Position,
   isScrollAllowed: boolean,
 ): CompleteLiftAction => ({
@@ -87,7 +85,6 @@ const completeLift = (id: DraggableId,
     id,
     type,
     client,
-    page,
     windowScroll,
     isScrollAllowed,
   },
@@ -154,20 +151,17 @@ export type MoveAction = {|
   payload: {|
     id: DraggableId,
     client: Position,
-    page: Position,
     windowScroll: Position,
   |}
 |}
 
 export const move = (id: DraggableId,
   client: Position,
-  page: Position,
   windowScroll: Position): MoveAction => ({
     type: 'MOVE',
     payload: {
       id,
       client,
-      page,
       windowScroll,
     },
   });
@@ -421,7 +415,6 @@ export type LiftAction = {|
     id: DraggableId,
     type: TypeId,
     client: InitialDragLocation,
-    page: InitialDragLocation,
     windowScroll: Position,
     isScrollAllowed: boolean,
   |}
@@ -431,7 +424,6 @@ export type LiftAction = {|
 export const lift = (id: DraggableId,
   type: TypeId,
   client: InitialDragLocation,
-  page: InitialDragLocation,
   windowScroll: Position,
   isScrollAllowed: boolean,
 ) => (dispatch: Dispatch, getState: Function) => {
@@ -471,7 +463,7 @@ export const lift = (id: DraggableId,
       if (newState.phase !== 'COLLECTING_DIMENSIONS') {
         return;
       }
-      dispatch(completeLift(id, type, client, page, windowScroll, isScrollAllowed));
+      dispatch(completeLift(id, type, client, windowScroll, isScrollAllowed));
     });
   });
 };

src/state/get-drag-impact/in-foreign-list.js

@@ -0,0 +1,61 @@
+// @flow
+import type {
+  DraggableId,
+  DroppableId,
+  DragMovement,
+  DraggableDimension,
+  DroppableDimension,
+  DragImpact,
+  Axis,
+  Position,
+} from '../../types';
+import { add, subtract, patch } from '../position';
+
+type Args = {|
+  pageCenter: Position,
+  draggable: DraggableDimension,
+  destination: DroppableDimension,
+  insideDestination: DraggableDimension[],
+|}
+
+export default ({
+  pageCenter,
+  draggable,
+  destination,
+  insideDestination,
+}: Args): DragImpact => {
+  const axis: Axis = destination.axis;
+
+  const destinationScrollDiff: Position = subtract(
+    destination.scroll.current, destination.scroll.initial
+  );
+
+  const currentCenter: Position = add(pageCenter, destinationScrollDiff);
+
+  const moved: DraggableId[] = insideDestination
+    .filter((child: DraggableDimension): boolean => {
+      // Items will be displaced forward if they sit ahead of the dragging item
+      const threshold: number = child.page.withoutMargin[axis.end];
+      return threshold > currentCenter[axis.line];
+    })
+    .map((dimension: DraggableDimension): DroppableId => dimension.id);
+
+  const newIndex: number = insideDestination.length - moved.length;
+
+  const movement: DragMovement = {
+    amount: patch(axis.line, draggable.page.withMargin[axis.size]),
+    draggables: moved,
+    isBeyondStartPosition: false,
+  };
+
+  const impact: DragImpact = {
+    movement,
+    direction: axis.direction,
+    destination: {
+      droppableId: destination.id,
+      index: newIndex,
+    },
+  };
+
+  return impact;
+};