animated droppable placeholder spike

package.json

@@ -38,7 +38,8 @@
     "react-redux": "5.0.6",
     "redux": "^3.6.0",
     "redux-thunk": "2.2.0",
-    "reselect": "3.0.1"
+    "reselect": "3.0.1",
+    "uuid": "^3.1.0"
   },
   "devDependencies": {
     "@atlaskit/css-reset": "1.1.5",

src/view/animation.js

@@ -23,6 +23,11 @@ export const physics = (() => {
   return { standard, fast };
 })();
 
+const transitionCurve = 'cubic-bezier(0.2, 0, 0, 1)';
+const transitionTime = '0.2s';
+
 export const css = {
-  outOfTheWay: 'transform 0.2s cubic-bezier(0.2, 0, 0, 1)',
+  outOfTheWay: `transform ${transitionTime} ${transitionCurve}`,
+  transitionCurve,
+  transitionTime,
 };

src/view/draggable/draggable.jsx

@@ -20,7 +20,7 @@ import type {
   Provided as DragHandleProvided,
 } from '../drag-handle/drag-handle-types';
 import getCenterPosition from '../get-center-position';
-import Placeholder from '../placeholder';
+import { StaticPlaceholder as Placeholder } from '../placeholder';
 import { droppableIdKey } from '../context-keys';
 import { add } from '../../state/position';
 import type {

src/view/droppable/connected-droppable.js

@@ -79,9 +79,10 @@ export const makeSelector = (): Selector => {
   );
 
   const getMapProps = memoizeOne(
-    (isDraggingOver: boolean, placeholder: ?Placeholder): MapProps => ({
+    (isDraggingOver: boolean, placeholder: ?Placeholder, phase: ?string): MapProps => ({
       isDraggingOver,
       placeholder,
+      phase,
     })
   );
 
@@ -107,7 +108,7 @@ export const makeSelector = (): Selector => {
       if (phase === 'DRAGGING') {
         if (!drag) {
           console.error('cannot determine dragging over as there is not drag');
-          return getMapProps(false, null);
+          return getMapProps(false, null, phase);
         }
 
         const isDraggingOver = getIsDraggingOver(id, drag.impact.destination);
@@ -117,13 +118,13 @@ export const makeSelector = (): Selector => {
           drag.impact.destination,
           draggable
         );
-        return getMapProps(isDraggingOver, placeholder);
+        return getMapProps(isDraggingOver, placeholder, phase);
       }
 
       if (phase === 'DROP_ANIMATING') {
         if (!pending) {
           console.error('cannot determine dragging over as there is no pending result');
-          return getMapProps(false, null);
+          return getMapProps(false, null, phase);
         }
 
         const isDraggingOver = getIsDraggingOver(id, pending.impact.destination);
@@ -133,10 +134,10 @@ export const makeSelector = (): Selector => {
           pending.result.destination,
           draggable
         );
-        return getMapProps(isDraggingOver, placeholder);
+        return getMapProps(isDraggingOver, placeholder, phase);
       }
 
-      return getMapProps(false, null);
+      return getMapProps(false, null, phase);
     },
   );
 };

src/view/droppable/droppable-types.js

@@ -31,6 +31,8 @@ export type MapProps = {|
   // not the user is dragging over a list that
   // is not the source list
   placeholder: ?Placeholder,
+  // whether the entire application is currently in the dragging state
+  phase: ?string,
 |}
 
 export type OwnProps = {|

src/view/droppable/droppable.jsx

@@ -14,6 +14,8 @@ type Context = {|
   [droppableIdKey]: DroppableId
 |}
 
+const defaultPlaceholderDimensions = { height: 0, width: 0 };
+
 export default class Droppable extends Component {
   /* eslint-disable react/sort-comp */
   props: Props
@@ -62,14 +64,16 @@ export default class Droppable extends Component {
   }
 
   getPlaceholder() {
-    if (!this.props.placeholder) {
-      return null;
-    }
+    const { phase } = this.props;
+    const isDraggedOver = Boolean(this.props.placeholder);
+    const { height, width } = this.props.placeholder || defaultPlaceholderDimensions;
 
     return (
       <Placeholder
-        height={this.props.placeholder.height}
-        width={this.props.placeholder.width}
+        phase={phase}
+        isDraggedOver={isDraggedOver}
+        height={height}
+        width={width}
       />
     );
   }

src/view/placeholder/Placeholder.jsx

@@ -0,0 +1,192 @@
+// @flow
+import React, { PureComponent } from 'react';
+import v4 from 'uuid/v4';
+import { css as transitionStyles } from '../animation';
+import type { Phase } from '../../types';
+
+type AnimatedProperties = {|
+  /** The height of the placeholder */
+  height: number,
+  /** The width of the placeholder */
+  width: number,
+|};
+
+type Props = {|
+  ...AnimatedProperties,
+  /** Whether the parent droppable is being dragged over */
+  isDraggedOver: boolean,
+  /** The phase of the drag */
+  phase: Phase,
+|};
+
+type State = {|
+  ...AnimatedProperties,
+  /** Whether the placeholder should be animating in */
+  isAnimatingIn: boolean,
+  /** Whether the placeholder should be animating out */
+  isAnimatingOut: boolean,
+|}
+
+const VENDOR_PREFIXES: string[] = ['-ms-', '-moz-', '-webkit-', ''];
+// We inject a stylesheet into the document so that we can dynamically
+// add CSS animations.
+const stylesheet: HTMLStyleElement = document.createElement('style');
+stylesheet.type = 'text/css';
+document.getElementsByTagName('head')[0].appendChild(stylesheet);
+// A global counter keeping track of how many style rules have been
+// added to the stylesheet.
+let globalRuleIndex = 0;
+
+export default class Placeholder extends PureComponent {
+  // eslint-disable-next-line react/sort-comp
+  props: Props
+
+  static defaultProps = {
+    isDraggedOver: false,
+  }
+
+  state: State = {
+    height: this.props.height,
+    isAnimatingIn: false,
+    isAnimatingOut: false,
+    width: this.props.width,
+  }
+
+  // Every time we instantiate a new placeholder we record the index
+  // of its animation rules, then increment the global counter
+  ruleIndex: number = (() => {
+    const ruleIndex = globalRuleIndex;
+    globalRuleIndex += VENDOR_PREFIXES.length;
+    return ruleIndex;
+  })()
+
+  componentWillReceiveProps(newProps: Props) {
+    if (newProps.phase === this.props.phase &&
+      newProps.isDraggedOver === this.props.isDraggedOver) {
+      return;
+    }
+
+    if (newProps.phase === 'DRAGGING') {
+      const height = newProps.height || this.state.height;
+      const width = newProps.width || this.state.width;
+      const isAnimatingIn = newProps.isDraggedOver;
+      const isAnimatingOut = !newProps.isDraggedOver;
+      this.setState({ height, isAnimatingIn, isAnimatingOut, width });
+    }
+
+    // Reset the state once the drop completes
+    if (newProps.phase === 'DROP_COMPLETE') {
+      this.setState({
+        height: 0,
+        isAnimatingIn: false,
+        isAnimatingOut: false,
+        width: 0,
+      });
+    }
+  }
+
+  getAnimationKeyframes = (animationName: string): string[] => {
+    const { height, isAnimatingIn, isAnimatingOut, width } = this.state;
+    const expanded = `height: ${height}px; width: ${width}px;`;
+    const collapsed = 'height: 0; width: 0;';
+    const keyframeSteps = (() => {
+      if (isAnimatingIn) {
+        return `from { ${collapsed} } to { ${expanded} }`;
+      }
+      if (isAnimatingOut) {
+        return `from { ${expanded} } to { ${collapsed} }`;
+      }
+      return '';
+    })();
+
+    return VENDOR_PREFIXES.map(
+      prefix => `@${prefix}keyframes ${animationName} { ${keyframeSteps} }`
+    );
+  }
+
+  createAnimation = (): ?string => {
+    const { sheet } = stylesheet;
+
+    // Stop flow complaining about possibly undefined properties
+    if (!sheet ||
+      !sheet.cssRules ||
+      !sheet.insertRule ||
+      !sheet.deleteRule) {
+      return null;
+    }
+
+    // We need to generate a random name for the animation every time
+    // because you can't dynamically update CSS animations
+    const animationName = `rbdnd-placeholder-animation-${v4()}`;
+    const keyframes = this.getAnimationKeyframes(animationName);
+    // It's easier to manage if we inject a dummy rule when the
+    // browser doesn't support a prefixed version
+    const dummyRule = '.rbdnd-placeholder-donotuse { display: initial; }';
+    const { ruleIndex } = this;
+
+    for (let i = 0; i < VENDOR_PREFIXES.length; i++) {
+      const thisRuleIndex = ruleIndex + i;
+      // `sheet` is a CSSStyleSheet but the definition of HTMLStyleElement indicates that it
+      // contains a StyleSheet which doesn't have all the methods of its child CSSStyleSheet
+      // $ExpectError - property cssRules not found in StyleSheet
+      if (sheet.cssRules[thisRuleIndex]) {
+        // $ExpectError - property deleteRule not found in StyleSheet
+        sheet.deleteRule(thisRuleIndex);
+      }
+      // The browser will throw if it doesn't support a prefixed version of the rule
+      try {
+        // $ExpectError - property insertRule not found in StyleSheet
+        sheet.insertRule(keyframes[i], thisRuleIndex);
+      } catch (err) {
+        // If it doesn't like it we inject a dummy rule instead
+        // $ExpectError - property insertRule not found in StyleSheet
+        sheet.insertRule(dummyRule, thisRuleIndex);
+      }
+    }
+
+    return animationName;
+  }
+
+  getPlaceholderStyle = () => {
+    const { isDraggedOver, phase } = this.props;
+    const { height, width } = this.state;
+
+    const animationName = this.createAnimation();
+
+    const staticStyles = {
+      height,
+      pointerEvents: 'none',
+      width,
+    };
+
+    // Hold the full height during a drop
+    if (phase === 'DROP_ANIMATING' && isDraggedOver) {
+      return staticStyles;
+    }
+
+    // Animate in/out during a drag
+    if (phase === 'DRAGGING') {
+      return {
+        ...staticStyles,
+        animationName,
+        animationDuration: transitionStyles.transitionTime,
+        animationTimingFunction: transitionStyles.transitionCurve,
+        animationDelay: '0.0s',
+        animationIterationCount: 1,
+        animationDirection: 'normal',
+        animationFillMode: 'forwards',
+      };
+    }
+
+    // Otherwise don't display
+    return {
+      display: 'none',
+    };
+  }
+
+  render() {
+    return (
+      <div style={this.getPlaceholderStyle()} />
+    );
+  }
+}

src/view/placeholder/StaticPlaceholder.jsx

@@ -0,0 +1,21 @@
+// @flow
+import React, { PureComponent } from 'react';
+
+type Props = {|
+  height: number,
+  width: number,
+|};
+
+export default class StaticPlaceholder extends PureComponent {
+  props: Props
+
+  render() {
+    const { height, width } = this.props;
+    const style = {
+      height,
+      pointerEvents: 'none',
+      width,
+    };
+    return <div style={style} />;
+  }
+}

src/view/placeholder/index.js

@@ -1 +1,2 @@
-export default from './placeholder';
+export default from './Placeholder';
+export { default as StaticPlaceholder } from './StaticPlaceholder';