Merge branch 'add-accordion'

1 files changed, 146 insertions, 0 deletions

diff --git a/app/components/Accordion.js b/app/components/Accordion.js
new file mode 100644
index 0000000000..456a95fe05
--- /dev/null
+++ b/app/components/Accordion.js
@@ -0,0 +1,146 @@
+// @flow
+
+import React, { Component } from 'react';
+
+export type AccordionProps = {
+  height?: number | string,
+  transitionStyle?: string,
+  children?: Array<React.Element<*>> | React.Element<*> // see https://github.com/facebook/flow/issues/1964
+};
+
+export type AccordionState = {
+  computedHeight: ?number | ?string,
+};
+
+export default class Accordion extends Component {
+  props: AccordionProps;
+  static defaultProps: $Shape<AccordionProps> = {
+    height: 'auto',
+    transitionStyle: 'height 0.25s ease-in-out'
+  };
+
+  state: AccordionState = {
+    computedHeight: null,
+  };
+
+  _containerElement: ?HTMLElement;
+  _contentElement: ?HTMLElement;
+
+  componentDidMount() {
+    const containerElement = this._containerElement;
+    if(!containerElement) {
+      throw new Error('containerElement cannot be null');
+    }
+
+    // update initial state
+    if(this.props.height !== Accordion.defaultProps.height) {
+      this._updateHeight();
+    }
+
+    containerElement.addEventListener('transitionend', this._onTransitionEnd);
+  }
+
+  componentWillUnmount() {
+    const containerElement = this._containerElement;
+    if(!containerElement) {
+      throw new Error('containerElement cannot be null');
+    }
+    containerElement.removeEventListener('transitionend', this._onTransitionEnd);
+  }
+
+  componentDidUpdate(prevProps: AccordionProps, _prevState: AccordionState) {
+    if(prevProps.height !== this.props.height) {
+      (async () => {
+        const { transitionStyle } = this.props;
+
+        // make sure to warm up CSS transition before updating height
+        // do not warm up transitions if they are not expected to run
+        if(transitionStyle && transitionStyle.toLowerCase() !== 'none') {
+          await this._warmupTransition();
+          this._updateHeight();
+        } else {
+          this._updateHeight();
+          this._onTransitionEnd();
+        }
+
+      })();
+    }
+  }
+
+  render() {
+    const { height: _height, children, transitionStyle, ...otherProps } = this.props;
+    let style = {
+      transition: transitionStyle,
+    };
+
+    if(typeof(this.state.computedHeight) === 'number') {
+      style = {
+        ...style,
+        overflow: 'hidden',
+        height: this.state.computedHeight.toString() + 'px',
+      };
+    }
+
+    return (
+      <div { ...otherProps } style={ style } ref={ this._onContainerRef }>
+        <div ref={ this._onContentRef }>
+          { children }
+        </div>
+      </div>
+    );
+  }
+
+  // Sets initial height and delays transition until next runloop
+  // to make sure CSS transitions properly kick in.
+  // This method resolves immediately if the height is already set.
+  _warmupTransition() {
+    const contentElement = this._contentElement;
+    if(!contentElement) {
+      throw new Error('contentElement cannot be null');
+    }
+    return new Promise((resolve, _) => {
+      // CSS transition always needs the initial height
+      // to perform the animation
+      if(this.state.computedHeight === null) {
+        this.setState({
+          computedHeight: contentElement.clientHeight
+        }, () => {
+          // important to skip a run loop
+          // for CSS transition to kick in
+          setTimeout(resolve, 0);
+        });
+      } else {
+        resolve();
+      }
+    });
+  }
+
+  _updateHeight() {
+    const contentElement = this._contentElement;
+    if(!contentElement) {
+      throw new Error('contentElement cannot be null');
+    }
+    this.setState({
+      computedHeight: this.props.height === 'auto' ?
+        contentElement.clientHeight :
+        this.props.height
+    });
+  }
+
+  _onTransitionEnd = () => {
+    // reset height after transition to let element layout naturally
+    if(this.props.height === 'auto') {
+      this.setState({
+        computedHeight: null,
+      });
+    }
+  }
+
+  _onContainerRef = (element) => {
+    this._containerElement = element;
+  }
+
+  _onContentRef = (element) => {
+    this._contentElement = element;
+  }
+}
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