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// @flow
import React, { Component } from 'react';
type ScrollbarUpdateContext = {
size: boolean,
position: boolean,
};
const AUTOHIDE_TIMEOUT = 1000;
export default class CustomScrollbars extends Component {
props: {
autoHide: boolean,
thumbInset: { x: number, y: number },
children: ?React.Element<*>,
};
static defaultProps = {
autoHide: true,
thumbInset: { x: 2, y: 2 },
};
state = {
canScroll: false,
showScrollIndicators: true,
};
_scrollableElement: ?HTMLElement;
_thumbElement: ?HTMLElement;
_autoHideTimer: ?number;
componentDidMount() {
this._updateScrollbarsHelper({
position: true,
size: true
});
// show scroll indicators briefly when mounted
if(this.props.autoHide) {
this._startAutoHide();
}
}
componentWillUnmount() {
this._stopAutoHide();
}
componentDidUpdate() {
this._updateScrollbarsHelper({
position: true,
size: true
});
}
render() {
const { autoHide: _autoHide, thumbInset: _thumbInset, children, ...otherProps } = this.props;
const showScrollbars = this.state.canScroll && this.state.showScrollIndicators;
const thumbAnimationClass = showScrollbars ? ' custom-scrollbars__thumb--visible' : '';
return (
<div {...otherProps } className="custom-scrollbars">
<div className={ `custom-scrollbars__thumb ${thumbAnimationClass}` }
style={{ position: 'absolute', top: 0, right: 0 }}
ref={ this._onThumbRef }></div>
<div className="custom-scrollbars__scrollable"
style={{ overflow: 'auto' }}
onScroll={ this._onScroll }
ref={ this._onScrollableRef }>
{ children }
</div>
</div>
);
}
_onScrollableRef = (ref) => {
this._scrollableElement = ref;
}
_onThumbRef = (ref) => {
this._thumbElement = ref;
}
_onScroll = () => {
this._updateScrollbarsHelper({ position: true });
if(this.props.autoHide) {
this._startAutoHide();
}
}
_startAutoHide() {
if(this._autoHideTimer) {
clearTimeout(this._autoHideTimer);
}
this._autoHideTimer = setTimeout(() => {
this.setState({
showScrollIndicators: false,
});
}, AUTOHIDE_TIMEOUT);
if(!this.state.showScrollIndicators) {
this.setState({
showScrollIndicators: true,
});
}
}
_stopAutoHide() {
if(this._autoHideTimer) {
clearTimeout(this._autoHideTimer);
this._autoHideTimer = null;
}
}
_computeThumbPosition(scrollable: HTMLElement, thumb: HTMLElement) {
// the content height of the scroll view
const scrollHeight = scrollable.scrollHeight;
// the visible height of the scroll view
const visibleHeight = scrollable.offsetHeight;
// scroll offset
const scrollTop = scrollable.scrollTop;
// lowest point of scrollTop
const maxScrollTop = scrollHeight - visibleHeight;
// calculate scroll position within 0..1 range
const scrollPosition = scrollHeight > 0 ? scrollTop / maxScrollTop : 0;
const thumbHeight = thumb.clientHeight;
// calculate the thumb boundary to make sure that the visual appearance of
// a thumb at lowest point matches the bottom of scrollable view
const thumbBoundary = visibleHeight - thumbHeight - (this.props.thumbInset.y * 2);
// calculate thumb position based on scroll progress and thumb boundary
// adding vertical inset to adjust the thumb's appearance
const thumbPosition = (thumbBoundary * scrollPosition) + this.props.thumbInset.y;
return {
x: -this.props.thumbInset.x,
y: thumbPosition,
};
}
_computeThumbHeight(scrollable: HTMLElement) {
const scrollHeight = scrollable.scrollHeight;
const visibleHeight = scrollable.offsetHeight;
const thumbHeight = (visibleHeight / scrollHeight) * visibleHeight;
// ensure that the scroll thumb doesn't shrink to nano size
return Math.max(thumbHeight, 8);
}
_updateScrollbarsHelper(updateFlags: $Shape<ScrollbarUpdateContext>) {
const scrollable = this._scrollableElement;
const thumb = this._thumbElement;
if(scrollable && thumb) {
this._updateScrollbars(scrollable, thumb, updateFlags);
}
}
_updateScrollbars(scrollable: HTMLElement, thumb: HTMLElement, context: $Shape<ScrollbarUpdateContext>) {
if(context.size) {
const thumbHeight = this._computeThumbHeight(scrollable);
thumb.style.setProperty('height', thumbHeight + 'px');
// hide thumb when there is nothing to scroll
const canScroll = (thumbHeight < scrollable.offsetHeight);
if(this.state.canScroll !== canScroll) {
this.setState({ canScroll });
// flash the scroll indicators when the view becomes scrollable
if(this.props.autoHide && canScroll) {
this._startAutoHide();
}
}
}
if(context.position) {
const { x, y } = this._computeThumbPosition(scrollable, thumb);
thumb.style.setProperty('transform', `translate(${x}px, ${y}px)`);
}
}
}
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