element-web/src/components/structures/IndicatorScrollbar.js

/*
Copyright 2018 New Vector Ltd

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import React from "react";
import PropTypes from "prop-types";
import AutoHideScrollbar from "./AutoHideScrollbar";

export default class IndicatorScrollbar extends React.Component {
    static PropTypes = {
        // If true, the scrollbar will append mx_IndicatorScrollbar_leftOverflowIndicator
        // and mx_IndicatorScrollbar_rightOverflowIndicator elements to the list for positioning
        // by the parent element.
        trackHorizontalOverflow: PropTypes.bool,
    };

    constructor(props) {
        super(props);
        this._collectScroller = this._collectScroller.bind(this);
        this._collectScrollerComponent = this._collectScrollerComponent.bind(this);
        this.checkOverflow = this.checkOverflow.bind(this);
        this._scrollElement = null;
        this._autoHideScrollbar = null;

        this.state = {
            leftIndicatorOffset: 0,
            rightIndicatorOffset: 0,
        };
    }

    _collectScroller(scroller) {
        if (scroller && !this._scrollElement) {
            this._scrollElement = scroller;
            this._scrollElement.addEventListener("scroll", this.checkOverflow);
            this.checkOverflow();
        }
    }

    _collectScrollerComponent(autoHideScrollbar) {
        this._autoHideScrollbar = autoHideScrollbar;
    }

    checkOverflow() {
        const hasTopOverflow = this._scrollElement.scrollTop > 0;
        const hasBottomOverflow = this._scrollElement.scrollHeight >
            (this._scrollElement.scrollTop + this._scrollElement.clientHeight);
        const hasLeftOverflow = this._scrollElement.scrollLeft > 0;
        const hasRightOverflow = this._scrollElement.scrollWidth >
            (this._scrollElement.scrollLeft + this._scrollElement.clientWidth);

        if (hasTopOverflow) {
            this._scrollElement.classList.add("mx_IndicatorScrollbar_topOverflow");
        } else {
            this._scrollElement.classList.remove("mx_IndicatorScrollbar_topOverflow");
        }
        if (hasBottomOverflow) {
            this._scrollElement.classList.add("mx_IndicatorScrollbar_bottomOverflow");
        } else {
            this._scrollElement.classList.remove("mx_IndicatorScrollbar_bottomOverflow");
        }
        if (hasLeftOverflow) {
            this._scrollElement.classList.add("mx_IndicatorScrollbar_leftOverflow");
        } else {
            this._scrollElement.classList.remove("mx_IndicatorScrollbar_leftOverflow");
        }
        if (hasRightOverflow) {
            this._scrollElement.classList.add("mx_IndicatorScrollbar_rightOverflow");
        } else {
            this._scrollElement.classList.remove("mx_IndicatorScrollbar_rightOverflow");
        }

        if (this._autoHideScrollbar) {
            this._autoHideScrollbar.checkOverflow();
        }

        if (this.props.trackHorizontalOverflow) {
            this.setState({
                // Offset from absolute position of the container
                leftIndicatorOffset: hasLeftOverflow ? `${this._scrollElement.scrollLeft}px` : '0',

                // Negative because we're coming from the right
                rightIndicatorOffset: hasRightOverflow ? `-${this._scrollElement.scrollLeft}px` : '0',
            });
        }
    }

    getScrollTop() {
        return this._autoHideScrollbar.getScrollTop();
    }

    componentWillUnmount() {
        if (this._scrollElement) {
            this._scrollElement.removeEventListener("scroll", this.checkOverflow);
        }
    }

    render() {
        const leftIndicatorStyle = {left: this.state.leftIndicatorOffset};
        const rightIndicatorStyle = {right: this.state.rightIndicatorOffset};
        const leftOverflowIndicator = this.props.trackHorizontalOverflow
            ? <div className="mx_IndicatorScrollbar_leftOverflowIndicator" style={leftIndicatorStyle} /> : null;
        const rightOverflowIndicator = this.props.trackHorizontalOverflow
            ? <div className="mx_IndicatorScrollbar_rightOverflowIndicator" style={rightIndicatorStyle} /> : null;

        return (<AutoHideScrollbar
            ref={this._collectScrollerComponent}
            wrappedRef={this._collectScroller}
            {... this.props}
        >
            { leftOverflowIndicator }
            { this.props.children }
            { rightOverflowIndicator }
        </AutoHideScrollbar>);
    }
}