Gab Social. All are welcome.

app/javascript/gabsocial/components/scrollable_list.js

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+import React, { PureComponent } from 'react';
+import { ScrollContainer } from 'react-router-scroll-4';
+import PropTypes from 'prop-types';
+import IntersectionObserverArticleContainer from '../containers/intersection_observer_article_container';
+import LoadMore from './load_more';
+import IntersectionObserverWrapper from '../features/ui/util/intersection_observer_wrapper';
+import { throttle } from 'lodash';
+import { List as ImmutableList } from 'immutable';
+import classNames from 'classnames';
+import LoadingIndicator from './loading_indicator';
+
+const MOUSE_IDLE_DELAY = 300;
+
+export default class ScrollableList extends PureComponent {
+
+  static contextTypes = {
+    router: PropTypes.object,
+  };
+
+  static propTypes = {
+    scrollKey: PropTypes.string.isRequired,
+    onLoadMore: PropTypes.func,
+    isLoading: PropTypes.bool,
+    showLoading: PropTypes.bool,
+    hasMore: PropTypes.bool,
+    prepend: PropTypes.node,
+    alwaysPrepend: PropTypes.bool,
+    emptyMessage: PropTypes.node,
+    children: PropTypes.node,
+  };
+
+  state = {
+    cachedMediaWidth: 250, // Default media/card width using default Gab Social theme
+  };
+
+  intersectionObserverWrapper = new IntersectionObserverWrapper();
+
+  mouseIdleTimer = null;
+  mouseMovedRecently = false;
+  lastScrollWasSynthetic = false;
+  scrollToTopOnMouseIdle = false;
+
+  setScrollTop = newScrollTop => {
+    if (this.node.scrollTop !== newScrollTop) {
+      this.lastScrollWasSynthetic = true;
+      this.node.scrollTop = newScrollTop;
+    }
+  };
+
+  clearMouseIdleTimer = () => {
+    if (this.mouseIdleTimer === null) {
+      return;
+    }
+
+    clearTimeout(this.mouseIdleTimer);
+    this.mouseIdleTimer = null;
+  };
+
+  handleMouseMove = throttle(() => {
+    // As long as the mouse keeps moving, clear and restart the idle timer.
+    this.clearMouseIdleTimer();
+    this.mouseIdleTimer = setTimeout(this.handleMouseIdle, MOUSE_IDLE_DELAY);
+
+    if (!this.mouseMovedRecently && this.node.scrollTop === 0) {
+      // Only set if we just started moving and are scrolled to the top.
+      this.scrollToTopOnMouseIdle = true;
+    }
+
+    // Save setting this flag for last, so we can do the comparison above.
+    this.mouseMovedRecently = true;
+  }, MOUSE_IDLE_DELAY / 2);
+
+  handleMouseIdle = () => {
+    if (this.scrollToTopOnMouseIdle) {
+      this.setScrollTop(0);
+    }
+
+    this.mouseMovedRecently = false;
+    this.scrollToTopOnMouseIdle = false;
+  }
+
+  componentDidMount () {
+    this.attachIntersectionObserver();
+  }
+
+  getScrollPosition = () => {
+    if (this.node && (this.node.scrollTop > 0 || this.mouseMovedRecently)) {
+      return { height: this.node.scrollHeight, top: this.node.scrollTop };
+    } else {
+      return null;
+    }
+  }
+
+  updateScrollBottom = (snapshot) => {
+    const newScrollTop = this.node.scrollHeight - snapshot;
+
+    this.setScrollTop(newScrollTop);
+  }
+
+  componentDidUpdate (prevProps, prevState, snapshot) {
+    // Reset the scroll position when a new child comes in in order not to
+    // jerk the scrollbar around if you're already scrolled down the page.
+    if (snapshot !== null) {
+      this.setScrollTop(this.node.scrollHeight - snapshot);
+    }
+  }
+
+  cacheMediaWidth = (width) => {
+    if (width && this.state.cachedMediaWidth !== width) {
+      this.setState({ cachedMediaWidth: width });
+    }
+  }
+
+  componentWillUnmount () {
+    this.clearMouseIdleTimer();
+    this.detachIntersectionObserver();
+  }
+
+  attachIntersectionObserver () {
+    this.intersectionObserverWrapper.connect({
+      root: this.node,
+      rootMargin: '300% 0px',
+    });
+  }
+
+  detachIntersectionObserver () {
+    this.intersectionObserverWrapper.disconnect();
+  }
+
+  getFirstChildKey (props) {
+    const { children } = props;
+    let firstChild     = children;
+
+    if (children instanceof ImmutableList) {
+      firstChild = children.get(0);
+    } else if (Array.isArray(children)) {
+      firstChild = children[0];
+    }
+
+    return firstChild && firstChild.key;
+  }
+
+  setRef = (c) => {
+    this.node = c;
+  }
+
+  handleLoadMore = e => {
+    e.preventDefault();
+    this.props.onLoadMore();
+  }
+
+  render () {
+    const { children, scrollKey, showLoading, isLoading, hasMore, prepend, alwaysPrepend, emptyMessage, onLoadMore } = this.props;
+    const childrenCount = React.Children.count(children);
+
+    const trackScroll = true; //placeholder
+
+    const loadMore     = (hasMore && onLoadMore) ? <LoadMore visible={!isLoading} onClick={this.handleLoadMore} /> : null;
+    let scrollableArea = null;
+
+    if (showLoading) {
+      scrollableArea = (
+        <div className='slist slist--flex' ref={this.setRef}>
+          <div role='feed' className='item-list'>
+            {prepend}
+          </div>
+
+          <div className='slist__append'>
+            <LoadingIndicator />
+          </div>
+        </div>
+      );
+    } else if (isLoading || childrenCount > 0 || hasMore || !emptyMessage) {
+      scrollableArea = (
+        <div className='slist' ref={this.setRef} onMouseMove={this.handleMouseMove}>
+          <div role='feed' className='item-list'>
+            {prepend}
+
+            {React.Children.map(this.props.children, (child, index) => (
+              <IntersectionObserverArticleContainer
+                key={child.key}
+                id={child.key}
+                index={index}
+                listLength={childrenCount}
+                intersectionObserverWrapper={this.intersectionObserverWrapper}
+                saveHeightKey={trackScroll ? `${this.context.router.route.location.key}:${scrollKey}` : null}
+              >
+                {React.cloneElement(child, {
+                  getScrollPosition: this.getScrollPosition,
+                  updateScrollBottom: this.updateScrollBottom,
+                  cachedMediaWidth: this.state.cachedMediaWidth,
+                  cacheMediaWidth: this.cacheMediaWidth,
+                })}
+              </IntersectionObserverArticleContainer>
+            ))}
+
+            {loadMore}
+          </div>
+        </div>
+      );
+    } else {
+      scrollableArea = (
+        <div className='slist slist--flex' ref={this.setRef}>
+          {alwaysPrepend && prepend}
+
+          <div className='empty-column-indicator'>
+            {emptyMessage}
+          </div>
+        </div>
+      );
+    }
+
+    return scrollableArea;
+  }
+
+}