Create HOC to handle chat scrolling

app/lib/components/Chat/MessageList.jsx

@@ -1,14 +1,9 @@
 import React, { Component } from 'react';
+import { compose } from 'redux';
 import PropTypes from 'prop-types';
 import marked from 'marked';
 import { connect } from 'react-redux';
-
-const scrollToBottom = () =>
-{
-	const messagesDiv = document.getElementById('messages');
-
-	messagesDiv.scrollTop = messagesDiv.scrollHeight;
-};
+import scrollToBottom from './scrollToBottom';
 
 const linkRenderer = new marked.Renderer();
 
@@ -22,16 +17,6 @@ linkRenderer.link = (href, title, text) =>
 
 class MessageList extends Component
 {
-	componentDidMount()
-	{
-		scrollToBottom();
-	}
-
-	componentDidUpdate()
-	{
-		scrollToBottom();
-	}
-	
 	getTimeString(time)
 	{
 		return `${(time.getHours() < 10 ? '0' : '')}${time.getHours()}:${(time.getMinutes() < 10 ? '0' : '')}${time.getMinutes()}`;
@@ -96,8 +81,9 @@ const mapStateToProps = (state) =>
 	};
 };
 
-const MessageListContainer = connect(
-	mapStateToProps
+const MessageListContainer = compose(
+	connect(mapStateToProps),
+	scrollToBottom()
 )(MessageList);
 
 export default MessageListContainer;

app/lib/components/Chat/scrollToBottom.jsx

@@ -0,0 +1,63 @@
+import React, { Component } from 'react';
+import { findDOMNode } from 'react-dom';
+
+/**
+ * A higher order component which scrolls the user to the bottom of the
+ * wrapped component, provided that the user already was at the bottom
+ * of the wrapped component. Useful for chats and similar use cases.
+ * @param {number} treshold The required distance from the bottom required.
+ */
+const scrollToBottom = (treshold = 0) => (WrappedComponent) =>
+{
+	return class AutoScroller extends Component
+	{
+		constructor(props)
+		{
+			super(props);
+
+			this.ref = React.createRef();
+		}
+
+		getSnapshotBeforeUpdate()
+		{
+			// Check if the user has scrolled close enough to the bottom for
+			// us to scroll to the bottom or not.
+			return this.elem.scrollHeight - this.elem.scrollTop <=
+				this.elem.clientHeight - treshold;
+		}
+
+		scrollToBottom = () =>
+		{
+			// Scroll the user to the bottom of the wrapped element.
+			this.elem.scrollTop = this.elem.scrollHeight;
+		};
+
+		componentDidMount()
+		{
+			// eslint-disable-next-line react/no-find-dom-node
+			this.elem = findDOMNode(this.ref.current);
+
+			this.scrollToBottom();
+		}
+
+		componentDidUpdate(prevProps, prevState, atBottom)
+		{
+			if (atBottom)
+			{
+				this.scrollToBottom();
+			}
+		}
+
+		render()
+		{
+			return (
+				<WrappedComponent
+					ref={this.ref}
+					{...this.props}
+				/>
+			);
+		}
+	};
+};
+
+export default scrollToBottom;