From 80aa672034941caa5243d3a889c4a156a49ae88d Mon Sep 17 00:00:00 2001
From: Audric Ackermann <audric@loki.network>
Date: Mon, 18 Oct 2021 17:34:13 +1100
Subject: [PATCH] link pgup and down in messages list

Fixes #1919
---
 .../conversation/SessionMessagesList.tsx      | 12 ++++++
 .../SessionMessagesListContainer.tsx          | 40 ++++++++++++++++---
 2 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/ts/components/session/conversation/SessionMessagesList.tsx b/ts/components/session/conversation/SessionMessagesList.tsx
index 5bcbafbc7..0a1e79a4e 100644
--- a/ts/components/session/conversation/SessionMessagesList.tsx
+++ b/ts/components/session/conversation/SessionMessagesList.tsx
@@ -1,5 +1,7 @@
 import React from 'react';
 import { useSelector } from 'react-redux';
+// tslint:disable-next-line: no-submodule-imports
+import useKey from 'react-use/lib/useKey';
 import { PropsForDataExtractionNotification, QuoteClickOptions } from '../../../models/messageType';
 import {
   PropsForExpirationTimer,
@@ -19,9 +21,19 @@ import { SessionLastSeenIndicator } from './SessionLastSeenIndicator';
 
 export const SessionMessagesList = (props: {
   scrollToQuoteMessage: (options: QuoteClickOptions) => Promise<void>;
+  onPageUpPressed: () => void;
+  onPageDownPressed: () => void;
 }) => {
   const messagesProps = useSelector(getSortedMessagesTypesOfSelectedConversation);
 
+  useKey('PageUp', () => {
+    props.onPageUpPressed();
+  });
+
+  useKey('PageDown', () => {
+    props.onPageDownPressed();
+  });
+
   return (
     <>
       {messagesProps.map(messageProps => {
diff --git a/ts/components/session/conversation/SessionMessagesListContainer.tsx b/ts/components/session/conversation/SessionMessagesListContainer.tsx
index 552e003e5..fc12d0a97 100644
--- a/ts/components/session/conversation/SessionMessagesListContainer.tsx
+++ b/ts/components/session/conversation/SessionMessagesListContainer.tsx
@@ -30,7 +30,7 @@ import {
 import { SessionMessagesList } from './SessionMessagesList';
 
 export type SessionMessageListProps = {
-  messageContainerRef: React.RefObject<any>;
+  messageContainerRef: React.RefObject<HTMLDivElement>;
 };
 
 type Props = SessionMessageListProps & {
@@ -82,7 +82,7 @@ class SessionMessagesListContainerInner extends React.Component<Props> {
     const newFirstMesssageId = this.props.messagesProps[0]?.propsForMessage.id;
     const messageAddedWasMoreRecentOne = prevFirstMesssageId !== newFirstMesssageId;
 
-    if (isSameConvo && snapShot?.realScrollTop && prevMsgLength !== newMsgLength) {
+    if (isSameConvo && snapShot?.realScrollTop && prevMsgLength !== newMsgLength && currentRef) {
       if (messageAddedWasMoreRecentOne) {
         if (snapShot.scrollHeight - snapShot.realScrollTop < 50) {
           // consider that we were scrolled to bottom
@@ -105,13 +105,13 @@ class SessionMessagesListContainerInner extends React.Component<Props> {
   public getSnapshotBeforeUpdate() {
     const messageContainer = this.props.messageContainerRef.current;
 
-    const scrollTop = messageContainer.scrollTop;
-    const scrollHeight = messageContainer.scrollHeight;
+    const scrollTop = messageContainer?.scrollTop || undefined;
+    const scrollHeight = messageContainer?.scrollHeight || undefined;
 
     // as we use column-reverse for displaying message list
     // the top is < 0
     // tslint:disable-next-line: restrict-plus-operands
-    const realScrollTop = scrollHeight + scrollTop;
+    const realScrollTop = scrollHeight && scrollTop ? scrollHeight + scrollTop : undefined;
     return {
       realScrollTop,
       fakeScrollTop: scrollTop,
@@ -147,7 +147,11 @@ class SessionMessagesListContainerInner extends React.Component<Props> {
           key="typing-bubble"
         />
 
-        <SessionMessagesList scrollToQuoteMessage={this.scrollToQuoteMessage} />
+        <SessionMessagesList
+          scrollToQuoteMessage={this.scrollToQuoteMessage}
+          onPageDownPressed={this.scrollPgDown}
+          onPageUpPressed={this.scrollPgUp}
+        />
 
         <SessionScrollButton onClick={this.scrollToBottom} key="scroll-down-button" />
       </div>
@@ -239,6 +243,30 @@ class SessionMessagesListContainerInner extends React.Component<Props> {
     messageContainer.scrollTop = messageContainer.scrollHeight - messageContainer.clientHeight;
   }
 
+  private scrollPgUp() {
+    const messageContainer = this.props.messageContainerRef.current;
+    if (!messageContainer) {
+      return;
+    }
+    messageContainer.scrollBy({
+      top: Math.floor(-messageContainer.clientHeight * 2) / 3,
+      behavior: 'smooth',
+    });
+  }
+
+  private scrollPgDown() {
+    const messageContainer = this.props.messageContainerRef.current;
+    if (!messageContainer) {
+      return;
+    }
+
+    // tslint:disable-next-line: restrict-plus-operands
+    messageContainer.scrollBy({
+      top: Math.floor(+messageContainer.clientHeight * 2) / 3,
+      behavior: 'smooth',
+    });
+  }
+
   private async scrollToQuoteMessage(options: QuoteClickOptions) {
     const { quoteAuthor, quoteId, referencedMessageNotFound } = options;