From eef89c99cfa596048146e20d458df5942f144dfd Mon Sep 17 00:00:00 2001
From: Situ Chandra Shil <108292595+situchan@users.noreply.github.com>
Date: Tue, 21 Nov 2023 22:02:11 +0600
Subject: [PATCH] Revert "Migrate LHNOptionsList to Flashlist"

---
 .../LHNOptionsList/LHNOptionsList.js          | 45 ++++++++++++++-----
 src/pages/home/sidebar/SidebarLinks.js        | 27 +++++------
 src/styles/styles.ts                          |  1 +
 tests/perf-test/SidebarLinks.perf-test.js     |  6 +--
 4 files changed, 50 insertions(+), 29 deletions(-)

diff --git a/src/components/LHNOptionsList/LHNOptionsList.js b/src/components/LHNOptionsList/LHNOptionsList.js
index 0d300c5e2179..5e77947187e9 100644
--- a/src/components/LHNOptionsList/LHNOptionsList.js
+++ b/src/components/LHNOptionsList/LHNOptionsList.js
@@ -1,8 +1,7 @@
-import {FlashList} from '@shopify/flash-list';
 import lodashGet from 'lodash/get';
 import PropTypes from 'prop-types';
 import React, {useCallback} from 'react';
-import {View} from 'react-native';
+import {FlatList, View} from 'react-native';
 import {withOnyx} from 'react-native-onyx';
 import _ from 'underscore';
 import participantPropTypes from '@components/participantPropTypes';
@@ -12,7 +11,6 @@ import compose from '@libs/compose';
 import * as OptionsListUtils from '@libs/OptionsListUtils';
 import reportActionPropTypes from '@pages/home/report/reportActionPropTypes';
 import reportPropTypes from '@pages/reportPropTypes';
-import stylePropTypes from '@styles/stylePropTypes';
 import useThemeStyles from '@styles/useThemeStyles';
 import variables from '@styles/variables';
 import CONST from '@src/CONST';
@@ -21,10 +19,12 @@ import OptionRowLHNData from './OptionRowLHNData';
 
 const propTypes = {
     /** Wrapper style for the section list */
-    style: stylePropTypes,
+    // eslint-disable-next-line react/forbid-prop-types
+    style: PropTypes.arrayOf(PropTypes.object),
 
     /** Extra styles for the section list container */
-    contentContainerStyles: stylePropTypes.isRequired,
+    // eslint-disable-next-line react/forbid-prop-types
+    contentContainerStyles: PropTypes.arrayOf(PropTypes.object).isRequired,
 
     /** Sections for the section list */
     data: PropTypes.arrayOf(PropTypes.string).isRequired,
@@ -80,7 +80,7 @@ const defaultProps = {
     ...withCurrentReportIDDefaultProps,
 };
 
-const keyExtractor = (item) => `report_${item}`;
+const keyExtractor = (item) => item;
 
 function LHNOptionsList({
     style,
@@ -99,6 +99,28 @@ function LHNOptionsList({
     currentReportID,
 }) {
     const styles = useThemeStyles();
+    /**
+     * This function is used to compute the layout of any given item in our list. Since we know that each item will have the exact same height, this is a performance optimization
+     * so that the heights can be determined before the options are rendered. Otherwise, the heights are determined when each option is rendering and it causes a lot of overhead on large
+     * lists.
+     *
+     * @param {Array} itemData - This is the same as the data we pass into the component
+     * @param {Number} index the current item's index in the set of data
+     *
+     * @returns {Object}
+     */
+    const getItemLayout = useCallback(
+        (itemData, index) => {
+            const optionHeight = optionMode === CONST.OPTION_MODE.COMPACT ? variables.optionRowHeightCompact : variables.optionRowHeight;
+            return {
+                length: optionHeight,
+                offset: index * optionHeight,
+                index,
+            };
+        },
+        [optionMode],
+    );
+
     /**
      * Function which renders a row in the list
      *
@@ -142,17 +164,20 @@ function LHNOptionsList({
 
     return (
         <View style={style || styles.flex1}>
-            <FlashList
+            <FlatList
                 indicatorStyle="white"
                 keyboardShouldPersistTaps="always"
                 contentContainerStyle={contentContainerStyles}
+                showsVerticalScrollIndicator={false}
                 data={data}
                 testID="lhn-options-list"
                 keyExtractor={keyExtractor}
+                stickySectionHeadersEnabled={false}
                 renderItem={renderItem}
-                estimatedItemSize={optionMode === CONST.OPTION_MODE.COMPACT ? variables.optionRowHeightCompact : variables.optionRowHeight}
-                extraData={[currentReportID]}
-                showsVerticalScrollIndicator={false}
+                getItemLayout={getItemLayout}
+                initialNumToRender={20}
+                maxToRenderPerBatch={5}
+                windowSize={5}
             />
         </View>
     );
diff --git a/src/pages/home/sidebar/SidebarLinks.js b/src/pages/home/sidebar/SidebarLinks.js
index a59dc81aad54..5e69be266342 100644
--- a/src/pages/home/sidebar/SidebarLinks.js
+++ b/src/pages/home/sidebar/SidebarLinks.js
@@ -1,7 +1,7 @@
 /* eslint-disable rulesdir/onyx-props-must-have-default */
 import PropTypes from 'prop-types';
 import React, {useCallback, useEffect, useRef} from 'react';
-import {InteractionManager, StyleSheet, View} from 'react-native';
+import {InteractionManager, View} from 'react-native';
 import _ from 'underscore';
 import LogoComponent from '@assets/images/expensify-wordmark.svg';
 import Header from '@components/Header';
@@ -177,21 +177,16 @@ function SidebarLinks({onLinkClick, insets, optionListItems, isLoading, priority
                 </Tooltip>
                 <SignInOrAvatarWithOptionalStatus isCreateMenuOpen={isCreateMenuOpen} />
             </View>
-            <View style={[styles.pRelative, styles.flex1]}>
-                <LHNOptionsList
-                    style={styles.flex1}
-                    contentContainerStyles={StyleSheet.flatten([styles.sidebarListContainer, {paddingBottom: StyleUtils.getSafeAreaMargins(insets).marginBottom}])}
-                    data={optionListItems}
-                    onSelectRow={showReportPage}
-                    shouldDisableFocusOptions={isSmallScreenWidth}
-                    optionMode={viewMode}
-                />
-                {isLoading && (
-                    <View style={[StyleSheet.absoluteFillObject, styles.appBG]}>
-                        <OptionsListSkeletonView shouldAnimate />
-                    </View>
-                )}
-            </View>
+
+            <LHNOptionsList
+                style={[isLoading ? styles.flexShrink1 : styles.flex1]}
+                contentContainerStyles={[styles.sidebarListContainer, {paddingBottom: StyleUtils.getSafeAreaMargins(insets).marginBottom}]}
+                data={optionListItems}
+                onSelectRow={showReportPage}
+                shouldDisableFocusOptions={isSmallScreenWidth}
+                optionMode={viewMode}
+            />
+            {isLoading && <OptionsListSkeletonView shouldAnimate />}
         </View>
     );
 }
diff --git a/src/styles/styles.ts b/src/styles/styles.ts
index c1b78a224eb3..e597f0ec874e 100644
--- a/src/styles/styles.ts
+++ b/src/styles/styles.ts
@@ -1367,6 +1367,7 @@ const styles = (theme: ThemeColors) =>
         },
 
         sidebarListContainer: {
+            scrollbarWidth: 'none',
             paddingBottom: 4,
         },
 
diff --git a/tests/perf-test/SidebarLinks.perf-test.js b/tests/perf-test/SidebarLinks.perf-test.js
index 5601c588bb93..f6819d40a48f 100644
--- a/tests/perf-test/SidebarLinks.perf-test.js
+++ b/tests/perf-test/SidebarLinks.perf-test.js
@@ -105,9 +105,9 @@ test('should scroll and click some of the items', () => {
         expect(lhnOptionsList).toBeDefined();
 
         fireEvent.scroll(lhnOptionsList, eventData);
-        // find elements that are currently visible in the viewport
-        const button1 = await screen.findByTestId('7');
-        const button2 = await screen.findByTestId('8');
+
+        const button1 = await screen.findByTestId('1');
+        const button2 = await screen.findByTestId('2');
         fireEvent.press(button1);
         fireEvent.press(button2);
     };