From 7f50fcdb54b2cd8fd52102a954525e6a738125c8 Mon Sep 17 00:00:00 2001
From: Evan Hahn <69474926+EvanHahn-Signal@users.noreply.github.com>
Date: Mon, 30 Aug 2021 11:39:03 -0500
Subject: [PATCH] Improve performance when rendering many emoji

---
 ts/components/conversation/Emojify.stories.tsx | 16 ++++++++++++++++
 ts/test-both/util/emoji_test.ts                | 18 ++++--------------
 ts/util/emoji.ts                               | 15 ++++++++++++---
 3 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/ts/components/conversation/Emojify.stories.tsx b/ts/components/conversation/Emojify.stories.tsx
index 547b03da9e..edb62cea67 100644
--- a/ts/components/conversation/Emojify.stories.tsx
+++ b/ts/components/conversation/Emojify.stories.tsx
@@ -96,3 +96,19 @@ story.add('Custom Text Render', () => {
 
   return <Emojify {...props} />;
 });
+
+story.add('Tens of thousands of emoji', () => {
+  const props = createProps({
+    text: '💅'.repeat(40000),
+  });
+
+  return <Emojify {...props} />;
+});
+
+story.add('Tens of thousands of emoji, interspersed with text', () => {
+  const props = createProps({
+    text: '💅 hi '.repeat(40000),
+  });
+
+  return <Emojify {...props} />;
+});
diff --git a/ts/test-both/util/emoji_test.ts b/ts/test-both/util/emoji_test.ts
index 0eb24968d0..c86081df67 100644
--- a/ts/test-both/util/emoji_test.ts
+++ b/ts/test-both/util/emoji_test.ts
@@ -28,25 +28,15 @@ describe('emoji', () => {
         { type: 'emoji', value: '😛' },
         { type: 'text', value: 'world' },
         { type: 'emoji', value: '😎' },
-        { type: 'text', value: '' },
         { type: 'emoji', value: '😛' },
         { type: 'text', value: '!' },
       ]);
     });
 
-    it('should return empty string after split at the end', () => {
-      assert.deepStrictEqual(splitByEmoji('hello😛'), [
-        { type: 'text', value: 'hello' },
-        { type: 'emoji', value: '😛' },
-        { type: 'text', value: '' },
-      ]);
-    });
-
-    it('should return empty string before the split at the start', () => {
-      assert.deepStrictEqual(splitByEmoji('😛hello'), [
-        { type: 'text', value: '' },
-        { type: 'emoji', value: '😛' },
-        { type: 'text', value: 'hello' },
+    it('returns emojis as text after 5,000 emojis are found', () => {
+      assert.deepStrictEqual(splitByEmoji('💬'.repeat(5002)), [
+        ...Array(5000).fill({ type: 'emoji', value: '💬' }),
+        { type: 'text', value: '💬💬' },
       ]);
     });
   });
diff --git a/ts/util/emoji.ts b/ts/util/emoji.ts
index bf0d044370..b26c3ac349 100644
--- a/ts/util/emoji.ts
+++ b/ts/util/emoji.ts
@@ -4,8 +4,10 @@
 import emojiRegex from 'emoji-regex/es2015/RGI_Emoji';
 
 import { assert } from './assert';
+import { take } from './iterables';
 
 const REGEXP = emojiRegex();
+const MAX_EMOJI_TO_MATCH = 5000;
 
 export function replaceEmojiWithSpaces(value: string): string {
   return value.replace(REGEXP, ' ');
@@ -17,19 +19,26 @@ export type SplitElement = Readonly<{
 }>;
 
 export function splitByEmoji(value: string): ReadonlyArray<SplitElement> {
-  const emojis = value.matchAll(REGEXP);
+  const emojis = take(value.matchAll(REGEXP), MAX_EMOJI_TO_MATCH);
 
   const result: Array<SplitElement> = [];
   let lastIndex = 0;
   for (const match of emojis) {
-    result.push({ type: 'text', value: value.slice(lastIndex, match.index) });
+    const nonEmojiText = value.slice(lastIndex, match.index);
+    if (nonEmojiText) {
+      result.push({ type: 'text', value: nonEmojiText });
+    }
+
     result.push({ type: 'emoji', value: match[0] });
 
     assert(match.index !== undefined, '`matchAll` should provide indices');
     lastIndex = match.index + match[0].length;
   }
 
-  result.push({ type: 'text', value: value.slice(lastIndex) });
+  const finalNonEmojiText = value.slice(lastIndex);
+  if (finalNonEmojiText) {
+    result.push({ type: 'text', value: finalNonEmojiText });
+  }
 
   return result;
 }