From 90adfdf5e058806bde82396cad871d15db55e3c4 Mon Sep 17 00:00:00 2001
From: Alexander Zinchuk <alx.zinchuk@gmail.com>
Date: Fri, 6 Sep 2024 15:42:43 +0200
Subject: [PATCH] [Perf] Animated Counter: Avoid redundant rerenders

---
 src/components/common/AnimatedCounter.tsx | 118 ++++++++++++++--------
 1 file changed, 75 insertions(+), 43 deletions(-)

diff --git a/src/components/common/AnimatedCounter.tsx b/src/components/common/AnimatedCounter.tsx
index 107418e4c..cb558c8b0 100644
--- a/src/components/common/AnimatedCounter.tsx
+++ b/src/components/common/AnimatedCounter.tsx
@@ -1,72 +1,104 @@
 import type { FC } from '../../lib/teact/teact';
-import React, {
-  useEffect, useMemo, useRef,
-} from '../../lib/teact/teact';
+import React, { memo, useEffect, useMemo } from '../../lib/teact/teact';
 import { getGlobal } from '../../global';
 
 import { selectCanAnimateInterface } from '../../global/selectors';
 import buildClassName from '../../util/buildClassName';
+import { throttleWithTickEnd } from '../../util/schedulers';
 
-import useFlag from '../../hooks/useFlag';
-import useOldLang from '../../hooks/useOldLang';
+import useForceUpdate from '../../hooks/useForceUpdate';
+import useLang from '../../hooks/useLang';
+import usePrevious from '../../hooks/usePrevious';
 
 import styles from './AnimatedCounter.module.scss';
 
 type OwnProps = {
   text: string;
   className?: string;
+  isDisabled?: boolean;
 };
 
+const ANIMATION_TIME = 200;
+const MAX_SIMULTANEOUS_ANIMATIONS = 10;
+
+let scheduledAnimationsCounter = 0;
+
+const resetCounterOnTickEnd = throttleWithTickEnd(() => {
+  scheduledAnimationsCounter = 0;
+});
+
 const AnimatedCounter: FC<OwnProps> = ({
   text,
   className,
+  isDisabled,
 }) => {
-  const lang = useOldLang();
+  const { isRtl } = useLang();
 
-  const prevTextRef = useRef<string>();
-  const [isAnimating, markAnimating, unmarkAnimating] = useFlag(false);
+  const prevText = usePrevious(text);
+  const forceUpdate = useForceUpdate();
 
-  const shouldAnimate = selectCanAnimateInterface(getGlobal());
+  const shouldAnimate = scheduleAnimation(
+    !isDisabled && selectCanAnimateInterface(getGlobal()) && prevText !== undefined && prevText !== text,
+  );
 
-  const textElement = useMemo(() => {
-    if (!shouldAnimate) {
-      return text;
-    }
-    if (!isAnimating) {
-      return prevTextRef.current || text;
-    }
-
-    const prevText = prevTextRef.current;
-
-    const elements = [];
-    for (let i = 0; i < text.length; i++) {
-      if (prevText && text[i] !== prevText[i]) {
-        elements.push(
-          <div className={styles.characterContainer}>
-            <div className={styles.character}>{text[i]}</div>
-            <div className={styles.characterOld} onAnimationEnd={unmarkAnimating}>{prevText[i]}</div>
-            <div className={styles.characterNew} onAnimationEnd={unmarkAnimating}>{text[i]}</div>
-          </div>,
-        );
-      } else {
-        elements.push(<span>{text[i]}</span>);
-      }
-    }
-
-    prevTextRef.current = text;
-
-    return elements;
-  }, [shouldAnimate, isAnimating, text]);
+  const characters = useMemo(() => {
+    return shouldAnimate ? renderAnimatedCharacters(text, prevText) : text;
+  }, [shouldAnimate, prevText, text]);
 
   useEffect(() => {
-    markAnimating();
-  }, [text]);
+    if (!shouldAnimate) return undefined;
+
+    const timeoutId = window.setTimeout(() => {
+      forceUpdate();
+    }, ANIMATION_TIME);
+
+    return () => {
+      window.clearTimeout(timeoutId);
+    };
+  }, [shouldAnimate, text]);
 
   return (
-    <span className={buildClassName(styles.root, className)} dir={lang.isRtl ? 'rtl' : undefined}>
-      {textElement}
+    <span className={buildClassName(className, !isDisabled && styles.root)} dir={isRtl ? 'rtl' : undefined}>
+      {characters}
     </span>
   );
 };
 
-export default AnimatedCounter;
+export default memo(AnimatedCounter);
+
+function scheduleAnimation(condition: boolean) {
+  if (!condition || scheduledAnimationsCounter >= MAX_SIMULTANEOUS_ANIMATIONS) return false;
+
+  if (scheduledAnimationsCounter === 0) {
+    resetCounterOnTickEnd();
+  }
+
+  scheduledAnimationsCounter++;
+
+  return true;
+}
+
+function renderAnimatedCharacters(text: string, prevText?: string) {
+  const elements: React.ReactNode[] = [];
+  const textLength = text.length;
+  const prevTextLength = prevText?.length ?? 0;
+
+  for (let i = 0; i <= textLength; i++) {
+    const charIndex = textLength - i;
+    const prevTextCharIndex = prevTextLength - i;
+
+    if (prevText && prevTextCharIndex >= 0 && text[charIndex] !== prevText[prevTextCharIndex]) {
+      elements.unshift(
+        <div className={styles.characterContainer}>
+          <div className={styles.character}>{text[charIndex] ?? ''}</div>
+          <div className={styles.characterOld}>{prevText[prevTextCharIndex]}</div>
+          <div className={styles.characterNew}>{text[charIndex] ?? ''}</div>
+        </div>,
+      );
+    } else {
+      elements.unshift(<span>{text[charIndex] ?? ''}</span>);
+    }
+  }
+
+  return elements;
+}