Rewrite AnimatedNumber component with React hooks (#24559)

app/javascript/mastodon/components/animated_number.tsx

@@ -0,0 +1,58 @@
+import React, { useCallback, useState } from 'react';
+import ShortNumber from './short_number';
+import { TransitionMotion, spring } from 'react-motion';
+import { reduceMotion } from '../initial_state';
+
+const obfuscatedCount = (count: number) => {
+  if (count < 0) {
+    return 0;
+  } else if (count <= 1) {
+    return count;
+  } else {
+    return '1+';
+  }
+};
+
+type Props = {
+  value: number;
+  obfuscate?: boolean;
+}
+export const AnimatedNumber: React.FC<Props> = ({
+  value,
+  obfuscate,
+})=> {
+  const [previousValue, setPreviousValue] = useState(value);
+  const [direction, setDirection] = useState<1|-1>(1);
+
+  if (previousValue !== value) {
+    setPreviousValue(value);
+    setDirection(value > previousValue ? 1 : -1);
+  }
+
+  const willEnter = useCallback(() => ({ y: -1 * direction }), [direction]);
+  const willLeave = useCallback(() => ({ y: spring(1 * direction, { damping: 35, stiffness: 400 }) }), [direction]);
+
+  if (reduceMotion) {
+    return obfuscate ? <>{obfuscatedCount(value)}</> : <ShortNumber value={value} />;
+  }
+
+  const styles = [{
+    key: `${value}`,
+    data: value,
+    style: { y: spring(0, { damping: 35, stiffness: 400 }) },
+  }];
+
+  return (
+    <TransitionMotion styles={styles} willEnter={willEnter} willLeave={willLeave}>
+      {items => (
+        <span className='animated-number'>
+          {items.map(({ key, data, style }) => (
+            <span key={key} style={{ position: (direction * style.y) > 0 ? 'absolute' : 'static', transform: `translateY(${style.y * 100}%)` }}>{obfuscate ? obfuscatedCount(data) : <ShortNumber value={data} />}</span>
+          ))}
+        </span>
+      )}
+    </TransitionMotion>
+  );
+};
+
+export default AnimatedNumber;