When floating loading spinner isn't visible, don't render it

stylesheets/components/TimelineFloatingHeader.scss

@@ -25,14 +25,5 @@
     @include timeline-floating-header-node;
     margin-top: 12px;
     padding: 6px;
-
-    &--visible {
-      opacity: 1;
-    }
-
-    &--hidden {
-      opacity: 0;
-      transition: opacity 0.25s ease-out 0.3s;
-    }
   }
 }

ts/components/conversation/TimelineFloatingHeader.stories.tsx

@@ -0,0 +1,41 @@
+// Copyright 2022 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import * as React from 'react';
+import { storiesOf } from '@storybook/react';
+import { isBoolean } from 'lodash';
+import { boolean } from '@storybook/addon-knobs';
+
+import { setupI18n } from '../../util/setupI18n';
+import enMessages from '../../../_locales/en/messages.json';
+
+import type { PropsType } from './TimelineFloatingHeader';
+import { TimelineFloatingHeader } from './TimelineFloatingHeader';
+
+const i18n = setupI18n('en', enMessages);
+
+function booleanOr(value: boolean | undefined, defaultValue: boolean): boolean {
+  return isBoolean(value) ? value : defaultValue;
+}
+
+const createProps = (overrideProps: Partial<PropsType> = {}): PropsType => ({
+  isLoading: boolean('isLoading', booleanOr(overrideProps.isLoading, false)),
+  style: overrideProps.style,
+  visible: boolean('visible', booleanOr(overrideProps.visible, false)),
+  i18n,
+  timestamp: overrideProps.timestamp || Date.now(),
+});
+
+const stories = storiesOf('Components/TimelineFloatingHeader', module);
+
+stories.add('Visible', () => {
+  return <TimelineFloatingHeader {...createProps({ visible: true })} />;
+});
+
+stories.add('Loading', () => {
+  return (
+    <TimelineFloatingHeader
+      {...createProps({ visible: true, isLoading: true })}
+    />
+  );
+});

ts/components/conversation/TimelineFloatingHeader.tsx

@@ -4,29 +4,67 @@
 import classNames from 'classnames';
 import type { CSSProperties, ReactElement } from 'react';
 import React, { useEffect, useState } from 'react';
+import { animated, useSpring } from '@react-spring/web';
+
 import type { LocalizerType } from '../../types/Util';
 import { TimelineDateHeader } from './TimelineDateHeader';
 import { Spinner } from '../Spinner';
 
+export type PropsType = Readonly<{
+  i18n: LocalizerType;
+  isLoading: boolean;
+  style?: CSSProperties;
+  timestamp: number;
+  visible: boolean;
+}>;
+
 export const TimelineFloatingHeader = ({
   i18n,
   isLoading,
   style,
   timestamp,
   visible,
-}: Readonly<{
-  i18n: LocalizerType;
-  isLoading: boolean;
-  style?: CSSProperties;
-  timestamp: number;
-  visible: boolean;
-}>): ReactElement => {
+}: PropsType): ReactElement => {
   const [hasRendered, setHasRendered] = useState(false);
+  const [showSpinner, setShowSpinner] = useState(isLoading);
 
   useEffect(() => {
     setHasRendered(true);
   }, []);
 
+  const [spinnerStyles, spinnerSpringRef] = useSpring(
+    () => ({
+      delay: 300,
+      duration: 250,
+      from: { opacity: 1 },
+      to: { opacity: 0 },
+      onRest: {
+        opacity: ({ value }) => {
+          if (value === 0) {
+            setShowSpinner(false);
+          }
+        },
+      },
+    }),
+    [isLoading]
+  );
+
+  useEffect(() => {
+    if (isLoading) {
+      spinnerSpringRef.stop();
+      spinnerSpringRef.set({ opacity: 1 });
+      setShowSpinner(true);
+    }
+
+    if (!isLoading && showSpinner) {
+      spinnerSpringRef.start();
+    }
+
+    if (!isLoading && !showSpinner) {
+      spinnerSpringRef.stop();
+    }
+  }, [isLoading, showSpinner, spinnerSpringRef]);
+
   return (
     <div
       className={classNames(
@@ -38,16 +76,14 @@ export const TimelineFloatingHeader = ({
       style={style}
     >
       <TimelineDateHeader floating i18n={i18n} timestamp={timestamp} />
-      <div
-        className={classNames(
-          'TimelineFloatingHeader__spinner-container',
-          `TimelineFloatingHeader__spinner-container--${
-            isLoading ? 'visible' : 'hidden'
-          }`
-        )}
-      >
-        <Spinner direction="on-background" size="20px" svgSize="small" />
-      </div>
+      {showSpinner && (
+        <animated.div
+          className="TimelineFloatingHeader__spinner-container"
+          style={spinnerStyles}
+        >
+          <Spinner direction="on-background" size="20px" svgSize="small" />
+        </animated.div>
+      )}
     </div>
   );
 };