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* @license
* Copyright 2025 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
import { useState, useLayoutEffect, useRef, useCallback } from 'react';
import { theme } from '../semantic-colors.js';
import { interpolateColor } from '../themes/color-utils.js';
import { debugState } from '../debug.js';
export function useAnimatedScrollbar(
isFocused: boolean,
scrollBy: (delta: number) => void,
) {
const [scrollbarColor, setScrollbarColor] = useState(theme.ui.dark);
const colorRef = useRef(scrollbarColor);
colorRef.current = scrollbarColor;
const animationFrame = useRef<NodeJS.Timeout | null>(null);
const timeout = useRef<NodeJS.Timeout | null>(null);
const isAnimatingRef = useRef(false);
const cleanup = useCallback(() => {
if (isAnimatingRef.current) {
debugState.debugNumAnimatedComponents--;
isAnimatingRef.current = false;
}
if (animationFrame.current) {
clearInterval(animationFrame.current);
animationFrame.current = null;
}
if (timeout.current) {
clearTimeout(timeout.current);
timeout.current = null;
}
}, []);
const flashScrollbar = useCallback(() => {
cleanup();
debugState.debugNumAnimatedComponents++;
isAnimatingRef.current = true;
const isTest =
typeof process !== 'undefined' && process.env['NODE_ENV'] === 'test';
const fadeInDuration = isTest ? 0 : 200;
const visibleDuration = isTest ? 0 : 1000;
const fadeOutDuration = isTest ? 0 : 300;
const focusedColor = theme.text.secondary;
const unfocusedColor = theme.ui.dark;
const startColor = colorRef.current;
if (!focusedColor || !unfocusedColor) {
return;
}
if (isTest) {
setScrollbarColor(unfocusedColor);
cleanup();
return;
}
// Phase 1: Fade In
let start = Date.now();
const animateFadeIn = () => {
if (!isAnimatingRef.current) return;
const elapsed = Date.now() - start;
const progress = Math.max(0, Math.min(elapsed / fadeInDuration, 1));
setScrollbarColor(interpolateColor(startColor, focusedColor, progress));
if (progress === 1) {
if (animationFrame.current) {
clearInterval(animationFrame.current);
animationFrame.current = null;
}
// Phase 2: Wait
timeout.current = setTimeout(() => {
// Phase 3: Fade Out
start = Date.now();
const animateFadeOut = () => {
if (!isAnimatingRef.current) return;
const elapsed = Date.now() - start;
const progress = Math.max(
0,
Math.min(elapsed / fadeOutDuration, 1),
);
setScrollbarColor(
interpolateColor(focusedColor, unfocusedColor, progress),
);
if (progress === 1) {
cleanup();
}
};
animationFrame.current = setInterval(animateFadeOut, 33);
}, visibleDuration);
}
};
animationFrame.current = setInterval(animateFadeIn, 33);
}, [cleanup]);
const wasFocused = useRef(isFocused);
useLayoutEffect(() => {
if (isFocused && !wasFocused.current) {
flashScrollbar();
} else if (!isFocused && wasFocused.current) {
cleanup();
setScrollbarColor(theme.ui.dark);
}
wasFocused.current = isFocused;
return cleanup;
}, [isFocused, flashScrollbar, cleanup]);
const scrollByWithAnimation = useCallback(
(delta: number) => {
scrollBy(delta);
flashScrollbar();
},
[scrollBy, flashScrollbar],
);
return { scrollbarColor, flashScrollbar, scrollByWithAnimation };
}
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