fix: tests

frontend/src/components/cmdKPalette/__test__/cmdkPalette.test.tsx

@@ -116,17 +116,28 @@ jest.mock('hooks/useNotifications', (): unknown => ({
 }));
 
 // mock theme hook
-jest.mock('hooks/useDarkMode', (): unknown => ({
-	useThemeMode: (): {
+jest.mock('hooks/useDarkMode', (): unknown => {
+	const useThemeModeMock = (): {
 		setAutoSwitch: jest.Mock;
 		setTheme: jest.Mock;
+		toggleTheme: jest.Mock;
 		theme: string;
+		autoSwitch: boolean;
 	} => ({
 		setAutoSwitch: jest.fn(),
 		setTheme: jest.fn(),
+		toggleTheme: jest.fn(),
 		theme: 'dark',
-	}),
-}));
+		autoSwitch: false,
+	});
+	return {
+		__esModule: true,
+		default: useThemeModeMock,
+		useThemeMode: useThemeModeMock,
+		useIsDarkMode: (): boolean => true,
+		useSystemTheme: (): 'dark' | 'light' => 'dark',
+	};
+});
 
 // mock updateUserPreference API and react-query mutation
 jest.mock('api/v1/user/preferences/name/update', (): jest.Mock => jest.fn());

frontend/src/components/cmdKPalette/cmdKPalette.tsx

@@ -10,6 +10,7 @@ import {
 } from '@signozhq/ui/command';
 import logEvent from 'api/common/logEvent';
 import { useThemeMode } from 'hooks/useDarkMode';
+import { useThemeSelection } from 'hooks/useDarkMode/useThemeSelection';
 import history from 'lib/history';
 import { ROLES as UserRole } from 'types/roles';
 
@@ -36,7 +37,8 @@ export function CmdKPalette({
 }): JSX.Element | null {
 	const { open, setOpen } = useCmdK();
 
-	const { setAutoSwitch, setTheme, theme } = useThemeMode();
+	const { theme } = useThemeMode();
+	const selectTheme = useThemeSelection();
 
 	// toggle palette with ⌘/Ctrl+K
 	function handleGlobalCmdK(
@@ -66,12 +68,10 @@ export function CmdKPalette({
 
 	function handleThemeChange(value: string): void {
 		logEvent('Account Settings: Theme Changed', { theme: value });
-		if (value === 'auto') {
-			setAutoSwitch(true);
-		} else {
-			setAutoSwitch(false);
-			setTheme(value);
-		}
+		// Close the palette inside the same flushSync batch as the theme change
+		// so its dismissal is part of the captured "new" frame of the wipe;
+		// otherwise the dialog would be visible in both snapshots and flicker.
+		selectTheme(value, () => setOpen(false));
 	}
 
 	function onClickHandler(key: string): void {

frontend/src/container/MySettings/__tests__/MySettings.test.tsx

@@ -12,6 +12,8 @@ import APIError from 'types/api/error';
 import { toast } from '@signozhq/ui/sonner';
 
 const toggleThemeFunction = jest.fn();
+const setThemeFunction = jest.fn();
+const setAutoSwitchFunction = jest.fn();
 const logEventFunction = jest.fn();
 const copyToClipboardFn = jest.fn();
 const editUserFn = jest.fn();
@@ -56,9 +58,11 @@ jest.mock('hooks/useDarkMode', () => ({
 	useIsDarkMode: jest.fn(() => true),
 	useSystemTheme: jest.fn(() => 'dark'),
 	default: jest.fn(() => ({
+		theme: 'dark',
+		setTheme: setThemeFunction,
 		toggleTheme: toggleThemeFunction,
 		autoSwitch: false,
-		setAutoSwitch: jest.fn(),
+		setAutoSwitch: setAutoSwitchFunction,
 	})),
 }));
 
@@ -134,7 +138,8 @@ describe('MySettings Flows', () => {
 			fireEvent.click(lightOption);
 
 			await waitFor(() => {
-				expect(toggleThemeFunction).toHaveBeenCalled();
+				expect(setAutoSwitchFunction).toHaveBeenCalledWith(false);
+				expect(setThemeFunction).toHaveBeenCalledWith('light');
 				expect(logEventFunction).toHaveBeenCalledWith(
 					'Account Settings: Theme Changed',
 					{

frontend/src/container/MySettings/index.tsx

@@ -8,6 +8,8 @@ import updateUserPreference from 'api/v1/user/preferences/name/update';
 import { AxiosError } from 'axios';
 import { USER_PREFERENCES } from 'constants/userPreferences';
 import useThemeMode, { useIsDarkMode, useSystemTheme } from 'hooks/useDarkMode';
+import { THEME_MODE } from 'hooks/useDarkMode/constant';
+import { useThemeSelection } from 'hooks/useDarkMode/useThemeSelection';
 import { useNotifications } from 'hooks/useNotifications';
 import { MonitorCog, Moon, Sun } from '@signozhq/icons';
 import { useAppContext } from 'providers/App/App';
@@ -23,9 +25,10 @@ import './MySettings.styles.scss';
 function MySettings(): JSX.Element {
 	const isDarkMode = useIsDarkMode();
 	const { userPreferences, updateUserPreferenceInContext } = useAppContext();
-	const { toggleTheme, autoSwitch, setAutoSwitch } = useThemeMode();
+	const { autoSwitch } = useThemeMode();
 	const systemTheme = useSystemTheme();
 	const { notifications } = useNotifications();
+	const selectTheme = useThemeSelection();
 
 	const [sideNavPinned, setSideNavPinned] = useState(false);
 
@@ -58,7 +61,7 @@ function MySettings(): JSX.Element {
 					<Moon data-testid="dark-theme-icon" size={12} /> Dark{' '}
 				</div>
 			),
-			value: 'dark',
+			value: THEME_MODE.DARK,
 		},
 		{
 			label: (
@@ -69,7 +72,7 @@ function MySettings(): JSX.Element {
 					</Tag>
 				</div>
 			),
-			value: 'light',
+			value: THEME_MODE.LIGHT,
 		},
 		{
 			label: (
@@ -77,46 +80,29 @@ function MySettings(): JSX.Element {
 					<MonitorCog size={12} data-testid="auto-theme-icon" /> System{' '}
 				</div>
 			),
-			value: 'auto',
+			value: THEME_MODE.SYSTEM,
 		},
 	];
 
 	const [theme, setTheme] = useState(() => {
 		if (autoSwitch) {
-			return 'auto';
+			return THEME_MODE.SYSTEM;
 		}
-		return isDarkMode ? 'dark' : 'light';
+		return isDarkMode ? THEME_MODE.DARK : THEME_MODE.LIGHT;
 	});
 
-	const handleThemeChange = ({ target: { value } }: RadioChangeEvent): void => {
-		logEvent('Account Settings: Theme Changed', {
-			theme: value,
-		});
-		setTheme(value);
-
-		if (value === 'auto') {
-			setAutoSwitch(true);
-		} else {
-			setAutoSwitch(false);
-			// Only toggle if the current theme is different from the target
-			const targetIsDark = value === 'dark';
-			if (targetIsDark !== isDarkMode) {
-				toggleTheme();
-			}
-		}
+	const handleThemeChange = (event: RadioChangeEvent): void => {
+		const { value } = event.target;
+		logEvent('Account Settings: Theme Changed', { theme: value });
+		selectTheme(value);
 	};
 
 	useEffect(() => {
 		if (autoSwitch) {
-			setTheme('auto');
+			setTheme(THEME_MODE.SYSTEM);
 			return;
 		}
-
-		if (isDarkMode) {
-			setTheme('dark');
-		} else {
-			setTheme('light');
-		}
+		setTheme(isDarkMode ? THEME_MODE.DARK : THEME_MODE.LIGHT);
 	}, [autoSwitch, isDarkMode]);
 
 	const handleSideNavPinnedChange = (checked: boolean): void => {

frontend/src/hooks/useDarkMode/useThemeSelection.ts

@@ -0,0 +1,64 @@
+import { useCallback } from 'react';
+import {
+	canAnimateThemeTransition,
+	runThemeTransition,
+} from 'utils/themeTransition';
+
+import useThemeMode, { useSystemTheme } from './index';
+import { THEME_MODE } from './constant';
+
+type SelectTheme = (value: string, onApplied?: () => void) => void;
+
+// Centralises the "apply a theme selection" flow used by MySettings and the
+// command palette: figures out whether the visible (dark↔light) theme is
+// actually flipping, applies the state change, and — when capable — wraps the
+// change in a left→right view-transition wipe.
+//
+// `value` is one of THEME_MODE.{LIGHT,DARK,SYSTEM}; `onApplied` runs inside the
+// same flushSync batch as the theme change (useful for, e.g., closing the
+// command palette so its dismissal is part of the captured "new" snapshot).
+export function useThemeSelection(): SelectTheme {
+	const { theme, setTheme, setAutoSwitch } = useThemeMode();
+	const systemTheme = useSystemTheme();
+
+	return useCallback<SelectTheme>(
+		(value, onApplied) => {
+			const currentIsDark = theme === THEME_MODE.DARK;
+
+			// When switching to SYSTEM, the visible theme flips iff the OS preference
+			// differs from what we're currently rendering.
+			const resolvedTargetIsDark =
+				value === THEME_MODE.SYSTEM
+					? systemTheme === THEME_MODE.DARK
+					: value === THEME_MODE.DARK;
+			const willFlipDarkMode = resolvedTargetIsDark !== currentIsDark;
+
+			const applyChange = (): void => {
+				if (value === THEME_MODE.SYSTEM) {
+					// Also push the resolved light/dark value through setTheme so the
+					// View Transition snapshot reflects the new theme synchronously.
+					// Otherwise the flip would only land via ThemeProvider's effect
+					// (setAutoSwitch → re-render → effect → setThemeState), which
+					// isn't guaranteed to run inside this flushSync batch and would
+					// cause the wipe to capture old → old followed by a post-animation snap.
+					setAutoSwitch(true);
+					setTheme(resolvedTargetIsDark ? THEME_MODE.DARK : THEME_MODE.LIGHT);
+				} else {
+					setAutoSwitch(false);
+					setTheme(value);
+				}
+				onApplied?.();
+			};
+
+			if (!willFlipDarkMode || !canAnimateThemeTransition()) {
+				applyChange();
+				return;
+			}
+
+			runThemeTransition(applyChange);
+		},
+		[theme, systemTheme, setTheme, setAutoSwitch],
+	);
+}
+
+export default useThemeSelection;

frontend/src/styles.scss

@@ -826,3 +826,22 @@ body.ai-assistant-panel-open {
 :root {
 	--input-focus-outline-width: 0;
 }
+
+// Scoped to .theme-wipe-active (toggled on <html> in runThemeTransition) so
+// these overrides don't leak into any unrelated view transitions added later.
+// We disable the default UA crossfade so the JS-driven clip-path wipe is the
+// only visible effect, and stack the new snapshot above the old.
+html.theme-wipe-active {
+	&::view-transition-old(root),
+	&::view-transition-new(root) {
+		animation: none;
+	}
+
+	&::view-transition-old(root) {
+		z-index: 1;
+	}
+
+	&::view-transition-new(root) {
+		z-index: 2;
+	}
+}

frontend/src/utils/__tests__/themeTransition.test.ts

@@ -0,0 +1,122 @@
+import {
+	canAnimateThemeTransition,
+	runThemeTransition,
+	THEME_WIPE_ACTIVE_CLASS,
+} from '../themeTransition';
+
+type StartVT = (cb: () => void) => {
+	ready: Promise<void>;
+	finished: Promise<void>;
+};
+
+const installStartViewTransition = (impl?: StartVT): jest.Mock => {
+	const defaultImpl: StartVT = (cb) => {
+		cb();
+		return { ready: Promise.resolve(), finished: Promise.resolve() };
+	};
+	const fn = jest.fn(impl ?? defaultImpl);
+	Object.defineProperty(document, 'startViewTransition', {
+		configurable: true,
+		writable: true,
+		value: fn,
+	});
+	return fn;
+};
+
+const removeStartViewTransition = (): void => {
+	Object.defineProperty(document, 'startViewTransition', {
+		configurable: true,
+		writable: true,
+		value: undefined,
+	});
+};
+
+const setReducedMotion = (matches: boolean): void => {
+	(window.matchMedia as jest.Mock) = jest
+		.fn()
+		.mockImplementation((query: string) => ({
+			matches: query === '(prefers-reduced-motion: reduce)' ? matches : false,
+			media: query,
+			addListener: jest.fn(),
+			removeListener: jest.fn(),
+			addEventListener: jest.fn(),
+			removeEventListener: jest.fn(),
+			dispatchEvent: jest.fn(),
+		}));
+};
+
+describe('canAnimateThemeTransition', () => {
+	afterEach(() => {
+		removeStartViewTransition();
+	});
+
+	it('returns false when document.startViewTransition is unavailable', () => {
+		removeStartViewTransition();
+		setReducedMotion(false);
+		expect(canAnimateThemeTransition()).toBe(false);
+	});
+
+	it('returns false when prefers-reduced-motion is reduce', () => {
+		installStartViewTransition();
+		setReducedMotion(true);
+		expect(canAnimateThemeTransition()).toBe(false);
+	});
+
+	it('returns true when API is supported and motion is allowed', () => {
+		installStartViewTransition();
+		setReducedMotion(false);
+		expect(canAnimateThemeTransition()).toBe(true);
+	});
+});
+
+describe('runThemeTransition', () => {
+	afterEach(() => {
+		removeStartViewTransition();
+		document.documentElement.classList.remove(THEME_WIPE_ACTIVE_CLASS);
+	});
+
+	it('falls back to running applyChange directly when API is missing', () => {
+		removeStartViewTransition();
+		const applyChange = jest.fn();
+		runThemeTransition(applyChange);
+		expect(applyChange).toHaveBeenCalledTimes(1);
+		expect(
+			document.documentElement.classList.contains(THEME_WIPE_ACTIVE_CLASS),
+		).toBe(false);
+	});
+
+	it('invokes startViewTransition and runs applyChange inside its callback', () => {
+		const startVT = installStartViewTransition();
+		const applyChange = jest.fn();
+		runThemeTransition(applyChange);
+		expect(startVT).toHaveBeenCalledTimes(1);
+		expect(applyChange).toHaveBeenCalledTimes(1);
+	});
+
+	it('toggles the wipe-active class on <html> for the lifetime of the transition', async () => {
+		let resolveFinished: () => void = (): void => {};
+		installStartViewTransition((cb) => {
+			cb();
+			return {
+				ready: Promise.resolve(),
+				finished: new Promise<void>((resolve) => {
+					resolveFinished = resolve;
+				}),
+			};
+		});
+
+		runThemeTransition(() => undefined);
+
+		expect(
+			document.documentElement.classList.contains(THEME_WIPE_ACTIVE_CLASS),
+		).toBe(true);
+
+		resolveFinished();
+		await Promise.resolve();
+		await Promise.resolve();
+
+		expect(
+			document.documentElement.classList.contains(THEME_WIPE_ACTIVE_CLASS),
+		).toBe(false);
+	});
+});

frontend/src/utils/themeTransition.ts

@@ -0,0 +1,67 @@
+import { flushSync } from 'react-dom';
+
+const WIPE_DURATION_MS = 400;
+const WIPE_EASING = 'ease-out';
+
+// Toggled on <html> for the duration of the wipe so the CSS overrides
+// (animation: none on ::view-transition-{old,new}(root)) don't leak into
+// any future, unrelated view transitions in the app.
+export const THEME_WIPE_ACTIVE_CLASS = 'theme-wipe-active';
+
+type ViewTransition = {
+	ready: Promise<void>;
+	finished: Promise<void>;
+};
+type DocumentWithVT = Document & {
+	startViewTransition?: (callback: () => void) => ViewTransition;
+};
+
+export function canAnimateThemeTransition(): boolean {
+	const doc = document as DocumentWithVT;
+	if (typeof doc.startViewTransition !== 'function') {
+		return false;
+	}
+	return !window.matchMedia('(prefers-reduced-motion: reduce)').matches;
+}
+
+// Runs `applyChange` inside a View Transition and wipes the new theme in from
+// left to right via a polygon clip-path on ::view-transition-new(root).
+// Callers should gate on canAnimateThemeTransition() first; this is a safe
+// no-animation fallback otherwise.
+export function runThemeTransition(applyChange: () => void): void {
+	const doc = document as DocumentWithVT;
+	if (!doc.startViewTransition) {
+		applyChange();
+		return;
+	}
+
+	const root = document.documentElement;
+	root.classList.add(THEME_WIPE_ACTIVE_CLASS);
+
+	const transition = doc.startViewTransition(() => {
+		flushSync(applyChange);
+	});
+
+	const from = 'polygon(0 0, 0 0, 0 100%, 0 100%)';
+	const to = 'polygon(0 0, 100% 0, 100% 100%, 0 100%)';
+
+	transition.ready
+		.then(() =>
+			root.animate(
+				{ clipPath: [from, to] },
+				{
+					duration: WIPE_DURATION_MS,
+					easing: WIPE_EASING,
+					pseudoElement: '::view-transition-new(root)',
+				},
+			),
+		)
+		.catch(() => {
+			// Transition cancelled — applyChange has already run.
+		});
+
+	const cleanup = (): void => {
+		root.classList.remove(THEME_WIPE_ACTIVE_CLASS);
+	};
+	transition.finished.then(cleanup).catch(cleanup);
+}