// SvelteKit `onNavigate` helper — wraps client-side navigation in the
// browser's View Transitions API so route changes cross-fade cleanly and
// shared-element transitions (Fleet card → Server detail hero) morph.
//
// Chromium ships the API today; Firefox and Safari fall through to a plain
// navigation — same behavior as before, just without the transition.

// Structural type — accepts whatever SvelteKit passes to onNavigate without
// coupling to a specific @sveltejs/kit version's type name.
type NavigationLike = { complete: Promise<unknown> };

export function enableViewTransitions(navigation: NavigationLike): Promise<void> | void {
    // Feature-detect without a custom Document extension — the DOM lib type
    // varies between TS versions, and any narrowing has to survive both.
    const start = (document as unknown as {
        startViewTransition?: (cb: () => void | Promise<void>) => unknown;
    }).startViewTransition;

    if (typeof start !== 'function') return;

    return new Promise<void>((resolve) => {
        start.call(document, async () => {
            resolve();
            await navigation.complete;
        });
    });
}