Dark Mode Toggle (No Flash)

// Dark Mode Toggle · Cube Burst Studios · CC0
// Follows the system setting until the visitor chooses; remembers the choice. Put the inline snippet from
// index.html in <head> so there's no white flash on load.
const KEY = "theme";
export function initThemeToggle(button) {
	const root = document.documentElement;
	const set = (theme, save) => {
		root.dataset.theme = theme;
		button.setAttribute("aria-pressed", String(theme === "dark"));
		button.querySelector("[data-label]").textContent = theme === "dark" ? "Dark" : "Light";
		if (save) try { localStorage.setItem(KEY, theme); } catch {}
	};
	set(root.dataset.theme || (matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light"), false);
	button.addEventListener("click", () => set(root.dataset.theme === "dark" ? "light" : "dark", true));
	matchMedia("(prefers-color-scheme: dark)").addEventListener("change", (e) => {
		let saved = null;
		try { saved = localStorage.getItem(KEY); } catch {}
		if (!saved) set(e.matches ? "dark" : "light", false);
	});
}