// тема интерфейса: "" — системная, light, dark; ключ graph-theme, как у прежней доски (links.html, строки 1000–1003)
export const THEMES = ["", "light", "dark"] as const;
export type Theme = (typeof THEMES)[number];
const KEY = "graph-theme";

export function readTheme(): Theme {
  let v: string | null = null;
  try { v = localStorage.getItem(KEY); } catch { /* закрытое хранилище */ }
  return (THEMES as readonly string[]).includes(v ?? "") ? ((v ?? "") as Theme) : "";
}

export function saveTheme(t: Theme): void {
  try { localStorage.setItem(KEY, t); } catch { /* закрытое хранилище */ }
}

export function applyTheme(t: Theme): void {
  if (t) document.documentElement.setAttribute("data-theme", t);
  else document.documentElement.removeAttribute("data-theme");
}

export function systemDark(): boolean {
  return typeof matchMedia === "function" && matchMedia("(prefers-color-scheme: dark)").matches;
}

export function effectiveDark(t: Theme): boolean {
  return t === "dark" || (t === "" && systemDark());
}