/** 外观主题：浅色 / 深色 / 跟随系统。写到 html[data-theme] + localStorage，避免首屏闪白。 */

export type Appearance = "light" | "dark" | "system";

export const THEME_STORAGE_KEY = "yingqing-appearance";

export function normalizeAppearance(value: unknown): Appearance {
  if (value === "light" || value === "dark" || value === "system") return value;
  return "system";
}

export function resolveTheme(appearance: Appearance): "light" | "dark" {
  if (appearance === "light" || appearance === "dark") return appearance;
  if (typeof window !== "undefined" && window.matchMedia("(prefers-color-scheme: dark)").matches) {
    return "dark";
  }
  return "light";
}

export function applyTheme(appearance: Appearance | string | null | undefined) {
  if (typeof document === "undefined") return;
  const normalized = normalizeAppearance(appearance);
  const theme = resolveTheme(normalized);
  const root = document.documentElement;
  root.setAttribute("data-theme", theme);
  root.style.colorScheme = theme;
  try {
    localStorage.setItem(THEME_STORAGE_KEY, normalized);
  } catch {
    /* ignore quota / private mode */
  }
}

export function readStoredAppearance(): Appearance {
  try {
    return normalizeAppearance(localStorage.getItem(THEME_STORAGE_KEY));
  } catch {
    return "system";
  }
}