import type { Theme } from '../types';

const STORAGE_KEY = 'gc_local_theme';

const VALID: readonly Theme[] = ['dark', 'light', 'blue'];

function isTheme(v: unknown): v is Theme {
  return typeof v === 'string' && (VALID as readonly string[]).includes(v);
}

/** 이 브라우저(기기)에 저장된 UI 테마. 계정·DB와 무관 */
export function loadLocalTheme(): Theme {
  try {
    const raw = localStorage.getItem(STORAGE_KEY);
    if (isTheme(raw)) return raw;
  } catch {
    /* private mode 등 */
  }
  return 'dark';
}

export function saveLocalTheme(theme: Theme): void {
  try {
    localStorage.setItem(STORAGE_KEY, theme);
  } catch {
    /* quota / private mode */
  }
}

/** localStorage에 없을 때만 DB defaultTheme을 이 기기에 1회 복사 */
export function migrateDbThemeToLocalIfNeeded(dbTheme: string | undefined): Theme {
  try {
    const existing = localStorage.getItem(STORAGE_KEY);
    if (isTheme(existing)) return existing;
  } catch {
    /* ignore */
  }
  const theme: Theme = isTheme(dbTheme) ? dbTheme : 'dark';
  saveLocalTheme(theme);
  return theme;
}