export const MIN_WALLPAPER_FREQUENCY_HOURS = 1;
export const MAX_WALLPAPER_FREQUENCY_HOURS = 48;
export const DEFAULT_WALLPAPER_FREQUENCY_HOURS = 24;

export const getWallpaperFrequencyHours = (frequency: string): number => {
  if (!frequency) return DEFAULT_WALLPAPER_FREQUENCY_HOURS;
  const match = frequency.match(/^(\d+)(h|d)$/);
  if (!match) return DEFAULT_WALLPAPER_FREQUENCY_HOURS;
  const value = parseInt(match[1], 10);
  const hours = match[2] === 'd' ? value * 24 : value;
  return Math.min(MAX_WALLPAPER_FREQUENCY_HOURS, Math.max(MIN_WALLPAPER_FREQUENCY_HOURS, hours));
};

export const getWallpaperFrequencyMs = (frequency: string): number =>
  getWallpaperFrequencyHours(frequency) * 60 * 60 * 1000;

export const formatWallpaperFrequency = (hours: number): string =>
  `${hours} ${hours === 1 ? 'hour' : 'hours'}`;

export const getRandomWallpaperIndex = (wallpaperCount: number, currentIndex: number): number => {
  if (wallpaperCount <= 1) return 0;
  const offset = Math.floor(Math.random() * (wallpaperCount - 1)) + 1;
  return (currentIndex + offset) % wallpaperCount;
};

export const loadWallpaperState = (names: string[], now = Date.now()) => {
  let state: Record<string, unknown> = {};
  try {
    const parsed: unknown = JSON.parse(localStorage.getItem('wallpaperState') || '{}');
    if (parsed && typeof parsed === 'object') state = parsed as Record<string, unknown>;
  } catch {
    state = {};
  }
  const namedIndex = typeof state.currentName === 'string' ? names.indexOf(state.currentName) : -1;
  const index = namedIndex >= 0 ? namedIndex : typeof state.currentName === 'string' ? 0 : state.currentIndex;
  const currentIndex = typeof index === 'number' && Number.isInteger(index) && index >= 0 && index < names.length ? index : 0;
  const timestamp = typeof state.lastWallpaperChange === 'string' ? Date.parse(state.lastWallpaperChange) : NaN;
  const lastChange = Number.isFinite(timestamp) && timestamp <= now && timestamp >= 0 ? timestamp : now;
  return { currentIndex, lastChange };
};

export const saveWallpaperState = (names: string[], currentIndex: number, lastChange: number): void => {
  const payload = JSON.stringify({
    currentIndex,
    currentName: names[currentIndex],
    lastWallpaperChange: new Date(lastChange).toISOString(),
  });
  if (localStorage.getItem('wallpaperState') !== payload) {
    localStorage.setItem('wallpaperState', payload);
  }
};