/**
 * Central state store with persistence.
 * Keys: user, windows, wallpaper, achievements, connection
 */
const STORAGE_KEY = 'meridian:state';

const State = (() => {
  const listeners = new Map();
  let _state = loadState();

  function loadState() {
    try {
      const raw = localStorage.getItem(STORAGE_KEY);
      if (raw) {
        const parsed = JSON.parse(raw);
        // achievements is stored as array, reconstruct as Set
        if (parsed.achievements) {
          parsed._achievementSet = new Set(parsed.achievements);
        }
        return parsed;
      }
    } catch (e) {
      console.warn('State load failed:', e);
    }
    return {
      user: null,
      windows: [],
      wallpaper: 'graphite',
      achievements: [],
      _achievementSet: new Set(),
      connection: navigator.onLine
    };
  }

  function saveState() {
    try {
      const toSave = {
        user: _state.user,
        windows: _state.windows,
        wallpaper: _state.wallpaper,
        achievements: Array.from(_state._achievementSet || _state.achievements)
      };
      localStorage.setItem(STORAGE_KEY, JSON.stringify(toSave));
    } catch (e) {
      console.warn('State save failed:', e);
    }
  }

  function set(key, val) {
    _state[key] = val;
    saveState();
    notify(key);
  }

  function get(key) {
    return _state[key];
  }

  function subscribe(key, cb) {
    if (!listeners.has(key)) listeners.set(key, new Set());
    listeners.get(key).add(cb);
    // immediate call with current value
    try { cb(_state[key]); } catch (e) { console.error('State subscribe error:', e); }
    return () => off(key, cb);
  }

  function off(key, cb) {
    const set = listeners.get(key);
    if (set) {
      set.delete(cb);
      if (set.size === 0) listeners.delete(key);
    }
  }

  function notify(key) {
    const set = listeners.get(key);
    if (set) {
      for (const cb of set) {
        try { cb(_state[key]); } catch (e) { console.error('State notify error:', e); }
      }
    }
  }

  function addAchievement(id) {
    if (!_state._achievementSet) {
      _state._achievementSet = new Set(_state.achievements || []);
      _state.achievements = Array.from(_state._achievementSet);
    }
    _state._achievementSet.add(id);
    _state.achievements = Array.from(_state._achievementSet);
    saveState();
    notify('achievements');
  }

  function initConnection() {
    _state.connection = navigator.onLine;
    window.addEventListener('online', () => { _state.connection = true; notify('connection'); saveState(); });
    window.addEventListener('offline', () => { _state.connection = false; notify('connection'); saveState(); });
  }

  return {
    set, get, subscribe, off, addAchievement, initConnection
  };
})();

export default State;
export { State };