/**
 * StateManager - Singleton pattern for global application state management
 * Manages AppState, provides getter/setter methods, and subscription system
 * Requirements: 2.6, 11.4
 */

const StateManager = (function () {
  // ─── Private State ────────────────────────────────────────────────────────

  /** @type {AppState} */
  const _state = {
    // Models
    currentModel: null,
    modelList: [],

    // UI State
    selectedNodeId: null,
    zoomLevel: 1,
    viewMode: 'single', // 'single' | 'comparison'
    comparisonModel: null,

    // Search/Filter
    searchQuery: '',
    filteredModelList: [],

    // Error State
    error: null,

    // Loading State
    isLoading: false,
    loadingProgress: 0,
  };

  /** @type {Map<string, Set<Function>>} */
  const _subscribers = new Map();

  // ─── Private Helpers ──────────────────────────────────────────────────────

  /**
   * Notify all subscribers for a given key.
   * @param {string} key
   * @param {*} newValue
   * @param {*} oldValue
   */
  function _notify(key, newValue, oldValue) {
    if (_subscribers.has(key)) {
      _subscribers.get(key).forEach((cb) => {
        try {
          cb(newValue, oldValue, key);
        } catch (err) {
          console.error(`[StateManager] Subscriber error for key "${key}":`, err);
        }
      });
    }
    // Also notify wildcard '*' subscribers
    if (_subscribers.has('*')) {
      _subscribers.get('*').forEach((cb) => {
        try {
          cb(newValue, oldValue, key);
        } catch (err) {
          console.error('[StateManager] Wildcard subscriber error:', err);
        }
      });
    }
  }

  /**
   * Generic setter that updates state and notifies subscribers.
   * @param {string} key
   * @param {*} value
   */
  function _set(key, value) {
    if (!(key in _state)) {
      console.warn(`[StateManager] Unknown state key: "${key}"`);
    }
    const old = _state[key];
    _state[key] = value;
    _notify(key, value, old);
  }

  // ─── Persistence Helpers ──────────────────────────────────────────────────

  function _persistSelectedModel(modelId) {
    try {
      if (modelId !== null && modelId !== undefined) {
        localStorage.setItem(CONFIG.STORAGE.SELECTED_MODEL, modelId);
      } else {
        localStorage.removeItem(CONFIG.STORAGE.SELECTED_MODEL);
      }
    } catch (err) {
      console.warn('[StateManager] localStorage write failed:', err);
    }
  }

  function _loadPersistedSelectedModel() {
    try {
      return localStorage.getItem(CONFIG.STORAGE.SELECTED_MODEL) || null;
    } catch (err) {
      console.warn('[StateManager] localStorage read failed:', err);
      return null;
    }
  }

  // ─── Public API ───────────────────────────────────────────────────────────

  return {
    // ── Getters ──────────────────────────────────────────────────────────────

    /** @returns {AppState} Shallow copy of the current state */
    getState() {
      return Object.assign({}, _state);
    },

    /** @returns {ParsedModel|null} */
    getCurrentModel() {
      return _state.currentModel;
    },

    /** @returns {Array} */
    getModelList() {
      return _state.modelList;
    },

    /** @returns {string|null} */
    getSelectedNodeId() {
      return _state.selectedNodeId;
    },

    /** @returns {number} */
    getZoomLevel() {
      return _state.zoomLevel;
    },

    /** @returns {'single'|'comparison'} */
    getViewMode() {
      return _state.viewMode;
    },

    /** @returns {ParsedModel|null} */
    getComparisonModel() {
      return _state.comparisonModel;
    },

    /** @returns {string} */
    getSearchQuery() {
      return _state.searchQuery;
    },

    /** @returns {Array} */
    getFilteredModelList() {
      return _state.filteredModelList;
    },

    /** @returns {{message:string, type:string, timestamp:number}|null} */
    getError() {
      return _state.error;
    },

    /** @returns {boolean} */
    isLoading() {
      return _state.isLoading;
    },

    /** @returns {number} */
    getLoadingProgress() {
      return _state.loadingProgress;
    },

    // ── Setters ──────────────────────────────────────────────────────────────

    /**
     * Set the current model and persist its id to localStorage.
     * @param {ParsedModel|null} model
     */
    setCurrentModel(model) {
      _set('currentModel', model);
      const modelId = model && model.metadata ? model.metadata.fileName : null;
      _persistSelectedModel(modelId);
    },

    /** @param {Array} list */
    setModelList(list) {
      _set('modelList', list);
    },

    /** @param {string|null} nodeId */
    setSelectedNodeId(nodeId) {
      _set('selectedNodeId', nodeId);
    },

    /** @param {number} level */
    setZoomLevel(level) {
      _set('zoomLevel', level);
    },

    /** @param {'single'|'comparison'} mode */
    setViewMode(mode) {
      _set('viewMode', mode);
    },

    /** @param {ParsedModel|null} model */
    setComparisonModel(model) {
      _set('comparisonModel', model);
    },

    /** @param {string} query */
    setSearchQuery(query) {
      _set('searchQuery', query);
    },

    /** @param {Array} list */
    setFilteredModelList(list) {
      _set('filteredModelList', list);
    },

    /**
     * Set an error in state.
     * @param {string} message
     * @param {'error'|'warning'|'info'} [type='error']
     */
    setError(message, type = 'error') {
      _set('error', { message, type, timestamp: Date.now() });
    },

    /** Clear the current error */
    clearError() {
      _set('error', null);
    },

    /** @param {boolean} loading */
    setLoading(loading) {
      _set('isLoading', loading);
    },

    /** @param {number} progress 0-100 */
    setLoadingProgress(progress) {
      _set('loadingProgress', progress);
    },

    // ── Subscription System ───────────────────────────────────────────────────

    /**
     * Subscribe to changes on a specific state key (or '*' for all changes).
     * @param {string} key - State key to watch, or '*' for all changes
     * @param {Function} callback - Called with (newValue, oldValue, key)
     * @returns {Function} Unsubscribe function
     */
    subscribe(key, callback) {
      if (typeof callback !== 'function') {
        throw new TypeError('[StateManager] subscribe() requires a function callback');
      }
      if (!_subscribers.has(key)) {
        _subscribers.set(key, new Set());
      }
      _subscribers.get(key).add(callback);

      // Return unsubscribe function
      return function unsubscribe() {
        const set = _subscribers.get(key);
        if (set) {
          set.delete(callback);
          if (set.size === 0) {
            _subscribers.delete(key);
          }
        }
      };
    },

    /**
     * Unsubscribe a specific callback from a key.
     * @param {string} key
     * @param {Function} callback
     */
    unsubscribe(key, callback) {
      const set = _subscribers.get(key);
      if (set) {
        set.delete(callback);
        if (set.size === 0) {
          _subscribers.delete(key);
        }
      }
    },

    // ── Persistence ───────────────────────────────────────────────────────────

    /**
     * Restore persisted selected model id from localStorage.
     * @returns {string|null} The persisted model id, or null
     */
    getPersistedSelectedModelId() {
      return _loadPersistedSelectedModel();
    },

    // ── Reset ─────────────────────────────────────────────────────────────────

    /**
     * Reset all state to initial values (useful for testing).
     */
    reset() {
      const keys = Object.keys(_state);
      const initial = {
        currentModel: null,
        modelList: [],
        selectedNodeId: null,
        zoomLevel: 1,
        viewMode: 'single',
        comparisonModel: null,
        searchQuery: '',
        filteredModelList: [],
        error: null,
        isLoading: false,
        loadingProgress: 0,
      };
      keys.forEach((key) => _set(key, initial[key]));
    },
  };
})();

// Export for global access in vanilla JS context
window.StateManager = StateManager;