/**
 * ErrorHandler - Global error handling utility
 * Classifies errors, creates user-friendly messages, logs to console,
 * updates StateManager error state, and attempts recovery where possible.
 * Requirements: 11.1, 11.2, 11.3, 11.4, 11.5
 */

const ErrorHandler = (function () {
  // ─── Error Type Constants ─────────────────────────────────────────────────

  const ErrorType = {
    FILE_NOT_FOUND: 'FILE_NOT_FOUND',
    INVALID_FILE_FORMAT: 'INVALID_FILE_FORMAT',
    PARSE_ERROR: 'PARSE_ERROR',
    LIBRARY_LOAD_ERROR: 'LIBRARY_LOAD_ERROR',
    UPLOAD_ERROR: 'UPLOAD_ERROR',
    EXPORT_ERROR: 'EXPORT_ERROR',
    UNKNOWN_ERROR: 'UNKNOWN_ERROR',
  };

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

  /**
   * Classify an error object or message into a known ErrorType.
   * @param {Error|string} error
   * @returns {string} One of the ErrorType values
   */
  function _classifyError(error) {
    const msg = (error && (error.message || String(error))).toLowerCase();

    if (msg.includes('not found') || msg.includes('404') || msg.includes('failed to fetch')) {
      return ErrorType.FILE_NOT_FOUND;
    }
    if (msg.includes('invalid') && (msg.includes('format') || msg.includes('onnx'))) {
      return ErrorType.INVALID_FILE_FORMAT;
    }
    if (msg.includes('parse') || msg.includes('protobuf') || msg.includes('corrupt')) {
      return ErrorType.PARSE_ERROR;
    }
    if (msg.includes('library') || msg.includes('cdn') || msg.includes('script') || msg.includes('load error') || msg.includes('protobuf')) {
      return ErrorType.LIBRARY_LOAD_ERROR;
    }
    if (msg.includes('upload')) {
      return ErrorType.UPLOAD_ERROR;
    }
    if (msg.includes('export')) {
      return ErrorType.EXPORT_ERROR;
    }
    return ErrorType.UNKNOWN_ERROR;
  }

  /**
   * Map an ErrorType to a user-friendly message from CONFIG.ERRORS.
   * @param {string} errorType
   * @returns {string}
   */
  function _getUserMessage(errorType) {
    if (typeof CONFIG !== 'undefined' && CONFIG.ERRORS && CONFIG.ERRORS[errorType]) {
      return CONFIG.ERRORS[errorType];
    }
    // Fallback messages if CONFIG is not available
    const fallback = {
      FILE_NOT_FOUND: 'File not found. Please check the file path.',
      INVALID_FILE_FORMAT: 'Invalid file format. Please upload a valid ONNX file.',
      PARSE_ERROR: 'Failed to parse the model. The file may be corrupted.',
      LIBRARY_LOAD_ERROR: 'Failed to load required libraries. Please check your internet connection.',
      UPLOAD_ERROR: 'Failed to upload the file. Please try again.',
      EXPORT_ERROR: 'Failed to export the model information.',
      UNKNOWN_ERROR: 'An unknown error occurred. Please try again.',
    };
    return fallback[errorType] || fallback.UNKNOWN_ERROR;
  }

  /**
   * Attempt recovery based on error type.
   * @param {string} errorType
   */
  function _attemptRecovery(errorType) {
    switch (errorType) {
      case ErrorType.LIBRARY_LOAD_ERROR:
        // Nothing we can do automatically; user must refresh
        console.info('[ErrorHandler] Recovery: User should refresh the page to reload libraries.');
        break;

      case ErrorType.FILE_NOT_FOUND:
      case ErrorType.PARSE_ERROR:
      case ErrorType.INVALID_FILE_FORMAT:
        // Clear the current model so the UI returns to a clean state
        if (typeof StateManager !== 'undefined') {
          StateManager.setCurrentModel(null);
          StateManager.setLoading(false);
        }
        break;

      case ErrorType.UPLOAD_ERROR:
        // Reset loading state so the upload button is usable again
        if (typeof StateManager !== 'undefined') {
          StateManager.setLoading(false);
        }
        break;

      case ErrorType.EXPORT_ERROR:
        // No state change needed; export is a side-effect operation
        break;

      default:
        // Generic recovery: ensure loading spinner is cleared
        if (typeof StateManager !== 'undefined') {
          StateManager.setLoading(false);
        }
        break;
    }
  }

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

  return {
    /**
     * Handle an error: log it, classify it, show a user-friendly message,
     * update StateManager, and attempt recovery.
     *
     * @param {Error|string} error - The error object or message
     * @param {string} [context='App'] - Context label for console logging
     * @param {'error'|'warning'|'info'} [severity='error'] - Display severity
     */
    handleError(error, context = 'App', severity = 'error') {
      // 1. Log to console
      console.error(`[ErrorHandler][${context}]`, error);

      // 2. Classify error type
      const errorType = _classifyError(error);

      // 3. Create user-friendly message
      const userMessage = _getUserMessage(errorType);

      // 4. Update StateManager error state
      if (typeof StateManager !== 'undefined') {
        StateManager.setError(userMessage, severity);
      }

      // 5. Attempt recovery
      _attemptRecovery(errorType);

      // Return structured info for callers that want it
      return { errorType, userMessage };
    },

    /**
     * Handle a warning (non-critical issue).
     * @param {string} message
     * @param {string} [context='App']
     */
    handleWarning(message, context = 'App') {
      console.warn(`[ErrorHandler][${context}]`, message);
      if (typeof StateManager !== 'undefined') {
        StateManager.setError(message, 'warning');
      }
    },

    /**
     * Handle an informational message.
     * @param {string} message
     * @param {string} [context='App']
     */
    handleInfo(message, context = 'App') {
      console.info(`[ErrorHandler][${context}]`, message);
      if (typeof StateManager !== 'undefined') {
        StateManager.setError(message, 'info');
      }
    },

    /**
     * Clear the current error state.
     */
    clearError() {
      if (typeof StateManager !== 'undefined') {
        StateManager.clearError();
      }
    },

    // Expose ErrorType constants for external use
    ErrorType,
  };
})();

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