package org.exolab.castor.xml;
   
   import java.util.Hashtable;
   import java.util.Map;
   
   /**
    * Default {@link IDResolver} for Castor XML during (un)marshaling.
    * 
    * @see org.exolab.castor.xml.IDResolver
   */
  class IDResolverImpl implements IDResolver {
  
    /**
     * A collection of IDREF --> target object mappings.
     */
    private Map<String, Object> _idReferences = new Hashtable<String, Object>();
  
    /**
     * A custom (user-injected) IDResolver instance to be used for IDREF resolution.
     */
    private IDResolver _idResolver = null;
  
    /**
     * Binds a mapping from an ID to the referenced target object.
     * 
     * @param id Object identifier
     * @param object Object being identified by ID
     * @param isValidating True if validation is enabled.
     * @throws ValidationException If an ID is used more than once.
     */
    void bind(final String id, final Object object, final boolean isValidating)
        throws ValidationException {
  
      if (isValidating && id == null) {
        throw new ValidationException("Invalid ID value 'null' encountered");
      }
  
      if (isValidating && id.equals("")) {
        throw new ValidationException("Empty ID value encountered");
      }
  
      if (isValidating && _idReferences.containsKey(id)) {
        if (!(id.equals("org.exolab.castor.mapping.MapItem") || id.equals("HIGH-LOW"))) {
          throw new ValidationException("Duplicate ID " + id + " encountered");
        }
      } else {
        _idReferences.put(id, object);
      }
  
    }
  
    /**
     * Returns the Object whose id matches the given IDREF, or 'null' if no object was found.
     * 
     * @param idref the IDREF to resolve.
     * @return the Object whose id matches the given IDREF.
     */
    public Object resolve(final String idref) {
  
      Object object = _idReferences.get(idref);
      if (object != null) {
        return object;
      }
  
      if (_idResolver != null) {
        return _idResolver.resolve(idref);
      }
  
      return null;
    }
  
    /**
     * Sets a custom IDResolver instance to be used for IDRef resolution.
     * 
     * @param idResolver a custom IDResolver instance to be used.
     */
    void setResolver(final IDResolver idResolver) {
      _idResolver = idResolver;
    }
  
  }