/*
 * Copyright 2005 by Oracle USA
 * 500 Oracle Parkway, Redwood Shores, California, 94065, U.S.A.
 * All rights reserved.
 */
package javax.ide.command;

import javax.ide.menu.IDEAction;
import javax.ide.util.MetaClass;

/**
 * Controllers encapulate extension defined {@link UpdateHandler}s and 
 * {@link InvokeHandler}s. Generally, {@link javax.ide.view.View}s use 
 * controllers to check whether a context sensitive command can be 
 * executed given the current context, and to do the actual execution of 
 * that command.
 */
public final class Controller 
{
  private MetaClass _updateClass;
  private MetaClass _invokeClass;
  
  private final boolean _isContextSensitive;
  
  private UpdateHandler _updateHandler;
  private InvokeHandler _invokeHandler;
  
  private static UpdateHandler _nullUpdateHandler;
  private static InvokeHandler _nullInvokeHandler;
  
  /**
   * Constructs a controller object, deferring class loading and instantiation
   * of its invoke and update handler objects until needed. Generally, this is
   * only used by IDE implementations when loading controllers from the manifest
   * file.
   * 
   * @param invokeHandlerClass a metaclass of an <tt>InvokeHandler</tt>.
   * @param updateHandlerClass a metaclass of an <tt>UpdateHandler</tt>. May
   *    be null.
   */
  public Controller( MetaClass invokeHandlerClass, 
    MetaClass updateHandlerClass )
  {
    if ( invokeHandlerClass == null )
    {
      throw new NullPointerException( "invokeHandlerClass is null" );
    }
    
    _isContextSensitive = updateHandlerClass == null;
  
    _updateClass = updateHandlerClass;
    _invokeClass = invokeHandlerClass;
  }
  
  /**
   * Constructs a controller object.
   * 
   * @param invokeHandler the invocation handler. Must not be null.
   * @param updateHandler the update handler. May be null for actions which
   * are always enabled.
   */
  public Controller( InvokeHandler invokeHandler, UpdateHandler updateHandler )
  {
    if ( _invokeHandler == null )
    {
      throw new NullPointerException( "invokeHandler is null" );
    }
    _isContextSensitive = _updateHandler == null;    
    _invokeHandler = invokeHandler;
    _updateHandler = updateHandler;
  }
  
  /**
   * Get the invoke handler for this controller.
   * 
   * @return the invoke handler for this controller. Will never return null. 
   */
  public InvokeHandler getInvokeHandler()
  {
    if ( _invokeHandler == null )
    {
      try
      {
        _invokeHandler = (InvokeHandler) _invokeClass.newInstance();
      }
      catch ( Exception e )
      {
        e.printStackTrace();
        // TODO report error.
        _nullInvokeHandler = new NullInvokeHandler();
        _invokeHandler = _nullInvokeHandler;
      }
    }
    return _invokeHandler;
  }
  
  /**
   * Get the update handler for this controller.
   * 
   * @return the update handler for this controller. If the action is always
   *    enabled, returns a handler that always sets the action enabled. Will
   *    never return null.
   */
  public UpdateHandler getUpdateHandler()
  {
    if ( _updateHandler == null && _updateClass != null )
    {
      try
      {
        _updateHandler = (UpdateHandler) _updateClass.newInstance();
      }
      catch ( Exception e )
      {
        e.printStackTrace();
        // TODO error handling.
      }
    }
    
    if ( _updateHandler == null )
    {
      // Either _updateClass == null or an exception occurred creating the
      // update class. 
      if ( _nullUpdateHandler == null )
      {
        _nullUpdateHandler = new NullUpdateHandler();
      }
      _updateHandler = _nullUpdateHandler;
    }
    
    return _updateHandler;
    
  }

  /**
   * Get whether this controller is context sensitive. A context sensitive
   * controller has an associated <tt>UpdateHandler</tt> that adjusts the 
   * action based on the context.
   * 
   * @return <tt>true</tt> if the <tt>UpdateHandler</tt> associated with this
   *    <tt>Controller</tt> may change the state of the action based on the
   *    context.
   */
  public boolean isContextSensitive()
  {
    return _isContextSensitive;
  }

  private static final class NullInvokeHandler implements InvokeHandler
  {
    public boolean invoke( IDEAction action, Context context )
    {
      return true;
    }
  }
  
  private static final class NullUpdateHandler implements UpdateHandler
  {
    public boolean update( IDEAction action, Context context )
    {
      action.setEnabled( true );
      return true;
    }
  }
}