import java.io.IOException;
import java.io.Writer;
import java.util.HashMap;
import javax.servlet.http.HttpSession;

import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.exception.ParseErrorException;
import org.apache.velocity.exception.MethodInvocationException;
import org.apache.velocity.runtime.directive.Directive;
import org.apache.velocity.runtime.directive.DirectiveConstants;
import org.apache.velocity.runtime.RuntimeServices;
import org.apache.velocity.context.InternalContextAdapter;
import org.apache.velocity.runtime.parser.node.Node;

/**
 * Example of a velocity directive which can be used to load a JavaBean into a velocity context
 * so that it can be accessed in a template.<br />
 * Note: this needs to be added to the properties of the velocity engine before it is initialised using:
 * <pre>
 * ve.setProperty("userdirective", ?UseBeanDirective?);
 * </pre>
 * @author Jason R Briggs
 */
public class UseBeanDirective extends Directive {
  private static final String APPLICATION_SCOPE = "application";
  private static final String EMPTY             = "";
  private static final String PAGE_SCOPE        = "page";
  private static final String QUOTES            = "\"'";
  private static final String SESSION_SCOPE     = "session";
  private static final String USEBEAN           = "usebean";
  
  private static final int APPLICATION = 1;
  private static final int SESSION     = 2;
  private static final int PAGE        = 3;
  
  private static HashMap beanClasses   = new HashMap();
  private static HashMap beanNames     = new HashMap();
  private static HashMap appScopeBeans = new HashMap();
  
  public boolean render(InternalContextAdapter context, Writer writer, Node node) throws IOException, ResourceNotFoundException, ParseErrorException, MethodInvocationException {
    int count = node.jjtGetNumChildren();
    String name = node.jjtGetChild(0).getFirstToken().toString();
    String className = node.jjtGetChild(1).getFirstToken().toString();
    int scope;
    String tmp;
    if (count >= 3) {
      tmp = node.jjtGetChild(2).getFirstToken().toString();
    }
    else {
      tmp = EMPTY;
    }
    
    // set the scope variable
    if (tmp.equals(APPLICATION_SCOPE)) {
      scope = APPLICATION;
    }
    else if (tmp.equals(SESSION_SCOPE)) {
      scope = SESSION;
    }
    else {
      scope = PAGE;
    }
    
    // cache the classnames, so we don't try to load the classes every time
    if (!beanClasses.containsKey(className)) {
      synchronized (beanClasses) {
        if (!beanClasses.containsKey(className)) {
          try {
            String cn = remove(className, QUOTES);
            Class c = Class.forName(cn);
            beanClasses.put(className, c);
          }
          catch (Exception e) {
            e.printStackTrace();
            throw new MethodInvocationException(e.getMessage(), e, getName());
          }
        }
      }
    }

    HttpSession session = null;
    try {
      Object obj = null;

      // if application scope, we use a hashmap to store the beans
      if (scope == APPLICATION && appScopeBeans.containsKey(name)) {
        obj = appScopeBeans.get(name);
      }
      // if session scope, try to get the bean from the user's session
      // (note: stored in the velocity context)
      else if (scope == SESSION) {
        session = (HttpSession)context.get(SESSION_SCOPE);

        obj = session.getAttribute(name);
      }
      
      // if we haven't managed to get an object by now, we'll
      // just instantiate it using the class
      if (obj == null) {
        Class c = (Class)beanClasses.get(className);
        obj = c.newInstance();
      }

      // put the object into the context
      context.put(name, obj);

      // depending upon the scope, put it in the cache of app beans
      // or into the session
      if (scope == APPLICATION && !appScopeBeans.containsKey(name)) {
        appScopeBeans.put(name, obj);
      }
      else if (scope == SESSION) {
        session.setAttribute(name, obj);
      }
      
    }
    catch (Exception e) {
      throw new MethodInvocationException(e.getMessage(), e, getName());
    }
    return true;
  }
  
  public int getType() {
    return DirectiveConstants.LINE;
  }
  
  public String getName() {
    return USEBEAN;
  }
 
  private static final String remove(String s, String chars) {
    if (s == null) {
      return EMPTY;
    }
    else {
      StringBuffer sb = new StringBuffer();
      for (int i = 0; i < s.length(); i++) {
        char c = s.charAt(i);
        if (chars.indexOf(c) < 0) {
          sb.append(c);
        }
      }
      return sb.toString();
    }
  }
 
}