/*******************************************************************************
    *   Gisgraphy Project 
    * 
    *   This library is free software; you can redistribute it and/or
    *   modify it under the terms of the GNU Lesser General Public
    *   License as published by the Free Software Foundation; either
    *   version 2.1 of the License, or (at your option) any later version.
    * 
    *   This library is distributed in the hope that it will be useful,
   *   but WITHOUT ANY WARRANTY; without even the implied warranty of
   *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   *   Lesser General Public License for more details.
   * 
   *   You should have received a copy of the GNU Lesser General Public
   *   License along with this library; if not, write to the Free Software
   *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA
   * 
   *  Copyright 2008  Gisgraphy project 
   *  David Masclet <davidmasclet@gisgraphy.com>
   *  
   *  
   *******************************************************************************/
  package com.gisgraphy.webapp.taglib;
  
  import java.lang.reflect.AccessibleObject;
  import java.lang.reflect.Field;
  import java.util.HashMap;
  import java.util.Map;
  
  import javax.servlet.jsp.JspException;
  import javax.servlet.jsp.PageContext;
  import javax.servlet.jsp.tagext.TagSupport;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import com.gisgraphy.Constants;
  
  /**
   * <p>
   * This class is designed to put all the public variables in a class to a
   * specified scope - designed for exposing a Constants class to Tag Libraries.
   * </p>
   * <p>
   * It is designed to be used as follows:
   * 
   * <pre>
   * &lt;tag:constants /&gt;
   * </pre>
   * 
   * </p>
   * <p>
   * Optional values are "className" (fully qualified) and "scope".
   * </p>
   * <p>
   * <a href="BaseAction.java.html"><i>View Source</i></a>
   * </p>
   * 
   * @author <a href="mailto:matt@raibledesigns.com">Matt Raible</a>
   */
  public class ConstantsTag extends TagSupport {
      private static final long serialVersionUID = 3258417209566116146L;
  
      private final Log log = LogFactory.getLog(ConstantsTag.class);
  
      /**
       * The class to expose the variables from.
       */
      private String clazz = Constants.class.getName();
  
      /**
       * The scope to be put the variable in.
       */
      protected String scope;
  
      /**
       * The single variable to expose.
       */
      protected String var;
  
      /**
       * Main method that does processing and exposes Constants in specified scope
       * 
       * @return int
       * @throws JspException
       *                 if processing fails
       */
      @Override
      public int doStartTag() throws JspException {
  	// Using reflection, get the available field names in the class
  	Class<?> c = null;
  	int toScope = PageContext.PAGE_SCOPE;
  
  	if (scope != null) {
  	    toScope = getScope(scope);
  	}
  
  	try {
  	    c = Class.forName(clazz);
 	} catch (ClassNotFoundException cnf) {
 	    log.error("ClassNotFound - maybe a typo?");
 	    throw new JspException(cnf.getMessage());
 	}
 
 	try {
 	    // if var is null, expose all variables
 	    if (var == null) {
 		Field[] fields = c.getDeclaredFields();
 
 		AccessibleObject.setAccessible(fields, true);
 
 		for (Field field : fields) {
 		    pageContext.setAttribute(field.getName(), field.get(this),
 			    toScope);
 		}
 	    } else {
 		try {
 		    Object value = c.getField(var).get(this);
 		    pageContext.setAttribute(c.getField(var).getName(), value,
 			    toScope);
 		} catch (NoSuchFieldException nsf) {
 		    log.error(nsf.getMessage());
 		    throw new JspException(nsf);
 		}
 	    }
 	} catch (IllegalAccessException iae) {
 	    log.error("Illegal Access Exception - maybe a classloader issue?");
 	    throw new JspException(iae);
 	}
 
 	// Continue processing this page
 	return (SKIP_BODY);
     }
 
     public void setClassName(String clazz) {
 	this.clazz = clazz;
     }
 
     public String getClassName() {
 	return this.clazz;
     }
 
     public void setScope(String scope) {
 	this.scope = scope;
     }
 
     public String getScope() {
 	return (this.scope);
     }
 
     public void setVar(String var) {
 	this.var = var;
     }
 
     public String getVar() {
 	return (this.var);
     }
 
     /**
      * Release all allocated resources.
      */
     @Override
     public void release() {
 	super.release();
 	clazz = null;
 	scope = Constants.class.getName();
     }
 
     /**
      * Maps lowercase JSP scope names to their PageContext integer constant
      * values.
      */
     private static final Map<String, Integer> SCOPES = new HashMap<String, Integer>();
 
     /**
      * Initialize the scope names map and the encode variable
      */
     static {
 	SCOPES.put("page", PageContext.PAGE_SCOPE);
 	SCOPES.put("request", PageContext.REQUEST_SCOPE);
 	SCOPES.put("session", PageContext.SESSION_SCOPE);
 	SCOPES.put("application", PageContext.APPLICATION_SCOPE);
     }
 
     /**
      * Converts the scope name into its corresponding PageContext constant
      * value.
      * 
      * @param scopeName
      *                Can be "page", "request", "session", or "application" in
      *                any case.
      * @return The constant representing the scope (ie.
      *         PageContext.REQUEST_SCOPE).
      * @throws JspException
      *                 if the scopeName is not a valid name.
      */
     public int getScope(String scopeName) throws JspException {
 	Integer scope = SCOPES.get(scopeName.toLowerCase());
 
 	if (scope == null) {
 	    throw new JspException("Scope '" + scopeName
 		    + "' not a valid option");
 	}
 
 	return scope;
     }
 }