/*
 * #!
 * Ontopia Navigator
 * #-
 * Copyright (C) 2001 - 2013 The Ontopia Project
 * #-
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * !#
 */

package net.ontopia.topicmaps.nav2.taglibs.logic;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import net.ontopia.topicmaps.nav2.core.FunctionIF;
import net.ontopia.topicmaps.nav2.core.NavigatorRuntimeException;
import net.ontopia.topicmaps.nav2.utils.FrameworkUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * INTERNAL: Logic Tag for loading and registering an external function.
 *
 * @see net.ontopia.topicmaps.nav2.taglibs.logic.CallTag
 */
public class ExternalFunctionTag extends TagSupport {

  // initialization of logging facility
  private static Logger log = LoggerFactory
    .getLogger(ExternalFunctionTag.class.getName());
  
  // tag attributes
  private String functionName;
  private String functionFQCN;
  
  /**
   * Process the start tag for this instance.
   */
  public int doStartTag() throws JspException {
    // get Context Tag
    ContextTag contextTag = FrameworkUtils.getContextTag(pageContext);
    
    // retrieve function object from central managed pool
    FunctionIF function = contextTag.getFunction(functionName);
    if (function == null) {
      // instantiate it fresh and put into central pool
      try {
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        function = (FunctionIF) Class.forName(functionFQCN, true, classLoader).newInstance();
        contextTag.registerFunction(functionName, function);
        if (log.isInfoEnabled())
          log.info("registered external function: " + function.toString());       
      } catch (InstantiationException e) {
        String msg = "ExternalFunctionTag: could not instantiate external" +
          " function " + functionFQCN + " with name '" + functionName +
          "'. Does it have a default constructor?";
        throw new NavigatorRuntimeException(msg, e);
      } catch (ClassNotFoundException e) {
        String msg = "ExternalFunctionTag function " + functionFQCN +
          " with name '" + functionName + "': " + e.getMessage() + " not found.";
        throw new NavigatorRuntimeException(msg, e);
      } catch (IllegalAccessException e) {
        String msg = "ExternalFunctionTag function " + functionFQCN +
          " with name '" + functionName + "': " + e.getMessage() + " can't be accessed.";
        throw new NavigatorRuntimeException(msg, e);
      }
    }
    // if still no function avail then throw exception
    if (function == null)
      throw new NavigatorRuntimeException("ExternalFunctionTag: function with name '" +
                                          functionName + "' not found.");

    // empty tag
    return SKIP_BODY;
  }

  /**
   * reset the state of the Tag.
   */
  public void release() {
    // overwrite default behaviour
    // do not set parent to null!!!
  }
  
  // -----------------------------------------------------------------
  // set methods for tag attributes
  // -----------------------------------------------------------------

  /**
   * INTERNAL: sets name of this function.
   */
  public void setName(String functionName) {
    this.functionName = functionName;
  }

  /**
   * INTERNAL: sets name of the class that implements the function and
   * should be called.
   */
  public void setFqcn(String fqcn) {
    this.functionFQCN = fqcn;
  }
  
}