/*

  * Copyright 1999-2001,2004 The Apache Software Foundation.

  * 

  * 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 org.apache.commons.workflow.core;

 import java.util.EmptyStackException;

 import org.apache.commons.workflow.Block;

 import org.apache.commons.workflow.BlockState;

 import org.apache.commons.workflow.Context;

 import org.apache.commons.workflow.Descriptor;

 import org.apache.commons.workflow.Iterator;

 import org.apache.commons.workflow.Step;

 import org.apache.commons.workflow.StepException;

 import org.apache.commons.workflow.base.BaseBlock;

 /**

  * <p>Repeatedly evaluate the properties specified by the associated

  * Descriptors, and execute the nested Steps if and only if

  * <strong>ALL</strong> of them evaluate to a positive result.

  * To avoid non-deterministic evaluation

  * stack behavior, all of the specified Descriptors are always

  * evaluated exactly once.</p>

  *

  * @version $Revision: 155475 $ $Date: 2005-02-26 13:31:11 +0000 (Sat, 26 Feb 2005) $

  * @author Craig R. McClanahan

  */

 public class WhileStep extends BaseBlock implements Iterator {

     // ----------------------------------------------------------= Constructors

     /**

      * Construct a default instance of this Step.

      */

     public WhileStep() {

         super();

     }

     /**

      * Construct an instance of this Step with the specified identifier.

      *

      * @param id Step identifier

      */

     public WhileStep(String id) {

         this(id, null);

     }

     /**

      * Construct a fully configured instance of this Step.

      *

      * @param id Step identifier of this step

      * @param descriptor Initial descriptor to be added

      */

     public WhileStep(String id, Descriptor descriptor) {

         super();

         setId(id);

         if (descriptor != null)

             addDescriptor(descriptor);

     }

     // --------------------------------------------------------- Public Methods

     /**

      * Render a string representation of this Step.

      */

     public String toString() {

         StringBuffer sb = new StringBuffer("<core:while");

         if (getId() != null) {

             sb.append(" id=\"");

             sb.append(getId());

             sb.append("\"");

         }

         sb.append(">");

         Descriptor descriptors[] = findDescriptors();

         for (int i = 0; i < descriptors.length; i++)

             sb.append(descriptors[i]);

         Step steps[] = getSteps();

         for (int i = 0; i < steps.length; i++)

             sb.append(steps[i]);

         sb.append("</core:while>");

         return (sb.toString());

     }

     // ------------------------------------------------------ Protected Methods

     /**

      * Evaluate the condition specified by the Descriptors associated with

      * this Block, and return the resulting boolean value.

      *

      * @param context Context within which to evaluate the descriptors

      */

     protected boolean evaluate(Context context) {

         boolean condition = true;

         Descriptor descriptors[] = findDescriptors();

         for (int i = 0; i < descriptors.length; i++) {

             if (descriptors[i] == null)

                 continue;

             if (!descriptors[i].positive(context))

                 condition = false;

         }

         return (condition);

     }

     /**

      * Process the initial entry into this Block.

      *

      * @param context Context within which to evaluate the condition

      */

     protected void initial(Context context) {

         if (evaluate(context)) {

             BlockState state = new BlockState(this, true);

             context.pushBlockState(state);

             context.setNextStep(getFirstStep());

         } else {

             context.setNextStep(getNextStep());

         }

     }

     /**

      * Process the return from nested execution of the Steps assocaited

      * with this Block.

      *

      * @param context Context within which to evaluate the condition

      * @param state BlockState for our block

      */

     protected void subsequent(Context context, BlockState state) {

         // Was a "break" Step executed within this Block?

         if (!state.getNest()) {

             context.popBlockState();

             context.setNextStep(getNextStep());

             return;

         }

         // Re-evaluate the loop conditions

         if (evaluate(context)) {

             context.setNextStep(getFirstStep());

         } else {

             context.popBlockState();

             context.setNextStep(getNextStep());

         }

     }

 }