/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 freemarker.template;

import java.io.IOException;

An interface that can be implemented by writers returned from TemplateTransformModel.getWriter(Writer, Map). The methods on this interfaces are callbacks that will be called by the template engine and that give the writer a chance to better control the evaluation of the transform body. The writer can instruct the engine to skip or to repeat body evaluation, and gets notified about exceptions that are thrown during the body evaluation. /**
 * An interface that can be implemented by writers returned from
 * {@link TemplateTransformModel#getWriter(java.io.Writer, java.util.Map)}. The
 * methods on this
 * interfaces are callbacks that will be called by the template engine and that
 * give the writer a chance to better control the evaluation of the transform
 * body. The writer can instruct the engine to skip or to repeat body 
 * evaluation, and gets notified about exceptions that are thrown during the
 * body evaluation.
 */
public interface TransformControl {
    
Constant returned from afterBody() that tells the template engine to repeat transform body evaluation and feed it again to the transform. /**
     * Constant returned from {@link #afterBody()} that tells the
     * template engine to repeat transform body evaluation and feed
     * it again to the transform.
     */
    public static final int REPEAT_EVALUATION = 0;

    
Constant returned from afterBody() that tells the template engine to end the transform and close the writer. /**
     * Constant returned from {@link #afterBody()} that tells the
     * template engine to end the transform and close the writer.
     */
    public static final int END_EVALUATION = 1;
 
    
Constant returned from onStart() that tells the template engine to skip evaluation of the body. /**
     * Constant returned from {@link #onStart()} that tells the
     * template engine to skip evaluation of the body.
     */
    public static final int SKIP_BODY = 0;
    
    
Constant returned from onStart() that tells the template engine to evaluate the body. /**
     * Constant returned from {@link #onStart()} that tells the
     * template engine to evaluate the body.
     */
    public static final int EVALUATE_BODY = 1;

    
Called before the body is evaluated for the first time.
Returns:


SKIP_BODY if the transform wants to ignore the body. In this case, only Writer.close() is called next and processing ends.
EVALUATE_BODY to normally evaluate the body of the transform
and feed it to the writer
/**
     * Called before the body is evaluated for the first time.
     * @return 
     * <ul>
     * <li><tt>SKIP_BODY</tt> if the transform wants to ignore the body. In this
     * case, only {@link java.io.Writer#close()} is called next and processing ends.</li>
     * <li><tt>EVALUATE_BODY</tt> to normally evaluate the body of the transform
     * and feed it to the writer</li>
     * </ul>
     */
    public int onStart() throws TemplateModelException, IOException;
    
    
Called after the body has been evaluated.
Returns:


END_EVALUATION if the transformation should be ended.
REPEAT_EVALUATION to have the engine re-evaluate the 
transform body and feed it again to the writer.
/**
     * Called after the body has been evaluated.
     * @return

     * <ul>
     * <li><tt>END_EVALUATION</tt> if the transformation should be ended.</li>
     * <li><tt>REPEAT_EVALUATION</tt> to have the engine re-evaluate the 
     * transform body and feed it again to the writer.</li>
     * </ul>
     */
    public int afterBody() throws TemplateModelException, IOException;
    
    
Called if any exception occurs during the transform between the TemplateTransformModel.getWriter(Writer, Map) call and the Writer.close() call. 
Params:
t – the throwable that represents the exception. It can be any non-checked throwable, as well as TemplateException and IOException.
Throws:
Throwable – is recommended that the methods rethrow the received throwable. If the method wants to throw another throwable, it should either throw a non-checked throwable, or an instance of TemplateException and IOException. Throwing any other checked exception will cause the engine to rethrow it as a UndeclaredThrowableException./**
     * Called if any exception occurs during the transform between the
     * {@link TemplateTransformModel#getWriter(java.io.Writer, java.util.Map)} call
     * and the {@link java.io.Writer#close()} call.
     * @param t the throwable that represents the exception. It can be any 
     * non-checked throwable, as well as {@link TemplateException} and 
     * {@link java.io.IOException}.
     * 
     * @throws Throwable is recommended that the methods rethrow the received 
     * throwable. If the method wants to throw another throwable, it should
     * either throw a non-checked throwable, or an instance of 
     * {@link TemplateException} and {@link java.io.IOException}. Throwing any
     * other checked exception will cause the engine to rethrow it as
     * a {@link java.lang.reflect.UndeclaredThrowableException}.
     */
    public void onError(Throwable t) throws Throwable;
}