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Freemarker support for APT-Jelly
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/*
 * Copyright 2006 Ryan Heaton
 *
 * 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.sf.jelly.apt.freemarker;

import freemarker.ext.beans.BeansWrapper;
import freemarker.template.TemplateModel;
import freemarker.template.TemplateModelException;
import freemarker.template.TemplateTransformModel;
import net.sf.jelly.apt.strategies.TemplateStrategyControl;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.io.IOException;
import java.io.Writer;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Map;

/**
 * Base class for freemarker transforms.
 *
 * @author Ryan Heaton
 */
public abstract class FreemarkerTransform implements TemplateTransformModel {

  private String namespace;

  /**
   * Construct a new transform under the specified namespace.  null or "" means the root namespace.
   *
   * @param namespace The namespace.
   */
  protected FreemarkerTransform(String namespace) {
    this.namespace = namespace;
  }

  //Inherited.
  public Writer getWriter(Writer out, Map args) throws TemplateModelException, IOException {
    S strategy = newStrategy();
    setupStrategy(strategy, args);
    return new FreemarkerTemplateBlock(out, strategy, getTransformName());
  }

  /**
   * Setup the strategy given the specified arguments to the template transform.
   *
   * @param strategy The strategy to set up.
   * @param args The arguments to the transform.
   */
  protected void setupStrategy(S strategy, Map args) throws TemplateModelException {
    //set up the strategy
    for (Object key : args.keySet()) {
      String property = (String) key;
      Object value = args.get(property);

      value = unwrap((TemplateModel) value, property);
      Method method = findSetter(property, strategy);

      if ((value instanceof String) && (!method.getParameterTypes()[0].isAssignableFrom(String.class))) {
        value = convertString(((String)value), method.getParameterTypes()[0]);
        if (value == null) {
          throw new TemplateModelException("The '" + getTransformName() + "' transform doesn't support the '" + property + "' attribute of type String.");
        }
      }

      try {
        method.invoke(strategy, value);
      }
      catch (IllegalArgumentException e) {
        throw new TemplateModelException("The '" + getTransformName() + "' transform doesn't support the '" + property + "' attribute of type " +
          value.getClass().getSimpleName() + ".");
      }
      catch (Exception e) {
        throw new TemplateModelException(e);
      }
    }
  }

  /**
   * Attempts to convert a string value to a given class using the "valueOf" method or "fromString" method.
   *
   * @param value The value to convert.
   * @param toClass The class to convert to.
   */
  protected Object convertString(String value, Class toClass) {

    if ((toClass == Boolean.TYPE) || (toClass == Boolean.class)) {
      return Boolean.valueOf(value);
    }
    else if ((toClass == Integer.TYPE) || (toClass == Integer.class)) {
      return Integer.valueOf(value);
    }
    else if ((toClass == Long.TYPE) || (toClass == Long.class)) {
      return Long.valueOf(value);
    }
    else if (Enum.class.isAssignableFrom(toClass)) {
      return Enum.valueOf(toClass, value);
    }
    else if ((toClass == Short.TYPE) || (toClass == Short.class)) {
      return Short.valueOf(value);
    }
    else if ((toClass == Double.TYPE) || (toClass == Double.class)) {
      return Double.valueOf(value);
    }
    else if ((toClass == Float.TYPE) || (toClass == Float.class)) {
      return Float.valueOf(value);
    }
    else {
      //try the "fromString" method, too.
      try {
        Method conversion = toClass.getMethod("fromString", String.class);
        if ((Modifier.isStatic(conversion.getModifiers())) && (toClass.isAssignableFrom(conversion.getReturnType()))) {
          return conversion.invoke(null, value);
        }
      }
      catch (Exception e) {
        //fall through...
      }
    }

    return null;
  }

  /**
   * Unwrap the specified value of the given property.
   *
   * @param value The value to unwrap.
   * @param property The property.
   * @return The unwrapped object.
   */
  protected Object unwrap(TemplateModel value, String property) throws TemplateModelException {
    try {
      return BeansWrapper.getDefaultInstance().unwrap(value);
    }
    catch (TemplateModelException e) {
      throw new TemplateModelException("Unsupported value for parameter '" + property + "' on transform '" + getTransformName() + "': " +
        value.getClass().getName());
    }
  }

  /**
   * Finds the setter for the given property on the specified strategy.
   *
   * @param property The property.
   * @param strategy The strategy.
   * @return The setter, or null if not found.
   */
  protected Method findSetter(String property, S strategy) throws TemplateModelException {
    try {
      BeanInfo beanInfo = Introspector.getBeanInfo(strategy.getClass());
      for (PropertyDescriptor descriptor : beanInfo.getPropertyDescriptors()) {
        if (descriptor.getName().equals(property)) {
          return descriptor.getWriteMethod();
        }
      }
    }
    catch (IntrospectionException e) {
      //fall through....
    }

    throw new TemplateModelException("The '" + getTransformName() + "' transform doesn't support the '" + property + "' attribute");
  }

  /**
   * Instantiate a new strategy instance.
   *
   * @return The strategy.
   */
  public abstract S newStrategy();

  /**
   * The name of the transform.  Default implementation uses the name of the class.
   *
   * @return The name of the transform.
   */
  public String getTransformName() {
    String transformName = getClass().getSimpleName();
    return Introspector.decapitalize(transformName.substring(0, transformName.lastIndexOf("Transform")));
  }

  /**
   * The namespace of the transform.  null or "" means the root namespace.
   * 
   * @return The namespace of the transform.
   */
  public String getTransformNamespace() {
    return namespace;
  }

}