// Copyright 2008 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.tapestry5.internal.transform;

 import org.apache.tapestry5.Binding;

 import org.apache.tapestry5.BindingConstants;

 import org.apache.tapestry5.annotations.Cached;

 import org.apache.tapestry5.ioc.util.BodyBuilder;

 import org.apache.tapestry5.model.MutableComponentModel;

 import org.apache.tapestry5.services.*;

 import static java.lang.reflect.Modifier.PRIVATE;

 import java.util.List;

 /**

  * Caches method return values for methods annotated with {@link Cached}.

  */

 public class CachedWorker implements ComponentClassTransformWorker

 {

     private final BindingSource bindingSource;

     public CachedWorker(BindingSource bindingSource)

     {

         this.bindingSource = bindingSource;

     }

     public void transform(ClassTransformation transformation, MutableComponentModel model)

     {

         List<TransformMethodSignature> methods = transformation.findMethodsWithAnnotation(Cached.class);

         if (methods.isEmpty())

             return;

         for (TransformMethodSignature method : methods)

         {

             if (method.getReturnType().equals("void"))

                 throw new IllegalArgumentException(TransformMessages.cachedMethodMustHaveReturnValue(method));

             if (method.getParameterTypes().length != 0)

                 throw new IllegalArgumentException(TransformMessages.cachedMethodsHaveNoParameters(method));

             String propertyName = method.getMethodName();

             // add a property to store whether or not the method has been called

             String fieldName = transformation.addField(PRIVATE, method.getReturnType(), propertyName);

             String calledField = transformation.addField(PRIVATE, "boolean", fieldName + "$called");

             Cached once = transformation.getMethodAnnotation(method, Cached.class);

             String bindingField = null;

             String bindingValueField = null;

             boolean watching = once.watch().length() > 0;

             if (watching)

             {

                 // add fields to store the binding and the value

                 bindingField = transformation.addField(PRIVATE, Binding.class.getCanonicalName(),

                                                        fieldName + "$binding");

                 bindingValueField = transformation.addField(PRIVATE, "java.lang.Object", fieldName + "$bindingValue");

                 String bindingSourceField = transformation.addInjectedField(BindingSource.class,

                                                                             fieldName + "$bindingsource",

                                                                             bindingSource);

                 String body = String.format("%s = %s.newBinding(\"Watch expression\", %s, \"%s\", \"%s\");",

                                             bindingField,

                                             bindingSourceField,

                                             transformation.getResourcesFieldName(),

                                             BindingConstants.PROP,

                                             once.watch());

                 transformation.extendMethod(TransformConstants.CONTAINING_PAGE_DID_LOAD_SIGNATURE, body);

             }

             BodyBuilder b = new BodyBuilder();

             // on cleanup, reset the field values

             b.begin();

             if (!TransformUtils.isPrimitive(method.getReturnType()))

                 b.addln("%s = null;", fieldName);

             b.addln("%s = false;", calledField);

             if (watching)

                 b.addln("%s = null;", bindingValueField);

             b.end();

             // TAPESTRY-2338: Cleanup at page detach, not render cleanup.  In an Ajax request, the rendering

             // objects may reference properties of components that don't render and so won't execute the

             // PostCleanupRender phase.

             transformation.extendMethod(TransformConstants.CONTAINING_PAGE_DID_DETACH_SIGNATURE, b.toString());

             // prefix the existing method to cache the result

             b.clear();

             b.begin();

             // if it has been called and watch is set and the old value is the same as the new value then return

             // get the old value and cache it

             /* NOTE: evaluates the binding twice when checking the new value.

                 * this is probably not a problem because in most cases properties

                 * that are being watched are not expensive operations. plus, we

                 * never guaranteed that it would be called exactly once when

                 * watching.

                 */

             if (watching)

             {

                 b.addln("if (%s && %s == %s.get()) return %s;",

                         calledField, bindingValueField, bindingField, fieldName);

                 b.addln("%s = %s.get();", bindingValueField, bindingField);

             }

             else

             {

                 b.addln("if (%s) return %s;", calledField, fieldName);

             }

             b.addln("%s = true;", calledField);

             b.end();

             transformation.prefixMethod(method, b.toString());

             // cache the return value

             b.clear();

             b.begin();

             b.addln("%s = $_;", fieldName);

             b.end();

             transformation.extendExistingMethod(method, b.toString());

         }

     }

 }