/* 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.activiti.engine.impl.variable;

import java.lang.reflect.Field;
import java.lang.reflect.Method;

import javax.persistence.Entity;
import javax.persistence.Id;

import org.activiti.engine.ActivitiException;


/**
 * Scans class and creates {@link EntityMetaData} based on it. 
 * 
 * @author Frederik Heremans
 */
public class JPAEntityScanner {

  public EntityMetaData scanClass(Class<?> clazz) {
    EntityMetaData metaData = new EntityMetaData();
    metaData.setEntityClass(clazz);
    
    // Class should have @Entity annotation
    boolean isEntity = isEntityAnnotationPresent(clazz);
    metaData.setJPAEntity(isEntity);
    
    if(isEntity) {
      // Try to find a field annotated with @Id
      Field idField = getIdField(clazz);
      if(idField != null) {
        metaData.setIdField(idField);
      } else {
        // Try to find a method annotated with @Id
        Method idMethod = getIdMethod(clazz);
        if(idMethod != null) {
          metaData.setIdMethod(idMethod);
        } else {
          throw new ActivitiException("Cannot find field or method with annotation @Id on class '" +
            clazz.getName() + "', only single-valued primary keys are supported on JPA-enities");
        }
      }
    }
    return metaData;
  }

  private Method getIdMethod(Class< ? > clazz) {
    Method idMethod = null;
    // Get all public declared methods on the class. According to spec, @Id should only be 
    // applied to fields and property get methods
    Method[] methods = clazz.getMethods();
    Id idAnnotation = null;
    for(Method method : methods) {
      idAnnotation = method.getAnnotation(Id.class);
      if(idAnnotation != null) {
        idMethod = method;
        break;
      }
    }
    return idMethod;
  }

  private Field getIdField(Class<?> clazz) {
   Field idField = null;
   Field[] fields = clazz.getDeclaredFields();
   Id idAnnotation = null;
   for(Field field : fields) {
     idAnnotation = field.getAnnotation(Id.class);
     if(idAnnotation != null) {
       idField = field;
       break;
     }
   }
   
   if(idField == null) {
     // Check superClass for fields with @Id, since getDeclaredFields does
     // not return superclass-fields.
     Class<?> superClass = clazz.getSuperclass();
     if(superClass != null && !superClass.equals(Object.class)) {
       // Recursively go up class hierarchy
       idField = getIdField(superClass);
     }
   }
   return idField;
  }

  private boolean isEntityAnnotationPresent(Class<?> clazz) {
    return (clazz.getAnnotation(Entity.class) != null);
  }
}