package org.kuali.student.enrollment.dao;

 import org.kuali.student.r2.common.exceptions.DoesNotExistException;

 import java.io.Serializable;

 import java.lang.reflect.ParameterizedType;

 import java.lang.reflect.Type;

 import java.util.ArrayList;

 import java.util.List;

 import javax.persistence.EntityManager;

 import javax.persistence.PersistenceContext;

 /**

  * @author Igor

  */

 public class GenericEntityDao<T> implements EntityDao<T> {

     /**

      * Entity class.

      */

     protected Class<T> entityClass;

     @PersistenceContext

     protected EntityManager em;

     public GenericEntityDao() {

         entityClass = getEntityClass();

     }

     @Override

     public T find(Serializable primaryKey) {

         return em.find(entityClass, primaryKey);

     }

     @Override

     public List<T> findByIds(List<? extends Serializable> primaryKeys) throws DoesNotExistException {

         List<T> resultList = new ArrayList<T>();

         for (Serializable primaryKey : primaryKeys) {

             T entity = find(primaryKey);

             if (entity == null) {

                 throw new DoesNotExistException("No data was found for :" + primaryKey);

             }

             resultList.add(entity);

         }

         return resultList;

     }

     @Override

     @SuppressWarnings("unchecked")

     public List<T> findAll() {

         return (List<T>) em.createQuery("from " + entityClass.getSimpleName()).getResultList();

     }

     @Override

     public void persist(T entity) {

         em.persist(entity);

     }

     @Override

     public void update(T entity) {

         em.merge(entity);

     }

     @Override

     public void remove(T entity) {

         em.remove(entity);

     }

     @Override

     public T merge(T entity) {

         return em.merge(entity);

     }

     @SuppressWarnings("unchecked")

     protected <K extends T> Class<K> getEntityClass() {

         if (entityClass == null) {

             entityClass = (Class<T>) getEntityType(this);

         }

         return (Class<K>) entityClass;

     }

     private Type getEntityType(Object object) {

         Type type = object.getClass().getGenericSuperclass();

         if (type instanceof ParameterizedType) {

             ParameterizedType paramType = (ParameterizedType) type;

             Type result = paramType.getActualTypeArguments()[0];

             return result;

         } else {

             throw new IllegalArgumentException("Could not guess entity type by reflection.");

         }

     }

     public void setEm(EntityManager em) {

         this.em = em;

     }

     public EntityManager getEm() {

         return em;

     }

 }