package org.kuali.student.enrollment.lpr.dao;
   
   import org.springframework.orm.jpa.JpaTemplate;
   import org.springframework.orm.jpa.support.JpaDaoSupport;
   
   import javax.persistence.EntityManager;
   import javax.persistence.PersistenceContext;
   import javax.persistence.PersistenceContextType;
   import java.io.Serializable;
  import java.lang.reflect.ParameterizedType;
  import java.lang.reflect.Type;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * @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) {
          List<T> resultList = new ArrayList<T>();
          for (Serializable primaryKey : primaryKeys) {
              resultList.add(find(primaryKey));
          }
          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.refresh(entity);
      }
  
      @Override
      public void remove(T entity) {
         em.remove(entity);
      }
  
      @Override
      public <T> 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;
      }
  }