package nu.xss.jpa.dao;

import java.io.Serializable;
import java.lang.reflect.ParameterizedType;
import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
import javax.persistence.NonUniqueResultException;
import javax.persistence.PersistenceContext;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;

import nu.xss.jpa.entity.TypedEntity;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public abstract class GenericJpaDao<E extends TypedEntity<K>, K> implements
		Dao<E, K>, Serializable {

	private static final long serialVersionUID = 4998055731089977476L;
	protected final Logger logger = LoggerFactory.getLogger(this.getClass());

	@PersistenceContext
	protected EntityManager entityManager;

	protected Class<E> entity;

	@SuppressWarnings("unchecked")
	public GenericJpaDao() {
		ParameterizedType genericSuperclass = (ParameterizedType) getClass()
				.getGenericSuperclass();
		this.entity = (Class<E>) genericSuperclass.getActualTypeArguments()[0];
	}

	public void save(E entity) {
		logger.info("Persist Entity: {}.", entity.toString());
		entityManager.persist(entity);
		entityManager.flush();
		logger.info("Saved entity: {}.", entity.toString());
	}

	public void merge(E entity) {
		logger.info("Merge Entity: {}.", entity.toString());
		entityManager.merge(entity);
		entityManager.flush();
		logger.info("Saved entity: {}.", entity.toString());
	}

	public void delete(E entity) {
		entityManager.remove(entity);
		logger.info("Deleted entity: {}.", entity.toString());
	}

	public E findById(K id) {
		return entityManager.find(entity, id);
	}

	public List<E> findAll() {
		return find(createSimpleQuery());
	}
	
	protected CriteriaBuilder getCriteriaBuilder() {
		return entityManager.getCriteriaBuilder();
	}

	protected CriteriaQuery<E> createQuery() {
		CriteriaQuery<E> c = getCriteriaBuilder().createQuery(this.entity);
		return c;
	}

	protected CriteriaQuery<E> createSimpleQuery() {
		CriteriaQuery<E> c = getCriteriaBuilder().createQuery(this.entity);
		Root<E> root = c.from(this.entity);
		c.select(root);
		return c;
	}

	protected List<E> find(CriteriaQuery<E> query) {
		return entityManager.createQuery(query).getResultList();
	}

	protected E findSingle(CriteriaQuery<E> query) {
		return entityManager.createQuery(query).getSingleResult();
	}

	protected E findSingleOrNull(CriteriaQuery<E> query) {
		try {
			return findSingle(query);
		} catch (final NoResultException e) {
			return null;
		} catch (final NonUniqueResultException e) {
			logger.error("Found more than one result.. return first one");
			return null;
		}
	}

	protected E findSingleFirstOrNull(CriteriaQuery<E> query) {
		try {
			return findSingle(query);
		} catch (final NoResultException e) {
			return null;
		} catch (final NonUniqueResultException e) {
			logger.warn("Found more than one result.. return first one");
			return find(query).get(0);
		}
	}
}