CmsAliasToBeanResultTransformer

/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
 */
package it.netservice.cms.hibernate;

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.function.Function;

import org.hibernate.HibernateException;
import org.hibernate.property.access.internal.PropertyAccessStrategyBasicImpl;
import org.hibernate.property.access.internal.PropertyAccessStrategyChainedImpl;
import org.hibernate.property.access.internal.PropertyAccessStrategyFieldImpl;
import org.hibernate.property.access.internal.PropertyAccessStrategyMapImpl;
import org.hibernate.property.access.spi.Setter;
import org.hibernate.transform.AliasedTupleSubsetResultTransformer;

/**
 * Result transformer that allows to transform a result to a user specified
 * class which will be populated via setter methods or fields matching the alias
 * names.
 * <p/>
 * 
 * <pre>
 * List resultWithAliasedBean = s.createCriteria(Enrolment.class)
 * 			.createAlias("student", "st")
 * 			.createAlias("course", "co")
 * 			.setProjection( Projections.projectionList()
 * 					.add( Projections.property("co.description"), "courseDescription" )
 * 			)
 * 			.setResultTransformer( new AliasToBeanResultTransformer(StudentDTO.class) )
 * 			.list();
 * <p/>
 *  StudentDTO dto = (StudentDTO)resultWithAliasedBean.get(0);
 * </pre>
 *
 */
public class CmsAliasToBeanResultTransformer extends AliasedTupleSubsetResultTransformer {

	// IMPL NOTE : due to the delayed population of setters (setters cached
	// for performance), we really cannot properly define equality for
	// this transformer

	private static final long serialVersionUID = 1L;

	private final Class<?> resultClass;
	private boolean isInitialized;
	private String[] aliases;
	private Setter[] setters;
	
	public static class CmsTransformer<T extends Object, R extends Object> {
		
		private Function<T, R> t;

		public CmsTransformer(Class<T> input, Class<R> output, Function<T, R> t) {
			this.t = t;
		}
		
		@SuppressWarnings("unchecked")
		public R transform(Object input) {
			return t.apply((T)input);
		}
	}

	private final Map<String, CmsTransformer<? extends Object, ? extends Object>> mapTransformer;

	private List<String> aliasList;

	public CmsAliasToBeanResultTransformer(Class<?> resultClass, Map<String, CmsTransformer<? extends Object, ? extends Object>> mapTransformer) {
		this(resultClass, mapTransformer, null);
		
	}
	
	public CmsAliasToBeanResultTransformer(Class<?> resultClass, Map<String, CmsTransformer<? extends Object, ? extends Object>> mapTransformer, List<String> aliasList) {
		if (resultClass == null) {
			throw new IllegalArgumentException("resultClass cannot be null");
		}
		isInitialized = false;
		this.resultClass = resultClass;
		this.mapTransformer = mapTransformer;
		this.aliasList = aliasList;
	}

	@Override
	public boolean isTransformedValueATupleElement(String[] aliases, int tupleLength) {
		return false;
	}
	
	@Override
	public Object transformTuple(Object[] tuple, String[] _aliases) {
		Object result;

		String[] aliases;
		if (this.aliasList == null) {
			aliases = _aliases;
		} else {
			aliases = (String[]) aliasList.toArray(new String[aliasList.size()]);
		}
		
		try {
			if (!isInitialized) {
				initialize(aliases);
			} else {
				check(aliases);
			}

			result = resultClass.newInstance();

			for (int i = 0; i < aliases.length; i++) {
				Setter setter = setters[i];
				if (setter != null) {
//					Class<?> setterType = setter.getMethod().getParameterTypes()[0];
					Object el = tuple[i];
					String alias = aliases[i];
					if (mapTransformer.containsKey(alias)) {
						CmsTransformer<? extends Object, ? extends Object> transformer = mapTransformer.get(alias);
						Object transformerResult = transformer.transform(el);
						setter.set(result, transformerResult, null);
					} else {
						setter.set(result, el, null);
					}
				}
			}
		} catch (InstantiationException e) {
			throw new HibernateException("Could not instantiate resultclass: " + resultClass.getName());
		} catch (IllegalAccessException e) {
			throw new HibernateException("Could not instantiate resultclass: " + resultClass.getName());
		}

		return result;
	}

	private void initialize(String[] aliases) {
		PropertyAccessStrategyChainedImpl propertyAccessStrategy = new PropertyAccessStrategyChainedImpl(
		    PropertyAccessStrategyBasicImpl.INSTANCE,
		    PropertyAccessStrategyFieldImpl.INSTANCE,
		    PropertyAccessStrategyMapImpl.INSTANCE);
		this.aliases = new String[aliases.length];
		setters = new Setter[aliases.length];
		for (int i = 0; i < aliases.length; i++) {
			String alias = aliases[i];
			if (alias != null) {
				this.aliases[i] = alias;
				setters[i] = propertyAccessStrategy.buildPropertyAccess(resultClass, alias).getSetter();
			}
		}
		isInitialized = true;
	}

	private void check(String[] aliases) {
		if (!Arrays.equals(aliases, this.aliases)) {
			throw new IllegalStateException(
			    "aliases are different from what is cached; aliases=" + Arrays.asList(aliases) +
			        " cached=" + Arrays.asList(this.aliases));
		}
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}

		CmsAliasToBeanResultTransformer that = (CmsAliasToBeanResultTransformer) o;

		if (!resultClass.equals(that.resultClass)) {
			return false;
		}
		if (!Arrays.equals(aliases, that.aliases)) {
			return false;
		}

		return true;
	}

	@Override
	public int hashCode() {
		int result = resultClass.hashCode();
		result = 31 * result + (aliases != null ? Arrays.hashCode(aliases) : 0);
		return result;
	}
}