/*
 * 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 org.hibernate.engine.query.spi;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.persistence.AttributeNode;
import javax.persistence.EntityGraph;
import javax.persistence.Subgraph;

import org.hibernate.QueryException;
import org.hibernate.engine.internal.JoinSequence;
import org.hibernate.hql.internal.ast.HqlSqlWalker;
import org.hibernate.hql.internal.ast.tree.FromClause;
import org.hibernate.hql.internal.ast.tree.FromElement;
import org.hibernate.hql.internal.ast.tree.FromElementFactory;
import org.hibernate.hql.internal.ast.tree.ImpliedFromElement;
import org.hibernate.persister.collection.QueryableCollection;
import org.hibernate.sql.JoinType;
import org.hibernate.type.CollectionType;
import org.hibernate.type.EntityType;
import org.hibernate.type.Type;

import static org.hibernate.jpa.QueryHints.HINT_FETCHGRAPH;
import static org.hibernate.jpa.QueryHints.HINT_LOADGRAPH;

Encapsulates a JPA EntityGraph provided through a JPQL query hint.  Converts the fetches into a list of AST
FromElements.  The logic is kept here as much as possible in order to make it easy to remove this in the future,
once our AST is improved and this "hack" is no longer needed.
Author:
Brett Meyer/**
 * Encapsulates a JPA EntityGraph provided through a JPQL query hint.  Converts the fetches into a list of AST
 * FromElements.  The logic is kept here as much as possible in order to make it easy to remove this in the future,
 * once our AST is improved and this "hack" is no longer needed.
 *
 * @author Brett Meyer
 */
public class EntityGraphQueryHint {
	private final String hintName;
	private final EntityGraph<?> originEntityGraph;

	public EntityGraphQueryHint(String hintName, EntityGraph<?> originEntityGraph) {
		assert hintName != null;
		assert HINT_FETCHGRAPH.equals( hintName ) || HINT_LOADGRAPH.equals( hintName );

		this.hintName = hintName;
		this.originEntityGraph = originEntityGraph;
	}

	public String getHintName() {
		return hintName;
	}

	public EntityGraph<?> getOriginEntityGraph() {
		return originEntityGraph;
	}

	public List<FromElement> toFromElements(FromClause fromClause, HqlSqlWalker walker) {
		// If a role already has an explicit fetch in the query, skip it in the graph.
		Map<String, FromElement> explicitFetches = new HashMap<String, FromElement>();
		for ( Object o : fromClause.getFromElements() ) {
			final FromElement fromElement = (FromElement) o;
			if ( fromElement.getRole() != null  && ! (fromElement instanceof ImpliedFromElement) ) {
				explicitFetches.put( fromElement.getRole(), fromElement );
			}
		}

		return getFromElements(
				fromClause.getLevel() == FromClause.ROOT_LEVEL ? originEntityGraph.getAttributeNodes():
					Collections.emptyList(),
				fromClause.getFromElement(),
				fromClause,
				walker,
				explicitFetches
		);
	}

	private List<FromElement> getFromElements(
			List attributeNodes,
			FromElement origin,
			FromClause fromClause,
			HqlSqlWalker walker,
			Map<String, FromElement> explicitFetches) {
		final List<FromElement> fromElements = new ArrayList<FromElement>();

		for ( Object obj : attributeNodes ) {
			final AttributeNode<?> attributeNode = (AttributeNode<?>) obj;

			final String attributeName = attributeNode.getAttributeName();
			final String className = origin.getClassName();
			// TODO: This is ignored by collection types and probably wrong for entity types.  Presumably it screws
			// with inheritance.
			final String role = className + "." + attributeName;
			final String classAlias = origin.getClassAlias();
			final String originTableAlias = origin.getTableAlias();
			final Type propertyType = origin.getPropertyType( attributeName, attributeName );

			try {
				FromElement fromElement = explicitFetches.get( role );
				boolean explicitFromElement = false;
				if ( fromElement == null ) {
					if ( propertyType.isEntityType() ) {
						final EntityType entityType = (EntityType) propertyType;

						final String[] columns = origin.toColumns( originTableAlias, attributeName, false );
						final String tableAlias = walker.getAliasGenerator().createName(
								entityType.getAssociatedEntityName()
						);

						final FromElementFactory fromElementFactory = new FromElementFactory(
								fromClause, origin,
								attributeName, classAlias, columns, false
						);
						final JoinSequence joinSequence = walker.getSessionFactoryHelper().createJoinSequence(
								false, entityType, tableAlias, JoinType.LEFT_OUTER_JOIN, columns
						);
						fromElement = fromElementFactory.createEntityJoin(
								entityType.getAssociatedEntityName(),
								tableAlias,
								joinSequence,
								true,
								walker.isInFrom(),
								entityType,
								role,
								null
						);
					}
					else if ( propertyType.isCollectionType() ) {
						CollectionType collectionType = (CollectionType) propertyType;
						final String[] columns = origin.toColumns( originTableAlias, attributeName, false );

						final FromElementFactory fromElementFactory = new FromElementFactory(
								fromClause, origin,
								attributeName, classAlias, columns, false
						);
						final QueryableCollection queryableCollection = walker.getSessionFactoryHelper()
								.requireQueryableCollection( collectionType.getRole() );
						fromElement = fromElementFactory.createCollection(
								queryableCollection, collectionType.getRole(), JoinType.LEFT_OUTER_JOIN, true, false
						);
					}
				}
				else {
					explicitFromElement = true;
					fromElement.setInProjectionList( true );
					fromElement.setFetch( true );
				}

				if ( fromElement != null ) {
					if( !explicitFromElement ){
						fromElements.add( fromElement );
					}

					// recurse into subgraphs
					for ( Subgraph<?> subgraph : attributeNode.getSubgraphs().values() ) {
						fromElements.addAll(
								getFromElements(
										subgraph.getAttributeNodes(), fromElement,
										fromClause, walker, explicitFetches
								)
						);
					}
				}
			}
			catch (Exception e) {
				throw new QueryException( "Could not apply the EntityGraph to the Query!", e );
			}
		}

		return fromElements;
	}
}