/*******************************************************************************
 * Copyright (c) 2011, 2014 Oracle and/or its affiliates. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Oracle - initial API and implementation
 *
 ******************************************************************************/
package org.eclipse.persistence.jpa.jpql.tools.model;

import org.eclipse.persistence.jpa.jpql.parser.*;
import org.eclipse.persistence.jpa.jpql.tools.model.query.JPQLQueryStateObject;
import org.eclipse.persistence.jpa.jpql.tools.model.query.StateObject;
import org.eclipse.persistence.jpa.jpql.tools.spi.IManagedTypeProvider;

/**
 * An abstract implementation of {@link IJPQLQueryBuilder} that parses a JPQL query or any JPQL
 * fragments and creates the {@link StateObject} representation by delegating the creation to an
 * instance of {@link BasicStateObjectBuilder}.
 *
 * @see DefaultJPQLQueryBuilder
 * @see EclipseLinkJPQLQueryBuilder
 *
 * @version 2.4
 * @since 2.4
 * @author Pascal Filion
 */
public abstract class AbstractJPQLQueryBuilder implements IJPQLQueryBuilder {

	/**
	 * Keeps a reference for future use.
	 */
	private BasicStateObjectBuilder builder;

	/**
	 * Creates a new <code>AbstractJPQLQueryBuilder</code>.
	 */
	protected AbstractJPQLQueryBuilder() {
		super();
	}

	/**
	 * {@inheritDoc}
	 */
	public ICaseExpressionStateObjectBuilder buildCaseExpressionStateObjectBuilder(StateObject parent) {
		return new DefaultCaseExpressionStateObjectBuilder(parent);
	}

	/**
	 * {@inheritDoc}
	 */
	public JPQLQueryStateObject buildStateObject(IManagedTypeProvider provider,
	                                             CharSequence jpqlQuery,
	                                             boolean tolerant) {

		return buildStateObject(provider, jpqlQuery, JPQLStatementBNF.ID, tolerant);
	}

	/**
	 * {@inheritDoc}
	 */
	public JPQLQueryStateObject buildStateObject(IManagedTypeProvider provider,
	                                             CharSequence jpqlQuery,
	                                             String queryBNFId,
	                                             boolean tolerant) {

		// First parse the JPQL query
		JPQLExpression jpqlExpression = parse(jpqlQuery, getGrammar(), tolerant);

		// Now visit the parsed expression and create the state object hierarchy
		BasicStateObjectBuilder builder = getStateObjectBuilder();

		try {
			builder.jpqlQueryBuilder    = this;
			builder.managedTypeProvider = provider;

			jpqlExpression.accept(wrap(builder));

			return builder.parent;
		}
		finally {
			builder.jpqlQueryBuilder    = null;
			builder.managedTypeProvider = null;
			builder.parent              = null;
			builder.stateObject         = null;
		}
	}

	/**
	 * {@inheritDoc}
	 */
	public StateObject buildStateObject(StateObject parent,
	                                    CharSequence jpqlFragment,
	                                    String queryBNFId) {

		// First parse the JPQL fragment
		JPQLExpression jpqlExpression = parse(jpqlFragment, parent.getGrammar(), queryBNFId);

		// We keep track of the old stuff because during the creation of a JPQLQueryStateObject,
		// it is possible the state model uses this builder to create some objects
		BasicStateObjectBuilder builder  = getStateObjectBuilder();
		IJPQLQueryBuilder oldBuilder     = builder.jpqlQueryBuilder;
		IManagedTypeProvider oldProvider = builder.managedTypeProvider;
		JPQLQueryStateObject oldParent   = builder.parent;
		StateObject oldStateObject       = builder.stateObject;

		try {
			builder.jpqlQueryBuilder    = this;
			builder.managedTypeProvider = parent.getManagedTypeProvider();
			builder.parent              = parent.getRoot();
			builder.stateObject         = parent;

			// Visit the Expression for which a StateObject is needed
			jpqlExpression.getQueryStatement().accept(wrap(builder));

			return builder.stateObject;
		}
		finally {
			builder.jpqlQueryBuilder    = oldBuilder;
			builder.managedTypeProvider = oldProvider;
			builder.parent              = oldParent;
			builder.stateObject         = oldStateObject;
		}
	}

	/**
	 * Creates the builder that creates the {@link StateObject} for each {@link org.eclipse.persistence.jpa.jpql.parser.Expression Expression}.
	 *
	 * @return The builder that will be visiting the {@link org.eclipse.persistence.jpa.jpql.parser.Expression Expression}
	 */
	protected abstract BasicStateObjectBuilder buildStateObjectBuilder();

	/**
	 * Returns the builder that creates the {@link StateObject} for each {@link org.eclipse.persistence.jpa.jpql.parser.Expression Expression}.
	 *
	 * @return The builder that will be visiting the {@link org.eclipse.persistence.jpa.jpql.parser.Expression Expression}
	 */
	protected final BasicStateObjectBuilder getStateObjectBuilder() {
		if (builder == null) {
			builder = buildStateObjectBuilder();
		}
		return builder;
	}

	/**
	 * Parses the given JPQL query with tolerant mode turned on.
	 *
	 * @param jpqlQuery The string representation of the JPQL query to parse
	 * @param jpqlGrammar The JPQL grammar that defines how to parse a JPQL query
	 * @param tolerant Determines if the parsing system should be tolerant, meaning if it should try
	 * to parse invalid or incomplete queries
	 * @return The root of the parsed tree representation of the JPQL query
	 */
	protected JPQLExpression parse(CharSequence jpqlQuery, JPQLGrammar jpqlGrammar, boolean tolerant) {
		return new JPQLExpression(jpqlQuery, jpqlGrammar, tolerant);
	}

	/**
	 * Parses the given JPQL fragment with tolerant mode turned on.
	 *
	 * @param jpqFragment The string representation of the portion of a JPQL query to parse
	 * @param jpqlGrammar The JPQL grammar that defines how to parse a JPQL query
	 * @param queryBNFId The unique identifier of the {@link JPQLQueryBNF}
	 * @return The root of the parsed tree representation of the JPQL fragment
	 */
	protected JPQLExpression parse(CharSequence jpqFragment,
	                               JPQLGrammar jpqlGrammar,
	                               String queryBNFId) {

		return new JPQLExpression(jpqFragment, jpqlGrammar, queryBNFId, true);
	}

	/**
	 * If a subclass needs to wrap the given {@link BasicStateObjectBuilder} with another visitor can
	 * do so by simply overriding this method. {@link #buildStateObjectBuilder()} can't be easily
	 * overridden with an {@link ExpressionVisitor} due to the constraint on the return type.
	 *
	 * @param builder The builder to wrap
	 * @return By default the given builder is returned
	 */
	protected ExpressionVisitor wrap(BasicStateObjectBuilder builder) {
		return builder;
	}
}