/*
 * Copyright (c) 2006, 2020 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 v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Oracle - initial API and implementation
//
package org.eclipse.persistence.internal.jpa.jpql;

import org.eclipse.persistence.jpa.jpql.parser.CollectionExpression;
import org.eclipse.persistence.jpa.jpql.parser.EclipseLinkAnonymousExpressionVisitor;
import org.eclipse.persistence.jpa.jpql.parser.Expression;
import org.eclipse.persistence.jpa.jpql.parser.IdentificationVariable;
import org.eclipse.persistence.jpa.jpql.parser.NullExpression;
import org.eclipse.persistence.jpa.jpql.parser.ObjectExpression;
import org.eclipse.persistence.jpa.jpql.parser.ResultVariable;
import org.eclipse.persistence.jpa.jpql.parser.SelectClause;
import org.eclipse.persistence.jpa.jpql.parser.SelectStatement;
import org.eclipse.persistence.queries.ReadAllQuery;
import org.eclipse.persistence.queries.ReportQuery;

/**
 * This visitor visits the select expression in order to create the correct {@link ReadAllQuery},
 * which is either a {@link ReportQuery} or a {@link ReadAllQuery}.
 *
 * @version 2.5
 * @since 2.3
 * @author Pascal Filion
 * @author John Bracken
 */
final class ReadAllQueryBuilder extends EclipseLinkAnonymousExpressionVisitor {

    /**
     * The query that was created based on the type of select clause.
     */
    ReadAllQuery query;

    /**
     * The {@link JPQLQueryContext} is used to query information about the application metadata and
     * cached information.
     */
    private final JPQLQueryContext queryContext;

    /**
     * The {@link Expression} being visited.
     */
    private SelectStatement selectStatement;

    /**
     * Creates a new <code>ReadAllQueryBuilder</code>.
     *
     * @param queryContext The context used to query information about the application metadata and
     * cached information
     */
    ReadAllQueryBuilder(JPQLQueryContext queryContext) {
        super();
        this.queryContext = queryContext;
    }

    private void initializeReadAllQuery() {
        ReadAllQuery query = new ReadAllQuery();
        query.dontUseDistinct();
        this.query = query;
    }

    private void initializeReportQuery() {
        ReportQuery query = new ReportQuery();
        query.returnWithoutReportQueryResult();
        query.dontUseDistinct();
        this.query = query;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void visit(CollectionExpression expression) {
        // Multiple expressions in the select clause => ReportQuery
        initializeReportQuery();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void visit(Expression expression) {
      // Does not select an identification variable
        // (e.g. projection or aggregate function) => ReportQuery
        initializeReportQuery();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void visit(IdentificationVariable expression) {

        // Use ReadAllQuery if the variable of the SELECT clause expression is the base variable
        // Example: ReadAllQuery = SELECT e FROM Employee e
        // Example: ReportQuery  = SELECT e FROM Department d JOIN d.employees e
        String variableName = expression.getVariableName();

        if (queryContext.isRangeIdentificationVariable(variableName)) {

            if (selectStatement.hasGroupByClause() ||
                selectStatement.hasHavingClause()  ||
                variableName != queryContext.getFirstDeclaration().getVariableName()) {

                initializeReportQuery();
            }
            else {
                initializeReadAllQuery();
            }
        }
        else {
            initializeReportQuery();
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void visit(NullExpression expression) {
        // For from clause only JPQL the full object is always selected, so is ReadAllQuery.
        initializeReadAllQuery();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void visit(ObjectExpression expression) {
        // Visit the identification variable directly
        expression.getExpression().accept(this);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void visit(ResultVariable expression) {
        // Make sure to traverse the select expression since
        // it has a result variable assigned to it
        expression.getSelectExpression().accept(this);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void visit(SelectClause expression) {
        expression.getSelectExpression().accept(this);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void visit(SelectStatement expression) {
        this.selectStatement = expression;
        expression.getSelectClause().accept(this);
    }
}