jpa/org.eclipse.persistence.jpa.jpql/src/main/java/org/eclipse/persistence/jpa/jpql/parser/HierarchicalQueryClause.java

/*
 * Copyright (c) 2012, 2021 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.jpa.jpql.parser;

import java.util.Collection;
import java.util.List;
import org.eclipse.persistence.jpa.jpql.WordParser;

/**
 * If a table contains hierarchical data, then rows can be selected in a hierarchical order using
 * the hierarchical query clause.
 * <p>
 * <code><b>START WITH</b></code> specifies the root row(s) of the hierarchy.
 * <p>
 * <code><b>CONNECT BY</b></code> specifies the relationship between parent rows and child rows of
 * the hierarchy.
 *
 * <div><b>BNF:</b> <code>hierarchical_query_clause ::= [start_with_clause] connectby_clause [order_siblings_by_clause]</code><p></p></div>
 *
 * @see StartWithClause
 * @see ConnectByClause
 * @see OrderSiblingsByClause
 *
 * @version 2.5
 * @since 2.5
 * @author Pascal Filion
 */
public final class HierarchicalQueryClause extends AbstractExpression {

    /**
     * The {@link Expression} that represents the <code><b>CONNECT BY</b></code> clause.
     */
    private AbstractExpression connectByClause;

    /**
     * Determines whether a whitespace was parsed after the <code><b>CONNECT BY</b></code> clause.
     */
    private boolean hasSpaceAfterConnectByClause;

    /**
     * Determines whether a whitespace was parsed after the <code><b>START WITH</b></code> clause.
     */
    private boolean hasSpaceAfterStartWithClause;

    /**
     * The {@link Expression} that represents the <code><b>ORDER SIBLINGS BY</b></code> clause.
     */
    private AbstractExpression orderSiblingsByClause;

    /**
     * The {@link Expression} that represents the <code><b>START WITH</b></code> clause.
     */
    private AbstractExpression startWithClause;

    /**
     * Creates a new <code>HierarchicalQueryClause</code>.
     *
     * @param parent The parent of this expression
     */
    public HierarchicalQueryClause(AbstractExpression parent) {
        super(parent);
    }

    @Override
    public void accept(ExpressionVisitor visitor) {
        acceptUnknownVisitor(visitor);
    }

    @Override
    public void acceptChildren(ExpressionVisitor visitor) {
        getStartWithClause().accept(visitor);
        getConnectByClause().accept(visitor);
        getOrderSiblingsByClause().accept(visitor);
    }

    @Override
    protected void addChildrenTo(Collection<Expression> children) {
        super.addChildrenTo(children);
        children.add(getStartWithClause());
        children.add(getConnectByClause());
        children.add(getOrderSiblingsByClause());
    }

    @Override
    protected void addOrderedChildrenTo(List<Expression> children) {

        // START WITH clause
        if (startWithClause != null) {
            children.add(startWithClause);
        }

        if (hasSpaceAfterStartWithClause) {
            children.add(buildStringExpression(SPACE));
        }

        // CONNECT BY clause
        if (connectByClause != null) {
            children.add(connectByClause);
        }

        if (hasSpaceAfterConnectByClause) {
            children.add(buildStringExpression(SPACE));
        }

        // ORDER SIBLINGS BY clause
        if (orderSiblingsByClause != null) {
            children.add(orderSiblingsByClause);
        }
    }

    @Override
    public JPQLQueryBNF findQueryBNF(Expression expression) {

        if ((startWithClause != null) && startWithClause.isAncestor(expression)) {
            return getQueryBNF(StartWithClauseBNF.ID);
        }

        if ((connectByClause != null) && connectByClause.isAncestor(expression)) {
            return getQueryBNF(ConnectByClauseBNF.ID);
        }

        if ((orderSiblingsByClause != null) && orderSiblingsByClause.isAncestor(expression)) {
            return getQueryBNF(OrderSiblingsByClauseBNF.ID);
        }

        return super.findQueryBNF(expression);
    }

    /**
     * Returns the {@link Expression} representing the <b>CONNECT BY</b> clause.
     *
     * @return The expression representing the <b>CONNECT BY</b> clause
     */
    public Expression getConnectByClause() {
        if (connectByClause == null) {
            connectByClause = buildNullExpression();
        }
        return connectByClause;
    }

    /**
     * Returns the {@link Expression} representing the <b>ORDER SIBLINGS BY</b> clause.
     *
     * @return The expression representing the <b>ORDER SIBLINGS BY</b> clause
     */
    public Expression getOrderSiblingsByClause() {
        if (orderSiblingsByClause == null) {
            orderSiblingsByClause = buildNullExpression();
        }
        return orderSiblingsByClause;
    }

    @Override
    public JPQLQueryBNF getQueryBNF() {
        return getQueryBNF(HierarchicalQueryClauseBNF.ID);
    }

    /**
     * Returns the {@link Expression} representing the <b>START WITH</b> clause.
     *
     * @return The expression representing the <b>START WITH</b> clause
     */
    public Expression getStartWithClause() {
        if (startWithClause == null) {
            startWithClause = buildNullExpression();
        }
        return startWithClause;
    }

    /**
     * Determines whether the <b>CONNECT BY</b> clause is defined.
     *
     * @return <code>true</code> if the query that got parsed had the <b>CONNECT BY</b> clause
     */
    public boolean hasConnectByClause() {
        return connectByClause != null &&
              !connectByClause.isNull();
    }

    /**
     * Determines whether the <b>ORDER SIBLINGS BY</b> clause is defined.
     *
     * @return <code>true</code> if the query that got parsed had the <b>ORDER SIBLINGS BY</b> clause
     */
    public boolean hasOrderSiblingsByClause() {
        return orderSiblingsByClause != null &&
              !orderSiblingsByClause.isNull();
    }

    /**
     * Determines whether a whitespace was found after the <code><b>CONNECT BY</b></code> clause. In
     * some cases, the space is owned by a child of the hierarchical query clause.
     *
     * @return <code>true</code> if there was a whitespace after the <code><b>CONNECT BY</b></code>
     * clause and owned by this expression; <code>false</code> otherwise
     */
    public boolean hasSpaceAfterConnectByClause() {
        return hasSpaceAfterConnectByClause;
    }

    /**
     * Determines whether a whitespace was found after the <code><b>START WITH</b></code> clause. In
     * some cases, the space is owned by a child of the hierarchical query clause.
     *
     * @return <code>true</code> if there was a whitespace after the <code><b>START WITH</b></code>
     * clause and owned by this expression; <code>false</code> otherwise
     */
    public boolean hasSpaceAfterStartWithClause() {
        return hasSpaceAfterStartWithClause;
    }

    /**
     * Determines whether the <b>START WITH</b> clause is defined.
     *
     * @return <code>true</code> if the query that got parsed had the <b>START WITH</b> clause
     */
    public boolean hasStartWithClause() {
        return startWithClause != null &&
              !startWithClause.isNull();
    }

    @Override
    protected void parse(WordParser wordParser, boolean tolerant) {

        int count = 0;

        // START WITH clause
        if (wordParser.startsWithIdentifier(START_WITH)) {
            startWithClause = new StartWithClause(this);
            startWithClause.parse(wordParser, tolerant);

            count = wordParser.skipLeadingWhitespace();
            hasSpaceAfterStartWithClause = (count > 0);
        }

        // CONNECT BY clause
        if (wordParser.startsWithIdentifier(CONNECT_BY)) {
            connectByClause = new ConnectByClause(this);
            connectByClause.parse(wordParser, tolerant);

            count = wordParser.skipLeadingWhitespace();
            hasSpaceAfterConnectByClause = (count > 0);
        }

        // ORDER SIBLINGS BY clause
        if (wordParser.startsWithIdentifier(ORDER_SIBLINGS_BY)) {
            orderSiblingsByClause = new OrderSiblingsByClause(this);
            orderSiblingsByClause.parse(wordParser, tolerant);
        }

        // Let's the parent statement own the whitespace
        if (hasSpaceAfterStartWithClause  &&
            connectByClause       == null &&
            orderSiblingsByClause == null) {

            hasSpaceAfterStartWithClause = false;
            wordParser.moveBackward(count);
        }
        else if (hasSpaceAfterConnectByClause &&
                 orderSiblingsByClause == null) {

            hasSpaceAfterConnectByClause = false;
            wordParser.moveBackward(count);
        }
    }

    @Override
    protected void toParsedText(StringBuilder writer, boolean actual) {

        // START WITH clause
        if (startWithClause != null) {
            startWithClause.toParsedText(writer, actual);

            if (hasSpaceAfterStartWithClause) {
                writer.append(SPACE);
            }
        }

        // CONNECT BY clause
        if (connectByClause != null) {
            connectByClause.toParsedText(writer, actual);

            if (hasSpaceAfterConnectByClause) {
                writer.append(SPACE);
            }
        }

        // ORDER SIBLINGS BY clause
        if (orderSiblingsByClause != null) {
            orderSiblingsByClause.toParsedText(writer, actual);
        }
    }
}