/*
 * 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;

/**
 * The <b>UNION</b> clause allows the results of two queries to be combined.
 *
 * <div><b>BNF:</b> <code>union_clause ::= <b>{ UNION | INTERSECT | EXCEPT }</b> [ALL] subquery</code></div>
 *
 * @version 2.5
 * @since 2.4
 * @author James Sutherland
 */
public final class UnionClause extends AbstractExpression {

    /**
     * The actual identifier found in the string representation of the JPQL query.
     */
    private String actualIdentifier;

    /**
     * The actual <b>All</b> identifier found in the string representation of the JPQL query.
     */
    private String allIdentifier;

    /**
     * Determines whether a whitespace was parsed after <b>ALL</b>.
     */
    private boolean hasSpaceAfterAll;

    /**
     * Determines whether a whitespace was parsed after <b>UNION</b>.
     */
    private boolean hasSpaceAfterIdentifier;

    /**
     * The {@link Expression} representing the unioned query.
     */
    private AbstractExpression query;

    /**
     * Creates a new <code>UnionClause</code>.
     *
     * @param parent The parent of this expression
     * @param identifier Either <code><b>UNION</b></code>, <code><b>INTERSECT</b></code> or
     * <code><b>EXCEPT</b></code>
     */
    public UnionClause(AbstractExpression parent, String identifier) {
        super(parent, identifier);
    }

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

    @Override
    public void acceptChildren(ExpressionVisitor visitor) {
        getQuery().accept(visitor);
    }

    @Override
    protected void addChildrenTo(Collection<Expression> children) {
        children.add(getQuery());
    }

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

        // 'UNION' or 'INTERSECT' or 'EXCEPT'
        children.add(buildStringExpression(getText()));

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

        // 'ALL'
        if (allIdentifier != null) {
            children.add(buildStringExpression(ALL));

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

        // Subquery
        if (query != null) {
            children.add(query);
        }
    }

    @Override
    public JPQLQueryBNF findQueryBNF(Expression expression) {

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

        return super.findQueryBNF(expression);
    }

    /**
     * Returns the actual <code><b>ALL</b></code> found in the string representation of the JPQL
     * query, which has the actual case that was used.
     *
     * @return The <code><b>ALL</b></code> identifier that was actually parsed
     */
    public String getActualAll() {
        return allIdentifier;
    }

    /**
     * Returns the actual identifier found in the string representation of the JPQL query, which
     * has the actual case that was used.
     *
     * @return The identifier that was actually parsed
     */
    public String getActualIdentifier() {
        return actualIdentifier;
    }

    /**
     * Returns the union identifier.
     *
     * @return Either "UNION", "INTERSECT", "EXCEPT"
     */
    public String getIdentifier() {
        return getText();
    }

    /**
     * Returns the {@link Expression} representing the unioned query.
     *
     * @return The {@link Expression} representing the subquery
     */
    public Expression getQuery() {
        if (query == null) {
            query = buildNullExpression();
        }
        return query;
    }

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

    /**
     * Determines whether <code><b>ALL</b></code> was parsed.
     *
     * @return <code>true</code> if <code><b>ALL</b></code> was parsed; <code>false</code> otherwise
     */
    public boolean hasAll() {
        return allIdentifier != null;
    }

    /**
     * Determines whether the query  was parsed.
     *
     * @return <code>true</code> the query was parsed; <code>false</code> otherwise
     */
    public boolean hasQuery() {
        return query != null &&
              !query.isNull();
    }

    /**
     * Determines whether a whitespace was parsed after <code><b>ALL</b></code>.
     *
     * @return <code>true</code> if a whitespace was parsed after <code><b>ALL</b></code>;
     * <code>false</code> otherwise
     */
    public boolean hasSpaceAfterAll() {
        return hasSpaceAfterAll;
    }

    /**
     * Determines whether a whitespace was parsed after the identifier.
     *
     * @return <code>true</code> if a whitespace was parsed after the identifier; <code>false</code> otherwise
     */
    public boolean hasSpaceAfterIdentifier() {
        return hasSpaceAfterIdentifier;
    }

    /**
     * Determines whether this {@link UnionClause} uses the <code><b>EXCEPT</b></code> identifier.
     *
     * @return <code>true</code> if the identifier is <code><b>EXCEPT</b></code>; <code>false</code> otherwise
     */
    public boolean isExcept() {
        return getText() == EXCEPT;
    }

    /**
     * Determines whether this {@link UnionClause} uses the <code><b>INTERSECT</b></code> identifier.
     *
     * @return <code>true</code> if the identifier is <code><b>INTERSECT</b></code>; <code>false</code> otherwise
     */
    public boolean isIntersect() {
        return getText() == INTERSECT;
    }

    @Override
    protected boolean isParsingComplete(WordParser wordParser, String word, Expression expression) {
        return word.equalsIgnoreCase(UNION)     ||
               word.equalsIgnoreCase(INTERSECT) ||
               word.equalsIgnoreCase(EXCEPT)    ||
               super.isParsingComplete(wordParser, word, expression);
    }

    /**
     * Determines whether this {@link UnionClause} uses the <code><b>UNION</b></code> identifier.
     *
     * @return <code>true</code> if the identifier is <code><b>UNION</b></code>; <code>false</code> otherwise
     */
    public boolean isUnion() {
        return getText() == UNION;
    }

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

        // Parse the identifier
        String identifier = parseIdentifier();
        actualIdentifier = wordParser.moveForward(identifier);
        setText(identifier);

        hasSpaceAfterIdentifier = wordParser.skipLeadingWhitespace() > 0;

        // Parse 'ALL'
        if (wordParser.startsWithIdentifier(ALL)) {
            allIdentifier = wordParser.moveForward(ALL);
            hasSpaceAfterAll = wordParser.skipLeadingWhitespace() > 0;
        }

        // Query
        if (tolerant) {
            query = parse(wordParser, SubqueryBNF.ID, tolerant);
        }
        else {
            query = new SimpleSelectStatement(this);
            query.parse(wordParser, tolerant);
        }
    }

    /**
     * Parses the JPQL identifier identifier the type of union.
     *
     * @return Either {@link Expression#UNION UNION}, {@link Expression#INTERSECT INTERSECT} or
     * {@link Expression#EXCEPT EXCEPT}
     */
    protected String parseIdentifier() {
        switch (getText().charAt(0)) {
            case 'U': case 'u': return UNION;
            case 'I': case 'i': return INTERSECT;
            case 'E': case 'e': return EXCEPT;
            default:            return null; // Never happens
        }
    }

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

        // 'UNION', 'INTERSECT' or 'EXCEPT'
        writer.append(actual ? actualIdentifier : getText());

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

        // 'ALL'
        if (allIdentifier != null) {
            writer.append(actual ? allIdentifier : ALL);

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

        // Query
        if (query != null) {
            query.toParsedText(writer, actual);
        }
    }
}