/*
 * Copyright (c) 2006, 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.ArrayList;
import java.util.Collection;
import java.util.List;
import org.eclipse.persistence.jpa.jpql.WordParser;

/**
 * The <b>SELECT</b> clause denotes the query result. More than one value may be returned from the
 * <b>SELECT</b> clause of a query. The <b>SELECT</b> clause may contain one or more of the
 * following elements: a single range variable or identification variable that ranges over an entity
 * abstract schema type, a single-valued path expression, an aggregate select expression, a
 * constructor expression.
 * <p>
 * The <b>DISTINCT</b> keyword is used to specify that duplicate values must be eliminated from the
 * query result. If <b>DISTINCT</b> is not specified, duplicate values are not eliminated.
 * Stand-alone identification variables in the <b>SELECT</b> clause may optionally be qualified by
 * the <b>OBJECT</b> operator. The <b>SELECT</b> clause must not use the <b>OBJECT</b> operator to
 * qualify path expressions.
 *
 * @see SelectClause
 * @see SimpleSelectClause
 *
 * @version 2.5
 * @since 2.3
 * @author Pascal Filion
 */
public abstract class AbstractSelectClause extends AbstractExpression {

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

    /**
     * Determines whether a whitespace was parsed after the <b>DISTINCT</b>.
     */
    private boolean hasSpaceAfterDistinct;

    /**
     * Determines whether a whitespace was parsed after the <b>SELECT</b>.
     */
    private boolean hasSpaceAfterSelect;

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

    /**
     * The actual expression of this select clause.
     */
    private AbstractExpression selectExpression;

    /**
     * Creates a new <code>SelectClause</code>.
     *
     * @param parent The parent of this expression
     */
    protected AbstractSelectClause(AbstractExpression parent) {
        super(parent, SELECT);
    }

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

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

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

        // 'SELECT'
        children.add(buildStringExpression(SELECT));

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

        // 'DISTINCT'
        if (distinctIdentifier != null) {
            children.add(buildStringExpression(DISTINCT));
        }

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

        // Select expression
        if (selectExpression != null) {
            children.add(selectExpression);
        }
    }

    /**
     * Creates a new {@link CollectionExpression} that will wrap the single select item.
     *
     * @return The single select item represented by a temporary collection
     */
    public CollectionExpression buildCollectionExpression() {

        List<AbstractExpression> children = new ArrayList<AbstractExpression>(1);
        children.add((AbstractExpression) getSelectExpression());

        List<Boolean> commas = new ArrayList<Boolean>(1);
        commas.add(Boolean.FALSE);

        List<Boolean> spaces = new ArrayList<Boolean>(1);
        spaces.add(Boolean.FALSE);

        return new CollectionExpression(this, children, commas, spaces, true);
    }

    @Override
    public JPQLQueryBNF findQueryBNF(Expression expression) {

        if ((selectExpression != null) && selectExpression.isAncestor(expression)) {
            return getQueryBNF(getSelectItemQueryBNFId());
        }

        return super.findQueryBNF(expression);
    }

    /**
     * Returns the actual <b>DISTINCT</b> identifier found in the string representation of the JPQL
     * query, which has the actual case that was used.
     *
     * @return The <b>DISTINCT</b> identifier that was actually parsed, or an empty string if it was
     * not parsed
     * @since 2.4
     */
    public final String getActualDistinctIdentifier() {
        return distinctIdentifier;
    }

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

    /**
     * Returns the {@link Expression} representing the select items.
     *
     * @return The expression representing the select items
     */
    public final Expression getSelectExpression() {
        if (selectExpression == null) {
            selectExpression = buildNullExpression();
        }
        return selectExpression;
    }

    /**
     * Returns the unique identifier of the {@link JPQLQueryBNF} for the list of select items to parse.
     *
     * @return The ID of the query BNF for the list of select items to parse
     */
    public abstract String getSelectItemQueryBNFId();

    /**
     * Determines whether the identifier <b>DISTINCT</b> was parsed or not.
     *
     * @return <code>true</code> if the identifier <b>DISTINCT</b> was parsed;
     * <code>false</code> otherwise
     */
    public final boolean hasDistinct() {
        return distinctIdentifier != null;
    }

    /**
     * Determines whether the list of select items was parsed.
     *
     * @return <code>true</code> the list of select items was parsed;
     * <code>false</code> otherwise
     */
    public final boolean hasSelectExpression() {
        return selectExpression != null &&
              !selectExpression.isNull();
    }

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

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

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

        // Parse 'SELECT'
        identifier = wordParser.moveForward(SELECT);

        hasSpaceAfterSelect = wordParser.skipLeadingWhitespace() > 0;

        // Parse 'DISTINCT'
        if (wordParser.startsWithIdentifier(DISTINCT)) {
            distinctIdentifier = wordParser.moveForward(DISTINCT);
            hasSpaceAfterDistinct = wordParser.skipLeadingWhitespace() > 0;
        }

        // Parse the select expression
        selectExpression = parse(wordParser, getSelectItemQueryBNFId(), tolerant);
    }

    @Override
    protected boolean shouldSkipLiteral(AbstractExpression expression) {
        return false;
    }

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

        // 'SELECT'
        writer.append(actual ? identifier : SELECT);

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

        // 'DISTINCT'
        if (distinctIdentifier != null) {
            writer.append(actual ? distinctIdentifier : DISTINCT);
        }

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

        // Select expression
        if (selectExpression != null) {
            selectExpression.toParsedText(writer, actual);
        }
    }
}