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

/**
 * A result variable may be used to name a select item in the query result.
 *
 * <div><b>BNF:</b> <code>select_item ::= select_expression [[AS] result_variable]</code></div>
 *
 * @version 2.5
 * @since 2.3
 * @author Pascal Filion
 */
public final class ResultVariable extends AbstractExpression {

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

    /**
     * Determines whether a whitespace was parsed after the identifier <b>AS</b>.
     */
    private boolean hasSpaceAfterAs;

    /**
     * The {@link Expression} used
     */
    private AbstractExpression resultVariable;

    /**
     * The {@link Expression} representing the select expression.
     */
    private AbstractExpression selectExpression;

    /**
     * Creates a new <code>ResultVariable</code>.
     *
     * @param parent The parent of this expression
     * @param selectExpression The expression that represents the select expression, which will have
     * a variable assigned to it
     */
    public ResultVariable(AbstractExpression parent, AbstractExpression selectExpression) {
        super(parent);

        if (selectExpression != null) {
            this.selectExpression = selectExpression;
            this.selectExpression.setParent(this);
        }
    }

    @Override
    public void accept(ExpressionVisitor visitor) {
        visitor.visit(this);
    }

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

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

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

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

        // 'AS'
        if (asIdentifier != null) {
            children.add(buildStringExpression(AS));
        }

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

        // Result variable
        if (resultVariable != null) {
            children.add(resultVariable);
        }
    }

    @Override
    public JPQLQueryBNF findQueryBNF(Expression expression) {

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

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

        return super.findQueryBNF(expression);
    }

    /**
     * Returns the actual <b>AS</b> found in the string representation of the JPQL query, which has
     * the actual case that was used.
     *
     * @return The <b>AS</b> identifier that was actually parsed, or an empty string if it was not parsed
     */
    public String getActualAsIdentifier() {
        return (asIdentifier != null) ? asIdentifier : ExpressionTools.EMPTY_STRING;
    }

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

    /**
     * Returns the {@link Expression} representing the result variable.
     *
     * @return The expression for the result variable
     */
    public Expression getResultVariable() {
        if (resultVariable == null) {
            resultVariable = buildNullExpression();
        }
        return resultVariable;
    }

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

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

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

    /**
     * Determines whether a select expression was defined for this result variable.
     *
     * @return <code>true</code> if the select expression was parsed; <code>false</code> if the
     * result variable was parsed without one
     */
    public boolean hasSelectExpression() {
        return selectExpression != null &&
              !selectExpression.isNull();
    }

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

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

        // Parse 'AS'
        if (wordParser.startsWithIdentifier(AS)) {
            asIdentifier = wordParser.moveForward(2);
            hasSpaceAfterAs = wordParser.skipLeadingWhitespace() > 0;
        }

        // Parse the result variable
        if (tolerant) {
            resultVariable = parse(wordParser, IdentificationVariableBNF.ID, tolerant);
        }
        else {
            resultVariable = new IdentificationVariable(this, wordParser.word());
            resultVariable.parse(wordParser, tolerant);
        }
    }

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

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

            if ((writer.length() > 0) && (writer.charAt(writer.length() - 1) != SPACE)) {
                writer.append(SPACE);
            }
        }

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

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

        // Result variable
        if (resultVariable != null) {
            resultVariable.toParsedText(writer, actual);
        }
    }
}