/*
 * 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.WordParser;

/**
 * A <code>CollectionExpression</code> wraps many expression which they are separated by spaces
 * and/or commas.
 *
 * <div><b>BNF:</b> <code>expression ::= child_item {, child_item }*</code></div>
 * <br>
 * or
 * <br>
 * <div><b>BNF:</b> <code>expression ::= child_item { child_item }*</code><p></p></div>
 *
 * @version 2.5
 * @since 2.3
 * @author Pascal Filion
 */
@SuppressWarnings("nls")
public final class CollectionExpression extends AbstractExpression {

    /**
     * The {@link Expression Expressions} that forms a collection within another expression.
     */
    private List<AbstractExpression> children;

    /**
     * The list of flags used to determine where to separate two child {@link Expression Expressions}
     * with a comma or with a space only.
     */
    private List<Boolean> commas;

    /**
     * Flag used to determine when a space is required after a comma.
     */
    private List<Boolean> spaces;

    /**
     * Creates a new <code>CollectionExpression</code>.
     *
     * @param parent The parent of this expression
     * @param children The list of children that are regrouped together
     * @param spaces The list of flags used to determine when to add a space after an {@link Expression}
     * @param commas The list of flags used to determine when to add a comma after an {@link Expression}
     */
    public CollectionExpression(AbstractExpression parent,
                                List<AbstractExpression> children,
                                List<Boolean> commas,
                                List<Boolean> spaces) {

        this(parent, children, commas, spaces, false);
    }

    /**
     * Creates a new <code>CollectionExpression</code>.
     *
     * @param parent The parent of this expression
     * @param children The list of children that are regrouped together
     * @param commas The list of flags used to determine when to add a comma after an {@link Expression}
     * @param spaces The list of flags used to determine when to add a space after an {@link Expression}
     * @param temporary Flag used to determine if this expression is temporarily used, which means
     * the children will not be parented to this object
     */
    public CollectionExpression(AbstractExpression parent,
                                List<AbstractExpression> children,
                                List<Boolean> commas,
                                List<Boolean> spaces,
                                boolean temporary) {
        super(parent);

        this.children = children;
        this.commas   = commas;
        this.spaces   = spaces;

        if (!temporary) {
            updateBackpointers();
        }
    }

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

    /**
     * Visits the child {@link Expression} at the given position by the given {@link ExpressionVisitor
     * visitor}.
     *
     * @param index The index of the child to visit
     * @param visitor The {@link ExpressionVisitor} to visit a specific child
     * @since 2.4
     */
    public void accept(int index, ExpressionVisitor visitor) {
        getChild(index).accept(visitor);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void acceptChildren(ExpressionVisitor visitor) {
        for (Expression child : children()) {
            child.accept(visitor);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void addChildrenTo(Collection<Expression> children) {

        // Make sure all children are non null
        for (int index = 0, childCount = this.children.size(); index < childCount; index++) {
            getChildInternal(index);
        }

        children.addAll(this.children);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void addOrderedChildrenTo(List<Expression> children) {

        children();

        for (int index = 0, count = this.children.size(); index < count; index++) {
            Expression expression = getChild(index);
            children.add(expression);

            // Write ','
            if (hasComma(index)) {
                children.add(buildStringExpression(COMMA));
            }

            // Write whitespace
            if (hasSpace(index)) {
                children.add(buildStringExpression(SPACE));
            }
        }
    }

    /**
     * Returns the count of child {@link Expression expressions}.
     *
     * @return The total count of {@link Expression expressions} aggregated with spaces and/or commas
     */
    public int childrenSize() {
        children();
        return children.size();
    }

    /**
     * Determines whether this {@link CollectionExpression} ends with a comma, which means the last
     * {@link Expression} is a "<code>null</code>" expression.
     *
     * @return <code>true</code> if the string representation of this {@link CollectionExpression}
     * ends with a comma (the ending space is not checked)
     */
    public boolean endsWithComma() {

        children();

        if (children.get(children.size() - 1).isNull()) {
            return commas.get(commas.size() - 2);
        }

        return false;
    }

    /**
     * Determines whether this {@link CollectionExpression} ends with a space, which means the last
     * {@link Expression} is a "<code>null</code>" expression.
     *
     * @return <code>true</code> if the string representation of this {@link CollectionExpression}
     * ends with a space (the ending comma is not checked)
     */
    public boolean endsWithSpace() {

        children();

        if (children.get(children.size() - 1).isNull()) {
            return spaces.get(spaces.size() - 2);
        }

        return false;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public JPQLQueryBNF findQueryBNF(Expression expression) {
        return getParent().findQueryBNF(expression);
    }

    /**
     * Retrieves the child {@link Expression} at the given position.
     *
     * @param index The position of the child {@link Expression} to retrieve
     * @return The child {@link Expression} at the given position
     */
    public Expression getChild(int index) {
        return getChildInternal(index);
    }

    private AbstractExpression getChildInternal(int index) {

        AbstractExpression child = children.get(index);

        if (child == null) {
            child = buildNullExpression();
            children.set(index, child);
        }

        return child;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public JPQLQueryBNF getQueryBNF() {
        return getParent().getQueryBNF();
    }

    /**
     * Determines whether a comma was parsed at the given position. The index is the position of the
     * comma that is following the child at the same position.
     *
     * @param index The index of the child {@link Expression} to verify if there is a comma following it
     * @return <code>true</code> if a comma is following the child {@link Expression} at the given
     * index; <code>false</code> otherwise
     */
    public boolean hasComma(int index) {
        children();
        return (index < commas.size()) && commas.get(index);
    }

    /**
     * Determines whether a space was parsed at the given position. The index is the position of the
     * space that is following the child at the same position, which is after a comma, if one was
     * also parsed at that location.
     *
     * @param index The index of the child {@link Expression} to verify if there is a space following
     * it, which could be after a comma, if one was parsed
     * @return <code>true</code> if a space is following the child {@link Expression} at the given
     * index; <code>false</code> otherwise
     */
    public boolean hasSpace(int index) {
        children();
        return (index < spaces.size()) && (spaces.get(index) || hasComma(index) && (index + 1 < children.size() ? !getChildInternal(index + 1).isNull() : false));
    }

    /**
     * Retrieves the index of the given <code>Expression</code>.
     *
     * @param expression The <code>Expression</code> that might be a child of this expression
     * @return The index in the collection of the given <code>Expression</code> or -1 if it is not a child
     */
    public int indexOf(Expression expression) {
        children();
        return children.indexOf(expression);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void parse(WordParser wordParser, boolean tolerant) {
        throw new IllegalAccessError("This method shouln't be invoked, text=" + wordParser);
    }

    /**
     * Returns a string representation of this {@link Expression} and its children. The expression
     * should contain whitespace even if the beautified version would not have any. For instance,
     * "SELECT e " should be returned where {@link Expression#toParsedText()} would return "SELECT e".
     *
     * @param endIndex The index used to determine when to create the string representation, which
     * is exclusive
     * @return The string representation of this {@link Expression}
     */
    public String toActualText(int endIndex) {
        StringBuilder writer = new StringBuilder();
        toParsedText(writer, endIndex, true);
        return writer.toString();
    }

    /**
     * Generates a string representation of this {@link CollectionExpression}.
     *
     * @param endIndex The index used to determine when to create the string representation, which
     * is exclusive
     * @return The string representation of this {@link Expression}
     */
    public String toParsedText(int endIndex) {
        StringBuilder writer = new StringBuilder();
        toParsedText(writer, endIndex, false);
        return writer.toString();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void toParsedText(StringBuilder writer, boolean actual) {
        toParsedText(writer, childrenSize(), actual);
    }

    private void toParsedText(StringBuilder writer, int endIndex, boolean actual) {

        for (int index = 0, count = children.size(); index < endIndex; index++) {

            AbstractExpression expression = children.get(index);

            // Write the child expression
            if (expression != null) {
                expression.toParsedText(writer, actual);
            }

            // Write ','
            if (commas.get(index)) {
                writer.append(COMMA);

                // If there is a space, then add it
                if (spaces.get(index)) {
                    writer.append(SPACE);
                }
                // Otherwise check if the next expression is not null, if it's null,
                // then a space will not be added
                else if (index + 1 < count) {
                    AbstractExpression nextExpression = children.get(index + 1);

                    if ((nextExpression != null) && !nextExpression.isNull()) {
                        writer.append(SPACE);
                    }
                }
            }
            // Write ' '
            else  if (spaces.get(index)) {
                writer.append(SPACE);
            }
        }
    }

    private void updateBackpointers() {
        for (AbstractExpression child : children) {
            if (child != null) {
                child.setParent(this);
            }
        }
    }
}