/*
 * Copyright (c) 2006, 2020 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 org.eclipse.persistence.jpa.jpql.utility.iterable.ListIterable;

/**
 * This is the root interface of the parsed tree representation of a JPQL query. The way a JPQL
 * query is parsed is based on the {@link JPQLGrammar JPQL grammar} used.
 * <p>
 * Provisional API: This interface is part of an interim API that is still under development and
 * expected to change significantly before reaching stability. It is available at this early stage
 * to solicit feedback from pioneering adopters on the understanding that any code that uses this
 * API will almost certainly be broken (repeatedly) as the API evolves.
 *
 * @see JPQLGrammar
 *
 * @version 2.5
 * @since 2.3
 * @author Pascal Filion
 */
@SuppressWarnings("nls")
public interface Expression {

    /**
     * The constant for 'ABS'.
     */
    String ABS = "ABS";

    /**
     * The constant for 'ALL'.
     */
    String ALL = "ALL";

    /**
     * The constant for 'AND'.
     */
    String AND = "AND";

    /**
     * The constant for 'ANY'.
     */
    String ANY = "ANY";

    /**
     * The constant for 'AS'.
     */
    String AS = "AS";

    /**
     * The constant for 'AS OF'.
     *
     * @since 2.5
     */
    String AS_OF = "AS OF";

    /**
     * The constant for 'ASC'.
     */
    String ASC = "ASC";

    /**
     * The constant for 'AVG'.
     */
    String AVG = "AVG";

    /**
     * The constant for 'BETWEEN'.
     */
    String BETWEEN = "BETWEEN";

    /**
     * The constant for 'BIT_LENGTH', which is an unused keyword.
     */
    String BIT_LENGTH = "BIT_LENGTH";

    /**
     * The constant for 'BOTH'.
     */
    String BOTH = "BOTH";

    /**
     * The constant for the identifier 'CASE'.
     */
    String CASE = "CASE";

    /**
     * The constant for the identifier 'CAST'.
     *
     * @since 2.4
     */
    String CAST = "CAST";

    /**
     * The constant for 'CHAR_LENGTH', which is an unused keyword.
     */
    String CHAR_LENGTH = "CHAR_LENGTH";

    /**
     * The constant for 'CHARACTER_LENGTH', which is an unused keyword.
     */
    String CHARACTER_LENGTH = "CHARACTER_LENGTH";

    /**
     * The constant for 'CLASS', which is an unused keyword.
     */
    String CLASS = "CLASS";

    /**
     * The constant for 'COALESCE'.
     */
    String COALESCE = "COALESCE";

    /**
     * The constant 'COLUMN', which is an EclipseLink specific identifier that was added in version 2.4.
     *
     * @since 2.4
     */
    String COLUMN = "COLUMN";

    /**
     * The constant for 'CONCAT'.
     */
    String CONCAT = "CONCAT";

    /**
     * The constant for 'CONNECT BY'.
     *
     * @since 2.5
     */
    String CONNECT_BY = "CONNECT BY";

    /**
     * The constant for 'COUNT'.
     */
    String COUNT = "COUNT";

    /**
     * The constant for 'CURRENT_DATE'.
     */
    String CURRENT_DATE = "CURRENT_DATE";

    /**
     * The constant for 'CURRENT_DATE'.
     */
    String CURRENT_TIME = "CURRENT_TIME";

    /**
     * The constant for 'CURRENT_TIMESTAMP'.
     */
    String CURRENT_TIMESTAMP = "CURRENT_TIMESTAMP";

    /**
     * The constant for 'DELETE'.
     */
    String DELETE = "DELETE";

    /**
     * The constant for 'DELETE FROM'.
     */
    String DELETE_FROM = "DELETE FROM";

    /**
     * The constant for 'DESC'.
     */
    String DESC = "DESC";

    /**
     * The constant for {@literal '<>'}.
     */
    String DIFFERENT = "<>";

    /**
     * The constant for 'DISTINCT'.
     */
    String DISTINCT = "DISTINCT";

    /**
     * The constant for the division sign '/'.
     */
    String DIVISION = "/";

    /**
     * The constant for the identifier 'ELSE'.
     */
    String ELSE = "ELSE";

    /**
     * The constant for 'EMPTY'.
     */
    String EMPTY = "EMPTY";

    /**
     * The constant for the identifier 'END'.
     */
    String END = "END";

    /**
     * The constant for 'ENTRY'.
     */
    String ENTRY = "ENTRY";

    /**
     * The constant for '='.
     */
    String EQUAL = "=";

    /**
     * The constant for 'ESCAPE'.
     */
    String ESCAPE = "ESCAPE";

    /**
     * The constant for 'EXCEPT'.
     *
     * @since 2.4
     */
    String EXCEPT = "EXCEPT";

    /**
     * The constant for 'EXISTS'.
     */
    String EXISTS = "EXISTS";

    /**
     * The constant for 'EXTRACT'.
     *
     * @since 2.4
     */
    String EXTRACT = "EXTRACT";

    /**
     * The constant for 'FALSE'.
     */
    String FALSE = "FALSE";

    /**
     * A constant for 'FETCH'.
     */
    String FETCH = "FETCH";

    /**
     * The constant for 'FIRST'.
     *
     * @since 2.5
     */
    String FIRST = "FIRST";

    /**
     * The constant for 'FROM'.
     */
    String FROM = "FROM";

    /**
     * The constant 'FUNC', which is an EclipseLink specific identifier that was added in version 2.1.
     */
    String FUNC = "FUNC";

    /**
     * The constant 'FUNCTION', part of JPA 2.1.
     *
     * @since 2.4
     */
    String FUNCTION = "FUNCTION";

    /**
     * The constant for {@literal '>'}.
     */
    String GREATER_THAN = ">";

    /**
     * The constant for {@literal '>='}.
     */
    String GREATER_THAN_OR_EQUAL = ">=";

    /**
     * The constant for 'GROUP BY'.
     */
    String GROUP_BY = "GROUP BY";

    /**
     * The constant for 'HAVING'.
     */
    String HAVING = "HAVING";

    /**
     * The constant for 'IN'.
     */
    String IN = "IN";

    /**
     * The constant for 'INDEX'.
     */
    String INDEX = "INDEX";

    /**
     * The constant for 'INNER'.
     */
    String INNER = "INNER";

    /**
     * The constant for 'INNER JOIN'.
     */
    String INNER_JOIN = "INNER JOIN";

    /**
     * The constant for 'INNER JOIN FETCH'.
     */
    String INNER_JOIN_FETCH = "INNER JOIN FETCH";

    /**
     * The constant for 'INTERSECT'.
     *
     * @since 2.4
     */
    String INTERSECT = "INTERSECT";

    /**
     * The constant for 'IS'.
     */
    String IS = "IS";

    /**
     * The constant for 'IS EMPTY'.
     */
    String IS_EMPTY = "IS EMPTY";

    /**
     * The constant for 'IS NOT EMPTY'.
     */
    String IS_NOT_EMPTY = "IS NOT EMPTY";

    /**
     * The constant for 'IS NOT NULL'.
     */
    String IS_NOT_NULL = "IS NOT NULL";

    /**
     * The constant for 'IS NULL'.
     */
    String IS_NULL = "IS NULL";

    /**
     * The constant for 'JOIN'.
     */
    String JOIN = "JOIN";

    /**
     * The constant for 'JOIN FETCH'.
     */
    String JOIN_FETCH = "JOIN FETCH";

    /**
     * The constant for 'KEY'.
     */
    String KEY = "KEY";

    /**
     * The constant for 'LAST'.
     *
     * @since 2.5
     */
    String LAST = "LAST";

    /**
     * The constant for 'LEADING'.
     */
    String LEADING = "LEADING";

    /**
     * The constant for 'LEFT'.
     */
    String LEFT = "LEFT";

    /**
     * The constant for 'LEFT JOIN'.
     */
    String LEFT_JOIN = "LEFT JOIN";

    /**
     * The constant for 'LEFT JOIN FETCH'.
     */
    String LEFT_JOIN_FETCH = "LEFT JOIN FETCH";

    /**
     * The constant for 'LEFT OUTER JOIN'.
     */
    String LEFT_OUTER_JOIN = "LEFT OUTER JOIN";

    /**
     * The constant for 'LEFT OUTER JOIN FETCH'.
     */
    String LEFT_OUTER_JOIN_FETCH = "LEFT OUTER JOIN FETCH";

    /**
     * The constant for 'LENGTH'.
     */
    String LENGTH = "LENGTH";

    /**
     * The constant for 'LIKE'.
     */
    String LIKE = "LIKE";

    /**
     * The constant for 'LOCATE'.
     */
    String LOCATE = "LOCATE";

    /**
     * The constant for 'LOWER'.
     */
    String LOWER = "LOWER";

    /**
     * The constant for {@literal '<'}.
     */
    String LOWER_THAN = "<";

    /**
     * The constant for {@literal '<='}.
     */
    String LOWER_THAN_OR_EQUAL = "<=";

    /**
     * The constant for 'MAX'.
     */
    String MAX = "MAX";

    /**
     * The constant for 'MEMBER'.
     */
    String MEMBER = "MEMBER";

    /**
     * The constant for 'MEMBER OF'.
     */
    String MEMBER_OF = "MEMBER OF";

    /**
     * The constant for 'MIN'.
     */
    String MIN = "MIN";

    /**
     * The constant for the minus sign '-'.
     */
    String MINUS = "-";

    /**
     * The constant for 'MOD'.
     */
    String MOD = "MOD";

    /**
     * The constant for multiplication sign '*'.
     */
    String MULTIPLICATION = "*";

    /**
     * The constant for ':'.
     */
    String NAMED_PARAMETER = ":";

    /**
     * The constant for 'NEW'.
     */
    String NEW = "NEW";

    /**
     * The constant for 'NOT'.
     */
    String NOT = "NOT";

    /**
     * The constant for 'NOT BETWEEN'.
     */
    String NOT_BETWEEN = "NOT BETWEEN";

    /**
     * The constant for '!='.
     *
     * @since 2.4
     */
    String NOT_EQUAL = "!=";

    /**
     * The constant for 'NOT EXISTS'.
     */
    String NOT_EXISTS = "NOT EXISTS";

    /**
     * The constant for 'NOT IN'.
     */
    String NOT_IN = "NOT IN";

    /**
     * The constant for 'NOT LIKE'.
     */
    String NOT_LIKE = "NOT LIKE";

    /**
     * The constant for 'NOT MEMBER'.
     */
    String NOT_MEMBER = "NOT MEMBER";

    /**
     * The constant for 'NOT MEMBER OF'.
     */
    String NOT_MEMBER_OF = "NOT MEMBER OF";

    /**
     * The constant for 'NULL'.
     */
    String NULL = "NULL";

    /**
     * The constant for 'NULLIF'.
     */
    String NULLIF = "NULLIF";

    /**
     * The constant for 'NULLS'.
     *
     * @since 2.5
     */
    String NULLS = "NULLS";

    /**
     * The constant for 'NULLS FIRST'.
     *
     * @since 2.4
     */
    String NULLS_FIRST = "NULLS FIRST";

    /**
     * The constant for 'NULLS LAST'.
     *
     * @since 2.4
     */
    String NULLS_LAST = "NULLS LAST";

    /**
     * The constant for 'OBJECT'.
     */
    String OBJECT = "OBJECT";

    /**
     * The constant for 'OF'.
     */
    String OF = "OF";

    /**
     * The constant for 'ON', which is an EclipseLink specific identifier that was added in version 2.4.
     *
     * @since 2.4
     */
    String ON = "ON";

    /**
     * The constant 'OPERATOR', which is an EclipseLink specific identifier that was added in version 2.4.
     *
     * @since 2.4
     */
    String OPERATOR = "OPERATOR";

    /**
     * The constant for 'OR'.
     */
    String OR = "OR";

    /**
     * The constant for 'ORDER BY'.
     */
    String ORDER_BY = "ORDER BY";

    /**
     * The constant for 'ORDER SIBLINGS BY'.
     *
     * @since 2.5
     */
    String ORDER_SIBLINGS_BY = "ORDER SIBLINGS BY";

    /**
     * The constant for 'OUTER'.
     */
    String OUTER = "OUTER";

    /**
     * The constant for for the plus sign '+'.
     */
    String PLUS = "+";

    /**
     * The constant for 'POSITION', which is an unused keyword.
     */
    String POSITION = "POSITION";

    /**
     * The constant for '?'.
     */
    String POSITIONAL_PARAMETER = "?";

    /**
     * The constant for single quote.
     */
    String QUOTE = "'";

    /**
     * The constant for 'REGEXP'.
     *
     * @since 2.4
     */
    String REGEXP = "REGEXP";

    /**
     * The constant for 'SCN'.
     *
     * @since 2.5
     */
    String SCN = "SCN";

    /**
     * The constant for 'SELECT'.
     */
    String SELECT = "SELECT";

    /**
     * The constant for 'SET'.
     */
    String SET = "SET";

    /**
     * The constant for 'SIZE'.
     */
    String SIZE = "SIZE";

    /**
     * The constant for 'SOME'.
     */
    String SOME = "SOME";

    /**
     * The constant 'SQL', which is an EclipseLink specific identifier that was added in version 2.4.
     *
     * @since 2.4
     */
    String SQL = "SQL";

    /**
     * The constant for 'SQRT'.
     */
    String SQRT = "SQRT";

    /**
     * The constant for 'WHERE'.
     *
     * @version 2.5
     */
    String START_WITH = "START WITH";

    /**
     * The constant for 'SUBSTRING'.
     */
    String SUBSTRING = "SUBSTRING";

    /**
     * The constant for 'SUM'.
     */
    String SUM = "SUM";

    /**
     * The constant for 'TABLE'.
     *
     * @since 2.4
     */
    String TABLE = "TABLE";

    /**
     * The constant for 'THEN'.
     */
    String THEN = "THEN";

    /**
     * The constant for 'TIMESTAMP'.
     *
     * @since 2.5
     */
    String TIMESTAMP = "TIMESTAMP";

    /**
     * The constant for 'TRAILING'.
     */
    String TRAILING = "TRAILING";

    /**
     * The constant for 'TREAT', which is an EclipseLink specific identifier that was added in version 2.1.
     */
    String TREAT = "TREAT";

    /**
     * The constant for 'TRIM'.
     */
    String TRIM = "TRIM";

    /**
     * The constant for 'TRUE'.
     */
    String TRUE = "TRUE";

    /**
     * The constant for 'TYPE'.
     */
    String TYPE = "TYPE";

    /**
     * The constant for 'UNION'.
     *
     * @since 2.4
     */
    String UNION = "UNION";

    /**
     * The constant for 'UNKNOWN', which is an unused keyword.
     */
    String UNKNOWN = "UNKNOWN";

    /**
     * The constant for 'UPDATE'.
     */
    String UPDATE = "UPDATE";

    /**
     * The constant for 'UPPER'.
     */
    String UPPER = "UPPER";

    /**
     * The constant for 'VALUE'.
     */
    String VALUE = "VALUE";

    /**
     * The constant for the identifier 'WHEN'.
     */
    String WHEN = "WHEN";

    /**
     * The constant for 'WHERE'.
     */
    String WHERE = "WHERE";

    /**
     * Visits this {@link Expression} by the given {@link ExpressionVisitor visitor}.
     *
     * @param visitor The {@link ExpressionVisitor} to visit this object
     */
    void accept(ExpressionVisitor visitor);

    /**
     * Visits the children of this {@link Expression}. This method can be used to optimize traversing
     * the children since a new list is not created every time {@link #children()} is called.
     * <p>
     * This does not traverse the {@link Expression} sub-hierarchy, use a subclass of
     * {@link AbstractTraverseChildrenVisitor} in order to traverse the entire sub-hierarchy.
     *
     * @param visitor The {@link ExpressionVisitor visitor} to visit the children of this object.
     */
    void acceptChildren(ExpressionVisitor visitor);

    /**
     * Returns the children of this {@link Expression}.
     *
     * @return The children of this {@link Expression} or an empty {@link ListIterable}
     */
    ListIterable<Expression> children();

    /**
     * Retrieves the {@link JPQLQueryBNF} that represents the fragment of this {@link Expression}
     * that was used when parsing the given {@link Expression}.
     *
     * @param expression The {@link Expression} that is a descendant of this one
     * @return The {@link JPQLQueryBNF} that was used to parse the given expression
     * @since 2.5
     */
    JPQLQueryBNF findQueryBNF(Expression expression);

    /**
     * Returns the {@link JPQLGrammar} that defines how the JPQL query was parsed.
     *
     * @return The {@link JPQLGrammar} that was used to parse this {@link Expression}
     * @since 2.4
     */
    JPQLGrammar getGrammar();

    /**
     * Returns the length of the string representation of this {@link Expression}, which is the
     * length of the text generated by {@link #toActualText()}.
     *
     * @return The length of the string representation of this {@link Expression}
     * @since 2.4
     */
    int getLength();

    /**
     * Returns the position of this {@link Expression} within its parent hierarchy.
     *
     * @return The length of the string representation of what is coming before this object
     * @since 2.4
     */
    int getOffset();

    /**
     * Returns the parent of this {@link Expression}.
     *
     * @return The parent of this {@link Expression}, which is never <code>null</code> except for the
     * root of the tree
     */
    Expression getParent();

    /**
     * Returns the BNF of this {@link Expression}.
     *
     * @return The {@link JPQLQueryBNF}, which represents the grammar of this {@link Expression}
     * @since 2.4
     */
    JPQLQueryBNF getQueryBNF();

    /**
     * Retrieves the root node of the parsed tree hierarchy.
     *
     * @return The root of the {@link Expression} tree
     */
    JPQLExpression getRoot();

    /**
     * Determines whether this {@link Expression} is a parent of the given {@link Expression}.
     *
     * @param expression The {@link Expression} to verify its paternity with this {@link Expression}
     * @return <code>true</code> if this {@link Expression} is the same as the given {@link Expression}
     * or one of its parent; <code>false</code> otherwise
     */
    boolean isAncestor(Expression expression);

    /**
     * Returns the list representing this {@link Expression} and its children.
     *
     * @return The {@link Expression Expressions} representing this {@link Expression}
     */
    ListIterable<Expression> orderedChildren();

    /**
     * Retrieves the <code>Expression</code> located at the given position using the actual query,
     * which may have extra whitespace.
     *
     * @param position The array has one element and is the position of the {@link Expression} to retrieve
     */
    void populatePosition(QueryPosition queryPosition, int position);

    /**
     * Generates a string representation of this {@link Expression}, which needs to include any
     * characters that are considered virtual, i.e. that was parsed when the query is incomplete and
     * is needed for functionality like content assist.
     *
     * @return The string representation of this {@link Expression}
     */
    String toActualText();

    /**
     * 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".
     *
     * @return The string representation of this {@link Expression}
     */
    String toParsedText();
}