/*
 * This file is part of Soprano Project.
 *
 * Copyright (C) 2007 Sebastian Trueg <trueg@kde.org>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

#ifndef _SOPRANO_INFERENCE_RULE_H_
#define _SOPRANO_INFERENCE_RULE_H_

#include <QtCore/QSharedDataPointer>
#include <QtCore/QList>

#include "statementpattern.h"
#include "statement.h"
#include "soprano_export.h"


namespace Soprano {

    class BindingSet;

    namespace Inference {

        /**
         * \class Rule inferencerule.h Soprano/Inference/Rule
         *
         * \brief A rule used by the InferenceModel to generate inferenced statements.
         *
         * Rules can be created manually by adding preconditions and the effect via addPrecondition() and
         * setEffect() or from a rules file through the RuleParser.
         *
         * \author Sebastian Trueg <trueg@kde.org>
         */
        class SOPRANO_EXPORT Rule
        {
        public:
            Rule();
            Rule( const Rule& other );
            ~Rule();

            Rule& operator=( const Rule& other );

            /**
             * The list of preconditions for the rule. Each condition
             * is a StatementPattern which can contain variables.
             * These variables are identified by their name and matched
             * accordingly.
             */
            QList<StatementPattern> preconditions() const;

            void addPrecondition( const StatementPattern& );

            /**
             * The effect of a rule is a pattern that repeats variables from
             * the preconditions and thus, identifies the statements that
             * are to be infered from the preconditions.
             */
            StatementPattern effect() const;

            void setEffect( const StatementPattern& );

            /**
             * Check if a statement matches any of the statement patterns
             * in this rule.
             *
             * \return true if statement matches any of the patterns, false otherwise.
             * Be aware that createSparqlQuery() might still return an empty string
             * since it does perform some aditional optimization checks based on the
             * bound statement.
             */
            bool match( const Statement& statement ) const;

            /**
             * Bind this rule to a specific Statement.
             *
             * The purpose of this method is to allow retricting the application of
             * a rule to one statement, i.e. a newly added one.
             * 
             * \param statement The Statement to bind this rule to.
             *
             * \sa createSparqlQuery, bindEffect, bindPreconditions
             */
            void bindToStatement( const Statement& statement );

            /**
             * \return The statement set ia bindToStatement() or
             * an invalid one if none was set.
             */
            Statement boundToStatement() const;

            /**
             * Create a SPARQL query that retrieves all resources matching this rule.
             *
             * \param bindVariables If true and a valid binding statement is set the query
             * will be bound to this statement resulting in a UNION query of all possible
             * bindings.
             *
             * \return A full SPARQL query or an empty string if this rule does not apply
             * to the statement set via bindToStatement.
             *
             * \sa bindToStatement
             */
            QString createSparqlQuery( bool bindVariables = false ) const;

            /**
             * Bind the rule's effect to a set of bindings as reveived from a query.
             * If the bindings do not contain all variables the bound statement is used as backup.
             *
             * \param bindings The bindings to apply to this rule.
             *
             * \return The statement infered by this rule under the application of bindings.
             *
             * \sa bindToStatement, bindPreconditions
             */
            Statement bindEffect( const BindingSet& bindings ) const;

            /**
             * Bind the rule's preconditions to a set of bindings as reveived from a query.
             * If the bindings do not contain all variables the bound statement is used as backup.
             *
             * \param bindings The bindings to apply to this rule.
             *
             * \return The statements that have to be valid in order for this rule to infer the statement
             * returned by bindEffect under the same bindings.
             *
             * \sa bindToStatement, bindEffect
             */
            QList<Statement> bindPreconditions( const BindingSet& bindings ) const;

        private:
            /**
             * Merges in binding information from the bindingStatement by matching it to the preconditions.
             * This is necessary for optimized queries.
             */
            BindingSet mergeBindingStatement( const BindingSet& bindings ) const;
            Statement bindStatementPattern( const StatementPattern& pattern, const BindingSet& bindings ) const;

            class Private;
            QSharedDataPointer<Private> d;
        };
    }
}

SOPRANO_EXPORT QDebug operator<<( QDebug s, const Soprano::Inference::Rule& );

#endif
