/*
    This file is part of the syndication library
    SPDX-FileCopyrightText: 2006 Frank Osterfeld <osterfeld@kde.org>

    SPDX-License-Identifier: LGPL-2.0-or-later
*/

#ifndef SYNDICATION_RDF_STATEMENT_H
#define SYNDICATION_RDF_STATEMENT_H

#include <syndication/rdf/property.h>

class QString;

namespace Syndication
{
namespace RDF
{

//@cond PRIVATE
class Statement;
typedef QSharedPointer<Statement> StatementPtr;
//@endcond

/**
 * An RDF statement, consisting of a triple
 * (subject, predicate, object).
 */
class SYNDICATION_EXPORT Statement
{
    friend class Model;
public:

    /**
     * creates a null statement
     */
    Statement();

    /**
     * creates a copy of another statement
     *
     * @param other the statement to copy
     */
    Statement(const Statement &other);

    /**
     * creates a statement
     * Do not call this in your code, use Model::createStatement() instead.
     *
     * @param subject the subject resource of the statement
     * @param predicate the predicate of the statement
     * @param object the object node of the statement
     */
    Statement(ResourcePtr subject, PropertyPtr predicate, NodePtr object);

    /**
     * destructor
     */
    virtual ~Statement();

    /**
     * assigns another statement
     *
     * @param other the statement to assign
     */
    Statement &operator=(const Statement &other);

    /**
     * returns whether two statements are equal.
     * Currently statements are equal, if they are from the same model (!)
     * and subject, predicate and object are equal.
     *
     * @param other the statement to compare to
     */
    virtual bool operator==(const Statement &other) const;

    /**
     * returns whether this statement is a null statement (i.e. was created
     * using Statement())
     */
    virtual bool isNull() const;

    /**
     * the subject of the statement.
     */
    virtual ResourcePtr subject() const;

    /**
     * the predicate of the statement
     */
    virtual PropertyPtr predicate() const;

    /**
     * the object of the statement
     */
    virtual NodePtr object() const;

    /**
     * returns the object of this statement as resource, if possible.
     *
     * @return the object node as Resource, or @c null if the object
     * is not a resource
     */
    virtual ResourcePtr asResource() const;

    /**
     * returns the object of this statement as string, if possible.
     *
     * @return the literal text as QString, or a null string if the object
     * is not a literal
     */
    virtual QString asString() const;

private:
    class StatementPrivate;
    QSharedPointer<StatementPrivate> d;
};

} // namespace RDF
} // namespace Syndication

#endif // SYNDICATION_RDF_STATEMENT_H
