// Copyright (c) 2005  Stanford University (USA).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org); you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public License as
// published by the Free Software Foundation; version 2.1 of the License.
// See the file LICENSE.LGPL distributed with CGAL.
//
// Licensees holding a valid commercial license may use this file in
// accordance with the commercial license agreement provided with the software.
//
// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
//
// $URL$
// $Id$
// 
//
// Author(s)     : Daniel Russel <drussel@alumni.princeton.edu>

#ifndef CGAL_LABEL_H_
#define CGAL_LABEL_H_
#include <CGAL/basic.h>
#include <iostream>
#include <sstream>

CGAL_BEGIN_NAMESPACE

//! A type which provides opaque, typed identifiers.
/*!
    Basically this is just an int with a type associated with it
    and one value (-1) picked out as the null value. It implements
    comparisons and things.
*/
template <class A_Type>
class Label
{
    protected:
        typedef Label<A_Type> This;
        int id_;

    public:
//! Construct it from an int
        Label(int i):id_(i){}
//! Construct a default (null) label
        Label():id_(-1) {
            if(0) print();                        // make sure it is compiled
        }
//! Make the next label
        This  next_label() {
            return Label(id_+1);
        }
//! Return the null label
        operator bool() const
        {
            return id_ != -1;
        }
//! Convert to an index value, -1 is invalid
        int index() const
        {
            return id_;
        }
        bool operator<(const This &o) const
        {
            return id_ < o.id_;
        }
        bool operator>(const This &o) const
        {
            return id_ > o.id_;
        }
        bool operator==(const This &o) const
        {
            return id_ ==o.id_;
        }
        bool operator!=(const This &o) const
        {
            return id_ !=o.id_;
        }

        template <class OS>
            void write(OS &out) const
        {
            if (id_==-1) out << "N";
            else out << id_;
        }
        void print() const
        {
            write(std::cout);
        }
//! Convert to a string
        std::string string() const
        {
            std::ostringstream os;
            write(os);
            return os.str();
        }
};

template <class A_type>
std::ostream& operator<<(std::ostream &out, const Label<A_type> &label)
{
    out << "(";
    label.write(out);
    out << ")";
    return out;
}


CGAL_END_NAMESPACE
#endif