//

//=======================================================================

// Copyright 1997-2001 University of Notre Dame.

// Authors: Andrew Lumsdaine, Lie-Quan Lee, Jeremy G. Siek

//

// Distributed under the Boost Software License, Version 1.0. (See

// accompanying file LICENSE_1_0.txt or copy at

// http://www.boost.org/LICENSE_1_0.txt)

//=======================================================================

//

#ifndef BOOST_GRAPH_CONNECTED_COMPONENTS_HPP

#define BOOST_GRAPH_CONNECTED_COMPONENTS_HPP

#include <boost/config.hpp>

#include <boost/graph/depth_first_search.hpp>

#include <boost/graph/properties.hpp>

#include <boost/graph/graph_concepts.hpp>

#include <boost/static_assert.hpp>

namespace boost {

  namespace detail {

    // This visitor is used both in the connected_components algorithm

    // and in the kosaraju strong components algorithm during the

    // second DFS traversal.

    template <class ComponentsMap>

    class components_recorder : public dfs_visitor<>

    {

      typedef typename property_traits<ComponentsMap>::value_type comp_type;

    public:

      components_recorder(ComponentsMap c, 

                          comp_type& c_count)

        : m_component(c), m_count(c_count) {}

      template <class Vertex, class Graph>

      void start_vertex(Vertex, Graph&) {

        if (m_count == (std::numeric_limits<comp_type>::max)())

          m_count = 0; // start counting components at zero

        else

          ++m_count;

      }

      template <class Vertex, class Graph>

      void discover_vertex(Vertex u, Graph&) {

        put(m_component, u, m_count);

      }

    protected:

      ComponentsMap m_component;

      comp_type& m_count;

    };

  } // namespace detail

  // This function computes the connected components of an undirected

  // graph using a single application of depth first search.

  template <class Graph, class ComponentMap, class P, class T, class R>

  inline typename property_traits<ComponentMap>::value_type

  connected_components(const Graph& g, ComponentMap c, 

                       const bgl_named_params<P, T, R>& params)

  {

    if (num_vertices(g) == 0) return 0;

    typedef typename graph_traits<Graph>::vertex_descriptor Vertex;

    function_requires< WritablePropertyMapConcept<ComponentMap, Vertex> >();

    typedef typename boost::graph_traits<Graph>::directed_category directed;

    BOOST_STATIC_ASSERT((boost::is_same<directed, undirected_tag>::value));

    typedef typename property_traits<ComponentMap>::value_type comp_type;

    // c_count initialized to "nil" (with nil represented by (max)())

    comp_type c_count((std::numeric_limits<comp_type>::max)());

    detail::components_recorder<ComponentMap> vis(c, c_count);

    depth_first_search(g, params.visitor(vis));

    return c_count + 1;

  }

  template <class Graph, class ComponentMap>

  inline typename property_traits<ComponentMap>::value_type

  connected_components(const Graph& g, ComponentMap c)

  {

    if (num_vertices(g) == 0) return 0;

    typedef typename graph_traits<Graph>::vertex_descriptor Vertex;

    function_requires< WritablePropertyMapConcept<ComponentMap, Vertex> >();

    typedef typename boost::graph_traits<Graph>::directed_category directed;

    BOOST_STATIC_ASSERT((boost::is_same<directed, undirected_tag>::value));

    typedef typename property_traits<ComponentMap>::value_type comp_type;

    // c_count initialized to "nil" (with nil represented by (max)())

    comp_type c_count((std::numeric_limits<comp_type>::max)());

    detail::components_recorder<ComponentMap> vis(c, c_count);

    depth_first_search(g, visitor(vis));

    return c_count + 1;

  }

} // namespace boost

#endif // BOOST_GRAPH_CONNECTED_COMPONENTS_HPP