// Copyright 2004, 2005 The Trustees of Indiana University.

// Use, modification and distribution is subject to 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)

//  Authors: Nick Edmonds
//           Andrew Lumsdaine
#ifndef BOOST_GRAPH_SSCA_GENERATOR_HPP
#define BOOST_GRAPH_SSCA_GENERATOR_HPP

#include <iterator>
#include <utility>
#include <vector>
#include <queue>
#include <boost/config.hpp>
#include <boost/random/uniform_int.hpp>
#include <boost/graph/graph_traits.hpp>
#include <boost/type_traits/is_base_and_derived.hpp>
#include <boost/type_traits/is_same.hpp>

enum Direction {FORWARD = 1, BACKWARD = 2, BOTH = FORWARD | BACKWARD};

namespace boost {

  // This generator generates graphs according to the method specified
  // in SSCA 1.1.  Current versions of SSCA use R-MAT graphs

  template<typename RandomGenerator, typename Graph>
  class ssca_iterator
  {
    typedef typename graph_traits<Graph>::directed_category directed_category;
    typedef typename graph_traits<Graph>::vertices_size_type 
      vertices_size_type;

  public:
    typedef std::input_iterator_tag iterator_category;
    typedef std::pair<vertices_size_type, vertices_size_type> value_type;
    typedef const value_type& reference;
    typedef const value_type* pointer;
    typedef void difference_type;

    // No argument constructor, set to terminating condition
    ssca_iterator()
      : gen(), verticesRemaining(0) { }

    // Initialize for edge generation
    ssca_iterator(RandomGenerator& gen, vertices_size_type totVertices, 
                  vertices_size_type maxCliqueSize, double probUnidirectional, 
                  int maxParallelEdges, double probIntercliqueEdges) 
      : gen(&gen), totVertices(totVertices), maxCliqueSize(maxCliqueSize), 
        probUnidirectional(probUnidirectional), maxParallelEdges(maxParallelEdges),
        probIntercliqueEdges(probIntercliqueEdges), currentClique(0), 
        verticesRemaining(totVertices)
    { 
      cliqueNum = std::vector<int>(totVertices, -1);
      current = std::make_pair(0,0);
    }

    reference operator*() const { return current; }
    pointer operator->() const { return &current; }
    
    ssca_iterator& operator++()
    {
      BOOST_USING_STD_MIN();
      while (values.empty() && verticesRemaining > 0) { // If there are no values left, generate a new clique
        uniform_int<vertices_size_type> clique_size(1, maxCliqueSize);
        uniform_int<vertices_size_type> rand_vertex(0, totVertices-1);
        uniform_int<int> num_parallel_edges(1, maxParallelEdges);
        uniform_int<short> direction(0,1);
        uniform_01<RandomGenerator> prob(*gen);
        std::vector<vertices_size_type> cliqueVertices;

        cliqueVertices.clear();
        vertices_size_type size = min BOOST_PREVENT_MACRO_SUBSTITUTION (clique_size(*gen), verticesRemaining);
        while (cliqueVertices.size() < size) {
          vertices_size_type v = rand_vertex(*gen);
          if (cliqueNum[v] == -1) {
            cliqueNum[v] = currentClique;
            cliqueVertices.push_back(v);
            verticesRemaining--;
          }
        }  // Nick: This is inefficient when only a few vertices remain...
           //       I should probably just select the remaining vertices 
           //       in order when only a certain fraction remain.

        typename std::vector<vertices_size_type>::iterator first, second;
        for (first = cliqueVertices.begin(); first != cliqueVertices.end(); ++first)
          for (second = first+1; second != cliqueVertices.end(); ++second) {
            Direction d;
            int edges;

            d = prob() < probUnidirectional ? (direction(*gen) == 0 ? FORWARD : BACKWARD) : BOTH;

            if (d & FORWARD) {
              edges = num_parallel_edges(*gen);
              for (int i = 0; i < edges; ++i)
                values.push(std::make_pair(*first, *second));
            }
              
            if (d & BACKWARD) {
              edges = num_parallel_edges(*gen);
              for (int i = 0; i < edges; ++i)
                values.push(std::make_pair(*second, *first));
            }
          }

        if (verticesRemaining == 0) {
          // Generate interclique edges
          for (vertices_size_type i = 0; i < totVertices; ++i) {
            double p = probIntercliqueEdges;
            for (vertices_size_type d = 2; d < totVertices/2; d *= 2, p/= 2) {
              vertices_size_type j = (i+d) % totVertices;
              if (cliqueNum[j] != cliqueNum[i] && prob() < p) {
                int edges = num_parallel_edges(*gen);
                for (int i = 0; i < edges; ++i)
                  values.push(std::make_pair(i, j));
              }
            }
          }
        }

        currentClique++;
      } 

      if (!values.empty()) { // If we're not done return a value
        current = values.front();
        values.pop();
      }

      return *this;
    }

    ssca_iterator operator++(int)
    {
      ssca_iterator temp(*this);
      ++(*this);
      return temp;
    }

    bool operator==(const ssca_iterator& other) const
    {
      return verticesRemaining == other.verticesRemaining && values.empty() && other.values.empty();
    }

    bool operator!=(const ssca_iterator& other) const
    { return !(*this == other); }

  private:

    // Parameters
    RandomGenerator* gen;
    vertices_size_type totVertices;
    vertices_size_type maxCliqueSize;
    double probUnidirectional;
    int maxParallelEdges;
    double probIntercliqueEdges;

    // Internal data structures
    std::vector<int> cliqueNum;
    std::queue<value_type> values;
    int currentClique;
    vertices_size_type verticesRemaining;
    value_type current;
  };

} // end namespace boost

#endif // BOOST_GRAPH_SSCA_GENERATOR_HPP