// Ceres Solver - A fast non-linear least squares minimizer

// Copyright 2015 Google Inc. All rights reserved.

// http://ceres-solver.org/

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// Author: sameeragarwal@google.com (Sameer Agarwal)

#include "ceres/parameter_block_ordering.h"

#include "ceres/graph.h"

#include "ceres/graph_algorithms.h"

#include "ceres/internal/scoped_ptr.h"

#include "ceres/map_util.h"

#include "ceres/parameter_block.h"

#include "ceres/program.h"

#include "ceres/residual_block.h"

#include "ceres/wall_time.h"

#include "glog/logging.h"

namespace ceres {

namespace internal {

using std::map;

using std::set;

using std::vector;

int ComputeStableSchurOrdering(const Program& program,

                         vector<ParameterBlock*>* ordering) {

  CHECK_NOTNULL(ordering)->clear();

  EventLogger event_logger("ComputeStableSchurOrdering");

  scoped_ptr<Graph< ParameterBlock*> > graph(CreateHessianGraph(program));

  event_logger.AddEvent("CreateHessianGraph");

  const vector<ParameterBlock*>& parameter_blocks = program.parameter_blocks();

  const HashSet<ParameterBlock*>& vertices = graph->vertices();

  for (int i = 0; i < parameter_blocks.size(); ++i) {

    if (vertices.count(parameter_blocks[i]) > 0) {

      ordering->push_back(parameter_blocks[i]);

    }

  }

  event_logger.AddEvent("Preordering");

  int independent_set_size = StableIndependentSetOrdering(*graph, ordering);

  event_logger.AddEvent("StableIndependentSet");

  // Add the excluded blocks to back of the ordering vector.

  for (int i = 0; i < parameter_blocks.size(); ++i) {

    ParameterBlock* parameter_block = parameter_blocks[i];

    if (parameter_block->IsConstant()) {

      ordering->push_back(parameter_block);

    }

  }

  event_logger.AddEvent("ConstantParameterBlocks");

  return independent_set_size;

}

int ComputeSchurOrdering(const Program& program,

                         vector<ParameterBlock*>* ordering) {

  CHECK_NOTNULL(ordering)->clear();

  scoped_ptr<Graph< ParameterBlock*> > graph(CreateHessianGraph(program));

  int independent_set_size = IndependentSetOrdering(*graph, ordering);

  const vector<ParameterBlock*>& parameter_blocks = program.parameter_blocks();

  // Add the excluded blocks to back of the ordering vector.

  for (int i = 0; i < parameter_blocks.size(); ++i) {

    ParameterBlock* parameter_block = parameter_blocks[i];

    if (parameter_block->IsConstant()) {

      ordering->push_back(parameter_block);

    }

  }

  return independent_set_size;

}

void ComputeRecursiveIndependentSetOrdering(const Program& program,

                                            ParameterBlockOrdering* ordering) {

  CHECK_NOTNULL(ordering)->Clear();

  const vector<ParameterBlock*> parameter_blocks = program.parameter_blocks();

  scoped_ptr<Graph< ParameterBlock*> > graph(CreateHessianGraph(program));

  int num_covered = 0;

  int round = 0;

  while (num_covered < parameter_blocks.size()) {

    vector<ParameterBlock*> independent_set_ordering;

    const int independent_set_size =

        IndependentSetOrdering(*graph, &independent_set_ordering);

    for (int i = 0; i < independent_set_size; ++i) {

      ParameterBlock* parameter_block = independent_set_ordering[i];

      ordering->AddElementToGroup(parameter_block->mutable_user_state(), round);

      graph->RemoveVertex(parameter_block);

    }

    num_covered += independent_set_size;

    ++round;

  }

}

Graph<ParameterBlock*>* CreateHessianGraph(const Program& program) {

  Graph<ParameterBlock*>* graph = CHECK_NOTNULL(new Graph<ParameterBlock*>);

  const vector<ParameterBlock*>& parameter_blocks = program.parameter_blocks();

  for (int i = 0; i < parameter_blocks.size(); ++i) {

    ParameterBlock* parameter_block = parameter_blocks[i];

    if (!parameter_block->IsConstant()) {

      graph->AddVertex(parameter_block);

    }

  }

  const vector<ResidualBlock*>& residual_blocks = program.residual_blocks();

  for (int i = 0; i < residual_blocks.size(); ++i) {

    const ResidualBlock* residual_block = residual_blocks[i];

    const int num_parameter_blocks = residual_block->NumParameterBlocks();

    ParameterBlock* const* parameter_blocks =

        residual_block->parameter_blocks();

    for (int j = 0; j < num_parameter_blocks; ++j) {

      if (parameter_blocks[j]->IsConstant()) {

        continue;

      }

      for (int k = j + 1; k < num_parameter_blocks; ++k) {

        if (parameter_blocks[k]->IsConstant()) {

          continue;

        }

        graph->AddEdge(parameter_blocks[j], parameter_blocks[k]);

      }

    }

  }

  return graph;

}

void OrderingToGroupSizes(const ParameterBlockOrdering* ordering,

                          vector<int>* group_sizes) {

  CHECK_NOTNULL(group_sizes)->clear();

  if (ordering == NULL) {

    return;

  }

  const map<int, set<double*> >& group_to_elements =

      ordering->group_to_elements();

  for (map<int, set<double*> >::const_iterator it = group_to_elements.begin();

       it != group_to_elements.end();

       ++it) {

    group_sizes->push_back(it->second.size());

  }

}

}  // namespace internal

}  // namespace ceres