/* ----------------------------------------------------------------------------

 * GTSAM Copyright 2010, Georgia Tech Research Corporation,
 * Atlanta, Georgia 30332-0415
 * All Rights Reserved
 * Authors: Frank Dellaert, et al. (see THANKS for the full author list)

 * See LICENSE for the license information

 * -------------------------------------------------------------------------- */

/**
 * @brief sampling that can be parameterized using a NoiseModel to generate samples from
 * @file Sampler.h
 * the given distribution
 * @author Alex Cunningham
 */

#pragma once

#include <gtsam/linear/NoiseModel.h>

#include <boost/random.hpp>

namespace gtsam {

/**
 * Sampling structure that keeps internal random number generators for
 * diagonal distributions specified by NoiseModel
 *
 * This is primarily to allow for variable seeds, and does roughly the same
 * thing as sample() in NoiseModel.
 */
class GTSAM_EXPORT Sampler {
protected:
  /** noiseModel created at generation */
  noiseModel::Diagonal::shared_ptr model_;

  /** generator */
  boost::mt19937_64 generator_;

public:
  typedef boost::shared_ptr<Sampler> shared_ptr;

  /**
   * Create a sampler for the distribution specified by a diagonal NoiseModel
   * with a manually specified seed
   *
   * NOTE: do not use zero as a seed, it will break the generator
   */
  Sampler(const noiseModel::Diagonal::shared_ptr& model, int32_t seed = 42u);

  /**
   * Create a sampler for a distribution specified by a vector of sigmas directly
   *
   * NOTE: do not use zero as a seed, it will break the generator
   */
  Sampler(const Vector& sigmas, int32_t seed = 42u);

  /**
   * Create a sampler without a given noisemodel - pass in to sample
   *
   * NOTE: do not use zero as a seed, it will break the generator
   */
  Sampler(int32_t seed = 42u);

  /** access functions */
  size_t dim() const { assert(model_.get()); return model_->dim(); }
  Vector sigmas() const { assert(model_.get()); return model_->sigmas(); }
  const noiseModel::Diagonal::shared_ptr& model() const { return model_; }

  /**
   * sample from distribution
   * NOTE: not const due to need to update the underlying generator
   */
  Vector sample();

  /**
   * Sample from noisemodel passed in as an argument,
   * can be used without having initialized a model for the system.
   *
   * NOTE: not const due to need to update the underlying generator
   */
  Vector sampleNewModel(const noiseModel::Diagonal::shared_ptr& model);

protected:

  /** given sigmas for a diagonal model, returns a sample */
  Vector sampleDiagonal(const Vector& sigmas);

};

} // \namespace gtsam