#ifndef STAN_SERVICES_UTIL_GQ_WRITER_HPP
#define STAN_SERVICES_UTIL_GQ_WRITER_HPP

#include <stan/callbacks/logger.hpp>
#include <stan/callbacks/writer.hpp>
#include <stan/mcmc/base_mcmc.hpp>
#include <stan/mcmc/sample.hpp>
#include <stan/model/prob_grad.hpp>
#include <sstream>
#include <iomanip>
#include <string>
#include <vector>

namespace stan {
namespace services {
namespace util {

/**
 * gq_writer writes out
 *
 * @tparam Model Model class
 */
class gq_writer {
 private:
  callbacks::writer& sample_writer_;
  callbacks::logger& logger_;
  int num_constrained_params_;

 public:
  /**
   * Constructor.
   *
   * @param[in,out] sample_writer samples are "written" to this stream
   * @param[in,out] logger messages are written through the logger
   * @param[in] num_constrained_params offset into write_array gqs
   */
  gq_writer(callbacks::writer& sample_writer, callbacks::logger& logger,
            int num_constrained_params)
      : sample_writer_(sample_writer),
        logger_(logger),
        num_constrained_params_(num_constrained_params) {}

  /**
   * Write names of variables declared in the generated quantities block
   * to stream `sample_writer_`.
   *
   * @tparam M model class
   */
  template <class Model>
  void write_gq_names(const Model& model) {
    static const bool include_tparams = false;
    static const bool include_gqs = true;
    std::vector<std::string> names;
    model.constrained_param_names(names, include_tparams, include_gqs);
    std::vector<std::string> gq_names(names.begin() + num_constrained_params_,
                                      names.end());
    sample_writer_(gq_names);
  }

  /**
   * Calls model's `write_array` method and writes values of
   * variables defined in the generated quantities block
   * to stream `sample_writer_`.
   *
   * @tparam M model class
   * @tparam RNG pseudo random number generator class
   * @param[in] model instantiated model
   * @param[in] rng instantiated RNG
   * @param[in] draw sequence unconstrained parameters values.
   */
  template <class Model, class RNG>
  void write_gq_values(const Model& model, RNG& rng,
                       const std::vector<double>& draw) {
    std::vector<double> values;
    std::vector<int> params_i;  // unused - no discrete params
    std::stringstream ss;
    try {
      model.write_array(rng, const_cast<std::vector<double>&>(draw), params_i,
                        values, false, true, &ss);
    } catch (const std::exception& e) {
      if (ss.str().length() > 0)
        logger_.info(ss);
      logger_.info(e.what());
      return;
    }
    if (ss.str().length() > 0)
      logger_.info(ss);

    std::vector<double> gq_values(values.begin() + num_constrained_params_,
                                  values.end());
    sample_writer_(gq_values);
  }
};

}  // namespace util
}  // namespace services
}  // namespace stan
#endif
