#ifndef STAN_MATH_PRIM_SCAL_PROB_LOGISTIC_LPDF_HPP
#define STAN_MATH_PRIM_SCAL_PROB_LOGISTIC_LPDF_HPP

#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/scal/err/check_consistent_sizes.hpp>
#include <stan/math/prim/scal/err/check_finite.hpp>
#include <stan/math/prim/scal/err/check_positive_finite.hpp>
#include <stan/math/prim/scal/fun/size_zero.hpp>
#include <stan/math/prim/scal/fun/value_of.hpp>
#include <stan/math/prim/scal/fun/log1p.hpp>
#include <cmath>

namespace stan {
namespace math {

// Logistic(y|mu, sigma)    [sigma > 0]
template <bool propto, typename T_y, typename T_loc, typename T_scale>
return_type_t<T_y, T_loc, T_scale> logistic_lpdf(const T_y& y, const T_loc& mu,
                                                 const T_scale& sigma) {
  static const char* function = "logistic_lpdf";
  using T_partials_return = partials_return_t<T_y, T_loc, T_scale>;

  using std::exp;
  using std::log;

  if (size_zero(y, mu, sigma)) {
    return 0.0;
  }

  T_partials_return logp(0.0);

  check_finite(function, "Random variable", y);
  check_finite(function, "Location parameter", mu);
  check_positive_finite(function, "Scale parameter", sigma);
  check_consistent_sizes(function, "Random variable", y, "Location parameter",
                         mu, "Scale parameter", sigma);

  if (!include_summand<propto, T_y, T_loc, T_scale>::value) {
    return 0.0;
  }

  operands_and_partials<T_y, T_loc, T_scale> ops_partials(y, mu, sigma);

  scalar_seq_view<T_y> y_vec(y);
  scalar_seq_view<T_loc> mu_vec(mu);
  scalar_seq_view<T_scale> sigma_vec(sigma);
  size_t N = max_size(y, mu, sigma);

  VectorBuilder<true, T_partials_return, T_scale> inv_sigma(length(sigma));
  VectorBuilder<include_summand<propto, T_scale>::value, T_partials_return,
                T_scale>
      log_sigma(length(sigma));
  for (size_t i = 0; i < length(sigma); i++) {
    inv_sigma[i] = 1.0 / value_of(sigma_vec[i]);
    if (include_summand<propto, T_scale>::value) {
      log_sigma[i] = log(value_of(sigma_vec[i]));
    }
  }

  VectorBuilder<!is_constant_all<T_loc>::value, T_partials_return, T_loc,
                T_scale>
      exp_mu_div_sigma(max_size(mu, sigma));
  VectorBuilder<!is_constant_all<T_loc>::value, T_partials_return, T_y, T_scale>
      exp_y_div_sigma(max_size(y, sigma));
  if (!is_constant_all<T_loc>::value) {
    for (size_t n = 0; n < max_size(mu, sigma); n++) {
      exp_mu_div_sigma[n] = exp(value_of(mu_vec[n]) / value_of(sigma_vec[n]));
    }
    for (size_t n = 0; n < max_size(y, sigma); n++) {
      exp_y_div_sigma[n] = exp(value_of(y_vec[n]) / value_of(sigma_vec[n]));
    }
  }

  for (size_t n = 0; n < N; n++) {
    const T_partials_return y_dbl = value_of(y_vec[n]);
    const T_partials_return mu_dbl = value_of(mu_vec[n]);

    const T_partials_return y_minus_mu = y_dbl - mu_dbl;
    const T_partials_return y_minus_mu_div_sigma = y_minus_mu * inv_sigma[n];
    T_partials_return exp_m_y_minus_mu_div_sigma(0);
    if (include_summand<propto, T_y, T_loc, T_scale>::value) {
      exp_m_y_minus_mu_div_sigma = exp(-y_minus_mu_div_sigma);
    }
    T_partials_return inv_1p_exp_y_minus_mu_div_sigma(0);
    if (!is_constant_all<T_y, T_scale>::value) {
      inv_1p_exp_y_minus_mu_div_sigma = 1 / (1 + exp(y_minus_mu_div_sigma));
    }

    if (include_summand<propto, T_y, T_loc, T_scale>::value) {
      logp -= y_minus_mu_div_sigma;
    }
    if (include_summand<propto, T_scale>::value) {
      logp -= log_sigma[n];
    }
    if (include_summand<propto, T_y, T_loc, T_scale>::value) {
      logp -= 2.0 * log1p(exp_m_y_minus_mu_div_sigma);
    }

    if (!is_constant_all<T_y>::value) {
      ops_partials.edge1_.partials_[n]
          += (2 * inv_1p_exp_y_minus_mu_div_sigma - 1) * inv_sigma[n];
    }
    if (!is_constant_all<T_loc>::value) {
      ops_partials.edge2_.partials_[n]
          += (1
              - 2 * exp_mu_div_sigma[n]
                    / (exp_mu_div_sigma[n] + exp_y_div_sigma[n]))
             * inv_sigma[n];
    }
    if (!is_constant_all<T_scale>::value) {
      ops_partials.edge3_.partials_[n]
          += ((1 - 2 * inv_1p_exp_y_minus_mu_div_sigma) * y_minus_mu
                  * inv_sigma[n]
              - 1)
             * inv_sigma[n];
    }
  }
  return ops_partials.build(logp);
}

template <typename T_y, typename T_loc, typename T_scale>
inline return_type_t<T_y, T_loc, T_scale> logistic_lpdf(const T_y& y,
                                                        const T_loc& mu,
                                                        const T_scale& sigma) {
  return logistic_lpdf<false>(y, mu, sigma);
}

}  // namespace math
}  // namespace stan
#endif
