#ifndef STAN_MATH_PRIM_SCAL_PROB_GUMBEL_CCDF_LOG_HPP
#define STAN_MATH_PRIM_SCAL_PROB_GUMBEL_CCDF_LOG_HPP

#include <boost/random/uniform_01.hpp>
#include <boost/random/variate_generator.hpp>
#include <stan/math/prim/scal/meta/OperandsAndPartials.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_not_nan.hpp>
#include <stan/math/prim/scal/err/check_positive.hpp>
#include <stan/math/prim/scal/meta/length.hpp>
#include <stan/math/prim/scal/meta/is_constant_struct.hpp>
#include <stan/math/prim/scal/meta/VectorView.hpp>
#include <stan/math/prim/scal/meta/VectorBuilder.hpp>
#include <stan/math/prim/scal/meta/partials_return_type.hpp>
#include <stan/math/prim/scal/meta/return_type.hpp>
#include <stan/math/prim/scal/fun/constants.hpp>
#include <stan/math/prim/scal/meta/include_summand.hpp>
#include <stan/math/prim/scal/fun/value_of.hpp>
#include <cmath>

namespace stan {
  namespace math {

    template <typename T_y, typename T_loc, typename T_scale>
    typename return_type<T_y, T_loc, T_scale>::type
    gumbel_ccdf_log(const T_y& y, const T_loc& mu, const T_scale& beta) {
      static const char* function("gumbel_ccdf_log");
      typedef typename stan::partials_return_type<T_y, T_loc, T_scale>::type
        T_partials_return;

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

      T_partials_return ccdf_log(0.0);
      if (!(stan::length(y)
            && stan::length(mu)
            && stan::length(beta)))
        return ccdf_log;

      check_not_nan(function, "Random variable", y);
      check_finite(function, "Location parameter", mu);
      check_not_nan(function, "Scale parameter", beta);
      check_positive(function, "Scale parameter", beta);
      check_consistent_sizes(function,
                             "Random variable", y,
                             "Location parameter", mu,
                             "Scale parameter", beta);

      OperandsAndPartials<T_y, T_loc, T_scale>
        operands_and_partials(y, mu, beta);

      VectorView<const T_y> y_vec(y);
      VectorView<const T_loc> mu_vec(mu);
      VectorView<const T_scale> beta_vec(beta);
      size_t N = max_size(y, mu, beta);

      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 beta_dbl = value_of(beta_vec[n]);
        const T_partials_return scaled_diff = (y_dbl - mu_dbl) / beta_dbl;
        const T_partials_return rep_deriv = exp(-scaled_diff
                                                - exp(-scaled_diff))
          / beta_dbl;
        const T_partials_return ccdf_log_ = 1.0 - exp(-exp(-scaled_diff));
        ccdf_log += log(ccdf_log_);

        if (!is_constant_struct<T_y>::value)
          operands_and_partials.d_x1[n] -= rep_deriv / ccdf_log_;
        if (!is_constant_struct<T_loc>::value)
          operands_and_partials.d_x2[n] += rep_deriv / ccdf_log_;
        if (!is_constant_struct<T_scale>::value)
          operands_and_partials.d_x3[n] += rep_deriv * scaled_diff / ccdf_log_;
      }

      return operands_and_partials.value(ccdf_log);
    }

  }
}
#endif
