#ifndef STAN_MATH_REV_SCAL_FUN_GAMMA_Q_HPP
#define STAN_MATH_REV_SCAL_FUN_GAMMA_Q_HPP

#include <stan/math/rev/core.hpp>
#include <stan/math/prim/scal/fun/digamma.hpp>
#include <stan/math/prim/scal/fun/gamma_q.hpp>
#include <stan/math/prim/scal/fun/grad_reg_inc_gamma.hpp>
#include <stan/math/prim/scal/fun/tgamma.hpp>
#include <boost/math/special_functions/gamma.hpp>
#include <valarray>

namespace stan {
namespace math {

namespace {
class gamma_q_vv_vari : public op_vv_vari {
 public:
  gamma_q_vv_vari(vari* avi, vari* bvi)
      : op_vv_vari(gamma_q(avi->val_, bvi->val_), avi, bvi) {}
  void chain() {
    avi_->adj_ += adj_
                  * grad_reg_inc_gamma(avi_->val_, bvi_->val_,
                                       tgamma(avi_->val_), digamma(avi_->val_));
    bvi_->adj_
        -= adj_ * boost::math::gamma_p_derivative(avi_->val_, bvi_->val_);
  }
};

class gamma_q_vd_vari : public op_vd_vari {
 public:
  gamma_q_vd_vari(vari* avi, double b)
      : op_vd_vari(gamma_q(avi->val_, b), avi, b) {}
  void chain() {
    avi_->adj_ += adj_
                  * grad_reg_inc_gamma(avi_->val_, bd_, tgamma(avi_->val_),
                                       digamma(avi_->val_));
  }
};

class gamma_q_dv_vari : public op_dv_vari {
 public:
  gamma_q_dv_vari(double a, vari* bvi)
      : op_dv_vari(gamma_q(a, bvi->val_), a, bvi) {}
  void chain() {
    bvi_->adj_ -= adj_ * boost::math::gamma_p_derivative(ad_, bvi_->val_);
  }
};
}  // namespace

inline var gamma_q(const var& a, const var& b) {
  return var(new gamma_q_vv_vari(a.vi_, b.vi_));
}

inline var gamma_q(const var& a, double b) {
  return var(new gamma_q_vd_vari(a.vi_, b));
}

inline var gamma_q(double a, const var& b) {
  return var(new gamma_q_dv_vari(a, b.vi_));
}

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