#ifndef STAN_MATH_REV_SCAL_FUN_INC_BETA_HPP
#define STAN_MATH_REV_SCAL_FUN_INC_BETA_HPP

#include <stan/math/rev/core.hpp>
#include <stan/math/prim/scal/fun/constants.hpp>
#include <stan/math/prim/scal/fun/grad_reg_inc_beta.hpp>
#include <stan/math/rev/scal/fun/pow.hpp>
#include <stan/math/prim/scal/fun/lbeta.hpp>
#include <stan/math/prim/scal/fun/digamma.hpp>
#include <valarray>

namespace stan {
  namespace math {

    namespace {

      class inc_beta_vvv_vari : public op_vvv_vari {
      public:
        inc_beta_vvv_vari(vari* avi, vari* bvi, vari* cvi) :
          op_vvv_vari(inc_beta(avi->val_, bvi->val_, cvi->val_),
                      avi, bvi, cvi) {
        }
        void chain() {
          double d_a; double d_b;
          grad_reg_inc_beta(d_a, d_b, avi_->val_, bvi_->val_,
                            cvi_->val_, digamma(avi_->val_),
                            digamma(bvi_->val_),
                            digamma(avi_->val_ + bvi_->val_),
                            std::exp(lbeta(avi_->val_,
                                           bvi_->val_)));

          avi_->adj_ += adj_ * d_a;
          bvi_->adj_ += adj_ * d_b;
          cvi_->adj_ += adj_ * std::pow((1-cvi_->val_), bvi_->val_-1)
            * std::pow(cvi_->val_, avi_->val_-1)
            / std::exp(lbeta(avi_->val_, bvi_->val_));
        }
      };

    }

    inline var inc_beta(const var& a,
                        const var& b,
                        const var& c) {
      return var(new inc_beta_vvv_vari(a.vi_, b.vi_, c.vi_));
    }

  }
}
#endif
