#ifndef STAN_MATH_PRIM_MAT_ERR_CHECK_SIMPLEX_HPP
#define STAN_MATH_PRIM_MAT_ERR_CHECK_SIMPLEX_HPP

#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/arr/err/check_nonzero_size.hpp>
#include <stan/math/prim/mat/err/constraint_tolerance.hpp>
#include <stan/math/prim/mat/fun/Eigen.hpp>
#include <stan/math/prim/scal/err/domain_error.hpp>
#include <sstream>
#include <string>

namespace stan {
namespace math {

/**
 * Check if the specified vector is simplex.
 * To be a simplex, all values must be greater than or equal to 0
 * and the values must sum to 1.
 * A valid simplex is one where the sum of hte elements is equal
 * to 1.  This function tests that the sum is within the tolerance
 * specified by <code>CONSTRAINT_TOLERANCE</code>. This function
 * only accepts Eigen vectors, statically typed vectors, not
 * general matrices with 1 column.
 * @tparam T_prob Scalar type of the vector
 * @param function Function name (for error messages)
 * @param name Variable name (for error messages)
 * @param theta Vector to test.
 * @throw <code>std::invalid_argument</code> if <code>theta</code>
 *   is a 0-vector.
 * @throw <code>std::domain_error</code> if the vector is not a
 *   simplex or if any element is <code>NaN</code>.
 */
template <typename T_prob>
void check_simplex(const char* function, const char* name,
                   const Eigen::Matrix<T_prob, Eigen::Dynamic, 1>& theta) {
  using size_type =
      typename index_type<Eigen::Matrix<T_prob, Eigen::Dynamic, 1> >::type;

  check_nonzero_size(function, name, theta);
  if (!(fabs(1.0 - theta.sum()) <= CONSTRAINT_TOLERANCE)) {
    std::stringstream msg;
    T_prob sum = theta.sum();
    msg << "is not a valid simplex.";
    msg.precision(10);
    msg << " sum(" << name << ") = " << sum << ", but should be ";
    std::string msg_str(msg.str());
    domain_error(function, name, 1.0, msg_str.c_str());
  }
  for (size_type n = 0; n < theta.size(); n++) {
    if (!(theta[n] >= 0)) {
      std::ostringstream msg;
      msg << "is not a valid simplex. " << name << "["
          << n + stan::error_index::value << "]"
          << " = ";
      std::string msg_str(msg.str());
      domain_error(function, name, theta[n], msg_str.c_str(),
                   ", but should be greater than or equal to 0");
    }
  }
}
}  // namespace math
}  // namespace stan
#endif
