// SPDX-License-Identifier: Apache-2.0
//
// Copyright 2008-2016 Conrad Sanderson (http://conradsanderson.id.au)
// Copyright 2008-2016 National ICT Australia (NICTA)
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ------------------------------------------------------------------------

//! \addtogroup glue_polyfit
//! @{

template <typename eT>
inline bool glue_polyfit::apply_noalias(Mat<eT>& out, const Col<eT>& X, const Col<eT>& Y,
                                        const uword N) {
  arma_debug_sigprint();

  // create Vandermonde matrix

  Mat<eT> V(X.n_elem, N + 1, arma_nozeros_indicator());

  V.tail_cols(1).ones();

  for (uword i = 1; i <= N; ++i) {
    const uword j = N - i;

    Col<eT> V_col_j(V.colptr(j), V.n_rows, false, false);
    Col<eT> V_col_jp1(V.colptr(j + 1), V.n_rows, false, false);

    V_col_j = V_col_jp1 % X;
  }

  Mat<eT> Q;
  Mat<eT> R;

  const bool status1 = auxlib::qr_econ(Q, R, V);

  if (status1 == false) {
    return false;
  }

  const bool status2 = auxlib::solve_trimat_fast(out, R, (Q.t() * Y), uword(0));

  if (status2 == false) {
    return false;
  }

  return true;
}

template <typename T1, typename T2>
inline bool glue_polyfit::apply_direct(Mat<typename T1::elem_type>& out,
                                       const Base<typename T1::elem_type, T1>& X_expr,
                                       const Base<typename T1::elem_type, T2>& Y_expr,
                                       const uword N) {
  arma_debug_sigprint();

  typedef typename T1::elem_type eT;

  const quasi_unwrap<T1> UX(X_expr.get_ref());
  const quasi_unwrap<T2> UY(Y_expr.get_ref());

  const Mat<eT>& X = UX.M;
  const Mat<eT>& Y = UY.M;

  arma_conform_check((((X.is_vec() == false) && (X.is_empty() == false)) ||
                      ((Y.is_vec() == false) && (Y.is_empty() == false))),
                     "polyfit(): given object must be a vector");

  arma_conform_check((X.n_elem != Y.n_elem),
                     "polyfit(): given vectors must have the same number of elements");

  if (X.n_elem == 0) {
    out.reset();
    return true;
  }

  arma_conform_check((N >= X.n_elem),
                     "polyfit(): N must be less than the number of elements in X");

  const Col<eT> X_as_colvec(const_cast<eT*>(X.memptr()), X.n_elem, false, false);
  const Col<eT> Y_as_colvec(const_cast<eT*>(Y.memptr()), Y.n_elem, false, false);

  bool status = false;

  if (UX.is_alias(out) || UY.is_alias(out)) {
    Mat<eT> tmp;
    status = glue_polyfit::apply_noalias(tmp, X_as_colvec, Y_as_colvec, N);
    out.steal_mem(tmp);
  } else {
    status = glue_polyfit::apply_noalias(out, X_as_colvec, Y_as_colvec, N);
  }

  return status;
}

template <typename T1, typename T2>
inline void glue_polyfit::apply(Mat<typename T1::elem_type>& out,
                                const Glue<T1, T2, glue_polyfit>& expr) {
  arma_debug_sigprint();

  const bool status = glue_polyfit::apply_direct(out, expr.A, expr.B, expr.aux_uword);

  if (status == false) {
    out.soft_reset();
    arma_stop_runtime_error("polyfit(): failed");
  }
}

//! @}
