// 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 op_roots
//! @{

template <typename T1>
inline void op_roots::apply(
    Mat<std::complex<typename T1::pod_type> >& out,
    const mtOp<std::complex<typename T1::pod_type>, T1, op_roots>& expr) {
  arma_debug_sigprint();

  const bool status = op_roots::apply_direct(out, expr.m);

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

template <typename T1>
inline bool op_roots::apply_direct(Mat<std::complex<typename T1::pod_type> >& out,
                                   const Base<typename T1::elem_type, T1>& X) {
  arma_debug_sigprint();

  typedef std::complex<typename T1::pod_type> out_eT;

  const quasi_unwrap<T1> U(X.get_ref());

  bool status = false;

  if (U.is_alias(out)) {
    Mat<out_eT> tmp;

    status = op_roots::apply_noalias(tmp, U.M);

    out.steal_mem(tmp);
  } else {
    status = op_roots::apply_noalias(out, U.M);
  }

  return status;
}

template <typename eT>
inline bool op_roots::apply_noalias(
    Mat<std::complex<typename get_pod_type<eT>::result> >& out, const Mat<eT>& X) {
  arma_debug_sigprint();

  typedef typename get_pod_type<eT>::result T;

  typedef std::complex<typename get_pod_type<eT>::result> out_eT;

  arma_conform_check((X.is_vec() == false), "roots(): given object must be a vector");

  if (X.internal_has_nonfinite()) {
    return false;
  }

  // treat X as a column vector

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

  const T Y_max = (Y.is_empty() == false) ? T(max(abs(Y))) : T(0);

  if (Y_max == T(0)) {
    out.set_size(1, 0);
    return true;
  }

  const uvec indices = find(Y / Y_max);

  const uword n_tail_zeros = (indices.n_elem > 0)
                                 ? uword((Y.n_elem - 1) - indices[indices.n_elem - 1])
                                 : uword(0);

  const Col<eT> Z = Y.subvec(indices[0], indices[indices.n_elem - 1]);

  if (Z.n_elem >= uword(2)) {
    Mat<eT> tmp;

    if (Z.n_elem == uword(2)) {
      tmp.set_size(1, 1);

      tmp[0] = -Z[1] / Z[0];
    } else {
      tmp = diagmat(ones<Col<eT> >(Z.n_elem - 2), -1);

      tmp.row(0) = strans(-Z.subvec(1, Z.n_elem - 1) / Z[0]);
    }

    Mat<out_eT> junk;

    const bool status = auxlib::eig_gen(out, junk, false, tmp);

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

    if (n_tail_zeros > 0) {
      out.resize(out.n_rows + n_tail_zeros, 1);
    }
  } else {
    out.zeros(n_tail_zeros, 1);
  }

  return true;
}

//! @}
