// 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 fn_inplace_strans
//! @{

template <typename eT>
inline void inplace_strans(Mat<eT>& X, const char* method = "std") {
  arma_debug_sigprint();

  const char sig = (method != nullptr) ? method[0] : char(0);

  arma_conform_check(((sig != 's') && (sig != 'l')),
                     "inplace_strans(): unknown method specified");

  const bool low_memory = (sig == 'l');

  if ((low_memory == false) || (X.n_rows == X.n_cols)) {
    op_strans::apply_mat_inplace(X);
  } else {
    // in-place algorithm inspired by:
    // Fred G. Gustavson, Tadeusz Swirszcz.
    // In-Place Transposition of Rectangular Matrices.
    // Applied Parallel Computing. State of the Art in Scientific Computing.
    // Lecture Notes in Computer Science. Volume 4699, pp. 560-569, 2007.

    // X.set_size() will check whether we can change the dimensions of X;
    // X.set_size() will also reuse existing memory, as the number of elements hasn't
    // changed

    X.set_size(X.n_cols, X.n_rows);

    const uword m = X.n_cols;
    const uword n = X.n_rows;

    std::vector<bool> visited(
        X.n_elem);  // TODO: replace std::vector<bool> with a better implementation

    for (uword col = 0; col < m; ++col)
      for (uword row = 0; row < n; ++row) {
        const uword pos = col * n + row;

        if (visited[pos] == false) {
          uword curr_pos = pos;

          eT val = X.at(row, col);

          while (visited[curr_pos] == false) {
            visited[curr_pos] = true;

            const uword j = curr_pos / m;
            const uword i = curr_pos - m * j;

            const eT tmp = X.at(j, i);
            X.at(j, i) = val;
            val = tmp;

            curr_pos = i * n + j;
          }
        }
      }
  }
}

//! @}
