// 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 spop_mean
//! @{

template <typename T1>
inline void spop_mean::apply(SpMat<typename T1::elem_type>& out,
                             const SpOp<T1, spop_mean>& in) {
  arma_extra_debug_sigprint();

  typedef typename T1::elem_type eT;

  const uword dim = in.aux_uword_a;
  arma_debug_check((dim > 1), "mean(): parameter 'dim' must be 0 or 1");

  const SpProxy<T1> p(in.m);

  if (p.is_alias(out) == false) {
    spop_mean::apply_noalias_fast(out, p, dim);
  } else {
    SpMat<eT> tmp;

    spop_mean::apply_noalias_fast(tmp, p, dim);

    out.steal_mem(tmp);
  }
}

template <typename T1>
inline void spop_mean::apply_noalias_fast(SpMat<typename T1::elem_type>& out,
                                          const SpProxy<T1>& p, const uword dim) {
  arma_extra_debug_sigprint();

  typedef typename T1::elem_type eT;
  typedef typename T1::pod_type T;

  const uword p_n_rows = p.get_n_rows();
  const uword p_n_cols = p.get_n_cols();

  if ((p_n_rows == 0) || (p_n_cols == 0) || (p.get_n_nonzero() == 0)) {
    if (dim == 0) {
      out.zeros((p_n_rows > 0) ? 1 : 0, p_n_cols);
    }
    if (dim == 1) {
      out.zeros(p_n_rows, (p_n_cols > 0) ? 1 : 0);
    }

    return;
  }

  if (dim == 0)  // find the mean in each column
  {
    Row<eT> acc(p_n_cols, arma_zeros_indicator());

    eT* acc_mem = acc.memptr();

    if (SpProxy<T1>::use_iterator) {
      typename SpProxy<T1>::const_iterator_type it = p.begin();

      const uword N = p.get_n_nonzero();

      for (uword i = 0; i < N; ++i) {
        acc_mem[it.col()] += (*it);
        ++it;
      }

      acc /= T(p_n_rows);
    } else {
      for (uword col = 0; col < p_n_cols; ++col) {
        acc_mem[col] =
            arrayops::accumulate(&p.get_values()[p.get_col_ptrs()[col]],
                                 p.get_col_ptrs()[col + 1] - p.get_col_ptrs()[col]) /
            T(p_n_rows);
      }
    }

    out = acc;
  } else if (dim == 1)  // find the mean in each row
  {
    Col<eT> acc(p_n_rows, arma_zeros_indicator());

    eT* acc_mem = acc.memptr();

    typename SpProxy<T1>::const_iterator_type it = p.begin();

    const uword N = p.get_n_nonzero();

    for (uword i = 0; i < N; ++i) {
      acc_mem[it.row()] += (*it);
      ++it;
    }

    acc /= T(p_n_cols);

    out = acc;
  }

  if (out.internal_has_nonfinite()) {
    spop_mean::apply_noalias_slow(out, p, dim);
  }
}

template <typename T1>
inline void spop_mean::apply_noalias_slow(SpMat<typename T1::elem_type>& out,
                                          const SpProxy<T1>& p, const uword dim) {
  arma_extra_debug_sigprint();

  typedef typename T1::elem_type eT;

  const uword p_n_rows = p.get_n_rows();
  const uword p_n_cols = p.get_n_cols();

  if (dim == 0)  // find the mean in each column
  {
    arma_extra_debug_print("spop_mean::apply_noalias(): dim = 0");

    out.set_size((p_n_rows > 0) ? 1 : 0, p_n_cols);

    if ((p_n_rows == 0) || (p.get_n_nonzero() == 0)) {
      return;
    }

    for (uword col = 0; col < p_n_cols; ++col) {
      // Do we have to use an iterator or can we use memory directly?
      if (SpProxy<T1>::use_iterator) {
        typename SpProxy<T1>::const_iterator_type it = p.begin_col(col);
        typename SpProxy<T1>::const_iterator_type end = p.begin_col(col + 1);

        const uword n_zero = p_n_rows - (end.pos() - it.pos());

        out.at(0, col) = spop_mean::iterator_mean(it, end, n_zero, eT(0));
      } else {
        out.at(0, col) = spop_mean::direct_mean(
            &p.get_values()[p.get_col_ptrs()[col]],
            p.get_col_ptrs()[col + 1] - p.get_col_ptrs()[col], p_n_rows);
      }
    }
  } else if (dim == 1)  // find the mean in each row
  {
    arma_extra_debug_print("spop_mean::apply_noalias(): dim = 1");

    out.set_size(p_n_rows, (p_n_cols > 0) ? 1 : 0);

    if ((p_n_cols == 0) || (p.get_n_nonzero() == 0)) {
      return;
    }

    for (uword row = 0; row < p_n_rows; ++row) {
      // We must use an iterator regardless of how it is stored.
      typename SpProxy<T1>::const_row_iterator_type it = p.begin_row(row);
      typename SpProxy<T1>::const_row_iterator_type end = p.end_row(row);

      const uword n_zero = p_n_cols - (end.pos() - it.pos());

      out.at(row, 0) = spop_mean::iterator_mean(it, end, n_zero, eT(0));
    }
  }
}

template <typename eT>
inline eT spop_mean::direct_mean(const eT* const X, const uword length, const uword N) {
  arma_extra_debug_sigprint();

  typedef typename get_pod_type<eT>::result T;

  const eT result =
      ((length > 0) && (N > 0)) ? eT(arrayops::accumulate(X, length) / T(N)) : eT(0);

  return arma_isfinite(result) ? result : spop_mean::direct_mean_robust(X, length, N);
}

template <typename eT>
inline eT spop_mean::direct_mean_robust(const eT* const X, const uword length,
                                        const uword N) {
  arma_extra_debug_sigprint();

  typedef typename get_pod_type<eT>::result T;

  uword i, j;

  eT r_mean = eT(0);

  const uword diff = (N - length);  // number of zeros

  for (i = 0, j = 1; j < length; i += 2, j += 2) {
    const eT Xi = X[i];
    const eT Xj = X[j];

    r_mean += (Xi - r_mean) / T(diff + j);
    r_mean += (Xj - r_mean) / T(diff + j + 1);
  }

  if (i < length) {
    const eT Xi = X[i];

    r_mean += (Xi - r_mean) / T(diff + i + 1);
  }

  return r_mean;
}

template <typename T1>
inline typename T1::elem_type spop_mean::mean_all(
    const SpBase<typename T1::elem_type, T1>& X) {
  arma_extra_debug_sigprint();

  SpProxy<T1> p(X.get_ref());

  if (SpProxy<T1>::use_iterator) {
    typename SpProxy<T1>::const_iterator_type it = p.begin();
    typename SpProxy<T1>::const_iterator_type end = p.end();

    return spop_mean::iterator_mean(it, end, p.get_n_elem() - p.get_n_nonzero(),
                                    typename T1::elem_type(0));
  } else  // use_iterator == false; that is, we can directly access the values array
  {
    return spop_mean::direct_mean(p.get_values(), p.get_n_nonzero(), p.get_n_elem());
  }
}

template <typename T1, typename spop_type>
inline typename T1::elem_type spop_mean::mean_all(const SpOp<T1, spop_type>& expr) {
  arma_extra_debug_sigprint();

  typedef typename T1::elem_type eT;

  const bool is_vectorise = (is_same_type<spop_type, spop_vectorise_row>::yes) ||
                            (is_same_type<spop_type, spop_vectorise_col>::yes) ||
                            (is_same_type<spop_type, spop_vectorise_all>::yes);

  if (is_vectorise) {
    return spop_mean::mean_all(expr.m);
  }

  const SpMat<eT> tmp = expr;

  return spop_mean::mean_all(tmp);
}

template <typename T1, typename eT>
inline eT spop_mean::iterator_mean(T1& it, const T1& end, const uword n_zero,
                                   const eT junk) {
  arma_extra_debug_sigprint();
  arma_ignore(junk);

  typedef typename get_pod_type<eT>::result T;

  eT acc = eT(0);

  T1 backup_it(it);  // in case we have to use robust iterator_mean

  const uword it_begin_pos = it.pos();

  while (it != end) {
    acc += (*it);
    ++it;
  }

  const uword count = n_zero + (it.pos() - it_begin_pos);

  const eT result = (count > 0) ? eT(acc / T(count)) : eT(0);

  return arma_isfinite(result)
             ? result
             : spop_mean::iterator_mean_robust(backup_it, end, n_zero, eT(0));
}

template <typename T1, typename eT>
inline eT spop_mean::iterator_mean_robust(T1& it, const T1& end, const uword n_zero,
                                          const eT junk) {
  arma_extra_debug_sigprint();
  arma_ignore(junk);

  typedef typename get_pod_type<eT>::result T;

  eT r_mean = eT(0);

  const uword it_begin_pos = it.pos();

  while (it != end) {
    r_mean += ((*it - r_mean) / T(n_zero + (it.pos() - it_begin_pos) + 1));
    ++it;
  }

  return r_mean;
}

//! @}
