// SPDX-License-Identifier: Apache-2.0
// 
// Copyright 2008-2016 Conrad Sanderson (https://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
// https://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_sp_mean
//! @{



template<typename T1>
inline
void
op_sp_mean::apply(Mat<typename T1::elem_type>& out, const mtSpReduceOp<typename T1::elem_type, T1, op_sp_mean>& in)
  {
  arma_debug_sigprint();
  
  const uword dim = in.aux_uword_a;
  arma_conform_check( (dim > 1), "mean(): parameter 'dim' must be 0 or 1" );
  
  const SpProxy<T1> p(in.m);
  
  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;
    }
  
  op_sp_mean::apply_fast(out, p, dim);
  }



template<typename T1>
inline
void
op_sp_mean::apply_fast
  (
        Mat<typename T1::elem_type>& out,
  const SpProxy<T1>&                 p,
  const uword                        dim
  )
  {
  arma_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(dim == 0) // find the mean in each column
    {
    arma_debug_print("op_sp_mean::apply_fast(): dim = 0");
    
    out.zeros(1, p_n_cols);
    
    eT* out_mem = out.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)  { out_mem[it.col()] += (*it); ++it; }
      
      out /= T(p_n_rows);
      }
    else
      {
      for(uword col = 0; col < p_n_cols; ++col)
        {
        out_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);
        }
      }
    }
  else
  if(dim == 1)  // find the mean in each row
    {
    arma_debug_print("op_sp_mean::apply_fast(): dim = 1");
    
    out.zeros(p_n_rows, 1);
    
    eT* out_mem = out.memptr();
    
    typename SpProxy<T1>::const_iterator_type it = p.begin();
    
    const uword N = p.get_n_nonzero();
    
    for(uword i=0; i < N; ++i)  { out_mem[it.row()] += (*it); ++it; }
    
    out /= T(p_n_cols);
    }
  
  if(out.internal_has_nonfinite())
    {
    op_sp_mean::apply_slow(out, p, dim);
    }
  }



template<typename T1>
inline
void
op_sp_mean::apply_slow
  (
        Mat<typename T1::elem_type>& out,
  const SpProxy<T1>&                 p,
  const uword                        dim
  )
  {
  arma_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_debug_print("op_sp_mean::apply_slow(): dim = 0");
    
    out.zeros(1, p_n_cols);
    
    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) = op_sp_mean::iterator_mean(it, end, n_zero, eT(0));
        }
      else
        {
        out.at(0,col) = op_sp_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_debug_print("op_sp_mean::apply_slow(): dim = 1");
    
    out.zeros(p_n_rows, 1);
    
    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) = op_sp_mean::iterator_mean(it, end, n_zero, eT(0));
      }
    }
  }



template<typename eT>
inline
eT
op_sp_mean::direct_mean
  (
  const eT* const X,
  const uword length,
  const uword N
  )
  {
  arma_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 : op_sp_mean::direct_mean_robust(X, length, N);
  }



template<typename eT>
inline
eT
op_sp_mean::direct_mean_robust
  (
  const eT* const X,
  const uword length,
  const uword N
  )
  {
  arma_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
op_sp_mean::mean_all(const SpBase<typename T1::elem_type, T1>& X)
  {
  arma_debug_sigprint();
  
  typedef typename T1::elem_type eT;
  
  SpProxy<T1> p(X.get_ref());
  
  if(p.get_n_elem() == 0)
    {
    arma_conform_check(true, "mean(): object has no elements");
    
    return Datum<eT>::nan;
    }
  
  if(SpProxy<T1>::use_iterator)
    {
    typename SpProxy<T1>::const_iterator_type it  = p.begin();
    typename SpProxy<T1>::const_iterator_type end = p.end();
    
    return op_sp_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 op_sp_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
op_sp_mean::mean_all(const SpOp<T1, spop_type>& expr)
  {
  arma_debug_sigprint();
  
  typedef typename T1::elem_type eT;
  
  constexpr 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 op_sp_mean::mean_all(expr.m);
    }
  
  const SpMat<eT> tmp = expr;
  
  return op_sp_mean::mean_all(tmp);
  }



template<typename T1, typename eT>
inline
eT
op_sp_mean::iterator_mean(T1& it, const T1& end, const uword n_zero, const eT junk)
  {
  arma_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 : op_sp_mean::iterator_mean_robust(backup_it, end, n_zero, eT(0));
  }



template<typename T1, typename eT>
inline
eT
op_sp_mean::iterator_mean_robust(T1& it, const T1& end, const uword n_zero, const eT junk)
  {
  arma_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;
  }



//! @}
