/**
 * \file    v1.hpp
 * \brief
 *
 * \author
 *    Christos Choutouridis AEM:8997
 *    <cchoutou@ece.auth.gr>
 */
#ifndef V1_HPP_
#define V1_HPP_

#include <vector>
#include <algorithm>

#include "matrix.hpp"
#include "v0.hpp"
#include "config.h"

#if defined CILK
#include <cilk/cilk.h>
#include <cilk/cilk_api.h>
//#include <cilk/reducer_opadd.h>

#elif defined OMP
#include <omp.h>

#elif defined PTHREADS
#include <thread>
#include <numeric>
#include <functional>
//#include <random>

#else
#endif


void init_workers();

namespace v1 {


/*!
 *
 * Merge knnsearch results and select the closest neighbors
 *
 * \tparam DataType
 * \tparam IndexType
 * \param N1   Neighbors results from one knnsearch
 * \param D1   Distances results from one knnsearcs
 * \param N2   Neighbors results from second knnsearch
 * \param D2   Distances results from second knnsearch
 * \param k    How many
 * \param m    How accurate
 * \param N    Output for Neighbors
 * \param D    Output for Distances
 */
template <typename DataType, typename IndexType>
void mergeResultsWithM(mtx::Matrix<IndexType>& N1, mtx::Matrix<DataType>& D1,
                       mtx::Matrix<IndexType>& N2, mtx::Matrix<DataType>& D2,
                       size_t k, size_t m,
                       mtx::Matrix<IndexType>& N, mtx::Matrix<DataType>& D) {
   size_t numQueries = N1.rows();
   size_t maxCandidates = std::min((IndexType)m, (IndexType)(N1.columns() + N2.columns()));

   for (size_t q = 0; q < numQueries; ++q) {
      // Combine distances and neighbors
      std::vector<std::pair<DataType, IndexType>> candidates(N1.columns() + N2.columns());

      // Concatenate N1 and N2 rows
      for (size_t i = 0; i < N1.columns(); ++i) {
         candidates[i] = {D1.get(q, i), N1.get(q, i)};
      }
      for (size_t i = 0; i < N2.columns(); ++i) {
         candidates[i + N1.columns()] = {D2.get(q, i), N2.get(q, i)};
      }

      // Keep only the top-m candidates
      v0::quickselect(candidates, maxCandidates);

      // Sort the top-m candidates
      std::sort(candidates.begin(), candidates.begin() + maxCandidates);

      // If m < k, pad the remaining slots with invalid values
      for (size_t i = 0; i < k; ++i) {
         if (i < maxCandidates) {
            D.set(candidates[i].first, q, i);
            N.set(candidates[i].second, q, i);
         } else {
            D.set(std::numeric_limits<DataType>::infinity(), q, i);
            N.set(static_cast<IndexType>(-1), q, i); // Invalid index (end)
         }
      }
    }
}

/*!
 * The main parallelizable body
 */
template<typename MatrixD, typename MatrixI>
void worker_body (std::vector<MatrixD>& corpus_slices,
                  std::vector<MatrixD>& query_slices,
                  MatrixI& idx,
                  MatrixD& dst,
                  size_t slice,
                  size_t num_slices, size_t corpus_slice_size, size_t query_slice_size,
                  size_t k,
                  size_t m) {
   // "load" types
   using DstType = typename MatrixD::dataType;
   using IdxType = typename MatrixI::dataType;


   for (size_t ci = 0; ci < num_slices; ++ci) {
      size_t idx_offset = ci * corpus_slice_size;

      // Intermediate matrixes for intermediate results
      MatrixI temp_idx(query_slices[slice].rows(), k);
      MatrixD temp_dst(query_slices[slice].rows(), k);

      // kNN for each combination
      v0::knnsearch(corpus_slices[ci], query_slices[slice], idx_offset, k, m, temp_idx, temp_dst);

      // Merge temporary results to final results
      MatrixI idx_slice((IdxType*)idx.data(), slice * query_slice_size, query_slices[slice].rows(), k);
      MatrixD dst_slice((DstType*)dst.data(), slice * query_slice_size, query_slices[slice].rows(), k);

      mergeResultsWithM(idx_slice, dst_slice, temp_idx, temp_dst, k, m, idx_slice, dst_slice);
   }
}

/*!
 * \param C    Is a MxD matrix (Corpus)
 * \param Q    Is a NxD matrix (Query)
 * \param num_slices How many slices to Corpus-Query
 * \param k    The number of nearest neighbors needed
 * \param m    accuracy
 * \param idx  Is the Nxk matrix with the k indexes of the C points, that are
 *             neighbors of the nth point of Q
 * \param dst  Is the Nxk matrix with the k distances to the C points of the nth
 *             point of Q
 */
template<typename MatrixD, typename MatrixI>
void knnsearch(MatrixD& C, MatrixD& Q, size_t num_slices, size_t k, size_t m, MatrixI& idx, MatrixD& dst) {
    using DstType = typename MatrixD::dataType;
    using IdxType = typename MatrixI::dataType;

    //Slice calculations
    size_t corpus_slice_size = C.rows() / ((num_slices == 0)? 1:num_slices);
    size_t query_slice_size = Q.rows() / ((num_slices == 0)? 1:num_slices);

    // Make slices
    std::vector<MatrixD> corpus_slices;
    std::vector<MatrixD> query_slices;

   for (size_t i = 0; i < num_slices; ++i) {
      corpus_slices.emplace_back(
         (DstType*)C.data(),
         i * corpus_slice_size,
         (i == num_slices - 1 ? C.rows() - i * corpus_slice_size : corpus_slice_size),
         C.columns());
      query_slices.emplace_back(
         (DstType*)Q.data(),
         i * query_slice_size,
         (i == num_slices - 1 ? Q.rows() - i * query_slice_size : query_slice_size),
         Q.columns());
   }

   // Intermediate results
   for (size_t i = 0; i < dst.rows(); ++i) {
      for (size_t j = 0; j < dst.columns(); ++j) {
         dst.set(std::numeric_limits<DstType>::infinity(), i, j);
         idx.set(static_cast<IdxType>(-1), i, j);
      }
   }

    // Main loop
#if defined OMP
   #pragma omp parallel for
   for (size_t qi = 0; qi < num_slices; ++qi) {
         worker_body (corpus_slices, query_slices, idx, dst, qi, num_slices, corpus_slice_size, query_slice_size, k, m);
   }
#elif defined CILK
   cilk_for (size_t qi = 0; qi < num_slices; ++qi) {
         worker_body (corpus_slices, query_slices, idx, dst, qi, num_slices, corpus_slice_size, query_slice_size, k, m);
   }
#elif defined PTHREADS
   std::vector<std::thread> workers;
   for (size_t qi = 0; qi < num_slices; ++qi) {
      workers.push_back(
         std::thread (worker_body<MatrixD, MatrixI>,
                      std::ref(corpus_slices), std::ref(query_slices),
                      std::ref(idx), std::ref(dst),
                      qi,
                      num_slices, corpus_slice_size, query_slice_size,
                      k, m)
      );
   }
   // Join threads
   std::for_each(workers.begin(), workers.end(), [](std::thread& t){
      t.join();
   });

#else
   for (size_t qi = 0; qi < num_slices; ++qi) {
      for (size_t qi = 0; qi < num_slices; ++qi) {
         worker_body (corpus_slices, query_slices, idx, dst, qi, num_slices, corpus_slice_size, query_slice_size, k, m);
      }
   }
#endif

}

} // namespace v1

#endif /* V1_HPP_ */