/*!
 *  Copyright (c) 2019 by Contributors
 * \file array/cpu/csr_sum.cc
 * \brief CSR Summation
 */

#include <dgl/array.h>
#include <dgl/runtime/parallel_for.h>
#include <parallel_hashmap/phmap.h>
#include <vector>
#include "array_utils.h"

namespace dgl {

using dgl::runtime::NDArray;

namespace aten {

namespace {

// TODO(BarclayII): avoid using map for sorted CSRs
template <typename IdType>
void CountNNZPerRow(
    const std::vector<const IdType*>& A_indptr,
    const std::vector<const IdType*>& A_indices,
    IdType* C_indptr_data,
    int64_t M) {
  int64_t n = A_indptr.size();

  runtime::parallel_for(0, M, [=](size_t b, size_t e) {
    for (size_t i = b; i < e; ++i) {
      phmap::flat_hash_set<IdType> set;
      for (int64_t k = 0; k < n; ++k) {
        for (IdType u = A_indptr[k][i]; u < A_indptr[k][i + 1]; ++u)
          set.insert(A_indices[k][u]);
      }
      C_indptr_data[i] = set.size();
    }
  });
}

template <typename IdType>
int64_t ComputeIndptrInPlace(IdType* C_indptr_data, int64_t M) {
  int64_t nnz = 0;
  IdType len = 0;
  for (IdType i = 0; i < M; ++i) {
    len = C_indptr_data[i];
    C_indptr_data[i] = nnz;
    nnz += len;
  }
  C_indptr_data[M] = nnz;
  return nnz;
}

template <typename IdType, typename DType>
void ComputeIndicesAndData(
    const std::vector<const IdType*>& A_indptr,
    const std::vector<const IdType*>& A_indices,
    const std::vector<const IdType*>& A_eids,
    const std::vector<const DType*>& A_data,
    const IdType* C_indptr_data,
    IdType* C_indices_data,
    DType* C_weights_data,
    int64_t M) {
  int64_t n = A_indptr.size();
  runtime::parallel_for(0, M, [=](size_t b, size_t e) {
    for (auto i = b; i < e; ++i) {
      phmap::flat_hash_map<IdType, DType> map;
      for (int64_t k = 0; k < n; ++k) {
        for (IdType u = A_indptr[k][i]; u < A_indptr[k][i + 1]; ++u) {
          IdType kA = A_indices[k][u];
          DType vA = A_data[k][A_eids[k] ? A_eids[k][u] : u];
          map[kA] += vA;
        }
      }
      IdType j = C_indptr_data[i];
      for (auto it : map) {
        C_indices_data[j] = it.first;
        C_weights_data[j] = it.second;
        ++j;
      }
    }
  });
}

};  // namespace

template <int XPU, typename IdType, typename DType>
std::pair<CSRMatrix, NDArray> CSRSum(
    const std::vector<CSRMatrix>& A,
    const std::vector<NDArray>& A_weights) {
  CHECK(A.size() > 0) << "List of matrices can't be empty.";
  CHECK_EQ(A.size(), A_weights.size()) << "List of matrices and weights must have same length";
  const int64_t M = A[0].num_rows;
  const int64_t N = A[0].num_cols;
  const int64_t n = A.size();

  std::vector<bool> A_has_eid(n);
  std::vector<const IdType*> A_indptr(n);
  std::vector<const IdType*> A_indices(n);
  std::vector<const IdType*> A_eids(n);
  std::vector<const DType*> A_data(n);

  for (int64_t i = 0; i < n; ++i) {
    const CSRMatrix& csr = A[i];
    const NDArray& data = A_weights[i];
    A_has_eid[i] = !IsNullArray(csr.data);
    A_indptr[i] = csr.indptr.Ptr<IdType>();
    A_indices[i] = csr.indices.Ptr<IdType>();
    A_eids[i] = A_has_eid[i] ? csr.data.Ptr<IdType>() : nullptr;
    A_data[i] = data.Ptr<DType>();
  }

  IdArray C_indptr = IdArray::Empty({M + 1}, A[0].indptr->dtype, A[0].indptr->ctx);
  IdType* C_indptr_data = C_indptr.Ptr<IdType>();

  CountNNZPerRow<IdType>(A_indptr, A_indices, C_indptr_data, M);
  IdType nnz = ComputeIndptrInPlace<IdType>(C_indptr_data, M);
  // Allocate indices and weights array
  IdArray C_indices = IdArray::Empty({nnz}, A[0].indices->dtype, A[0].indices->ctx);
  NDArray C_weights = NDArray::Empty({nnz}, A_weights[0]->dtype, A_weights[0]->ctx);
  IdType* C_indices_data = C_indices.Ptr<IdType>();
  DType* C_weights_data = C_weights.Ptr<DType>();
  ComputeIndicesAndData<IdType, DType>(
      A_indptr, A_indices, A_eids, A_data,
      C_indptr_data, C_indices_data, C_weights_data, M);

  return {
      CSRMatrix(M, N, C_indptr, C_indices, NullArray(C_indptr->dtype, C_indptr->ctx)),
      C_weights};
}

template std::pair<CSRMatrix, NDArray> CSRSum<kDLCPU, int32_t, float>(
    const std::vector<CSRMatrix>&, const std::vector<NDArray>&);
template std::pair<CSRMatrix, NDArray> CSRSum<kDLCPU, int64_t, float>(
    const std::vector<CSRMatrix>&, const std::vector<NDArray>&);
template std::pair<CSRMatrix, NDArray> CSRSum<kDLCPU, int32_t, double>(
    const std::vector<CSRMatrix>&, const std::vector<NDArray>&);
template std::pair<CSRMatrix, NDArray> CSRSum<kDLCPU, int64_t, double>(
    const std::vector<CSRMatrix>&, const std::vector<NDArray>&);

};  // namespace aten
};  // namespace dgl
