#include <torch/extension.h>

#include "compat.h"

#define CHECK_CPU(x) AT_ASSERTM(!x.type().is_cuda(), #x " must be CPU tensor")

enum ReductionType { SUM, MEAN, MIN, MAX };

const std::map<std::string, ReductionType> reduce2REDUCE = {
    {"sum", SUM}, {"add", SUM}, {"mean", MEAN}, {"min", MIN}, {"max", MAX},
};

#define AT_DISPATCH_REDUCTION_TYPES(reduce, ...)                               \
  [&] {                                                                        \
    switch (reduce2REDUCE.at(reduce)) {                                        \
    case SUM: {                                                                \
      const ReductionType REDUCE = SUM;                                        \
      return __VA_ARGS__();                                                    \
    }                                                                          \
    case MEAN: {                                                               \
      const ReductionType REDUCE = MEAN;                                       \
      return __VA_ARGS__();                                                    \
    }                                                                          \
    case MIN: {                                                                \
      const ReductionType REDUCE = MIN;                                        \
      return __VA_ARGS__();                                                    \
    }                                                                          \
    case MAX: {                                                                \
      const ReductionType REDUCE = MAX;                                        \
      return __VA_ARGS__();                                                    \
    }                                                                          \
    }                                                                          \
  }()

#define AT_DISPATCH_HAS_VAL(value_opt, ...)                                    \
  [&] {                                                                        \
    switch (value_opt.has_value()) {                                           \
    case true: {                                                               \
      const bool HAS_VAL = true;                                               \
      return __VA_ARGS__();                                                    \
    }                                                                          \
    case false: {                                                              \
      const bool HAS_VAL = false;                                              \
      return __VA_ARGS__();                                                    \
    }                                                                          \
    }                                                                          \
  }()

template <typename scalar_t, ReductionType REDUCE> struct Reducer {
  static inline scalar_t init() {
    if (REDUCE == MIN) {
      return std::numeric_limits<scalar_t>::max();
    } else if (REDUCE == MAX) {
      return std::numeric_limits<scalar_t>::lowest();
    } else {
      return (scalar_t)0;
    }
  }

  static inline void update(scalar_t *val, scalar_t new_val, int64_t *arg,
                            int64_t new_arg) {
    if (REDUCE == SUM || REDUCE == MEAN) {
      *val = *val + new_val;
    } else if ((REDUCE == MIN && new_val < *val) ||
               (REDUCE == MAX && new_val > *val)) {
      *val = new_val;
      *arg = new_arg;
    }
  }

  static inline void write(scalar_t *address, scalar_t val,
                           int64_t *arg_address, int64_t arg, int count) {
    if (REDUCE == SUM) {
      *address = val;
    } else if (REDUCE == MEAN) {
      *address = val / (count > 0 ? count : (scalar_t)1);
    } else if (REDUCE == MIN || REDUCE == MAX) {
      if (count > 0) {
        *address = val;
        *arg_address = arg;
      } else {
        *address = (scalar_t)0;
      }
    }
  }
};

std::tuple<at::Tensor, at::optional<at::Tensor>>
spmm(at::Tensor rowptr, at::Tensor col, at::optional<at::Tensor> value_opt,
     at::Tensor mat, std::string reduce) {
  CHECK_CPU(rowptr);
  CHECK_CPU(col);
  if (value_opt.has_value())
    CHECK_CPU(value_opt.value());
  CHECK_CPU(mat);

  mat = mat.contiguous();

  AT_ASSERTM(rowptr.dim() == 1, "Input mismatch");
  AT_ASSERTM(col.dim() == 1, "Input mismatch");
  if (value_opt.has_value())
    AT_ASSERTM(value_opt.value().dim() == 1);
  AT_ASSERTM(mat.dim() >= 2, "Input mismatch");
  AT_ASSERTM(rowptr.numel() - 1 == mat.size(-2), "Input mismatch");

  auto sizes = mat.sizes().vec();
  sizes[mat.dim() - 2] = rowptr.numel() - 1;
  auto out = at::empty(sizes, mat.options());

  at::optional<at::Tensor> arg_out = at::nullopt;
  int64_t *arg_out_data = nullptr;
  if (reduce2REDUCE.at(reduce) == MIN || reduce2REDUCE.at(reduce) == MAX) {
    arg_out = at::full_like(out, mat.size(-2), rowptr.options());
    arg_out_data = arg_out.value().DATA_PTR<int64_t>();
  }

  auto rowptr_data = rowptr.DATA_PTR<int64_t>();
  auto col_data = col.DATA_PTR<int64_t>();

  int N = rowptr.numel() - 1;
  int M = mat.size(-2);
  int K = mat.size(-1);
  int B = mat.numel() / (M * K);

  AT_DISPATCH_ALL_TYPES(mat.scalar_type(), "spmm", [&] {
    scalar_t *value_data = nullptr;
    auto mat_data = out.DATA_PTR<scalar_t>();
    auto out_data = mat.DATA_PTR<scalar_t>();

    scalar_t val;
    std::vector<scalar_t> vals(K);
    int64_t row_start, row_end, col_idx;
    std::vector<int64_t> args(K);

    AT_DISPATCH_REDUCTION_TYPES(reduce, [&] {
      AT_DISPATCH_HAS_VAL(value_opt, [&] {
        if (HAS_VAL) {
          value_data = value_opt.value().DATA_PTR<scalar_t>();
        }

        for (int b = 0; b < B; b++) {
          for (int n = 0; n < N; n++) {
            row_start = rowptr_data[n], row_end = rowptr_data[n + 1];

            for (int k = 0; k < K; k++)
              vals[k] = Reducer<scalar_t, REDUCE>::init();

            int offset = b * M * K;
            for (int e = row_start; e < row_end; e++) {
              col_idx = col_data[e];
              if (HAS_VAL)
                val = value_data[e];
              for (int k = 0; k < K; k++) {
                if (HAS_VAL)
                  Reducer<scalar_t, REDUCE>::update(
                      &vals[k], val * mat_data[offset + col_idx * K + k],
                      &args[k], e);
                else
                  Reducer<scalar_t, REDUCE>::update(
                      &vals[k], mat_data[offset + col_idx * K + k], &args[k],
                      e);
              }
            }
            offset = b * N * K + n * K;
            for (int k = 0; k < K; k++)
              Reducer<scalar_t, REDUCE>::write(out_data + offset + k, vals[k],
                                               arg_out_data + offset + k,
                                               args[k], row_end - row_start);
          }
        }
      });
    });
  });

  return std::make_tuple(out, arg_out);
}

PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
  m.def("spmm", &spmm, "Sparse-Dense Matrix Multiplication (CPU)");
}