#pragma once

#include <ATen/core/Tensor.h>
#include <ATen/EmptyTensor.h>
#include <ATen/TensorIterator.h>
#include <ATen/native/DispatchStub.h>

#ifndef AT_PER_OPERATOR_HEADERS
#include <ATen/Functions.h>
#else
#include <ATen/ops/scalar_tensor.h>
#endif

namespace at { namespace native {
// Different combinations of row, col, and offset can lead to two cases:
//
// Case 1 - Trapezoid (Triangle as a special case): row + offset <= col
//    Example A: offset > 0
//      1 1 0 0 0
//      1 1 1 0 0
//      1 1 1 1 0
//    Example B: offset <= 0
//      0 0 0
//      1 0 0
//      1 1 0
//    In this case, we calculate the number of elements in the first row and
//    last row of the tril respectively, and then compute the tril size.
//
// Case 2 - Trapezoid + Rectangle: row + offset > col
//    Example:
//      1 1 0
//      1 1 1
//      1 1 1
//    In this case, we first calculate the size of top trapezoid, and then
//    calculate the size of the bottom rectangle.
inline int64_t get_tril_size(int64_t row, int64_t col, int64_t offset) {
  // If either dimension is 0 then the there is no tril
  if (row == 0 || col == 0) {
    return 0;
  }
  // number of elements in the first row of the tril
  auto m_first_row = offset > 0 ?
    std::min<int64_t>(col, 1 + offset) : // upper bounded by col
    row + offset > 0; // either 0 or 1
  // number of elements in the last row of the tril, bounded by [0, col]
  auto m_last_row = std::max<int64_t>(0, std::min<int64_t>(col, row + offset));
  // number of rows, bounded by [0, row]
  auto n_row_all = std::max<int64_t>(0, std::min<int64_t>(row, row + offset));
  auto n_row_trapezoid = (m_last_row - m_first_row + 1);

  // calculate # of elements in the top trapezoid
  auto tril_size = (m_first_row + m_last_row) * n_row_trapezoid >> 1;

  // calculate # of elements in the bottom rectangle if there is any
  auto diff_row = n_row_all - n_row_trapezoid;
  if (diff_row > 0) {
    tril_size += diff_row * col;
  }

  return tril_size;
}

inline void check_args(
    int64_t row, int64_t col, c10::optional<Layout> layout_opt) {
  TORCH_CHECK(row >= 0, "row must be non-negative, got", row);
  TORCH_CHECK(col >= 0, "col must be non-negative, got", col);
  if (layout_opt.has_value()) {
    TORCH_CHECK(
      *layout_opt == at::kStrided,
      "only support layout=torch.strided, got",
      *layout_opt)
  }
}

using at::check_size_nonnegative;

// assumes maximum value in created tensor is n-1 (e.g., torch.randperm(n))
inline void check_supported_max_int_with_precision(int64_t n, const Tensor& tensor) {
  // match defined() to behavior of checks below
  TORCH_CHECK(at::scalar_tensor(n>0?n-1:n, tensor.options()).defined(),
              "n is too large for result tensor type: '", tensor.toString(), "'");

  // Ensure sufficient precision for floating point representation.
  switch (tensor.scalar_type()) {
    case at::ScalarType::Half:
      TORCH_CHECK(n <= (int64_t(1) << 11) + 1, "n cannot be greater than 2049 for Half type.");
      break;
    case at::ScalarType::Float:
      TORCH_CHECK(n <= (int64_t(1) << 24) + 1, "n cannot be greater than 2^24+1 for Float type.");
      break;
    case at::ScalarType::Double:  // Unlikely to happen, but doesn't hurt to check
      TORCH_CHECK(n <= (int64_t(1) << 53) + 1, "n cannot be greater than 2^53+1 for Double type.");
      break;
    default:
      break;
  }
}

// The ZeroTensor allocator ignores whatever allocation is requested and always
// gives you nullptr
struct ZeroTensorAllocator final : public at::Allocator {
  ZeroTensorAllocator(at::Device device) : device_(device) {};
  ~ZeroTensorAllocator() override = default;
  static void deleter(void* const pointer) {
    TORCH_INTERNAL_ASSERT(!pointer);
  }
  DataPtr allocate(const size_t /*nbytes*/) const override {
    return {nullptr, nullptr, &deleter, device_};
  }
  DeleterFnPtr raw_deleter() const override {
    return deleter;
  }
  at::Device device_;
};

using binary_fn = void (*)(TensorIterator&);

DECLARE_DISPATCH(binary_fn, complex_stub);
DECLARE_DISPATCH(binary_fn, polar_stub);

} // namespace native
} // namespace at