#define TORCH_ASSERT_NO_OPERATORS
#include <ATen/AccumulateType.h>
#include <ATen/Context.h>
#include <ATen/Dispatch.h>
#include <ATen/native/cuda/Loops.cuh>
#include <ATen/native/cuda/JitLoops.cuh>
#include <ATen/native/DispatchStub.h>
#include <ATen/native/TensorIterator.h>
#include <ATen/native/PointwiseOps.h>
#include <c10/core/Scalar.h>

namespace at::native {

#if AT_USE_JITERATOR() && CUDA_VERSION >= 11050
CONSTEXPR_EXCEPT_WIN_CUDA char addcmul_name[] = "addcmul";
#endif
void addcmul_cuda_kernel(TensorIteratorBase& iter, const Scalar& value) {
  auto dtype = iter.common_dtype();
  if (at::isComplexType(dtype)) {
    // When using Jiterator, addcmul and addcdiv kernels get stuck during a
    // promotion test on CUDA 11.3, so only enable that from CUDA 11.5:
    // https://github.com/pytorch/pytorch/pull/74234#issuecomment-1100932209
    #if AT_USE_JITERATOR() && CUDA_VERSION >= 11050
      AT_DISPATCH_COMPLEX_TYPES(dtype, "addcmul_cuda", [&]() {
        auto alpha = value.to<scalar_t>();
        static const auto addcmul_string = jiterator_stringify(
          template <typename T> T addcmul(T a, T b, T c, T alpha) { return a + alpha * (b * c); });
        jitted_gpu_kernel<
            /*name=*/addcmul_name,
            /*return_dtype=*/scalar_t,
            /*common_dtype=*/scalar_t,
            /*arity=*/3>(
            iter,
            addcmul_string,
            /*scalar_pos=*/at::cuda::jit::BinaryFuncVariant::NoScalar,
            /*scalar_val=*/0,
            /*extra_args=*/std::make_tuple(alpha));
      });
    #else
      AT_DISPATCH_COMPLEX_TYPES(dtype, "addcmul_cuda", [&]() {
        auto alpha = value.to<scalar_t>();
        gpu_kernel(iter, [alpha]GPU_LAMBDA(scalar_t a, scalar_t b, scalar_t c) -> scalar_t {
          return a + alpha * b * c;
        });
      });
    #endif
  } else {
    AT_DISPATCH_ALL_TYPES_AND2(kHalf, kBFloat16, dtype, "addcmul_cuda", [&]() {
      // note(mkozuki): If scalar_t is fp16 or bfloat16, cast scalar to float
      // and do math in fp32 for better accuracy.
      using accscalar_t = at::acc_type<scalar_t, true>;
      auto alpha = value.to<accscalar_t>();
      gpu_kernel(iter, [alpha]GPU_LAMBDA(scalar_t a, scalar_t b, scalar_t c) -> scalar_t {
        return a + alpha * (static_cast<accscalar_t>(b) * static_cast<accscalar_t>(c));
      });
    });
  }
}

#if AT_USE_JITERATOR() && CUDA_VERSION >= 11050
// return a + alpha * (b / static_cast<accscalar_t>(c));
CONSTEXPR_EXCEPT_WIN_CUDA char addcdiv_name[] = "addcdiv";
#endif
void addcdiv_cuda_kernel(TensorIteratorBase& iter, const Scalar& value) {
  auto dtype = iter.common_dtype();
  if (at::isComplexType(dtype)) {
    // When using Jiterator, addcmul and addcdiv kernels get stuck during a
    // promotion test on CUDA 11.3, so only enable that from CUDA 11.5:
    // https://github.com/pytorch/pytorch/pull/74234#issuecomment-1100932209
    #if AT_USE_JITERATOR() && CUDA_VERSION >= 11050
      AT_DISPATCH_COMPLEX_TYPES(dtype, "addcdiv_cuda", [&]() {
        auto alpha = value.to<scalar_t>();
        static const auto addcdiv_string =
            jiterator_stringify(template <typename T> T addcdiv(
                T a, T b, T c, T alpha) { return a + alpha * (b / c); });
        jitted_gpu_kernel<
            /*name=*/addcdiv_name,
            /*return_dtype=*/scalar_t,
            /*common_dtype=*/scalar_t,
            /*arity=*/3>(
            iter,
            addcdiv_string,
            /*scalar_pos=*/at::cuda::jit::BinaryFuncVariant::NoScalar,
            /*scalar_val=*/0,
            /*extra_args=*/std::make_tuple(alpha));
      });
    #else
      AT_DISPATCH_COMPLEX_TYPES(dtype, "addcdiv_cuda", [&]() {
        auto alpha = value.to<scalar_t>();
        gpu_kernel(iter, [alpha]GPU_LAMBDA(scalar_t a, scalar_t b, scalar_t c) -> scalar_t {
          return a + alpha * (b / c);
        });
      });
    #endif
  } else {
    AT_DISPATCH_ALL_TYPES_AND2(kHalf, kBFloat16, dtype, "addcdiv_cuda", [&]() {
      // note(mkozuki): If scalar_t is fp16 or bfloat16, cast scalar to float
      // and do math in fp32 for better accuracy.
      using accscalar_t = at::acc_type<scalar_t, true>;
      auto alpha = value.to<accscalar_t>();
      gpu_kernel(iter, [alpha]GPU_LAMBDA(scalar_t a, scalar_t b, scalar_t c) -> scalar_t {
        return a + alpha * (b / static_cast<accscalar_t>(c));
      });
    });
  }
}

void smooth_l1_backward_cuda_kernel(TensorIterator& iter, const Scalar& norm, double beta) {
  AT_DISPATCH_ALL_TYPES_AND2(kHalf, kBFloat16, iter.dtype(), "smooth_l1_backward_cuda", [&iter, &norm, beta] {
      auto norm_val = norm.to<scalar_t>();
      scalar_t beta_val(beta);
      gpu_kernel(iter, [norm_val, beta_val]GPU_LAMBDA(scalar_t input, scalar_t target, scalar_t grad_output) -> scalar_t {
        const auto x = input - target;
        if (x < -beta_val)
          return -norm_val * grad_output;
        else if (x > beta_val)
          return norm_val * grad_output;
        else
          return norm_val * x * grad_output / beta_val;
    });
  });
}

void huber_backward_cuda_kernel(TensorIterator& iter, const Scalar& norm, double delta) {
  AT_DISPATCH_FLOATING_TYPES_AND2(kBFloat16, kHalf, iter.dtype(), "huber_backward_cuda", [&iter, &norm, delta] {
    auto norm_val = norm.to<scalar_t>();
    scalar_t delta_val(delta);
    gpu_kernel(iter, [norm_val, delta_val]GPU_LAMBDA(scalar_t input, scalar_t target, scalar_t grad_output) -> scalar_t {
      const auto x = input - target;
      if (x < -delta_val) {
        return -norm_val * grad_output * delta_val;
      } else if (x > delta_val) {
        return norm_val * grad_output * delta_val;
      } else {
        return norm_val * x * grad_output;
      }
    });
  });
}

void mse_backward_cuda_kernel(TensorIterator& iter, const Scalar& value) {
  AT_DISPATCH_FLOATING_TYPES_AND2(at::ScalarType::Half, at::ScalarType::BFloat16, iter.dtype(), "mse_backward_cuda", [&]() {
    auto alpha = value.to<scalar_t>();
    gpu_kernel(iter, [alpha]GPU_LAMBDA(scalar_t a, scalar_t b, scalar_t c) -> scalar_t {
      return alpha * (a - b) * c;
    });
  });
}

REGISTER_DISPATCH(addcdiv_stub, &addcdiv_cuda_kernel);
REGISTER_DISPATCH(addcmul_stub, &addcmul_cuda_kernel);
REGISTER_DISPATCH(smooth_l1_backward_stub, &smooth_l1_backward_cuda_kernel);
REGISTER_DISPATCH(huber_backward_stub, &huber_backward_cuda_kernel);
REGISTER_DISPATCH(mse_backward_stub, &mse_backward_cuda_kernel);
} // namespace at::native