#include <unordered_map>
#include <c10/core/impl/alloc_cpu.h>
#include <c10/core/Allocator.h>
#include <c10/core/ScalarType.h>
#include <c10/util/ArrayRef.h>

#include <torch/csrc/Device.h>
#include <torch/csrc/jit/serialization/pickler.h>
#include <c10/core/impl/DeviceGuardImplInterface.h>
#include <c10/macros/Macros.h>
#include <torch/extension.h>

#include <ATen/native/cpu/Loops.h>
#include <ATen/native/quantized/AffineQuantizer.h>
#include <ATen/native/DispatchStub.h>
#include <ATen/native/Resize.h>
#include <ATen/native/UnaryOps.h>
#include <ATen/native/CPUFallback.h>
#include <ATen/ops/abs_native.h>
#include <ATen/EmptyTensor.h>
#include <ATen/core/GeneratorForPrivateuseone.h>
#include <ATen/detail/PrivateUse1HooksInterface.h>
#include <ATen/ops/view.h>
#include <ATen/native/transformers/sdp_utils_cpp.h>
#include <ATen/native/transformers/attention.h>

static uint64_t add_counter = 0;
static uint64_t last_saved_value = 0;
static c10::DeviceIndex custom_device_index = 0;

static uint64_t abs_counter = 0;
static uint64_t last_abs_saved_value = 0;

static uint64_t storageImpl_counter = 0;
static uint64_t last_storageImpl_saved_value = 0;
// register guard
namespace at {
namespace detail {

C10_REGISTER_GUARD_IMPL(
    PrivateUse1,
    c10::impl::NoOpDeviceGuardImpl<DeviceType::PrivateUse1>);

}} // namespace at::detail

namespace {

// Using the simplest way to obtain continuous Tensor data and process it.
// This is a demo for using operand API, and you can add more complex logic
// for input and output tensor based on your custom device kernel.
void abs_kernel(at::TensorIteratorBase& iter) {
  // Abs only have a input tensor and a output tensor.
  auto& output_operand = iter.operand(0);
  auto& input_operand = iter.operand(1);
  auto& output_tensor_base = output_operand.tensor_base();
  auto& input_tensor_base = input_operand.tensor_base();
  TORCH_CHECK(!input_operand.original_tensor_base().defined(),
    "input original tensor is defined.");
  TORCH_CHECK(!output_operand.original_tensor_base().defined(),
    "output original tensor is defined.");
  // For easy test, only accept contiguous input tensor for calculate.
  auto memory_format = input_tensor_base.suggest_memory_format();
  TORCH_CHECK(input_tensor_base.is_contiguous(memory_format),
    "Input tensor need be contiguous.");
  // Add necessary restrictions to ensure the security of the demo.
  TORCH_CHECK(input_tensor_base.sizes() == output_tensor_base.sizes(),
    "Intput and output tensor size are not equal.");
  // Common dtype is calculate in TensorIteratorBase.
  TORCH_CHECK(iter.common_dtype() == at::ScalarType::Float,
    "Only support float type.")
  // Using for loop for abs calculate.
  auto abs_function = [](float* output_ptr, const float* input_ptr,
                         const int64_t NUM) {
    for (int64_t i = 0; i < NUM; ++i) {
      *(output_ptr + i) = std::abs(*(input_ptr + i));
    }
  };
  // To simplify the logic of the test demo code,
  // we only use contiguous tensor to calculate on device side.
  // And using input tensor memory format.
  if (iter.is_contiguous()) {
    // Add for will_resize flag check. You can convert to differernt
    // tensor memory format when will_resize is True.
    // If TensorIteratorConfig resize_outputs_ flag is true, and there are two
    // situations:
    // 1) Out tensor is undefined, and TensorIterator set will_resize to true;
    // 2) Out tensor is defined and tensor size is not equal to input tensor size;
    //    TensorIterator set will_resize to true, and call set_output_raw_strided
    //    to resize output tensor.
    // When output operand will_resize flag is ture, dummy
    // device can convert tensor to dummy device preferred memory format.
    // Here we don't convert tensor memory format, because it will become complex
    // when dummy device want keep same memory format for training network.
    TORCH_CHECK(output_operand.will_resize,
      "output operand will_resize flag need be True.");
    abs_function((float*)iter.data_ptr(0), (float*)iter.data_ptr(1), iter.numel());
  } else {
    // Stride copy is not support for foo device, using cpu device instead.
    // For abs op, the last situation is: output tensor is not contiguous with
    // operand will_resize is False.
    TORCH_CHECK(!output_operand.will_resize, "output operand will_resize is True.");
    // Get a contiguous tensor with input memory format.
    at::Tensor output = at::empty(output_tensor_base.sizes(),
                                  input_tensor_base.options()
                                                   .memory_format(memory_format));
    // For structured op which inheried from TensorIteratorBase, maybe you need to
    // call set_output_raw_strided function to update output stored in op sturctured.
    // abs op is no need to do this.
    output_operand.exchange_tensor(c10::MaybeOwned<at::TensorBase>::owned(std::in_place, output));
    abs_function((float*)output_operand.tensor_base().mutable_data_ptr(),
                 (float*)iter.data_ptr(1), iter.numel());
    // Copy tensor base to original tensor base, and keep same scalar type and
    // stride with cpu and gpu.
    if (output_operand.original_tensor_base().defined() &&
        !output_operand.original_tensor_base().is_same(output_operand.tensor_base())) {
      output_operand.original_tensor().copy_(output_operand.tensor());
      output_operand.restore_original_tensor();
    }
  }
}

void quantize_tensor_per_tensor_affine_privateuse1(
    const at::Tensor& rtensor,
    at::Tensor& qtensor,
    double scale,
    int64_t zero_point) {
    // do nothing
}

int64_t _fused_sdp_choice_privateuse1(const at::Tensor & query, const at::Tensor & key, const at::Tensor & value,
    const std::optional<at::Tensor> & attn_mask, double dropout_p, bool is_causal, std::optional<double> scale, bool enable_gqa){
  auto backend = sdp::SDPBackend::overrideable;
  return static_cast<int64_t>(backend);
}
} // namespace

namespace at::native {

REGISTER_PRIVATEUSE1_DISPATCH(abs_stub, &abs_kernel);
REGISTER_PRIVATEUSE1_DISPATCH(quantize_tensor_per_tensor_affine_stub, &quantize_tensor_per_tensor_affine_privateuse1);
REGISTER_PRIVATEUSE1_DISPATCH(_fused_sdp_choice_stub, &_fused_sdp_choice_privateuse1);

} // namespace at::native
struct CustomBackendMetadata : public c10::BackendMeta {
  // for testing this field will mutate when clone() is called by shallow_copy_from.
  int backend_version_format_{-1};
  int format_number_{-1};
  mutable bool cloned_{false};
  // define the constructor
  CustomBackendMetadata(int backend_version_format, int format_number) :
      backend_version_format_(backend_version_format), format_number_(format_number) {}
  c10::intrusive_ptr<c10::BackendMeta> clone(
      const c10::intrusive_ptr<c10::BackendMeta>& ptr) const override {
    cloned_ = true;
    return c10::BackendMeta::clone(ptr);
  }
};

// we need to register two functions for serialization
void for_serialization(const at::Tensor& t, std::unordered_map<std::string, bool>& m) {
  if (t.unsafeGetTensorImpl()->get_backend_meta_intrusive_ptr() == nullptr) {
    return;
  }
  auto tmeta = dynamic_cast<CustomBackendMetadata*>(t.unsafeGetTensorImpl()->get_backend_meta());
  if (tmeta->backend_version_format_ == 1) {
    m["backend_version_format"] = true;
  }
  if (tmeta->format_number_ == 29) {
    m["format_number"] = true;
  }
}

void for_deserialization(const at::Tensor& t, std::unordered_map<std::string, bool>& m) {
  int backend_version_format{-1};
  int format_number{-1};
  if (m.find("backend_version_format") != m.end()) {
    backend_version_format = 1;
  }
  if (m.find("format_number") != m.end()) {
    format_number = 29;
  }
  c10::intrusive_ptr<c10::BackendMeta> new_tmeta{std::unique_ptr<c10::BackendMeta>(
      new CustomBackendMetadata(backend_version_format, format_number))};
  t.unsafeGetTensorImpl()->set_backend_meta(new_tmeta);
}

void custom_serialization_registry() {
  torch::jit::TensorBackendMetaRegistry(c10::DeviceType::PrivateUse1,
                                        &for_serialization,
                                        &for_deserialization);
}

//check if BackendMeta serialization correctly
bool check_backend_meta(const at::Tensor& t) {
  if (t.unsafeGetTensorImpl()->get_backend_meta_intrusive_ptr()) {
    CustomBackendMetadata* tmeta = dynamic_cast<CustomBackendMetadata*>(
        t.unsafeGetTensorImpl()->get_backend_meta());
    if (tmeta->backend_version_format_==1 && tmeta->format_number_==29) {
      return true;
    }
  }
  return false;
}

// a fake set function is exposed to the Python side
void custom_set_backend_meta(const at::Tensor& t) {
  int backend_version_format{1};
  int format_number{29};
  c10::intrusive_ptr<c10::BackendMeta> new_tmeta{std::unique_ptr<c10::BackendMeta>(
      new CustomBackendMetadata(backend_version_format, format_number))};
  t.unsafeGetTensorImpl()->set_backend_meta(new_tmeta);
}

// A dummy storageImpl for our custom device, that secretly uses the CPU
c10::intrusive_ptr<c10::StorageImpl> make_custom_storage_impl(c10::StorageImpl::use_byte_size_t,
                                                              c10::SymInt size_bytes,
                                                              c10::DataPtr data_ptr,
                                                              c10::Allocator* allocator,
                                                              bool resizable) {
  c10::intrusive_ptr<c10::StorageImpl> custom_storage_impl;
  if (data_ptr == nullptr){
    custom_storage_impl = c10::make_intrusive<c10::StorageImpl>(
      c10::StorageImpl::use_byte_size_t(), size_bytes, allocator, resizable);
  } else {
    custom_storage_impl = c10::make_intrusive<c10::StorageImpl>(
      c10::StorageImpl::use_byte_size_t(), size_bytes, std::move(data_ptr), allocator, resizable);
  }
  storageImpl_counter += 1;
  return custom_storage_impl;
}

// Register our dummy storageImpl create method.
void custom_storage_registry() {
  c10::SetStorageImplCreate(c10::DeviceType::PrivateUse1, &make_custom_storage_impl);
}

bool custom_storageImpl_called() {
  if (storageImpl_counter > last_storageImpl_saved_value) {
    last_storageImpl_saved_value = storageImpl_counter;
    return true;
  }
  return false;
}

// basic dummy add function
at::Tensor custom_add_Tensor(const at::Tensor& self, const at::Tensor& other, const at::Scalar& alpha) {
  add_counter += 1;
  // Since this custom device is just for testing, not bothering to implement kernels.
  return at::empty(self.sizes(), self.options());
}

// basic abs function
at::Tensor& custom_abs_out(const at::Tensor& self, at::Tensor& out) {
  return at::native::abs_out(self, out);
}

// A dummy allocator for our custom device, that secretly uses the CPU
struct DummyCustomAllocator final : at::Allocator {
  DummyCustomAllocator() = default;
  at::DataPtr allocate(size_t nbytes) override {
    void* data = c10::alloc_cpu(nbytes);
    return {data, data, &ReportAndDelete, at::Device(at::DeviceType::PrivateUse1, custom_device_index)};
  }

  static void ReportAndDelete(void* ptr) {
    if (!ptr) {
      return;
    }
    c10::free_cpu(ptr);
  }

  at::DeleterFnPtr raw_deleter() const override {
    return &ReportAndDelete;
  }

  void copy_data(void* dest, const void* src, std::size_t count) const final {
    default_copy_data(dest, src, count);
  }
};

// Register our dummy allocator
static DummyCustomAllocator global_custom_alloc;
REGISTER_ALLOCATOR(c10::DeviceType::PrivateUse1, &global_custom_alloc);

// basic dummy empty function, so we can directly construct tensors on the custom device
// This dummy test device will just use the CPU allocator, and ignores pinned memory.
at::Tensor custom_empty_memory_format(at::IntArrayRef size,
                                      std::optional<at::ScalarType> dtype,
                                      std::optional<at::Layout> layout,
                                      std::optional<at::Device> device,
                                      std::optional<bool> pin_memory,
                                      std::optional<at::MemoryFormat> memory_format) {
  constexpr c10::DispatchKeySet private_use_ks(c10::DispatchKey::PrivateUse1);
  return at::detail::empty_generic(size,
                                   &global_custom_alloc,
                                   private_use_ks,
                                   c10::dtype_or_default(dtype),
                                   memory_format);
}
at::Tensor custom_empty_symint(c10::IntArrayRef size,
                               std::optional<at::ScalarType> dtype,
                               std::optional<at::Layout> layout,
                               std::optional<at::Device> device,
                               std::optional<bool> pin_memory,
                               std::optional<at::MemoryFormat> memory_format) {
  constexpr c10::DispatchKeySet private_use_ks(c10::DispatchKey::PrivateUse1);
  return at::detail::empty_generic(size,
    &global_custom_alloc, private_use_ks, c10::dtype_or_default(dtype), memory_format);
}

at::Tensor & custom_fill__scalar(at::Tensor & self, const at::Scalar & value) {
  // Not bothering to implement.
  return self;
}

// Unsafe using dummy device data_ptr to creat a cpu tensor, and shared data_ptr.
at::Tensor unsafe_create_cpu_tensor_from_dummy_tensor(const at::Tensor& src) {
  TORCH_CHECK(src.device().type() == c10::DeviceType::PrivateUse1,
              "Only support dummy device.");
  const auto& sizes_ = src.sizes();
  const auto& strides_ = src.strides();
  auto storage_offset_ = src.storage_offset();
  at::detail::check_size_nonnegative(sizes_);

  size_t size_bytes = at::detail::computeStorageNbytes(sizes_, strides_,
                                                       src.element_size(),
                                                       storage_offset_);

  at::DataPtr data_ptr =
    c10::InefficientStdFunctionContext::makeDataPtr(src.storage().mutable_data_ptr().get(),
                                                    [](void*){}, at::kCPU);

  c10::Storage storage{c10::Storage::use_byte_size_t{}, size_bytes, std::move(data_ptr),
    /*allocator=*/&global_custom_alloc, /*resizeable=*/false};

  constexpr c10::DispatchKeySet cpu_ks(c10::DispatchKey::CPU);
  at::Tensor tensor = at::detail::make_tensor<c10::TensorImpl>(
       std::move(storage), cpu_ks, src.dtype());

  c10::TensorImpl* tensor_impl = tensor.unsafeGetTensorImpl();
  tensor_impl->set_sizes_and_strides(sizes_, strides_);
  tensor_impl->set_storage_offset(storage_offset_);
  return tensor;
}

// basic dummy copy_() function, so we can copy from the custom device to/from CPU
at::Tensor custom__copy_from(const at::Tensor& self, const at::Tensor& dst, bool non_blocking) {
  TORCH_CHECK(
      self.is_cpu() || self.device().type() == c10::DeviceType::PrivateUse1,
      "Dummy test only allows copy from cpu -> dummy device.");
  TORCH_CHECK(
      dst.is_cpu() || dst.device().type() == c10::DeviceType::PrivateUse1,
      "Dummy test only allows copy from cpu -> dummy device.");

  // Some dummy asserts for the basic use case: inputs are the same size / dtype, all contiguous.
  TORCH_CHECK(self.sizes() == dst.sizes());
  TORCH_CHECK(self.scalar_type() == dst.scalar_type());

  if (self.is_contiguous() && dst.is_contiguous()) {
    std::memcpy(dst.storage().data_ptr().get(),
                self.storage().data_ptr().get(),
                self.storage().nbytes());
  } else {
    // Using cpu tensor to accomplishment stride copy.
    auto convert_to_cpu_tensor = [](const at::Tensor& src) -> at::Tensor {
      if (src.device().type() == c10::DeviceType::PrivateUse1) {
        return unsafe_create_cpu_tensor_from_dummy_tensor(src);
      } else {
        return src;
      }
    };
    at::Tensor cpu_self = convert_to_cpu_tensor(self);
    at::Tensor cpu_dst = convert_to_cpu_tensor(dst);
    cpu_dst.copy_(cpu_self);
  }

  return dst;
}

at::Tensor custom__copy_from_and_resize(const at::Tensor& self, const at::Tensor& dst) {
  return custom__copy_from(self, dst, false);
}

at::Tensor custom_empty_strided(c10::IntArrayRef size,
                                c10::IntArrayRef stride,
                                std::optional<at::ScalarType> dtype_opt,
                                std::optional<at::Layout> layout_opt,
                                std::optional<at::Device> device_opt,
                                std::optional<bool> pin_memory_opt) {
  constexpr c10::DispatchKeySet private_use_ks(c10::DispatchKey::PrivateUse1);
  auto dtype = c10::dtype_or_default(dtype_opt);
  return  at::detail::empty_strided_generic(size, stride, &global_custom_alloc, private_use_ks, dtype);
}

// Some set operations for the basic use case
at::Tensor& custom_set_source_Storage(at::Tensor& result, c10::Storage src) {
  int64_t new_size = static_cast<int64_t>(src.nbytes() / result.dtype().itemsize());
  c10::IntArrayRef stride = {};
  result.unsafeGetTensorImpl()->set_storage_offset(0);
  at::OptionalIntArrayRef stride_opt = stride.data() != nullptr ? at::OptionalIntArrayRef(stride) : std::nullopt;
  at::native::resize_impl_cpu_(result.unsafeGetTensorImpl(),
                               new_size, stride_opt,
                               /*resize_storage=*/!result.is_meta());
  return result;
}

// Some set operations for the basic use case
at::Tensor& custom_set_source_Storage_storage_offset(at::Tensor& result,
                                                     c10::Storage storage,
                                                     int64_t storage_offset,
                                                     c10::IntArrayRef size,
                                                     c10::IntArrayRef stride) {
  result.unsafeGetTensorImpl()->set_storage_offset(storage_offset);
  at::OptionalIntArrayRef stride_opt = stride.data() != nullptr ? at::OptionalIntArrayRef(stride) : std::nullopt;
  at::native::resize_impl_cpu_(result.unsafeGetTensorImpl(),
                               size, stride_opt,
                               /*resize_storage=*/!result.is_meta());
  return result;
}

const at::Tensor& custom_resize_(const at::Tensor& self, at::IntArrayRef size,
                          std::optional<at::MemoryFormat> optional_memory_format) {
  at::TensorImpl* tensor_impl = self.unsafeGetTensorImpl();
  tensor_impl->set_sizes_contiguous(size);
  const auto itemsize = tensor_impl->dtype().itemsize();
  const auto offset = tensor_impl->storage_offset();
  const auto storage_size = at::detail::computeStorageNbytesContiguous(size, itemsize, offset);
  // Dummy device is using cpu allocator, so here just call cpu
  // function maybe_resize_storage_cpu in aten/src/ATen/native/Resize.h
  // to get a sufficient memory space.
  at::native::maybe_resize_storage_cpu(tensor_impl, storage_size);
  if (optional_memory_format.has_value()) {
    auto memory_format =
        optional_memory_format.value();
    TORCH_CHECK(
        memory_format != at::MemoryFormat::Preserve,
        "Unsupported memory format",
        memory_format);
    tensor_impl->empty_tensor_restride(memory_format);
  }
  return self;
}

std::tuple<at::Tensor, at::Tensor, at::Tensor, at::Tensor, c10::SymInt, c10::SymInt, at::Tensor, at::Tensor, at::Tensor>
custom_scaled_dot_product_fused_attention_overrideable(
    const at::Tensor & query,
    const at::Tensor & key,
    const at::Tensor & value,
    const std::optional<at::Tensor> & attn_bias,
    double dropout_p,
    bool is_causal,
    bool return_debug_mask,
    std::optional<double> scale) {
  const int64_t batch_size = query.size(0);
  const int64_t num_heads = query.size(1);
  const int64_t head_dim_qk = query.size(3);
  const int64_t head_dim_v = value.size(3);
  const int64_t max_seqlen_q = query.size(2);
  const int64_t max_seqlen_kv = key.size(2);

  auto opts = query.options();
  auto output = at::empty({batch_size, num_heads, max_seqlen_q, head_dim_v}, opts);
  auto logsumexp = at::empty({batch_size, num_heads, max_seqlen_q}, opts.dtype(at::kFloat));
  auto debug_attn_mask = at::empty({batch_size, num_heads, max_seqlen_q, max_seqlen_kv},
                                   opts.dtype(at::kFloat));
  auto philox_seed = at::empty({}, at::dtype(at::kLong));
  auto philox_offset = at::empty({}, at::dtype(at::kLong));

  return std::make_tuple(output, logsumexp, at::Tensor(), at::Tensor(), max_seqlen_q, max_seqlen_kv, philox_seed, philox_offset, debug_attn_mask);
}
std::tuple<at::Tensor, at::Tensor, at::Tensor, at::Tensor>
custom_scaled_dot_product_fused_attention_overrideable_backward(
    const at::Tensor & grad_out,
    const at::Tensor & query,
    const at::Tensor & key,
    const at::Tensor & value,
    const at::Tensor & attn_bias,
    std::array<bool,4> grad_input_mask,
    const at::Tensor & out,
    const at::Tensor & logsumexp,
    const at::Tensor & cum_seq_q,
    const at::Tensor & cum_seq_k,
    int64_t max_q,
    int64_t max_k,
    double dropout_p,
    bool is_causal,
    const at::Tensor & philox_seed,
    const at::Tensor & philox_offset,
    std::optional<double> scale) {
  return std::tuple<at::Tensor, at::Tensor, at::Tensor, at::Tensor>(
          at::empty_like(query),
          at::empty_like(key),
          at::empty_like(value),
          at::empty_like(attn_bias));
}

// This macro does the heavy lifting.
// With TORCH_LIBRARY_IMPL, you can register custom kernels for your backend.
// For open registration, we're registering all of our kernels to the PrivateUse1 dispatch key.
// Later in this file, we map a custom device to the PrivateUse1 device type,
// which allows user code that puts a tensor on your custom_device to eventually get plumbed
// into the kernels registered here.
//
// This macro registers your kernels to the PyTorch Dispatcher.
// More details on the dispatcher can be found at http://blog.ezyang.com/2020/09/lets-talk-about-the-pytorch-dispatcher/.
TORCH_LIBRARY_IMPL(aten, PrivateUse1, m) {
  m.impl("abs.out", &custom_abs_out);
  m.impl("add.Tensor", &custom_add_Tensor);
  m.impl("empty.memory_format", &custom_empty_symint);
  m.impl("fill_.Scalar", &custom_fill__scalar);
  m.impl("_copy_from", &custom__copy_from);
  m.impl("_copy_from_and_resize", &custom__copy_from_and_resize);
  m.impl("empty_strided", &custom_empty_strided);
  m.impl("set_.source_Storage", &custom_set_source_Storage);
  m.impl("set_.source_Storage_storage_offset",&custom_set_source_Storage_storage_offset);
  m.impl("resize_", &custom_resize_);
  m.impl("as_strided", at::native::as_strided_tensorimpl);
  m.impl("quantize_per_tensor", at::native::quantize_per_tensor);
  m.impl("_fused_sdp_choice", &_fused_sdp_choice_privateuse1);
  m.impl("_scaled_dot_product_fused_attention_overrideable", &custom_scaled_dot_product_fused_attention_overrideable);
  m.impl("_scaled_dot_product_fused_attention_overrideable_backward", &custom_scaled_dot_product_fused_attention_overrideable_backward);
}

void custom_cpu_fallback(const c10::OperatorHandle& op, torch::jit::Stack* stack) {
  at::native::cpu_fallback(op, stack);
}

TORCH_LIBRARY_IMPL(aten, PrivateUse1, m) {
  m.impl("sub.Tensor", torch::CppFunction::makeFromBoxedFunction<&custom_cpu_fallback>());
  m.impl("_foreach_add.List", torch::CppFunction::makeFromBoxedFunction<&custom_cpu_fallback>());
  m.impl("_fused_adamw_", torch::CppFunction::makeFromBoxedFunction<&custom_cpu_fallback>());
  m.impl("index.Tensor", torch::CppFunction::makeFromBoxedFunction<&custom_cpu_fallback>());
  m.impl("triu_indices", torch::CppFunction::makeFromBoxedFunction<&custom_cpu_fallback>());
}

// This basic implementation doesn't bother dealing with different device indices
// (e.g. custom_device:0 vs. custom_device:1).
// We could do that by letting the user pass in a device index in our exposed device function.
// Note that if you do that, you'll also need to register a device guard to core.
// See `c10/core/impl/DeviceGuardImplInterface.h:C10_REGISTER_GUARD_IMPL`.
c10::Device get_custom_device() {
  return c10::Device(c10::DeviceType::PrivateUse1, 0);
}

bool custom_add_called() {
  bool called = false;
  if (add_counter > last_saved_value) {
    called = true;
    last_saved_value = add_counter;
  }
  return called;
}

class PrivateGeneratorImpl : public at::CPUGeneratorImpl {
public:
  // Constructors
  PrivateGeneratorImpl(c10::DeviceIndex device_index) {
    device_ = c10::Device(c10::DeviceType::PrivateUse1, device_index);
    key_set_ = c10::DispatchKeySet(c10::DispatchKey::PrivateUse1);
  }
  ~PrivateGeneratorImpl() override = default;
};

// this is used to register generator
at::Generator make_generator_privateuse1(c10::DeviceIndex device_index) {
  return at::make_generator<PrivateGeneratorImpl>(device_index);
}

void register_generator_first() {
  REGISTER_GENERATOR_PRIVATEUSE1(make_generator_privateuse1)
}

void register_generator_second() {
  REGISTER_GENERATOR_PRIVATEUSE1(make_generator_privateuse1)
}

void set_custom_device_index(c10::DeviceIndex device_index) {
  custom_device_index = device_index;
}

// a global flag used for dummy pin_memory of custom device
bool custom_pinned_flag = false;

struct FooHooksArgs : public at::PrivateUse1HooksArgs {};

struct FooHooksInterface : public at::PrivateUse1HooksInterface {
    FooHooksInterface(FooHooksArgs) {}
    ~FooHooksInterface() override = default;
    const at::Generator& getDefaultGenerator(c10::DeviceIndex device_index) const override {
      static auto device_gen = make_generator_privateuse1(device_index);
      return device_gen;
    }
    // this is a simple implementation, custom_pinned_flag will be set as true
    // once tensor.pin_memory() is called. And then tensor.is_pinned()
    // always return true no matter what tensor it's called on.
    bool isPinnedPtr(const void* data) const override {
      return custom_pinned_flag;
    }
    c10::Allocator* getPinnedMemoryAllocator() const override {
      custom_pinned_flag = true;
      return c10::GetCPUAllocator();
    }
};

TORCH_DECLARE_REGISTRY(PrivateUse1HooksRegistry, FooHooksInterface, FooHooksArgs);
C10_DEFINE_REGISTRY(PrivateUse1HooksRegistry, FooHooksInterface, FooHooksArgs)
// Using Create function to get PrivateUse1HooksInterface point from PrivateUse1HooksRegistry class.
C10_REGISTER_TYPED_CLASS(PrivateUse1HooksRegistry, "FooHooks", FooHooksInterface)

static at::PrivateUse1HooksInterface* privateuse1_hooks_local = nullptr;
static at::PrivateUse1HooksInterface* get_private_hooks() {
  static c10::once_flag once;
  c10::call_once(once, [] {
    privateuse1_hooks_local = PrivateUse1HooksRegistry()->Create("FooHooks", {}).release();
    if (!privateuse1_hooks_local) {
      privateuse1_hooks_local = new FooHooksInterface(FooHooksArgs{});
    }
  });
  return privateuse1_hooks_local;
}

void register_hook() {
  at::RegisterPrivateUse1HooksInterface(get_private_hooks());
}

bool is_register_hook() {
  return privateuse1_hooks_local != nullptr;
}

const at::Generator& default_generator(c10::DeviceIndex device_index) {
  return at::globalContext().defaultGenerator(at::Device(c10::DeviceType::PrivateUse1, device_index));;
}

void fallback_with_undefined_tensor() {
  at::Tensor first = at::empty((2,3)).to(at::DeviceType::PrivateUse1);
  at::Tensor second = at::Tensor();
  at::Tensor step = at::empty({}).fill_(2).to(at::DeviceType::PrivateUse1);
  at::Tensor grad_scale = at::empty({}).fill_(0.00001).to(at::DeviceType::PrivateUse1);
  at::Tensor found_inf = at::empty({}).fill_(1).to(at::DeviceType::PrivateUse1);
  at::TensorList tensors = {first, first};
  at::TensorList undefined_tensors = {first, second};
  at::TensorList steps = {step, step};
  return at::_fused_adamw_(tensors, tensors, tensors, tensors, undefined_tensors,
                           steps, 0.001, 0.9, 0.999, 1e-2, 1e-8, false, false,
                           grad_scale, found_inf);
}

struct CustomAutogradFnReturnsSelf : public torch::autograd::Function<CustomAutogradFnReturnsSelf> {

  static at::Tensor forward(torch::autograd::AutogradContext* ctx, at::Tensor self) {
    return self;
  }

  static torch::autograd::variable_list backward(torch::autograd::AutogradContext* ctx, torch::autograd::variable_list grad_output) {
    return {grad_output[0] * 0.5};
  }
};

struct CustomAutogradFnAliasing : public torch::autograd::Function<CustomAutogradFnAliasing> {

  static at::Tensor forward(torch::autograd::AutogradContext* ctx, at::Tensor self) {
    return self.view_symint(self.sym_sizes());
  }

  static torch::autograd::variable_list backward(torch::autograd::AutogradContext* ctx, torch::autograd::variable_list grad_output) {
    return {grad_output[0] * 0.5};
  }
};

at::Tensor custom_autograd_fn_returns_self(at::Tensor x) {
  return CustomAutogradFnReturnsSelf::apply(x);
}

at::Tensor custom_autograd_fn_aliasing(at::Tensor x) {
  return CustomAutogradFnAliasing::apply(x);
}

// Here, we're exposing a custom device object that corresponds to our custom backend.
// We do this using pybind: exposing an "extension_name.custom_device()" function in python,
// that's implemented in C++.
// The implementation in this file maps directly to the `PrivateUse1` device type.
PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
    m.def("custom_device", &get_custom_device, "get custom device object");
    m.def("custom_add_called", &custom_add_called, "check if our custom add function was called");
    m.def("register_generator_first", &register_generator_first, "register generator for custom device firstly");
    m.def("register_generator_second", &register_generator_second, "register generator for custom device secondly");
    m.def("set_custom_device_index", &set_custom_device_index, "set custom device index");
    m.def("custom_storage_registry", &custom_storage_registry, "set custom storageImpl creat method");
    m.def("custom_storageImpl_called", &custom_storageImpl_called, "check if our custom abs function was called");
    m.def("custom_set_backend_meta", &custom_set_backend_meta, "a fake set tensor BackendMeta function");
    m.def("check_backend_meta", &check_backend_meta, "check if BackendMeta serialization correctly");
    m.def("custom_serialization_registry", &custom_serialization_registry, "register custom serialization function");
    m.def("register_hook", &register_hook, "register_hook for privateuse1");
    m.def("is_register_hook", &is_register_hook, "is_register_hook for privateuse1");
    m.def("default_generator", &default_generator, "default_generator for privateuse1");
    m.def("fallback_with_undefined_tensor", &fallback_with_undefined_tensor, "fallback_with_undefined_tensor for privateuse1");

    // Co-opting this file to more easily test torch.compile'ing of custom autograd functions in C++
    m.def("custom_autograd_fn_returns_self", &custom_autograd_fn_returns_self);
}

TORCH_LIBRARY(_test_funcs, m) {
  m.def("custom_autograd_fn_aliasing(Tensor(a) input)-> Tensor(a)");
}
TORCH_LIBRARY_IMPL(_test_funcs, AutogradCPU, m) {
  m.impl("custom_autograd_fn_aliasing", &custom_autograd_fn_aliasing);
}