//  Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#pragma once

#include <memory>
#include <string>
#include <typeindex>
#include <typeinfo>

#include "paddle/fluid/framework/selected_rows.h"
#include "paddle/fluid/framework/var_type_traits.h"
namespace paddle {
namespace framework {

class Variable {
 public:
  template <typename T>
  const T& Get() const {
    static_assert(
        IsRegisteredVarType<T>(),
        "Not registered type. Please register T inside var_type_traits.h");
    PADDLE_ENFORCE_NOT_NULL(
        holder_, platform::errors::NotFound("Variable is not initialized."));
    PADDLE_ENFORCE_EQ(
        holder_->Type(), VarTypeTrait<T>::kId,
        platform::errors::InvalidArgument(
            "The Variable type must be %s, but the type it holds is %s.",
            ToTypeName(VarTypeTrait<T>::kId), ToTypeName(holder_->Type())));
    return *static_cast<const T*>(holder_->Ptr());
  }

  bool IsInitialized() const { return holder_ != nullptr; }

  template <typename T>
  T* GetMutable() {
    if (!holder_) {
      holder_.reset(new PlaceholderImpl<T>());
    } else {
      PADDLE_ENFORCE_EQ(
          holder_->Type(), VarTypeTrait<T>::kId,
          platform::errors::InvalidArgument(
              "The Variable type must be %s, but the type it holds is %s.",
              ToTypeName(VarTypeTrait<T>::kId), ToTypeName(holder_->Type())));
    }
    return static_cast<T*>(holder_->Ptr());
  }

  template <typename T>
  bool IsType() const {
    return holder_ && holder_->Type() == VarTypeTrait<T>::kId;
  }

  void Clear() { holder_.reset(); }

  int Type() const {
    PADDLE_ENFORCE_NOT_NULL(
        holder_, platform::errors::NotFound("Variable is not initialized."));
    return holder_->Type();
  }

  /**
   * The internal of two Variables share the same Placeholder whose type can be
   * Tensor, LoDTensor, SelectedRows, LoDTensorArray, etc.
   *
   * NOTE(liym27): In dynamic mode, sharing the same Placeholder also means
   * share the same TensorInplaceVersion, which is very important for inplace
   * operations.
   */
  void SharePlaceholderWith(const Variable& var);

 private:
  // This method hides type T, so it doesn't appear as a template parameter of
  // Variable.
  framework::TensorInplaceVersion* InplaceVersionCounter();

 public:
  uint32_t CurrentInplaceVersion();
  void BumpInplaceVersion();

 private:
  struct Placeholder {
    virtual ~Placeholder() PADDLE_MAY_THROW {}

    inline int Type() const { return type_; }
    inline const void* Ptr() const { return ptr_; }
    inline void* Ptr() { return ptr_; }

   protected:
    inline void Init(void* p, int type) {
      ptr_ = p;
      type_ = type;
    }

    void* ptr_;
    int type_;
  };

  // Placeholder hides type T, so it doesn't appear as a template
  // parameter of Variable.
  template <typename T>
  struct PlaceholderImpl : public Placeholder {
    static_assert(
        IsRegisteredVarType<T>(),
        "Not registered type. Please register T inside var_type_traits.h");
    PlaceholderImpl() { this->Init(&obj_, VarTypeTrait<T>::kId); }

   private:
    T obj_;
  };

  // pointers to a PlaceholderImpl object indeed.
  std::shared_ptr<Placeholder> holder_;
};

inline void Variable::SharePlaceholderWith(const Variable& var) {
  PADDLE_ENFORCE_EQ(var.IsInitialized(), true,
                    platform::errors::PreconditionNotMet(
                        "Variable holds no memory. "
                        "Call Variable::GetMutable() firstly."));
  holder_ = var.holder_;
}

inline framework::TensorInplaceVersion* Variable::InplaceVersionCounter() {
  framework::TensorInplaceVersion* version_counter_ptr(nullptr);
  if (IsType<framework::LoDTensor>()) {
    version_counter_ptr =
        &GetMutable<framework::LoDTensor>()->InplaceVersionCounter();
  } else if (IsType<framework::Tensor>()) {
    version_counter_ptr =
        &GetMutable<framework::Tensor>()->InplaceVersionCounter();

  } else if (IsType<framework::SelectedRows>()) {
    version_counter_ptr = &GetMutable<framework::SelectedRows>()
                               ->mutable_value()
                               ->InplaceVersionCounter();
  } else {
    VLOG(4) << "Only supports Tensor, LoDTensor, SelectedRows to have "
               "TensorInplaceVersion, but received type "
            << platform::demangle(framework::ToTypeName(Type()));
  }
  return version_counter_ptr;
}

inline uint32_t Variable::CurrentInplaceVersion() {
  auto version_counter_ptr = InplaceVersionCounter();
  if (version_counter_ptr) {
    return version_counter_ptr->CurrentVersion();
  } else {
    return 0;
  }
}

inline void Variable::BumpInplaceVersion() {
  auto version_counter_ptr = InplaceVersionCounter();
  if (version_counter_ptr) {
    return version_counter_ptr->Bump();
  } else {
    VLOG(4) << "Only supports Tensor, LoDTensor, SelectedRows to have "
               "TensorInplaceVersion, but received type "
            << platform::demangle(framework::ToTypeName(Type()));
  }
}
}  // namespace framework
}  // namespace paddle