//  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 <typeindex>
#include <typeinfo>

#include "paddle/fluid/platform/enforce.h"

namespace paddle {
namespace framework {

class Variable {
 public:
  template <typename T>
  const T& Get() const {
    PADDLE_ENFORCE(holder_ != nullptr, "Variable must hold some thing");
    PADDLE_ENFORCE(IsType<T>(),
                   "Variable must be type %s, the holding type is %s",
                   typeid(T).name(), holder_->Type().name());
    return *static_cast<const T*>(holder_->Ptr());
  }

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

  template <typename T>
  T* GetMutable() {
    if (!IsType<T>()) {
      holder_.reset(new PlaceholderImpl<T>(new T()));
    }
    return static_cast<T*>(holder_->Ptr());
  }

  template <typename T>
  bool IsType() const {
    return holder_ != nullptr &&
           std::type_index(typeid(T)) == std::type_index(holder_->Type());
  }

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

  std::type_index Type() const {
    PADDLE_ENFORCE(holder_ != nullptr, "Must hold memory");
    return holder_->Type();
  }

 private:
  struct Placeholder {
    virtual ~Placeholder() {}
    virtual const std::type_info& Type() const = 0;
    virtual void* Ptr() const = 0;
  };

  // Placeholder hides type T, so it doesn't appear as a template
  // parameter of Variable.
  template <typename T>
  struct PlaceholderImpl : public Placeholder {
    PlaceholderImpl(T* ptr) : ptr_(ptr), type_(typeid(T)) {}

    virtual const std::type_info& Type() const { return type_; }
    virtual void* Ptr() const { return static_cast<void*>(ptr_.get()); }

    std::unique_ptr<T> ptr_;
    const std::type_info& type_;
  };

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

  // name_ is only meaningful with a Scope and accessible by it.
  //
  // NOTE: Please don't expose name_ by adding methods like
  // Variable::Name or Scope::VarName!  A variable could have a human
  // readable name or an auto-generated scope-unique name.  In the
  // former case, the caller knows the name and doesn't need to access
  // the name; in the latter case, the variable should be identified
  // by its address but not the unreadable name.
  friend class Scope;
  const std::string* name_;
};

}  // namespace framework
}  // namespace paddle
