/**
 * Most of the utils in this file is adapted from PyTorch/XLA
 * https://github.com/pytorch/xla/blob/master/third_party/xla_client/util.h
 */

#pragma once

#include <exception>
#include <functional>
#include <vector>

#include <c10/util/Optional.h>
#include <c10/util/OptionalArrayRef.h>

namespace torch {
namespace lazy {

// Similar to c10::scope_exit but with a status.
// TODO(alanwaketan): Consolidate it with c10::scope_exit.
template <typename T>
class Cleanup {
 public:
  using StatusType = T;

  explicit Cleanup(std::function<void(StatusType&&)>&& func)
      : func_(std::move(func)) {}
  Cleanup(Cleanup&& ref) noexcept
      : func_(std::move(ref.func_)), status_(std::move(ref.status_)) {}
  Cleanup(const Cleanup&) = delete;

  ~Cleanup() {
    if (func_ != nullptr) {
      func_(std::move(status_));
    }
  }

  Cleanup& operator=(const Cleanup&) = delete;

  Cleanup& operator=(Cleanup&& ref) {
    if (this != &ref) {
      func_ = std::move(ref.func_);
      status_ = std::move(ref.status_);
    }
    return *this;
  }

  void Release() {
    func_ = nullptr;
  }

  void SetStatus(StatusType&& status) {
    status_ = std::move(status);
  }

  const StatusType& GetStatus() const {
    return status_;
  }

 private:
  std::function<void(StatusType&&)> func_;
  StatusType status_;
};

using ExceptionCleanup = Cleanup<std::exception_ptr>;

// Allows APIs which might return const references and values, to not be forced
// to return values in the signature.
// TODO(alanwaketan): This is clever, but is there really no std or c10
// supports? Needs more investigations.
template <typename T>
class MaybeRef {
 public:
  /* implicit */ MaybeRef(const T& ref) : ref_(ref) {}
  /* implicit */ MaybeRef(T&& value)
      : storage_(std::move(value)), ref_(*storage_) {}

  const T& Get() const {
    return ref_;
  }
  const T& operator*() const {
    return Get();
  }
  operator const T&() const {
    return Get();
  }

  bool IsStored() const {
    return storage_.has_value();
  }

 private:
  c10::optional<T> storage_;
  const T& ref_;
};

template <typename T>
std::vector<T> Iota(size_t size, T init = 0, T incr = 1) {
  std::vector<T> result(size);
  T value = init;
  for (size_t i = 0; i < size; ++i, value += incr) {
    result[i] = value;
  }
  return result;
}

template <typename T, typename S>
std::vector<T> ToVector(const S& input) {
  return std::vector<T>(input.begin(), input.end());
}

template <typename T>
c10::optional<std::vector<T>> ToOptionalVector(
    c10::OptionalArrayRef<T> arrayRef) {
  if (arrayRef) {
    return arrayRef->vec();
  }
  return c10::nullopt;
}

template <typename T>
typename std::underlying_type<T>::type GetEnumValue(T value) {
  return static_cast<typename std::underlying_type<T>::type>(value);
}

} // namespace lazy
} // namespace torch
