/**
 * Copyright 2019 Huawei Technologies Co., Ltd
 *
 * 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.
 */
#ifndef DATASET_UTIL_QUEUE_H_
#define DATASET_UTIL_QUEUE_H_

#include <atomic>
#include <memory>
#include <mutex>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>

#include "common/utils.h"
#include "utils/log_adapter.h"
#include "dataset/util/allocator.h"
#include "dataset/util/services.h"
#include "dataset/util/cond_var.h"
#include "dataset/util/task_manager.h"

namespace mindspore {
namespace dataset {
template <typename T>
struct is_shared_ptr : public std::false_type {};

template <typename T>
struct is_shared_ptr<std::shared_ptr<T>> : public std::true_type {};

template <typename T>
struct is_unique_ptr : public std::false_type {};

template <typename T>
struct is_unique_ptr<std::unique_ptr<T>> : public std::true_type {};

// A simple thread safe queue using a fixed size array
template <typename T>
class Queue {
 public:
  using value_type = T;
  using pointer = T *;
  using const_pointer = const T *;
  using reference = T &;
  using const_reference = const T &;

  void Init() {
    if (sz_ > 0) {
      // We allocate a block of memory and then call the default constructor for each slot. Maybe simpler to call
      // new[] but we want to control where the memory is allocated from.
      arr_ = alloc_.allocate(sz_);
      for (uint64_t i = 0; i < sz_; i++) {
        std::allocator_traits<Allocator<T>>::construct(alloc_, &(arr_[i]));
      }
    }
  }

  explicit Queue(int sz)
      : sz_(sz),
        arr_(nullptr),
        head_(0),
        tail_(0),
        my_name_(Services::GetUniqueID()),
        alloc_(Services::GetInstance().GetServiceMemPool()) {
    Init();
    MS_LOG(DEBUG) << "Create Q with uuid " << my_name_ << " of size " << sz_ << ".";
  }

  virtual ~Queue() {
    ResetQue();
    if (arr_) {
      // Simply free the pointer. Since there is nothing in the queue. We don't want to invoke the destructor
      // of T in each slot.
      alloc_.deallocate(arr_);
      arr_ = nullptr;
    }
  }

  int size() const {
    int v = tail_ - head_;
    return (v >= 0) ? v : 0;
  }

  int capacity() const { return sz_; }

  bool empty() const { return head_ == tail_; }

  void Reset() { ResetQue(); }

  // Producer
  Status Add(const_reference ele) noexcept {
    std::unique_lock<std::mutex> _lock(mux_);
    // Block when full
    Status rc = full_cv_.Wait(&_lock, [this]() -> bool { return (size() != capacity()); });
    if (rc.IsOk()) {
      uint32_t k = tail_++ % sz_;
      arr_[k] = ele;
      empty_cv_.NotifyAll();
      _lock.unlock();
    } else {
      empty_cv_.Interrupt();
    }
    return rc;
  }

  Status Add(T &&ele) noexcept {
    std::unique_lock<std::mutex> _lock(mux_);
    // Block when full
    Status rc = full_cv_.Wait(&_lock, [this]() -> bool { return (size() != capacity()); });
    if (rc.IsOk()) {
      uint32_t k = tail_++ % sz_;
      arr_[k] = std::forward<T>(ele);
      empty_cv_.NotifyAll();
      _lock.unlock();
    } else {
      empty_cv_.Interrupt();
    }
    return rc;
  }

  template <typename... Ts>
  Status EmplaceBack(Ts &&... args) noexcept {
    std::unique_lock<std::mutex> _lock(mux_);
    // Block when full
    Status rc = full_cv_.Wait(&_lock, [this]() -> bool { return (size() != capacity()); });
    if (rc.IsOk()) {
      uint32_t k = tail_++ % sz_;
      new (&(arr_[k])) T(std::forward<Ts>(args)...);
      empty_cv_.NotifyAll();
      _lock.unlock();
    } else {
      empty_cv_.Interrupt();
    }
    return rc;
  }

  // Consumer
  Status PopFront(pointer p) {
    std::unique_lock<std::mutex> _lock(mux_);
    // Block when empty
    Status rc = empty_cv_.Wait(&_lock, [this]() -> bool { return !empty(); });
    if (rc.IsOk()) {
      uint32_t k = head_++ % sz_;
      *p = std::move(arr_[k]);
      if (std::is_destructible<T>::value) {
        // std::move above only changes arr_[k] from rvalue to lvalue.
        // The real implementation of move constructor depends on T.
        // It may be compiler generated or user defined. But either case
        // the result of arr_[k] is still a valid object of type T, and
        // we will not keep any extra copy in the queue.
        arr_[k].~T();
        // For gcc 9, an extra fix is needed here to clear the memory content
        // of arr_[k] because this slot can be reused by another Add which can
        // do another std::move. We have seen SEGV here in this case.
        std::allocator_traits<Allocator<T>>::construct(alloc_, &(arr_[k]));
      }
      full_cv_.NotifyAll();
      _lock.unlock();
    } else {
      full_cv_.Interrupt();
    }
    return rc;
  }

  void ResetQue() noexcept {
    std::unique_lock<std::mutex> _lock(mux_);
    // If there are elements in the queue, invoke its destructor one by one.
    if (!empty() && std::is_destructible<T>::value) {
      for (uint64_t i = head_; i < tail_; i++) {
        uint32_t k = i % sz_;
        arr_[k].~T();
      }
    }
    empty_cv_.ResetIntrpState();
    full_cv_.ResetIntrpState();
    head_ = 0;
    tail_ = 0;
  }

  Status Register(TaskGroup *vg) {
    Status rc1 = empty_cv_.Register(vg->GetIntrpService());
    Status rc2 = full_cv_.Register(vg->GetIntrpService());
    if (rc1.IsOk()) {
      return rc2;
    } else {
      return rc1;
    }
  }

 private:
  uint64_t sz_;
  pointer arr_;
  uint64_t head_;
  uint64_t tail_;
  std::string my_name_;
  std::mutex mux_;
  CondVar empty_cv_;
  CondVar full_cv_;
  Allocator<T> alloc_;
};

// A container of queues with [] operator accessors.  Basically this is a wrapper over of a vector of queues
// to help abstract/simplify code that is maintaining multiple queues.
template <typename T>
class QueueList {
 public:
  QueueList() {}

  void Init(int num_queues, int capacity) {
    queue_list_.reserve(num_queues);
    for (int i = 0; i < num_queues; i++) {
      queue_list_.emplace_back(std::make_unique<Queue<T>>(capacity));
    }
  }

  Status Register(TaskGroup *vg) {
    if (vg == nullptr) {
      return Status(StatusCode::kUnexpectedError, __LINE__, __FILE__, "Null task group during QueueList registration.");
    }
    for (int i = 0; i < queue_list_.size(); ++i) {
      RETURN_IF_NOT_OK(queue_list_[i]->Register(vg));
    }
    return Status::OK();
  }

  int size() const { return queue_list_.size(); }

  std::unique_ptr<Queue<T>> &operator[](const int index) { return queue_list_[index]; }

  const std::unique_ptr<Queue<T>> &operator[](const int index) const { return queue_list_[index]; }

  ~QueueList() = default;

 private:
  // Queue contains non-copyable objects, so it cannot be added to a vector due to the vector
  // requirement that objects must have copy semantics.  To resolve this, we use a vector of unique
  // pointers.  This allows us to provide dynamic creation of queues in a container.
  std::vector<std::unique_ptr<Queue<T>>> queue_list_;
};
}  // namespace dataset
}  // namespace mindspore
#endif  // DATASET_UTIL_QUEUE_H_