#pragma once

#include <twist/stdlike/atomic.hpp>
#include <twist/threading/spin_wait.hpp>

namespace solutions {

/*  QueueSpinLock spinlock;
 *
 *  {
 *    QueueSpinLock::Guard guard(spinlock);  // Acquires spinlock
 *    // Critical section starts here
 *  }  // Releases spinlock
 */

class QueueSpinLock {
 public:
  class Guard {
   public:
    explicit Guard(QueueSpinLock& spinlock) : spinlock_(spinlock) {
      Guard * prev_tail = spinlock_.tail_.exchange(this);
      if (prev_tail) {
        prev_tail->next_ = this;
        while(!owner_) {
        }
      }
    }

    ~Guard() {
      Guard * cur = this;
      bool f = spinlock_.tail_.compare_exchange_strong(cur, nullptr);
      if (!f) {
        while (!next_) {
        }
        next_->owner_ = true;
      }
    }

   private:
    QueueSpinLock& spinlock_;
    Guard * next_ = nullptr;
    bool owner_ = false;
  };

 private:
  twist::atomic<Guard *> tail_ = nullptr;
};

}