cursor.h

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// === cursor.h ========================================================================================================
//                                               Sen Infrastructure
//                   Released under the Apache License v2.0 (SPDX-License-Identifier Apache-2.0).
//                                    See the LICENSE.txt file for more information.
//                   © Airbus SAS, Airbus Helicopters, and Airbus Defence and Space SAU/GmbH/SAS.
// =====================================================================================================================
 
#ifndef SEN_DB_CURSOR_H
#define SEN_DB_CURSOR_H
 
#include "sen/core/base/class_helpers.h"
#include "sen/core/base/timestamp.h"
 
#include <functional>
#include <variant>
 
namespace sen::db
{
 
class Input;

template <typename End, typename... T>
class Cursor
{
  SEN_MOVE_ONLY(Cursor)
 
public:
  using Payload = std::variant<std::monostate, T..., End>;

  struct Entry
  {
    TimeStamp time;   
    Payload payload;  
  };
 
public:
  ~Cursor() = default;
 
public:
  [[nodiscard]] bool atEnd() const noexcept { return std::holds_alternative<End>(entry_.payload); }

  [[nodiscard]] bool atBegining() const noexcept { return std::holds_alternative<std::monostate>(entry_.payload); }

  [[nodiscard]] const Entry& get() const noexcept { return entry_; }

  [[nodiscard]] const Entry& operator->() const noexcept { return entry_; }

  Cursor& operator++()
  {
    frontProvider_(entry_);
    return *this;
  }
 
private:
  friend class Input;
  using Provider = std::function<void(Entry&)>;
 
private:
  explicit Cursor(Provider frontProvider): frontProvider_(std::move(frontProvider)) {}
 
private:
  Entry entry_;
  Provider frontProvider_;
};
 
}  // namespace sen::db
 
#endif  // SEN_DB_CURSOR_H