expiration_tracker.hpp

#pragma once
 
#include "../dependency_tracker/data_kind.hpp"
#include "../dependency_tracker/tagged_data.hpp"
 
#include <array>
#include <chrono>
#include <optional>
#include <ostream>
#include <string>
#include <unordered_map>
#include <vector>
 
namespace launchdarkly::server_side::data_components {
 
class ExpirationTracker {
   public:
    using TimePoint = std::chrono::time_point<std::chrono::steady_clock>;
 
    enum class TrackState {
        kFresh,
        kStale,
        kNotTracked
    };
 
    void Add(std::string const& key, TimePoint expiration);
 
    void Remove(std::string const& key);
 
    TrackState State(std::string const& key, TimePoint current_time) const;
 
    void Add(DataKind kind, std::string const& key, TimePoint expiration);
 
    void Remove(DataKind kind, std::string const& key);
 
    TrackState State(DataKind kind,
                     std::string const& key,
                     TimePoint current_time) const;
 
    void Clear();
 
    std::vector<std::pair<std::optional<DataKind>, std::string>> Prune(
        TimePoint current_time);
 
   private:
    using TtlMap = std::unordered_map<std::string, TimePoint>;
 
    TtlMap unscoped_;
 
    static TrackState State(TimePoint expiration, TimePoint current_time);
 
    class ScopedTtls {
       public:
        ScopedTtls();
 
        using DataType =
            std::array<TaggedData<TtlMap>,
                       static_cast<std::underlying_type_t<DataKind>>(
                           DataKind::kKindCount)>;
        void Set(DataKind kind, std::string const& key, TimePoint expiration);
        void Remove(DataKind kind, std::string const& key);
        std::optional<TimePoint> Get(DataKind kind,
                                     std::string const& key) const;
        void Clear();
 
        [[nodiscard]] typename DataType::iterator begin();
 
        [[nodiscard]] typename DataType::iterator end();
 
       private:
        DataType data_;
    };
 
    ScopedTtls scoped_;
};
 
std::ostream& operator<<(std::ostream& out,
                         ExpirationTracker::TrackState const& state);
 
}  // namespace launchdarkly::server_side::data_components