BackendRegistry.h

Go to the documentation of this file.

/*
 * Copyright (c) 2026 MQSS Maintainers
 * All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 */

 
#pragma once
 
#include "qrmci/BackendWrapper.h"
 
#include <chrono>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <map>
#include <string>
#include <string_view>
 
namespace mqss::qrmci {

enum class BackendSelectionPolicy : std::uint8_t {
  LowestName,
  SmallestSufficient,
};

class BackendRegistry {
public:
  using Clock = std::chrono::steady_clock;

  static constexpr Clock::duration DefaultTimeToLive = std::chrono::seconds(30);

  BackendRegistry() = default;

  explicit BackendRegistry(Clock::duration timeToLive);

  bool insertOrRefresh(BackendWrapper backend,
                       Clock::time_point now = Clock::now());

  std::size_t expire(Clock::time_point now = Clock::now());

  [[nodiscard]] const BackendWrapper *find(std::string_view backendName) const;

  [[nodiscard]] bool contains(std::string_view backendName) const;

  [[nodiscard]] std::size_t size() const noexcept { return entries.size(); }

  [[nodiscard]] bool empty() const noexcept { return entries.empty(); }

  [[nodiscard]] Clock::duration getTimeToLive() const noexcept {
    return entryTimeToLive;
  }

  template <typename Fn> void forEachBackend(Fn &&fn) const {
    for (const auto &[backendName, entry] : entries) {
      std::invoke(fn, backendName, entry.backend);
    }
  }
 
private:
  struct Entry {
    BackendWrapper backend;
    Clock::time_point lastRefreshed;
  };
 
  // Ordered, so iteration -- and therefore selection -- is deterministic.
  // std::less<> gives heterogeneous lookup from std::string_view without
  // materialising a std::string per query.
  std::map<std::string, Entry, std::less<>> entries;
  Clock::duration entryTimeToLive{DefaultTimeToLive};
};
 
} // namespace mqss::qrmci