notification_bus.h

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#pragma once
 
#include <chrono>
#include <cstdint>
#include <functional>
#include <nlohmann/json.hpp>
#include <optional>
#include <string>
#include <string_view>
#include <thread>
#include <vector>
 
 
namespace mm::node {
 
inline constexpr std::string_view kNotificationTopic = "notifications";
 
class NotificationBus {
 public:
  struct Source {
    std::function<std::uint64_t()> revision;
    std::function<std::optional<nlohmann::json>()> render;
    std::chrono::milliseconds interval{20};
  };
 
  using PublishFn = std::function<void(std::string topic, std::string json)>;
 
  NotificationBus();
 
  ~NotificationBus();
 
  NotificationBus(const NotificationBus&) = delete;
  NotificationBus& operator=(const NotificationBus&) = delete;
  NotificationBus(NotificationBus&&) = delete;
  NotificationBus& operator=(NotificationBus&&) = delete;
 
  void setPublish(PublishFn publish);
 
  void addSource(Source source);
 
  void start();
 
  void stop();
 
 private:
  void run(std::stop_token stopToken);
 
  static std::string envelope(const nlohmann::json& data);
 
  std::chrono::steady_clock::time_point nextDeadline() const;
 
  PublishFn publish_;
  std::vector<Source> sources_;
  std::vector<std::uint64_t> lastSeen_;
  std::vector<std::chrono::steady_clock::time_point> nextDue_;
  // Last on purpose: everything above is fully built before the thread that reads it starts, and
  // the thread is joined before any of it goes away.
  std::jthread thread_;
};
 
}  // namespace mm::node