moloapp/example/fw/Observ.hpp

#pragma once

// Observability skeletons: typed event bus, metrics registry, and tracer.
// All three compile to near-zero overhead when kEnabled is false.
// Gap: real 02-observability.md owns the log format, Prometheus and OTel
// export, and the zero-cost macro layer.

#include <functional>
#include <map>
#include <mutex>
#include <string>
#include <vector>

namespace molo::example::fw {

struct Event {
  std::string type;
  std::string payload;
  std::string correlation_id;
};

class EventBus {
 public:
  static constexpr bool kEnabled = true;

  void on(const std::string& type, std::function<void(const Event&)> listener);
  void emit(const Event& event);
  std::vector<Event> delivered() const;

 private:
  mutable std::mutex mu_;
  std::map<std::string, std::vector<std::function<void(const Event&)>>>
      listeners_;
  std::vector<Event> delivered_;
};

class Metrics {
 public:
  static constexpr bool kEnabled = true;

  void inc(const std::string& name, double value = 1.0);
  void gauge(const std::string& name, double value);
  double get(const std::string& name) const;
  std::string render_prometheus() const;

 private:
  mutable std::mutex mu_;
  std::map<std::string, double> values_;
};

struct Span {
  std::string trace_id;
  std::string span_id;
  std::string name;
  std::string correlation_id;
};

class Telemetry {
 public:
  static constexpr bool kEnabled = true;

  Span start_span(const std::string& name, const std::string& correlation_id);
  void finish_span(const Span& span);
  std::vector<Span> spans() const;

 private:
  mutable std::mutex mu_;
  std::vector<Span> spans_;
  unsigned long next_id_ = 1;
};

}  // namespace molo::example::fw