extended statement_cache with message bus events

include/matador/sql/statement_cache.hpp

@@ -4,6 +4,8 @@
 #include "matador/sql/executor.hpp"
 #include "matador/sql/statement.hpp"
 
+#include "matador/utils/message_bus.hpp"
+
 #include <list>
 #include <mutex>
 #include <unordered_map>
@@ -12,17 +14,18 @@ namespace matador::sql {
 
 class connection_pool;
 
-struct statement_cache_event {
-  enum class Type { Accessed, Added, Evicted };
-  Type type;
+struct statement_event {
   std::string sql;
   std::chrono::steady_clock::time_point timestamp;
 };
 
-class statement_cache_observer_interface {
-public:
-  virtual void on_event(const statement_cache_event&) = 0;
-  virtual ~statement_cache_observer_interface() = default;
+struct statement_accessed_event : statement_event {};
+struct statement_added_event : statement_event {};
+struct statement_evicted_event : statement_event {};
+
+
+struct statement_cache_config {
+  size_t max_size;
 };
 
 class statement_cache final {
@@ -36,7 +39,7 @@ private:
   };
 
 public:
-  explicit statement_cache(connection_pool &pool, size_t max_size = 50);
+  statement_cache(utils::message_bus &bus, connection_pool &pool, size_t max_size = 50);
   statement_cache(const statement_cache &) = delete;
   statement_cache &operator=(const statement_cache &) = delete;
   statement_cache(statement_cache &&) = delete;
@@ -49,13 +52,13 @@ public:
   [[nodiscard]] size_t capacity() const;
   [[nodiscard]] bool empty() const;
 
-  void subscribe(statement_cache_observer_interface &observer);
+  template<class EventType>
+  utils::subscription subscribe(std::function<void(const EventType&)> handler) {
+    return bus_.subscribe<EventType>(handler);
+  }
+
 
 private:
-  void push(statement_cache_event::Type type, const std::string& sql) const;
-
-private:
-
   size_t max_size_{};
   std::list<size_t> usage_list_;  // LRU: front = most recent, back = least recent
   std::unordered_map<size_t, cache_entry> cache_map_;
@@ -64,7 +67,8 @@ private:
   connection_pool &pool_;
   const sql::dialect &dialect_;
 
-  std::vector<statement_cache_observer_interface*> observers_;
+  utils::message_bus &bus_;
 };
+
 }
 #endif //STATEMENT_CACHE_HPP