postgres_listener_service.hpp

/* -*- mode: c++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * Copyright (C) 2025 Marco Craveiro <marco.craveiro@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation; either version 3 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */
#ifndef ORES_EVENTING_SERVICE_POSTGRES_LISTENER_SERVICE_HPP
#define ORES_EVENTING_SERVICE_POSTGRES_LISTENER_SERVICE_HPP
 
#include <mutex>
#include <atomic>
#include <string>
#include <thread>
#include <vector>
#include <optional>
#include <functional>
#include <condition_variable>
#include <sqlgen/postgres.hpp>
#include "ores.logging/make_logger.hpp"
#include "ores.database/domain/context.hpp"
#include "ores.eventing/domain/entity_change_event.hpp"
 
namespace ores::eventing::service {
 
class postgres_listener_service final {
private:
    [[nodiscard]] static auto& lg() {
        using namespace ores::logging;
        static auto instance = make_logger(
            "ores.eventing.service.postgres_listener_service");
        return instance;
    }
 
public:
    using notification_callback_t = std::function<void(const domain::entity_change_event&)>;
 
    explicit postgres_listener_service(database::context ctx,
        notification_callback_t callback);
 
    ~postgres_listener_service();
 
    // Deleted copy constructor and assignment operator to prevent copies.
    postgres_listener_service(const postgres_listener_service&) = delete;
    postgres_listener_service& operator=(const postgres_listener_service&) = delete;
 
    void start();
 
    void stop();
 
    void subscribe(const std::string& channel_name);
 
    void notify(const std::string& channel_name, const std::string& payload);
 
    bool wait_until_ready(std::chrono::milliseconds timeout = std::chrono::seconds(5));
 
private:
    bool open_connection();
 
    void issue_pending_listens();
 
    void listen_loop();
 
    void handle_notification(const sqlgen::postgres::Notification& notification);
 
private:
    database::context ctx_;
    notification_callback_t notification_callback_;
 
    mutable std::mutex mutex_;              
    std::optional<rfl::Ref<sqlgen::postgres::Connection>> connection_;
    std::vector<std::string> subscribed_channels_;
 
    std::thread listener_thread_;
    std::atomic<bool> running_;
 
    std::condition_variable ready_cv_;      
    bool ready_{false};                     
};
 
}
 
#endif