clio/src/cluster/impl/FallbackRecoveryTimer.hpp

#pragma once

#include "util/Mutex.hpp"

#include <boost/asio/any_io_executor.hpp>
#include <boost/asio/steady_timer.hpp>
#include <boost/asio/thread_pool.hpp>
#include <boost/system/error_code.hpp>

#include <chrono>
#include <memory>

namespace cluster::impl {

/**
 * @brief One-shot timer for fallback recovery, with internal thread-safety.
 *
 * The timer state — including the @c boost::asio::steady_timer, the running flag,
 * and the recovery duration — is held inside a mutex-protected @c Impl struct
 * referenced via @c shared_ptr.  This makes @c FallbackRecoveryTimer cheap to
 * copy: all copies share the same underlying state.  All public methods are
 * thread-safe; callers do not need an external @c util::Mutex.
 */
class FallbackRecoveryTimer {
    struct Impl {
        boost::asio::steady_timer timer;
        bool isRunning = false;
        std::chrono::steady_clock::duration recoveryTime;

        Impl(
            boost::asio::any_io_executor const& executor,
            std::chrono::steady_clock::duration recoveryTime
        )
            : timer(executor), recoveryTime(recoveryTime)
        {
        }
    };

    std::shared_ptr<util::Mutex<Impl>> impl_;

public:
    /**
     * @brief Construct a timer bound to the given thread pool.
     *
     * @param ctx          Thread pool whose executor the timer is posted to.
     * @param recoveryTime Duration to wait before the timer fires.
     */
    FallbackRecoveryTimer(
        boost::asio::thread_pool& ctx,
        std::chrono::steady_clock::duration recoveryTime
    );

    /**
     * @brief Returns @c true if an @c async_wait is currently pending.
     */
    [[nodiscard]] bool
    isRunning() const;

    /**
     * @brief Arm the timer and schedule @p callback for when it fires.
     *
     * Sets the running flag, calls @c expires_after, and posts @c async_wait.  The
     * internal async_wait handler clears the running flag before forwarding the
     * @c error_code to @p callback.  If the timer is cancelled, @p callback receives
     * @c boost::asio::error::operation_aborted — callers must handle this.
     *
     * @param callback Invoked with the error code when the timer fires or is cancelled.
     */
    template <typename Callback>
    void
    start(Callback&& callback)
    {
        auto locked = impl_->lock();
        locked->isRunning = true;
        locked->timer.expires_after(locked->recoveryTime);
        locked->timer.async_wait([impl = impl_, cb = std::forward<Callback>(callback)](
                                     boost::system::error_code ec
                                 ) mutable {
            impl->lock()->isRunning = false;
            cb(ec);
        });
    }

    /**
     * @brief Cancel any pending @c async_wait and clear the running flag.
     */
    void
    cancel();
};

}  // namespace cluster::impl