#include "NVMeDevice.hpp"

#include <boost/system/detail/error_code.hpp>
#include <phosphor-logging/lg2.hpp>

#include <cassert>

void NVMeDevice::start()
{
    subsys->start();

    if (intf.getProtocol() == NVMeIntf::Protocol::NVMeMI)
    {
        setup();
    }
}

void NVMeDevice::setup()
{
    dev->setup(
        [weak{weak_from_this()}](const std::error_code& ec,
                                 const std::shared_ptr<MctpEndpoint>& ep) {
        if (auto self = weak.lock())
        {
            self->finalize(ec, ep);
        }
    });
}

void NVMeDevice::stop()
{
    subsys->stop();
}

void NVMeDevice::finalize(const std::error_code& ec,
                          const std::shared_ptr<MctpEndpoint>& ep)
{
    assert(intf.getProtocol() == NVMeIntf::Protocol::NVMeMI);

    if (ec)
    {
        restart();
        return;
    }

    ep->subscribe(
        [weak{weak_from_this()}](const std::shared_ptr<MctpEndpoint>& ep) {
        if (auto self = weak.lock())
        {
            self->degraded(ep);
        }
    },
        [weak{weak_from_this()}](const std::shared_ptr<MctpEndpoint>& ep) {
        if (auto self = weak.lock())
        {
            self->available(ep);
        }
    },
        // Removed
        [weak{weak_from_this()}](const std::shared_ptr<MctpEndpoint>& ep) {
        if (auto self = weak.lock())
        {
            self->removed(ep);
        }
    });
}

void NVMeDevice::restart()
{
    assert(intf.getProtocol() == NVMeIntf::Protocol::NVMeMI);
    assert(timer);
    assert(gracePeriod);
    // Setup failed, wait a bit and try again
    timer->expires_after(*gracePeriod);
    timer->async_wait(
        [weak{weak_from_this()}](const boost::system::error_code& ec) {
        if (ec)
        {
            return;
        }

        if (auto self = weak.lock())
        {
            self->setup();
        }
    });
}

void NVMeDevice::degraded(const std::shared_ptr<MctpEndpoint>& ep)
{
    assert(intf.getProtocol() == NVMeIntf::Protocol::NVMeMI);
    lg2::info("[{ENDPOINT}]: Degraded", "ENDPOINT", ep->describe());
    recovering = true;
    gracePeriodActive = false;
    timer->cancel();
    std::get<std::shared_ptr<NVMeMiIntf>>(intf.getInferface())->stop();
}

void NVMeDevice::available(const std::shared_ptr<MctpEndpoint>& ep)
{
    assert(intf.getProtocol() == NVMeIntf::Protocol::NVMeMI);
    assert(timer);
    assert(gracePeriod);
    lg2::info("[{SUBSYS}][{ENDPOINT}]: Available", "SUBSYS", subsys->getName(),
              "ENDPOINT", ep->describe());

    // The behaviour of MctpEndpoint::subscribe() is to register the provided
    // callbacks, and then fetch the current state of the endpoint. As a
    // consequence of fetching the state, the appropriate callback is be
    // invoked.
    //
    // Unless circumstances are particularly rough, the endpoint will be in the
    // 'Available' state when it is first exposed on DBus.
    //
    // Beyond the start-up entry to the 'Available' state, we will only see an
    // 'Available' event if something has triggered endpoint recovery (putting
    // the endpoint into 'Degraded'), followed by the recovery succeeding.
    //
    // However, it's possible that recovery is triggered by the NVMe MI layer
    // being broken, while the MCTP endpoint continues to respond without error.
    // This can lead to a "tight" event cycle of entering 'Degraded',
    // immediately followed by entering 'Available', where NVMeMi::start() kicks
    // off the endpoint recovery again as the MI layer continues to fail.
    //
    // The impact of this event cycle is exacerbated by `nvme_mi_open_mctp()`
    // performing IO to the device for the purpose of quirk detection. Currently
    // `nvme_mi_open_mctp()` is issued on the main thread, and if the MI
    // layer is dead enough, the device fails to respond to the Admin Identify
    // command. The failure to respond blocks the main thread for the default
    // libnvme-mi command timeout (which, upstream, is 5000ms). This can lead
    // to misbehaviour of applications interacting with the DBus objects exposed
    // by nvmesensor.
    //
    // Mitigate the hazard of this event cycle by enforcing a grace-period after
    // MCTP endpoint recovery succeeds. This can provide some time for other
    // jobs on the main thread to be processed.
    //
    // We track whether the grace period is required via the `recovering`
    // boolean. If we've passed through the 'Degraded' state then we know we're
    // at risk of the tight event cycle, therefore we enforce the grace-period.
    // If we've not passed through 'Degraded' but we have an 'Available' event
    // we know we're in the start-up path, which we don't want to delay.
    //
    // State machine for events and grace period:
    // ```mermaid
    // stateDiagram-v2
    //     [*] --> Setup : Device Initialized
    //
    //     state "Setup (Initial State)" as Setup
    //     state "Active (Interface Started)" as Active
    //     state "Degraded State\n(recovering = true)" as Degraded
    //     state "Grace Period Active\n(Timer Ticking)" as GracePeriod
    //
    //     %% Setup transitions
    //     Setup --> Active : Available Event\n(Bypasses Grace Period)
    //     Setup --> Degraded : Degraded Event
    //
    //     %% Active transitions
    //     Active --> Degraded : Degraded Event\n(Stops Interface)
    //     Active --> Setup : Removed Event\n(Stops Interface, Restarts)
    //
    //     %% Degraded transitions
    //     Degraded --> GracePeriod : Available Event\n(Sets
    //     recovering=false,\nStarts Timer) Degraded --> Setup : Removed
    //     Event\n(Stops Interface, Restarts)
    //
    //     %% Grace Period transitions
    //     GracePeriod --> Active : Timer Expires\n(Starts Interface)
    //     GracePeriod --> GracePeriod : Available Event\n(Ignored, Timer
    //     Continues) GracePeriod --> Degraded : Degraded Event\n(Cancels Timer,
    //     Stops Interface) GracePeriod --> Setup : Removed Event\n(Cancels
    //     Timer, Restarts)
    // ```
    if (recovering)
    {
        recovering = false;
        gracePeriodActive = true;
        timer->expires_after(*gracePeriod);
        timer->async_wait(
            [weak{weak_from_this()}, ep](const boost::system::error_code& ec) {
            if (auto self = weak.lock())
            {
                if (ec)
                {
                    self->gracePeriodActive = false;
                    lg2::info(
                        "[{ENDPOINT}] grace period expired due to: {ERROR}",
                        "ENDPOINT", ep->describe(), "ERROR", ec.message());
                    return;
                }
                // Ensure we haven't degraded or been removed while the
                // callback was waiting in the ASIO event queue.
                if (!self->gracePeriodActive)
                {
                    return;
                }
                self->gracePeriodActive = false;
                std::get<std::shared_ptr<NVMeMiIntf>>(self->intf.getInferface())
                    ->start(ep);
            }
        });
    }
    else
    {
        // If the grace period is actively running, this is a consecutive
        // Available event. We ignore it to avoid bypassing the grace period.
        if (gracePeriodActive)
        {
            return;
        }

        // If we're not recovering we should only see an 'Available' event
        // when we're first initialising the device. There should be no timers
        // to cancel.
        std::size_t cancelled = timer->cancel();
        if (cancelled != 0)
        {
            lg2::error(
                "[{ENDPOINT}]: Unexpected timer cancellation ({CANCELLED}) in non-recovery path!",
                "ENDPOINT", ep->describe(), "CANCELLED", cancelled);
        }
        std::get<std::shared_ptr<NVMeMiIntf>>(intf.getInferface())->start(ep);
    }
}

void NVMeDevice::removed(const std::shared_ptr<MctpEndpoint>& ep)
{
    assert(intf.getProtocol() == NVMeIntf::Protocol::NVMeMI);
    lg2::info("[{ENDPOINT}]: Removed", "ENDPOINT", ep->describe());
    recovering = false;
    gracePeriodActive = false;
    std::get<std::shared_ptr<NVMeMiIntf>>(intf.getInferface())->stop();
    restart();
}