/*
 *
 * Modified by ScyllaDB
 * Copyright (C) 2015-present ScyllaDB
 */

/*
 * SPDX-License-Identifier: (AGPL-3.0-or-later and Apache-2.0)
 */

#include <boost/range/adaptor/map.hpp>
#include "gms/failure_detector.hh"
#include "gms/gossiper.hh"
#include "gms/i_failure_detection_event_listener.hh"
#include "gms/endpoint_state.hh"
#include "gms/application_state.hh"
#include "gms/inet_address.hh"
#include "log.hh"
#include <iostream>
#include <chrono>
#include "replica/database.hh"

namespace gms {

static logging::logger logger("failure_detector");

constexpr std::chrono::milliseconds failure_detector::DEFAULT_MAX_PAUSE;

using clk = arrival_window::clk;

void arrival_window::add(clk::time_point value, const gms::inet_address& ep) {
    if (_tlast > clk::time_point::min()) {
        auto inter_arrival_time = value - _tlast;
        if (inter_arrival_time <= _max_interval && inter_arrival_time >= _min_interval) {
            _arrival_intervals.add(inter_arrival_time.count());
        } else  {
            logger.debug("failure_detector: Ignoring interval time of {} for {}, mean={}, size={}", inter_arrival_time.count(), ep, mean(), size());
        }
    } else {
        // We use a very large initial interval since the "right" average depends on the cluster size
        // and it's better to err high (false negatives, which will be corrected by waiting a bit longer)
        // than low (false positives, which cause "flapping").
        _arrival_intervals.add(_initial.count());
    }
    _tlast = value;
}

double arrival_window::mean() const {
    return _arrival_intervals.mean();
}

double arrival_window::phi(clk::time_point tnow) {
    assert(_arrival_intervals.size() > 0 && _tlast > clk::time_point::min()); // should not be called before any samples arrive
    auto t = (tnow - _tlast).count();
    auto m = mean();
    double phi = t / m;
    logger.debug("failure_detector: now={}, tlast={}, t={}, mean={}, phi={}",
        tnow.time_since_epoch().count(), _tlast.time_since_epoch().count(), t, m, phi);
    return phi;
}

std::ostream& operator<<(std::ostream& os, const arrival_window& w) {
    for (auto& x : w._arrival_intervals.deque()) {
        os << x << " ";
    }
    return os;
}

void failure_detector::set_phi_convict_threshold(double phi) {
    _phi = phi;
}

double failure_detector::get_phi_convict_threshold() {
    return _phi;
}

void failure_detector::report(inet_address ep) {
    logger.trace("failure_detector: reporting {}", ep);
    auto now = clk::now();
    auto it = _arrival_samples.find(ep);
    if (it == _arrival_samples.end()) {
        // avoid adding an empty ArrivalWindow to the Map
        auto heartbeat_window = arrival_window(SAMPLE_SIZE, _initial, _max_interval, gossiper::INTERVAL);
        heartbeat_window.add(now, ep);
        _arrival_samples.emplace(ep, heartbeat_window);
    } else {
        it->second.add(now, ep);
    }
}

// Runs inside seastar::async context
void failure_detector::interpret(inet_address ep) {
    auto it = _arrival_samples.find(ep);
    if (it == _arrival_samples.end()) {
        return;
    }
    arrival_window& hb_wnd = it->second;
    auto now = clk::now();
    if (!_last_interpret) {
        *_last_interpret = now;
    }
    auto diff = std::chrono::duration_cast<std::chrono::milliseconds>(now - *_last_interpret);
    *_last_interpret = now;
    if (diff > get_max_local_pause()) {
        logger.warn("Not marking nodes down due to local pause of {} > {} (milliseconds)", diff.count(), get_max_local_pause().count());
        _last_paused = now;
        return;
    }
    if (clk::now() - _last_paused < get_max_local_pause()) {
        logger.debug("Still not marking nodes down due to local pause");
        return;
    }
    double phi = hb_wnd.phi(now);
    logger.trace("failure_detector: PHI for {} : {}", ep, phi);
    logger.trace("failure_detector: phi_convict_threshold={}", _phi);

    if (PHI_FACTOR * phi > get_phi_convict_threshold()) {
        logger.trace("failure_detector: notifying listeners that {} is down", ep);
        logger.trace("failure_detector: intervals: {} mean: {}", hb_wnd, hb_wnd.mean());
        for (auto& listener : _fd_evnt_listeners) {
            logger.debug("failure_detector: convict ep={} phi={}", ep, phi);
            listener->convict(ep, phi);
        }
    }
}

// Runs inside seastar::async context
void failure_detector::force_conviction(inet_address ep) {
    logger.debug("failure_detector: Forcing conviction of {}", ep);
    for (auto& listener : _fd_evnt_listeners) {
        listener->convict(ep, get_phi_convict_threshold());
    }
}

void failure_detector::remove(inet_address ep) {
    _arrival_samples.erase(ep);
}

void failure_detector::register_failure_detection_event_listener(i_failure_detection_event_listener* listener) {
    _fd_evnt_listeners.push_back(std::move(listener));
}

void failure_detector::unregister_failure_detection_event_listener(i_failure_detection_event_listener* listener) {
    _fd_evnt_listeners.remove(listener);
}

std::ostream& operator<<(std::ostream& os, const failure_detector& x) {
    for (auto& entry : x._arrival_samples) {
        const inet_address& ep = entry.first;
        const arrival_window& win = entry.second;
        os << ep << " : "  << win << "\n";
    }
    return os;
}

} // namespace gms