/*
 * This file is part of the Flowee project
 * Copyright (C) 2020-2026 Tom Zander <tom@flowee.org>
 *
 * 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, see <http://www.gnu.org/licenses/>.
 */
#include "SyncChainAction.h"
#include "DownloadManager.h"
#include "Peer.h"

#include <Logger.h>

#include <time.h>

static int MinGoodPeers = 4;
static int MaxGoodPeers = 8;
constexpr int RINGBUF_SIZE = 10;

SyncChainAction::SyncChainAction(DownloadManager *parent)
    : Action(parent),
    m_states(RINGBUF_SIZE)
{
    m_startHeight = parent->blockHeight();
    if (parent->chain() != P2PNet::MainChain) {
        MinGoodPeers = 3;
        MaxGoodPeers = 3;
    }
}

void SyncChainAction::execute(const boost::system::error_code &error)
{
    if (error)
        return;

    /*
     * This class observes the system, typically shortly after startup.
     * The point is to make sure we have a fully up-to-date chain.
     *
     * We also monitor the 'getheaders' updating of a big amount (again,
     * only at startup) and kick a node that is slow in giving us headers.
     * -----------------------------------------------------------
     *
     * The goal is to get various peers to agree on what is the 'tip'.
     * These peers should also come from different sections of the Internet
     * since most of the sybils would end up with very similar IPs. (TODO)
     *
     * The downloadmanager/connection manager duo make sure that all peers
     * get a 'getheaders'  call regularly, and kick out peers that are not on
     * our chain.
     * Additionally they make sure that INV announcements of blocks are validated
     * similarly and the Peer objects 'peerHeight()' is updated on a new block.
     */

    const int localHeight = m_dlm->blockHeight();
    const int goal = m_dlm->blockchain().expectedBlockHeight();
    const int theoreticalDiff = std::abs(localHeight - goal);

    const auto connected = m_dlm->connectionManager().connectedPeers();
    if (static_cast<int>(m_dlm->connectionManager().connectedPeers().size()) < MinGoodPeers) {
        logInfo(2021) << "SyncChain has" << connected.size() << "peers, which is less than I need. Connecting a new peer";
        int newPeers = 1;
        if (m_peerRequests++ > 13) // speed up after some time
            newPeers = 10;
        while (newPeers-- > 0)
            connectToNextPeer();
        m_dlm->connectionManager().setBlockHeightCertainty(P2PNet::NotCertain);
    }

    int peersAgree = 0;
    int goodPeers = 0;
    int peersGotRequestedToSendHeaders = 0;
    const uint32_t now = time(nullptr);
    const uint32_t headersOkTime = 3600 * 24 * 7; // a full week

    for (const auto &peer : connected) {
        if (!peer->receivedHeaders()
                    && now - peer->peerAddress().lastReceivedGoodHeaders() > headersOkTime) {
            if (peer->requestedHeader())
                ++peersGotRequestedToSendHeaders;
            continue;
        }
        if (peer->peerAddress().punishment() > 300)
            continue;
        ++goodPeers;
        if (peer->peerHeight() == localHeight)
            ++peersAgree;
    }
    if ((peersAgree >= MinGoodPeers && theoreticalDiff < 6)
            || peersAgree >= MaxGoodPeers) { // DONE!
        logInfo(2021) << "==== SyncChainAction ==== DONE";

        if (localHeight - m_startHeight > 800) { // 800 should match ConnectionManager::connectionEstablished
            // in ConnectionManager we check a peer is on the right chain by doing a 'headers' call.
            // Unless we are behind too far as that would not be useful.
            // So, now we are caught up, make those peers show some headers.
            for (const auto &peer : connected) {
                if (!peer->receivedHeaders()) {
                    logInfo(2021) << "Post catching up, request headers of peer" << peer->connectionId();
                    m_dlm->connectionManager().requestHeaders(peer, 4);
                }
            }
        }

        m_dlm->connectionManager().setBlockHeightCertainty(P2PNet::Certain);
        m_dlm->done(this); // deletes me
        return; // action is done
    }
    else if (peersAgree >= 3) {
        m_dlm->connectionManager().setBlockHeightCertainty(P2PNet::ReasonablyCertain);
    }

    if (m_dlm->peerDownloadingHeaders() != -1) { // a download is in progress
        // no need to do anything, just wait.

        // We will check if we are actually progressing up in block-height since
        // our peer might stop sending us headers for some reason.

        int score = 0;
        int prevHeight = 0;
        uint32_t oldestTime = 0;
        for (int i = m_stateIndex + 1; i != m_stateIndex; ++i) {
            if (prevHeight == 0) {
                if (i < RINGBUF_SIZE) {
                    prevHeight = m_states[i].height;
                    if (prevHeight == 0) // when no measurements present, allow starting
                        score += 100;
                    else
                        oldestTime = m_states[i].timestamp;
                }
            } else {
                int diff = m_states[i].height - prevHeight;
                if (diff > 900)
                    score += 100;
            }
            if (i >= RINGBUF_SIZE - 1) i = -1; // behave like a ring-buffer.
        }
        if (score <= 400) {
            // getting maybe 3000 block-headers in 15 secs is too slow :(

            assert(oldestTime > 0);
            if (now - oldestTime > 60) {
                // this action should run every 1.5 seconds, if 10 measurements took
                // more than a minute then we just slept or something.
                logDebug(2021) << "Slowness detected in header download, probably due to app-sleep. Waiting longer";
            }
            else {
                // take action, find a different peer to download from.
                auto &cm = m_dlm->connectionManager();
                if (cm.connectedPeers().size() > 1) { // only if we actually have another
                    logInfo(2021) << "SyncChain disconnects peer that is holding up downloads" << m_dlm->peerDownloadingHeaders();
                    auto p = cm.peer(m_dlm->peerDownloadingHeaders());
                    if (p)
                        cm.disconnect(p);

                    for (size_t i = 0; i < RINGBUF_SIZE; ++i) {
                        m_states[i].height = 0; // reset history and score.
                    }
                } else if (canAddNewPeer()){
                    logInfo(2021) << "SyncChain would like a faster peer. Connecting to new one";
                    connectToNextPeer();
                }
            }
        }
        m_states[m_stateIndex].height = std::max(1, m_dlm->blockHeight());
        m_states[m_stateIndex++].timestamp = now;
        if (m_stateIndex >= RINGBUF_SIZE)
            m_stateIndex = 0;
    }
    else {
        if (!connected.empty() && peersGotRequestedToSendHeaders == 0 && peersAgree == 0) {
            // make sure that we actually try to download headers if we weren't already
            m_dlm->getMoreHeaders();
        }
        if (static_cast<int>(connected.size()) >= MinGoodPeers && goodPeers > MinGoodPeers && peersAgree < MinGoodPeers) {
            // ok, this is annoying.
            // we have enough peers, they have all had the headers sent, we are not downloading any headers.
            // but we seem to be behind...

            // Lets add more peers.
            logInfo(2021) << "SyncChain has" << goodPeers << "good peers, but we are still behind. Connecting a new peer";
            connectToNextPeer();
        }
    }

    again();
}

void SyncChainAction::connectToNextPeer()
{
    auto address = m_dlm->connectionManager().peerAddressDb().findBest(5); // 5 is service Bloom and Network
    if (address.isValid()) {
        m_dlm->connectionManager().connect(address);
        m_lastPeerAddedTime = time(nullptr);
    }
}

bool SyncChainAction::canAddNewPeer()
{
    return time(nullptr) - m_lastPeerAddedTime > 30;
}