// Copyright (c) 2011-2021 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <node/blockstorage.h>

#include <chain.h>
#include <chainparams.h>
#include <clientversion.h>
#include <consensus/validation.h>
#include <flatfile.h>
#include <fs.h>
#include <hash.h>
#include <pow.h>
#include <reverse_iterator.h>
#include <shutdown.h>
#include <signet.h>
#include <streams.h>
#include <undo.h>
#include <util/syscall_sandbox.h>
#include <util/system.h>
#include <validation.h>

namespace node {
std::atomic_bool fImporting(false);
std::atomic_bool fReindex(false);
bool fHavePruned = false;
bool fPruneMode = false;
uint64_t nPruneTarget = 0;

static FILE* OpenUndoFile(const FlatFilePos& pos, bool fReadOnly = false);
static FlatFileSeq BlockFileSeq();
static FlatFileSeq UndoFileSeq();

CBlockIndex* BlockManager::LookupBlockIndex(const uint256& hash)
{
    AssertLockHeld(cs_main);
    BlockMap::iterator it = m_block_index.find(hash);
    return it == m_block_index.end() ? nullptr : &it->second;
}

const CBlockIndex* BlockManager::LookupBlockIndex(const uint256& hash) const
{
    AssertLockHeld(cs_main);
    BlockMap::const_iterator it = m_block_index.find(hash);
    return it == m_block_index.end() ? nullptr : &it->second;
}

CBlockIndex* BlockManager::AddToBlockIndex(const CBlockHeader& block)
{
    AssertLockHeld(cs_main);

    auto [mi, inserted] = m_block_index.try_emplace(block.GetHash(), block);
    if (!inserted) {
        return &mi->second;
    }
    CBlockIndex* pindexNew = &(*mi).second;

    // We assign the sequence id to blocks only when the full data is available,
    // to avoid miners withholding blocks but broadcasting headers, to get a
    // competitive advantage.
    pindexNew->nSequenceId = 0;

    pindexNew->phashBlock = &((*mi).first);
    BlockMap::iterator miPrev = m_block_index.find(block.hashPrevBlock);
    if (miPrev != m_block_index.end()) {
        pindexNew->pprev = &(*miPrev).second;
        pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
        pindexNew->BuildSkip();
    }
    pindexNew->nTimeMax = (pindexNew->pprev ? std::max(pindexNew->pprev->nTimeMax, pindexNew->nTime) : pindexNew->nTime);
    pindexNew->nChainWork = (pindexNew->pprev ? pindexNew->pprev->nChainWork : 0) + GetBlockProof(*pindexNew);
    pindexNew->RaiseValidity(BLOCK_VALID_TREE);
    if (pindexBestHeader == nullptr || pindexBestHeader->nChainWork < pindexNew->nChainWork)
        pindexBestHeader = pindexNew;

    m_dirty_blockindex.insert(pindexNew);

    return pindexNew;
}

void BlockManager::PruneOneBlockFile(const int fileNumber)
{
    AssertLockHeld(cs_main);
    LOCK(cs_LastBlockFile);

    for (auto& entry : m_block_index) {
        CBlockIndex* pindex = &entry.second;
        if (pindex->nFile == fileNumber) {
            pindex->nStatus &= ~BLOCK_HAVE_DATA;
            pindex->nStatus &= ~BLOCK_HAVE_UNDO;
            pindex->nFile = 0;
            pindex->nDataPos = 0;
            pindex->nUndoPos = 0;
            m_dirty_blockindex.insert(pindex);

            // Prune from m_blocks_unlinked -- any block we prune would have
            // to be downloaded again in order to consider its chain, at which
            // point it would be considered as a candidate for
            // m_blocks_unlinked or setBlockIndexCandidates.
            auto range = m_blocks_unlinked.equal_range(pindex->pprev);
            while (range.first != range.second) {
                std::multimap<CBlockIndex*, CBlockIndex*>::iterator _it = range.first;
                range.first++;
                if (_it->second == pindex) {
                    m_blocks_unlinked.erase(_it);
                }
            }
        }
    }

    m_blockfile_info[fileNumber].SetNull();
    m_dirty_fileinfo.insert(fileNumber);
}

void BlockManager::FindFilesToPruneManual(std::set<int>& setFilesToPrune, int nManualPruneHeight, int chain_tip_height)
{
    assert(fPruneMode && nManualPruneHeight > 0);

    LOCK2(cs_main, cs_LastBlockFile);
    if (chain_tip_height < 0) {
        return;
    }

    // last block to prune is the lesser of (user-specified height, MIN_BLOCKS_TO_KEEP from the tip)
    unsigned int nLastBlockWeCanPrune = std::min((unsigned)nManualPruneHeight, chain_tip_height - MIN_BLOCKS_TO_KEEP);
    int count = 0;
    for (int fileNumber = 0; fileNumber < m_last_blockfile; fileNumber++) {
        if (m_blockfile_info[fileNumber].nSize == 0 || m_blockfile_info[fileNumber].nHeightLast > nLastBlockWeCanPrune) {
            continue;
        }
        PruneOneBlockFile(fileNumber);
        setFilesToPrune.insert(fileNumber);
        count++;
    }
    LogPrintf("Prune (Manual): prune_height=%d removed %d blk/rev pairs\n", nLastBlockWeCanPrune, count);
}

void BlockManager::FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight, int chain_tip_height, int prune_height, bool is_ibd)
{
    LOCK2(cs_main, cs_LastBlockFile);
    if (chain_tip_height < 0 || nPruneTarget == 0) {
        return;
    }
    if ((uint64_t)chain_tip_height <= nPruneAfterHeight) {
        return;
    }

    unsigned int nLastBlockWeCanPrune{(unsigned)std::min(prune_height, chain_tip_height - static_cast<int>(MIN_BLOCKS_TO_KEEP))};
    uint64_t nCurrentUsage = CalculateCurrentUsage();
    // We don't check to prune until after we've allocated new space for files
    // So we should leave a buffer under our target to account for another allocation
    // before the next pruning.
    uint64_t nBuffer = BLOCKFILE_CHUNK_SIZE + UNDOFILE_CHUNK_SIZE;
    uint64_t nBytesToPrune;
    int count = 0;

    if (nCurrentUsage + nBuffer >= nPruneTarget) {
        // On a prune event, the chainstate DB is flushed.
        // To avoid excessive prune events negating the benefit of high dbcache
        // values, we should not prune too rapidly.
        // So when pruning in IBD, increase the buffer a bit to avoid a re-prune too soon.
        if (is_ibd) {
            // Since this is only relevant during IBD, we use a fixed 10%
            nBuffer += nPruneTarget / 10;
        }

        for (int fileNumber = 0; fileNumber < m_last_blockfile; fileNumber++) {
            nBytesToPrune = m_blockfile_info[fileNumber].nSize + m_blockfile_info[fileNumber].nUndoSize;

            if (m_blockfile_info[fileNumber].nSize == 0) {
                continue;
            }

            if (nCurrentUsage + nBuffer < nPruneTarget) { // are we below our target?
                break;
            }

            // don't prune files that could have a block within MIN_BLOCKS_TO_KEEP of the main chain's tip but keep scanning
            if (m_blockfile_info[fileNumber].nHeightLast > nLastBlockWeCanPrune) {
                continue;
            }

            PruneOneBlockFile(fileNumber);
            // Queue up the files for removal
            setFilesToPrune.insert(fileNumber);
            nCurrentUsage -= nBytesToPrune;
            count++;
        }
    }

    LogPrint(BCLog::PRUNE, "Prune: target=%dMiB actual=%dMiB diff=%dMiB max_prune_height=%d removed %d blk/rev pairs\n",
           nPruneTarget/1024/1024, nCurrentUsage/1024/1024,
           ((int64_t)nPruneTarget - (int64_t)nCurrentUsage)/1024/1024,
           nLastBlockWeCanPrune, count);
}

CBlockIndex* BlockManager::InsertBlockIndex(const uint256& hash)
{
    AssertLockHeld(cs_main);

    if (hash.IsNull()) {
        return nullptr;
    }

    // Return existing or create new
    auto [mi, inserted] = m_block_index.try_emplace(hash);
    CBlockIndex* pindex = &(*mi).second;
    if (inserted) {
        pindex->phashBlock = &((*mi).first);
    }
    return pindex;
}

bool BlockManager::LoadBlockIndex(
    const Consensus::Params& consensus_params,
    ChainstateManager& chainman)
{
    if (!m_block_tree_db->LoadBlockIndexGuts(consensus_params, [this](const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main) { return this->InsertBlockIndex(hash); })) {
        return false;
    }

    // Calculate nChainWork
    std::vector<std::pair<int, CBlockIndex*>> vSortedByHeight;
    vSortedByHeight.reserve(m_block_index.size());
    for (auto& [_, block_index] : m_block_index) {
        CBlockIndex* pindex = &block_index;
        vSortedByHeight.push_back(std::make_pair(pindex->nHeight, pindex));
    }
    sort(vSortedByHeight.begin(), vSortedByHeight.end());

    // Find start of assumed-valid region.
    int first_assumed_valid_height = std::numeric_limits<int>::max();

    for (const auto& [height, block] : vSortedByHeight) {
        if (block->IsAssumedValid()) {
            auto chainstates = chainman.GetAll();

            // If we encounter an assumed-valid block index entry, ensure that we have
            // one chainstate that tolerates assumed-valid entries and another that does
            // not (i.e. the background validation chainstate), since assumed-valid
            // entries should always be pending validation by a fully-validated chainstate.
            auto any_chain = [&](auto fnc) { return std::any_of(chainstates.cbegin(), chainstates.cend(), fnc); };
            assert(any_chain([](auto chainstate) { return chainstate->reliesOnAssumedValid(); }));
            assert(any_chain([](auto chainstate) { return !chainstate->reliesOnAssumedValid(); }));

            first_assumed_valid_height = height;
            break;
        }
    }

    for (const std::pair<int, CBlockIndex*>& item : vSortedByHeight) {
        if (ShutdownRequested()) return false;
        CBlockIndex* pindex = item.second;
        pindex->nChainWork = (pindex->pprev ? pindex->pprev->nChainWork : 0) + GetBlockProof(*pindex);
        pindex->nTimeMax = (pindex->pprev ? std::max(pindex->pprev->nTimeMax, pindex->nTime) : pindex->nTime);

        // We can link the chain of blocks for which we've received transactions at some point, or
        // blocks that are assumed-valid on the basis of snapshot load (see
        // PopulateAndValidateSnapshot()).
        // Pruned nodes may have deleted the block.
        if (pindex->nTx > 0) {
            if (pindex->pprev) {
                if (pindex->pprev->nChainTx > 0) {
                    pindex->nChainTx = pindex->pprev->nChainTx + pindex->nTx;
                } else {
                    pindex->nChainTx = 0;
                    m_blocks_unlinked.insert(std::make_pair(pindex->pprev, pindex));
                }
            } else {
                pindex->nChainTx = pindex->nTx;
            }
        }
        if (!(pindex->nStatus & BLOCK_FAILED_MASK) && pindex->pprev && (pindex->pprev->nStatus & BLOCK_FAILED_MASK)) {
            pindex->nStatus |= BLOCK_FAILED_CHILD;
            m_dirty_blockindex.insert(pindex);
        }
        if (pindex->IsAssumedValid() ||
                (pindex->IsValid(BLOCK_VALID_TRANSACTIONS) &&
                 (pindex->HaveTxsDownloaded() || pindex->pprev == nullptr))) {

            // Fill each chainstate's block candidate set. Only add assumed-valid
            // blocks to the tip candidate set if the chainstate is allowed to rely on
            // assumed-valid blocks.
            //
            // If all setBlockIndexCandidates contained the assumed-valid blocks, the
            // background chainstate's ActivateBestChain() call would add assumed-valid
            // blocks to the chain (based on how FindMostWorkChain() works). Obviously
            // we don't want this since the purpose of the background validation chain
            // is to validate assued-valid blocks.
            //
            // Note: This is considering all blocks whose height is greater or equal to
            // the first assumed-valid block to be assumed-valid blocks, and excluding
            // them from the background chainstate's setBlockIndexCandidates set. This
            // does mean that some blocks which are not technically assumed-valid
            // (later blocks on a fork beginning before the first assumed-valid block)
            // might not get added to the background chainstate, but this is ok,
            // because they will still be attached to the active chainstate if they
            // actually contain more work.
            //
            // Instead of this height-based approach, an earlier attempt was made at
            // detecting "holistically" whether the block index under consideration
            // relied on an assumed-valid ancestor, but this proved to be too slow to
            // be practical.
            for (CChainState* chainstate : chainman.GetAll()) {
                if (chainstate->reliesOnAssumedValid() ||
                        pindex->nHeight < first_assumed_valid_height) {
                    chainstate->setBlockIndexCandidates.insert(pindex);
                }
            }
        }
        if (pindex->nStatus & BLOCK_FAILED_MASK && (!chainman.m_best_invalid || pindex->nChainWork > chainman.m_best_invalid->nChainWork)) {
            chainman.m_best_invalid = pindex;
        }
        if (pindex->pprev) {
            pindex->BuildSkip();
        }
        if (pindex->IsValid(BLOCK_VALID_TREE) && (pindexBestHeader == nullptr || CBlockIndexWorkComparator()(pindexBestHeader, pindex)))
            pindexBestHeader = pindex;
    }

    return true;
}

void BlockManager::Unload()
{
    m_blocks_unlinked.clear();

    m_block_index.clear();

    m_blockfile_info.clear();
    m_last_blockfile = 0;
    m_dirty_blockindex.clear();
    m_dirty_fileinfo.clear();
}

bool BlockManager::WriteBlockIndexDB()
{
    AssertLockHeld(::cs_main);
    std::vector<std::pair<int, const CBlockFileInfo*>> vFiles;
    vFiles.reserve(m_dirty_fileinfo.size());
    for (std::set<int>::iterator it = m_dirty_fileinfo.begin(); it != m_dirty_fileinfo.end();) {
        vFiles.push_back(std::make_pair(*it, &m_blockfile_info[*it]));
        m_dirty_fileinfo.erase(it++);
    }
    std::vector<const CBlockIndex*> vBlocks;
    vBlocks.reserve(m_dirty_blockindex.size());
    for (std::set<CBlockIndex*>::iterator it = m_dirty_blockindex.begin(); it != m_dirty_blockindex.end();) {
        vBlocks.push_back(*it);
        m_dirty_blockindex.erase(it++);
    }
    if (!m_block_tree_db->WriteBatchSync(vFiles, m_last_blockfile, vBlocks)) {
        return false;
    }
    return true;
}

bool BlockManager::LoadBlockIndexDB(ChainstateManager& chainman)
{
    if (!LoadBlockIndex(::Params().GetConsensus(), chainman)) {
        return false;
    }

    // Load block file info
    m_block_tree_db->ReadLastBlockFile(m_last_blockfile);
    m_blockfile_info.resize(m_last_blockfile + 1);
    LogPrintf("%s: last block file = %i\n", __func__, m_last_blockfile);
    for (int nFile = 0; nFile <= m_last_blockfile; nFile++) {
        m_block_tree_db->ReadBlockFileInfo(nFile, m_blockfile_info[nFile]);
    }
    LogPrintf("%s: last block file info: %s\n", __func__, m_blockfile_info[m_last_blockfile].ToString());
    for (int nFile = m_last_blockfile + 1; true; nFile++) {
        CBlockFileInfo info;
        if (m_block_tree_db->ReadBlockFileInfo(nFile, info)) {
            m_blockfile_info.push_back(info);
        } else {
            break;
        }
    }

    // Check presence of blk files
    LogPrintf("Checking all blk files are present...\n");
    std::set<int> setBlkDataFiles;
    for (const auto& [_, block_index] : m_block_index) {
        const CBlockIndex* pindex = &block_index;
        if (pindex->nStatus & BLOCK_HAVE_DATA) {
            setBlkDataFiles.insert(pindex->nFile);
        }
    }
    for (std::set<int>::iterator it = setBlkDataFiles.begin(); it != setBlkDataFiles.end(); it++) {
        FlatFilePos pos(*it, 0);
        if (CAutoFile(OpenBlockFile(pos, true), SER_DISK, CLIENT_VERSION).IsNull()) {
            return false;
        }
    }

    // Check whether we have ever pruned block & undo files
    m_block_tree_db->ReadFlag("prunedblockfiles", fHavePruned);
    if (fHavePruned) {
        LogPrintf("LoadBlockIndexDB(): Block files have previously been pruned\n");
    }

    // Check whether we need to continue reindexing
    bool fReindexing = false;
    m_block_tree_db->ReadReindexing(fReindexing);
    if (fReindexing) fReindex = true;

    return true;
}

const CBlockIndex* BlockManager::GetLastCheckpoint(const CCheckpointData& data)
{
    const MapCheckpoints& checkpoints = data.mapCheckpoints;

    for (const MapCheckpoints::value_type& i : reverse_iterate(checkpoints)) {
        const uint256& hash = i.second;
        const CBlockIndex* pindex = LookupBlockIndex(hash);
        if (pindex) {
            return pindex;
        }
    }
    return nullptr;
}

bool IsBlockPruned(const CBlockIndex* pblockindex)
{
    AssertLockHeld(::cs_main);
    return (fHavePruned && !(pblockindex->nStatus & BLOCK_HAVE_DATA) && pblockindex->nTx > 0);
}

// If we're using -prune with -reindex, then delete block files that will be ignored by the
// reindex.  Since reindexing works by starting at block file 0 and looping until a blockfile
// is missing, do the same here to delete any later block files after a gap.  Also delete all
// rev files since they'll be rewritten by the reindex anyway.  This ensures that m_blockfile_info
// is in sync with what's actually on disk by the time we start downloading, so that pruning
// works correctly.
void CleanupBlockRevFiles()
{
    std::map<std::string, fs::path> mapBlockFiles;

    // Glob all blk?????.dat and rev?????.dat files from the blocks directory.
    // Remove the rev files immediately and insert the blk file paths into an
    // ordered map keyed by block file index.
    LogPrintf("Removing unusable blk?????.dat and rev?????.dat files for -reindex with -prune\n");
    fs::path blocksdir = gArgs.GetBlocksDirPath();
    for (fs::directory_iterator it(blocksdir); it != fs::directory_iterator(); it++) {
        const std::string path = fs::PathToString(it->path().filename());
        if (fs::is_regular_file(*it) &&
            path.length() == 12 &&
            path.substr(8,4) == ".dat")
        {
            if (path.substr(0, 3) == "blk") {
                mapBlockFiles[path.substr(3, 5)] = it->path();
            } else if (path.substr(0, 3) == "rev") {
                remove(it->path());
            }
        }
    }

    // Remove all block files that aren't part of a contiguous set starting at
    // zero by walking the ordered map (keys are block file indices) by
    // keeping a separate counter.  Once we hit a gap (or if 0 doesn't exist)
    // start removing block files.
    int nContigCounter = 0;
    for (const std::pair<const std::string, fs::path>& item : mapBlockFiles) {
        if (LocaleIndependentAtoi<int>(item.first) == nContigCounter) {
            nContigCounter++;
            continue;
        }
        remove(item.second);
    }
}

CBlockFileInfo* BlockManager::GetBlockFileInfo(size_t n)
{
    LOCK(cs_LastBlockFile);

    return &m_blockfile_info.at(n);
}

static bool UndoWriteToDisk(const CBlockUndo& blockundo, FlatFilePos& pos, const uint256& hashBlock, const CMessageHeader::MessageStartChars& messageStart)
{
    // Open history file to append
    CAutoFile fileout(OpenUndoFile(pos), SER_DISK, CLIENT_VERSION);
    if (fileout.IsNull()) {
        return error("%s: OpenUndoFile failed", __func__);
    }

    // Write index header
    unsigned int nSize = GetSerializeSize(blockundo, fileout.GetVersion());
    fileout << messageStart << nSize;

    // Write undo data
    long fileOutPos = ftell(fileout.Get());
    if (fileOutPos < 0) {
        return error("%s: ftell failed", __func__);
    }
    pos.nPos = (unsigned int)fileOutPos;
    fileout << blockundo;

    // calculate & write checksum
    CHashWriter hasher(SER_GETHASH, PROTOCOL_VERSION);
    hasher << hashBlock;
    hasher << blockundo;
    fileout << hasher.GetHash();

    return true;
}

bool UndoReadFromDisk(CBlockUndo& blockundo, const CBlockIndex* pindex)
{
    const FlatFilePos pos{WITH_LOCK(::cs_main, return pindex->GetUndoPos())};

    if (pos.IsNull()) {
        return error("%s: no undo data available", __func__);
    }

    // Open history file to read
    CAutoFile filein(OpenUndoFile(pos, true), SER_DISK, CLIENT_VERSION);
    if (filein.IsNull()) {
        return error("%s: OpenUndoFile failed", __func__);
    }

    // Read block
    uint256 hashChecksum;
    CHashVerifier<CAutoFile> verifier(&filein); // We need a CHashVerifier as reserializing may lose data
    try {
        verifier << pindex->pprev->GetBlockHash();
        verifier >> blockundo;
        filein >> hashChecksum;
    } catch (const std::exception& e) {
        return error("%s: Deserialize or I/O error - %s", __func__, e.what());
    }

    // Verify checksum
    if (hashChecksum != verifier.GetHash()) {
        return error("%s: Checksum mismatch", __func__);
    }

    return true;
}

void BlockManager::FlushUndoFile(int block_file, bool finalize)
{
    FlatFilePos undo_pos_old(block_file, m_blockfile_info[block_file].nUndoSize);
    if (!UndoFileSeq().Flush(undo_pos_old, finalize)) {
        AbortNode("Flushing undo file to disk failed. This is likely the result of an I/O error.");
    }
}

void BlockManager::FlushBlockFile(bool fFinalize, bool finalize_undo)
{
    LOCK(cs_LastBlockFile);
    FlatFilePos block_pos_old(m_last_blockfile, m_blockfile_info[m_last_blockfile].nSize);
    if (!BlockFileSeq().Flush(block_pos_old, fFinalize)) {
        AbortNode("Flushing block file to disk failed. This is likely the result of an I/O error.");
    }
    // we do not always flush the undo file, as the chain tip may be lagging behind the incoming blocks,
    // e.g. during IBD or a sync after a node going offline
    if (!fFinalize || finalize_undo) FlushUndoFile(m_last_blockfile, finalize_undo);
}

uint64_t BlockManager::CalculateCurrentUsage()
{
    LOCK(cs_LastBlockFile);

    uint64_t retval = 0;
    for (const CBlockFileInfo& file : m_blockfile_info) {
        retval += file.nSize + file.nUndoSize;
    }
    return retval;
}

void UnlinkPrunedFiles(const std::set<int>& setFilesToPrune)
{
    for (std::set<int>::iterator it = setFilesToPrune.begin(); it != setFilesToPrune.end(); ++it) {
        FlatFilePos pos(*it, 0);
        fs::remove(BlockFileSeq().FileName(pos));
        fs::remove(UndoFileSeq().FileName(pos));
        LogPrint(BCLog::BLOCKSTORE, "Prune: %s deleted blk/rev (%05u)\n", __func__, *it);
    }
}

static FlatFileSeq BlockFileSeq()
{
    return FlatFileSeq(gArgs.GetBlocksDirPath(), "blk", gArgs.GetBoolArg("-fastprune", false) ? 0x4000 /* 16kb */ : BLOCKFILE_CHUNK_SIZE);
}

static FlatFileSeq UndoFileSeq()
{
    return FlatFileSeq(gArgs.GetBlocksDirPath(), "rev", UNDOFILE_CHUNK_SIZE);
}

FILE* OpenBlockFile(const FlatFilePos& pos, bool fReadOnly)
{
    return BlockFileSeq().Open(pos, fReadOnly);
}

/** Open an undo file (rev?????.dat) */
static FILE* OpenUndoFile(const FlatFilePos& pos, bool fReadOnly)
{
    return UndoFileSeq().Open(pos, fReadOnly);
}

fs::path GetBlockPosFilename(const FlatFilePos& pos)
{
    return BlockFileSeq().FileName(pos);
}

bool BlockManager::FindBlockPos(FlatFilePos& pos, unsigned int nAddSize, unsigned int nHeight, CChain& active_chain, uint64_t nTime, bool fKnown)
{
    LOCK(cs_LastBlockFile);

    unsigned int nFile = fKnown ? pos.nFile : m_last_blockfile;
    if (m_blockfile_info.size() <= nFile) {
        m_blockfile_info.resize(nFile + 1);
    }

    bool finalize_undo = false;
    if (!fKnown) {
        while (m_blockfile_info[nFile].nSize + nAddSize >= (gArgs.GetBoolArg("-fastprune", false) ? 0x10000 /* 64kb */ : MAX_BLOCKFILE_SIZE)) {
            // when the undo file is keeping up with the block file, we want to flush it explicitly
            // when it is lagging behind (more blocks arrive than are being connected), we let the
            // undo block write case handle it
            finalize_undo = (m_blockfile_info[nFile].nHeightLast == (unsigned int)active_chain.Tip()->nHeight);
            nFile++;
            if (m_blockfile_info.size() <= nFile) {
                m_blockfile_info.resize(nFile + 1);
            }
        }
        pos.nFile = nFile;
        pos.nPos = m_blockfile_info[nFile].nSize;
    }

    if ((int)nFile != m_last_blockfile) {
        if (!fKnown) {
            LogPrint(BCLog::BLOCKSTORE, "Leaving block file %i: %s\n", m_last_blockfile, m_blockfile_info[m_last_blockfile].ToString());
        }
        FlushBlockFile(!fKnown, finalize_undo);
        m_last_blockfile = nFile;
    }

    m_blockfile_info[nFile].AddBlock(nHeight, nTime);
    if (fKnown) {
        m_blockfile_info[nFile].nSize = std::max(pos.nPos + nAddSize, m_blockfile_info[nFile].nSize);
    } else {
        m_blockfile_info[nFile].nSize += nAddSize;
    }

    if (!fKnown) {
        bool out_of_space;
        size_t bytes_allocated = BlockFileSeq().Allocate(pos, nAddSize, out_of_space);
        if (out_of_space) {
            return AbortNode("Disk space is too low!", _("Disk space is too low!"));
        }
        if (bytes_allocated != 0 && fPruneMode) {
            m_check_for_pruning = true;
        }
    }

    m_dirty_fileinfo.insert(nFile);
    return true;
}

bool BlockManager::FindUndoPos(BlockValidationState& state, int nFile, FlatFilePos& pos, unsigned int nAddSize)
{
    pos.nFile = nFile;

    LOCK(cs_LastBlockFile);

    pos.nPos = m_blockfile_info[nFile].nUndoSize;
    m_blockfile_info[nFile].nUndoSize += nAddSize;
    m_dirty_fileinfo.insert(nFile);

    bool out_of_space;
    size_t bytes_allocated = UndoFileSeq().Allocate(pos, nAddSize, out_of_space);
    if (out_of_space) {
        return AbortNode(state, "Disk space is too low!", _("Disk space is too low!"));
    }
    if (bytes_allocated != 0 && fPruneMode) {
        m_check_for_pruning = true;
    }

    return true;
}

static bool WriteBlockToDisk(const CBlock& block, FlatFilePos& pos, const CMessageHeader::MessageStartChars& messageStart)
{
    // Open history file to append
    CAutoFile fileout(OpenBlockFile(pos), SER_DISK, CLIENT_VERSION);
    if (fileout.IsNull()) {
        return error("WriteBlockToDisk: OpenBlockFile failed");
    }

    // Write index header
    unsigned int nSize = GetSerializeSize(block, fileout.GetVersion());
    fileout << messageStart << nSize;

    // Write block
    long fileOutPos = ftell(fileout.Get());
    if (fileOutPos < 0) {
        return error("WriteBlockToDisk: ftell failed");
    }
    pos.nPos = (unsigned int)fileOutPos;
    fileout << block;

    return true;
}

bool BlockManager::WriteUndoDataForBlock(const CBlockUndo& blockundo, BlockValidationState& state, CBlockIndex* pindex, const CChainParams& chainparams)
{
    AssertLockHeld(::cs_main);
    // Write undo information to disk
    if (pindex->GetUndoPos().IsNull()) {
        FlatFilePos _pos;
        if (!FindUndoPos(state, pindex->nFile, _pos, ::GetSerializeSize(blockundo, CLIENT_VERSION) + 40)) {
            return error("ConnectBlock(): FindUndoPos failed");
        }
        if (!UndoWriteToDisk(blockundo, _pos, pindex->pprev->GetBlockHash(), chainparams.MessageStart())) {
            return AbortNode(state, "Failed to write undo data");
        }
        // rev files are written in block height order, whereas blk files are written as blocks come in (often out of order)
        // we want to flush the rev (undo) file once we've written the last block, which is indicated by the last height
        // in the block file info as below; note that this does not catch the case where the undo writes are keeping up
        // with the block writes (usually when a synced up node is getting newly mined blocks) -- this case is caught in
        // the FindBlockPos function
        if (_pos.nFile < m_last_blockfile && static_cast<uint32_t>(pindex->nHeight) == m_blockfile_info[_pos.nFile].nHeightLast) {
            FlushUndoFile(_pos.nFile, true);
        }

        // update nUndoPos in block index
        pindex->nUndoPos = _pos.nPos;
        pindex->nStatus |= BLOCK_HAVE_UNDO;
        m_dirty_blockindex.insert(pindex);
    }

    return true;
}

bool ReadBlockFromDisk(CBlock& block, const FlatFilePos& pos, const Consensus::Params& consensusParams)
{
    block.SetNull();

    // Open history file to read
    CAutoFile filein(OpenBlockFile(pos, true), SER_DISK, CLIENT_VERSION);
    if (filein.IsNull()) {
        return error("ReadBlockFromDisk: OpenBlockFile failed for %s", pos.ToString());
    }

    // Read block
    try {
        filein >> block;
    } catch (const std::exception& e) {
        return error("%s: Deserialize or I/O error - %s at %s", __func__, e.what(), pos.ToString());
    }

    // Check the header
    if (!CheckProofOfWork(block.GetHash(), block.nBits, consensusParams)) {
        return error("ReadBlockFromDisk: Errors in block header at %s", pos.ToString());
    }

    // Signet only: check block solution
    if (consensusParams.signet_blocks && !CheckSignetBlockSolution(block, consensusParams)) {
        return error("ReadBlockFromDisk: Errors in block solution at %s", pos.ToString());
    }

    return true;
}

bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
{
    const FlatFilePos block_pos{WITH_LOCK(cs_main, return pindex->GetBlockPos())};

    if (!ReadBlockFromDisk(block, block_pos, consensusParams)) {
        return false;
    }
    if (block.GetHash() != pindex->GetBlockHash()) {
        return error("ReadBlockFromDisk(CBlock&, CBlockIndex*): GetHash() doesn't match index for %s at %s",
                     pindex->ToString(), block_pos.ToString());
    }
    return true;
}

bool ReadRawBlockFromDisk(std::vector<uint8_t>& block, const FlatFilePos& pos, const CMessageHeader::MessageStartChars& message_start)
{
    FlatFilePos hpos = pos;
    hpos.nPos -= 8; // Seek back 8 bytes for meta header
    CAutoFile filein(OpenBlockFile(hpos, true), SER_DISK, CLIENT_VERSION);
    if (filein.IsNull()) {
        return error("%s: OpenBlockFile failed for %s", __func__, pos.ToString());
    }

    try {
        CMessageHeader::MessageStartChars blk_start;
        unsigned int blk_size;

        filein >> blk_start >> blk_size;

        if (memcmp(blk_start, message_start, CMessageHeader::MESSAGE_START_SIZE)) {
            return error("%s: Block magic mismatch for %s: %s versus expected %s", __func__, pos.ToString(),
                         HexStr(blk_start),
                         HexStr(message_start));
        }

        if (blk_size > MAX_SIZE) {
            return error("%s: Block data is larger than maximum deserialization size for %s: %s versus %s", __func__, pos.ToString(),
                         blk_size, MAX_SIZE);
        }

        block.resize(blk_size); // Zeroing of memory is intentional here
        filein.read(MakeWritableByteSpan(block));
    } catch (const std::exception& e) {
        return error("%s: Read from block file failed: %s for %s", __func__, e.what(), pos.ToString());
    }

    return true;
}

/** Store block on disk. If dbp is non-nullptr, the file is known to already reside on disk */
FlatFilePos BlockManager::SaveBlockToDisk(const CBlock& block, int nHeight, CChain& active_chain, const CChainParams& chainparams, const FlatFilePos* dbp)
{
    unsigned int nBlockSize = ::GetSerializeSize(block, CLIENT_VERSION);
    FlatFilePos blockPos;
    if (dbp != nullptr) {
        blockPos = *dbp;
    }
    if (!FindBlockPos(blockPos, nBlockSize + 8, nHeight, active_chain, block.GetBlockTime(), dbp != nullptr)) {
        error("%s: FindBlockPos failed", __func__);
        return FlatFilePos();
    }
    if (dbp == nullptr) {
        if (!WriteBlockToDisk(block, blockPos, chainparams.MessageStart())) {
            AbortNode("Failed to write block");
            return FlatFilePos();
        }
    }
    return blockPos;
}

struct CImportingNow {
    CImportingNow()
    {
        assert(fImporting == false);
        fImporting = true;
    }

    ~CImportingNow()
    {
        assert(fImporting == true);
        fImporting = false;
    }
};

void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFiles, const ArgsManager& args)
{
    SetSyscallSandboxPolicy(SyscallSandboxPolicy::INITIALIZATION_LOAD_BLOCKS);
    ScheduleBatchPriority();

    {
        CImportingNow imp;

        // -reindex
        if (fReindex) {
            int nFile = 0;
            while (true) {
                FlatFilePos pos(nFile, 0);
                if (!fs::exists(GetBlockPosFilename(pos))) {
                    break; // No block files left to reindex
                }
                FILE* file = OpenBlockFile(pos, true);
                if (!file) {
                    break; // This error is logged in OpenBlockFile
                }
                LogPrintf("Reindexing block file blk%05u.dat...\n", (unsigned int)nFile);
                chainman.ActiveChainstate().LoadExternalBlockFile(file, &pos);
                if (ShutdownRequested()) {
                    LogPrintf("Shutdown requested. Exit %s\n", __func__);
                    return;
                }
                nFile++;
            }
            WITH_LOCK(::cs_main, chainman.m_blockman.m_block_tree_db->WriteReindexing(false));
            fReindex = false;
            LogPrintf("Reindexing finished\n");
            // To avoid ending up in a situation without genesis block, re-try initializing (no-op if reindexing worked):
            chainman.ActiveChainstate().LoadGenesisBlock();
        }

        // -loadblock=
        for (const fs::path& path : vImportFiles) {
            FILE* file = fsbridge::fopen(path, "rb");
            if (file) {
                LogPrintf("Importing blocks file %s...\n", fs::PathToString(path));
                chainman.ActiveChainstate().LoadExternalBlockFile(file);
                if (ShutdownRequested()) {
                    LogPrintf("Shutdown requested. Exit %s\n", __func__);
                    return;
                }
            } else {
                LogPrintf("Warning: Could not open blocks file %s\n", fs::PathToString(path));
            }
        }

        // scan for better chains in the block chain database, that are not yet connected in the active best chain

        // We can't hold cs_main during ActivateBestChain even though we're accessing
        // the chainman unique_ptrs since ABC requires us not to be holding cs_main, so retrieve
        // the relevant pointers before the ABC call.
        for (CChainState* chainstate : WITH_LOCK(::cs_main, return chainman.GetAll())) {
            BlockValidationState state;
            if (!chainstate->ActivateBestChain(state, nullptr)) {
                LogPrintf("Failed to connect best block (%s)\n", state.ToString());
                StartShutdown();
                return;
            }
        }

        if (args.GetBoolArg("-stopafterblockimport", DEFAULT_STOPAFTERBLOCKIMPORT)) {
            LogPrintf("Stopping after block import\n");
            StartShutdown();
            return;
        }
    } // End scope of CImportingNow
    chainman.ActiveChainstate().LoadMempool(args);
}
} // namespace node