// Copyright (c) 2024-present 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 <arith_uint256.h>

#include <blockencodings.h>

#include <net.h>

#include <net_processing.h>

#include <netmessagemaker.h>

#include <node/peerman_args.h>

#include <pow.h>

#include <test/fuzz/FuzzedDataProvider.h>

#include <test/fuzz/fuzz.h>

#include <test/fuzz/util.h>

#include <test/util/net.h>

#include <test/util/script.h>

#include <test/util/setup_common.h>

#include <test/util/time.h>

#include <uint256.h>

#include <validation.h>

namespace {

constexpr uint32_t FUZZ_MAX_HEADERS_RESULTS{16};

class HeadersSyncSetup : public TestingSetup

{

    std::vector<CNode*> m_connections;

public:

    HeadersSyncSetup(const ChainType chain_type, TestOpts opts) : TestingSetup(chain_type, opts)

    {

        PeerManager::Options peerman_opts;

        node::ApplyArgsManOptions(*m_node.args, peerman_opts);

        peerman_opts.max_headers_result = FUZZ_MAX_HEADERS_RESULTS;

        // The peerman's rng is a global that is re-used, so it will be re-used

        // and may cause non-determinism between runs. This may even influence

        // the global RNG, because seeding may be done from the gloabl one. For

        // now, avoid it influencing the global RNG, and initialize it with a

        // constant instead.

        peerman_opts.deterministic_rng = true;

        // No txs are relayed. Disable irrelevant and possibly

        // non-deterministic code paths.

        peerman_opts.ignore_incoming_txs = true;

        m_node.peerman = PeerManager::make(*m_node.connman, *m_node.addrman,

                                           m_node.banman.get(), *m_node.chainman,

                                           *m_node.mempool, *m_node.warnings, peerman_opts);

        CConnman::Options options;

        options.m_msgproc = m_node.peerman.get();

        m_node.connman->Init(options);

    }

    void ResetAndInitialize() EXCLUSIVE_LOCKS_REQUIRED(NetEventsInterface::g_msgproc_mutex);

    void SendMessage(FuzzedDataProvider& fuzzed_data_provider, CSerializedNetMsg&& msg)

        EXCLUSIVE_LOCKS_REQUIRED(NetEventsInterface::g_msgproc_mutex);

};

void HeadersSyncSetup::ResetAndInitialize()

{

    m_connections.clear();

    auto& connman = static_cast<ConnmanTestMsg&>(*m_node.connman);

    connman.StopNodes();

    static NodeId id{0};

    std::vector<ConnectionType> conn_types = {

        ConnectionType::OUTBOUND_FULL_RELAY,

        ConnectionType::BLOCK_RELAY,

        ConnectionType::INBOUND

    };

    for (auto conn_type : conn_types) {

        CAddress addr{};

        m_connections.push_back(new CNode(id++, nullptr, addr, 0, 0, addr, "", conn_type, false));

        CNode& p2p_node = *m_connections.back();

        connman.Handshake(

            /*node=*/p2p_node,

            /*successfully_connected=*/true,

            /*remote_services=*/ServiceFlags(NODE_NETWORK | NODE_WITNESS),

            /*local_services=*/ServiceFlags(NODE_NETWORK | NODE_WITNESS),

            /*version=*/PROTOCOL_VERSION,

            /*relay_txs=*/true);

        connman.AddTestNode(p2p_node);

    }

}

void HeadersSyncSetup::SendMessage(FuzzedDataProvider& fuzzed_data_provider, CSerializedNetMsg&& msg)

{

    auto& connman = static_cast<ConnmanTestMsg&>(*m_node.connman);

    CNode& connection = *PickValue(fuzzed_data_provider, m_connections);

    connman.FlushSendBuffer(connection);

    (void)connman.ReceiveMsgFrom(connection, std::move(msg));

    connection.fPauseSend = false;

    try {

        connman.ProcessMessagesOnce(connection);

    } catch (const std::ios_base::failure&) {

    }

    m_node.peerman->SendMessages(&connection);

}

CBlockHeader ConsumeHeader(FuzzedDataProvider& fuzzed_data_provider, const uint256& prev_hash, uint32_t prev_nbits)

{

    CBlockHeader header;

    header.nNonce = 0;

    // Either use the previous difficulty or let the fuzzer choose. The upper target in the

    // range comes from the bits value of the genesis block, which is 0x1d00ffff. The lower

    // target comes from the bits value of mainnet block 840000, which is 0x17034219.

    // Calling lower_target.SetCompact(0x17034219) and upper_target.SetCompact(0x1d00ffff)

    // should return the values below.

    //

    // RPC commands to verify:

    // getblockheader 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f

    // getblockheader 0000000000000000000320283a032748cef8227873ff4872689bf23f1cda83a5

    if (fuzzed_data_provider.ConsumeBool()) {

        header.nBits = prev_nbits;

    } else {

        arith_uint256 lower_target = UintToArith256(uint256{"0000000000000000000342190000000000000000000000000000000000000000"});

        arith_uint256 upper_target = UintToArith256(uint256{"00000000ffff0000000000000000000000000000000000000000000000000000"});

        arith_uint256 target = ConsumeArithUInt256InRange(fuzzed_data_provider, lower_target, upper_target);

        header.nBits = target.GetCompact();

    }

    header.nTime = ConsumeTime(fuzzed_data_provider);

    header.hashPrevBlock = prev_hash;

    header.nVersion = fuzzed_data_provider.ConsumeIntegral<int32_t>();

    return header;

}

CBlock ConsumeBlock(FuzzedDataProvider& fuzzed_data_provider, const uint256& prev_hash, uint32_t prev_nbits)

{

    auto header = ConsumeHeader(fuzzed_data_provider, prev_hash, prev_nbits);

    // In order to reach the headers acceptance logic, the block is

    // constructed in a way that will pass the mutation checks.

    CBlock block{header};

    CMutableTransaction tx;

    tx.vin.resize(1);

    tx.vout.resize(1);

    tx.vout[0].nValue = 0;

    tx.vin[0].scriptSig.resize(2);

    block.vtx.push_back(MakeTransactionRef(tx));

    block.hashMerkleRoot = block.vtx[0]->GetHash();

    return block;

}

void FinalizeHeader(CBlockHeader& header, const ChainstateManager& chainman)

{

    while (!CheckProofOfWork(header.GetHash(), header.nBits, chainman.GetParams().GetConsensus())) {

        ++(header.nNonce);

    }

}

// Global setup works for this test as state modification (specifically in the

// block index) would indicate a bug.

HeadersSyncSetup* g_testing_setup;

void initialize()

{

    static auto setup{

        MakeNoLogFileContext<HeadersSyncSetup>(ChainType::MAIN,

                                               {

                                                   .setup_validation_interface = false,

                                               }),

    };

    g_testing_setup = setup.get();

}

} // namespace

FUZZ_TARGET(p2p_headers_presync, .init = initialize)

{

    SeedRandomStateForTest(SeedRand::ZEROS);

    FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};

    // The steady clock is currently only used for logging, so a constant

    // time-point seems acceptable for now.

    ElapseSteady elapse_steady{};

    ChainstateManager& chainman = *g_testing_setup->m_node.chainman;

    CBlockHeader base{chainman.GetParams().GenesisBlock()};

    SetMockTime(base.nTime);

    LOCK(NetEventsInterface::g_msgproc_mutex);

    g_testing_setup->ResetAndInitialize();

    // The chain is just a single block, so this is equal to 1

    size_t original_index_size{WITH_LOCK(cs_main, return chainman.m_blockman.m_block_index.size())};

    arith_uint256 total_work{WITH_LOCK(cs_main, return chainman.m_best_header->nChainWork)};

    std::vector<CBlockHeader> all_headers;

    LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), 100)

    {

        auto finalized_block = [&]() {

            CBlock block = ConsumeBlock(fuzzed_data_provider, base.GetHash(), base.nBits);

            FinalizeHeader(block, chainman);

            return block;

        };

        // Send low-work headers, compact blocks, and blocks

        CallOneOf(

            fuzzed_data_provider,

            [&]() NO_THREAD_SAFETY_ANALYSIS {

                // Send FUZZ_MAX_HEADERS_RESULTS headers

                std::vector<CBlock> headers;

                headers.resize(FUZZ_MAX_HEADERS_RESULTS);

                for (CBlock& header : headers) {

                    header = ConsumeHeader(fuzzed_data_provider, base.GetHash(), base.nBits);

                    FinalizeHeader(header, chainman);

                    base = header;

                }

                all_headers.insert(all_headers.end(), headers.begin(), headers.end());

                auto headers_msg = NetMsg::Make(NetMsgType::HEADERS, TX_WITH_WITNESS(headers));

                g_testing_setup->SendMessage(fuzzed_data_provider, std::move(headers_msg));

            },

            [&]() NO_THREAD_SAFETY_ANALYSIS {

                // Send a compact block

                auto block = finalized_block();

                CBlockHeaderAndShortTxIDs cmpct_block{block, fuzzed_data_provider.ConsumeIntegral<uint64_t>()};

                all_headers.push_back(block);

                auto headers_msg = NetMsg::Make(NetMsgType::CMPCTBLOCK, TX_WITH_WITNESS(cmpct_block));

                g_testing_setup->SendMessage(fuzzed_data_provider, std::move(headers_msg));

            },

            [&]() NO_THREAD_SAFETY_ANALYSIS {

                // Send a block

                auto block = finalized_block();

                all_headers.push_back(block);

                auto headers_msg = NetMsg::Make(NetMsgType::BLOCK, TX_WITH_WITNESS(block));

                g_testing_setup->SendMessage(fuzzed_data_provider, std::move(headers_msg));

            });

    }

    // This is a conservative overestimate, as base is only moved forward when sending headers. In theory,

    // the longest chain generated by this test is 1600 (FUZZ_MAX_HEADERS_RESULTS * 100) headers. In that case,

    // this variable will accurately reflect the chain's total work.

    total_work += CalculateClaimedHeadersWork(all_headers);

    // This test should never create a chain with more work than MinimumChainWork.

    assert(total_work < chainman.MinimumChainWork());

    // The headers/blocks sent in this test should never be stored, as the chains don't have the work required

    // to meet the anti-DoS work threshold. So, if at any point the block index grew in size, then there's a bug

    // in the headers pre-sync logic.

    assert(WITH_LOCK(cs_main, return chainman.m_blockman.m_block_index.size()) == original_index_size);

}