// Copyright (c) 2020-2021 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 <chain.h>

#include <chainparams.h>

#include <common/args.h>

#include <consensus/params.h>

#include <primitives/block.h>

#include <util/chaintype.h>

#include <versionbits.h>

#include <versionbits_impl.h>

#include <test/fuzz/FuzzedDataProvider.h>

#include <test/fuzz/fuzz.h>

#include <test/fuzz/util.h>

#include <cstdint>

#include <limits>

#include <memory>

#include <vector>

namespace {

class TestConditionChecker : public VersionBitsConditionChecker

{

private:

    mutable ThresholdConditionCache m_cache;

public:

    TestConditionChecker(const Consensus::BIP9Deployment& dep) : VersionBitsConditionChecker{dep}

    {

        assert(dep.period > 0);

        assert(dep.threshold <= dep.period);

        assert(0 <= dep.bit && dep.bit < 32 && dep.bit < VERSIONBITS_NUM_BITS);

        assert(0 <= dep.min_activation_height);

    }

    ThresholdState GetStateFor(const CBlockIndex* pindexPrev) const { return AbstractThresholdConditionChecker::GetStateFor(pindexPrev, m_cache); }

    int GetStateSinceHeightFor(const CBlockIndex* pindexPrev) const { return AbstractThresholdConditionChecker::GetStateSinceHeightFor(pindexPrev, m_cache); }

};

/** Track blocks mined for test */

class Blocks

{

private:

    std::vector<std::unique_ptr<CBlockIndex>> m_blocks;

    const uint32_t m_start_time;

    const uint32_t m_interval;

    const int32_t m_signal;

    const int32_t m_no_signal;

public:

    Blocks(uint32_t start_time, uint32_t interval, int32_t signal, int32_t no_signal)

        : m_start_time{start_time}, m_interval{interval}, m_signal{signal}, m_no_signal{no_signal} {}

    size_t size() const { return m_blocks.size(); }

    CBlockIndex* tip() const

    {

        return m_blocks.empty() ? nullptr : m_blocks.back().get();

    }

    CBlockIndex* mine_block(bool signal)

    {

        CBlockHeader header;

        header.nVersion = signal ? m_signal : m_no_signal;

        header.nTime = m_start_time + m_blocks.size() * m_interval;

        header.nBits = 0x1d00ffff;

        auto current_block = std::make_unique<CBlockIndex>(header);

        current_block->pprev = tip();

        current_block->nHeight = m_blocks.size();

        current_block->BuildSkip();

        return m_blocks.emplace_back(std::move(current_block)).get();

    }

};

std::unique_ptr<const CChainParams> g_params;

void initialize()

{

    // this is actually comparatively slow, so only do it once

    g_params = CreateChainParams(ArgsManager{}, ChainType::MAIN);

    assert(g_params != nullptr);

}

constexpr uint32_t MAX_START_TIME = 4102444800; // 2100-01-01

FUZZ_TARGET(versionbits, .init = initialize)

{

    const CChainParams& params = *g_params;

    const int64_t interval = params.GetConsensus().nPowTargetSpacing;

    assert(interval > 1); // need to be able to halve it

    assert(interval < std::numeric_limits<int32_t>::max());

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

    // making period/max_periods larger slows these tests down significantly

    const uint32_t period = 32;

    const size_t max_periods = 16;

    const size_t max_blocks = 2 * period * max_periods;

    // too many blocks at 10min each might cause uint32_t time to overflow if

    // block_start_time is at the end of the range above

    assert(std::numeric_limits<uint32_t>::max() - MAX_START_TIME > interval * max_blocks);

    const int64_t block_start_time = fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(params.GenesisBlock().nTime, MAX_START_TIME);

    // what values for version will we use to signal / not signal?

    const int32_t ver_signal = fuzzed_data_provider.ConsumeIntegral<int32_t>();

    const int32_t ver_nosignal = fuzzed_data_provider.ConsumeIntegral<int32_t>();

    if (ver_nosignal < 0) return; // negative values are uninteresting

    // Now that we have chosen time and versions, setup to mine blocks

    Blocks blocks(block_start_time, interval, ver_signal, ver_nosignal);

    const bool always_active_test = fuzzed_data_provider.ConsumeBool();

    const bool never_active_test = !always_active_test && fuzzed_data_provider.ConsumeBool();

    const Consensus::BIP9Deployment dep{[&]() {

        Consensus::BIP9Deployment dep;

        dep.period = period;

        dep.threshold = fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(1, period);

        assert(0 < dep.threshold && dep.threshold <= dep.period); // must be able to both pass and fail threshold!

        // select deployment parameters: bit, start time, timeout

        dep.bit = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, VERSIONBITS_NUM_BITS - 1);

        if (always_active_test) {

            dep.nStartTime = Consensus::BIP9Deployment::ALWAYS_ACTIVE;

            dep.nTimeout = fuzzed_data_provider.ConsumeBool() ? Consensus::BIP9Deployment::NO_TIMEOUT : fuzzed_data_provider.ConsumeIntegral<int64_t>();

        } else if (never_active_test) {

            dep.nStartTime = Consensus::BIP9Deployment::NEVER_ACTIVE;

            dep.nTimeout = fuzzed_data_provider.ConsumeBool() ? Consensus::BIP9Deployment::NO_TIMEOUT : fuzzed_data_provider.ConsumeIntegral<int64_t>();

        } else {

            // pick the timestamp to switch based on a block

            // note states will change *after* these blocks because mediantime lags

            int start_block = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, period * (max_periods - 3));

            int end_block = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, period * (max_periods - 3));

            dep.nStartTime = block_start_time + start_block * interval;

            dep.nTimeout = block_start_time + end_block * interval;

            // allow for times to not exactly match a block

            if (fuzzed_data_provider.ConsumeBool()) dep.nStartTime += interval / 2;

            if (fuzzed_data_provider.ConsumeBool()) dep.nTimeout += interval / 2;

        }

        dep.min_activation_height = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, period * max_periods);

        return dep;

    }()};

    TestConditionChecker checker(dep);

    // Early exit if the versions don't signal sensibly for the deployment

    if (!checker.Condition(ver_signal)) return;

    if (checker.Condition(ver_nosignal)) return;

    // TOP_BITS should ensure version will be positive and meet min

    // version requirement

    assert(ver_signal > 0);

    assert(ver_signal >= VERSIONBITS_LAST_OLD_BLOCK_VERSION);

    /* Strategy:

     *  * we will mine a final period worth of blocks, with

     *    randomised signalling according to a mask

     *  * but before we mine those blocks, we will mine some

     *    randomised number of prior periods; with either all

     *    or no blocks in the period signalling

     *

     * We establish the mask first, then consume "bools" until

     * we run out of fuzz data to work out how many prior periods

     * there are and which ones will signal.

     */

    // establish the mask

    const uint32_t signalling_mask = fuzzed_data_provider.ConsumeIntegral<uint32_t>();

    // mine prior periods

    while (fuzzed_data_provider.remaining_bytes() > 0) { // early exit; no need for LIMITED_WHILE

        // all blocks in these periods either do or don't signal

        bool signal = fuzzed_data_provider.ConsumeBool();

        for (uint32_t b = 0; b < period; ++b) {

            blocks.mine_block(signal);

        }

        // don't risk exceeding max_blocks or times may wrap around

        if (blocks.size() + 2 * period > max_blocks) break;

    }

    // NOTE: fuzzed_data_provider may be fully consumed at this point and should not be used further

    // now we mine the final period and check that everything looks sane

    // count the number of signalling blocks

    uint32_t blocks_sig = 0;

    // get the info for the first block of the period

    CBlockIndex* prev = blocks.tip();

    const int exp_since = checker.GetStateSinceHeightFor(prev);

    const ThresholdState exp_state = checker.GetStateFor(prev);

    // get statistics from end of previous period, then reset

    BIP9Stats last_stats;

    last_stats.period = period;

    last_stats.threshold = dep.threshold;

    last_stats.count = last_stats.elapsed = 0;

    last_stats.possible = (period >= dep.threshold);

    std::vector<bool> last_signals{};

    int prev_next_height = (prev == nullptr ? 0 : prev->nHeight + 1);

    assert(exp_since <= prev_next_height);

    // mine (period-1) blocks and check state

    for (uint32_t b = 1; b < period; ++b) {

        const bool signal = (signalling_mask >> (b % 32)) & 1;

        if (signal) ++blocks_sig;

        CBlockIndex* current_block = blocks.mine_block(signal);

        // verify that signalling attempt was interpreted correctly

        assert(checker.Condition(current_block->nVersion) == signal);

        // state and since don't change within the period

        const ThresholdState state = checker.GetStateFor(current_block);

        const int since = checker.GetStateSinceHeightFor(current_block);

        assert(state == exp_state);

        assert(since == exp_since);

        // check that after mining this block stats change as expected

        std::vector<bool> signals;

        const BIP9Stats stats = checker.GetStateStatisticsFor(current_block, &signals);

        const BIP9Stats stats_no_signals = checker.GetStateStatisticsFor(current_block);

        assert(stats.period == stats_no_signals.period && stats.threshold == stats_no_signals.threshold

               && stats.elapsed == stats_no_signals.elapsed && stats.count == stats_no_signals.count

               && stats.possible == stats_no_signals.possible);

        assert(stats.period == period);

        assert(stats.threshold == dep.threshold);

        assert(stats.elapsed == b);

        assert(stats.count == last_stats.count + (signal ? 1 : 0));

        assert(stats.possible == (stats.count + period >= stats.elapsed + dep.threshold));

        last_stats = stats;

        assert(signals.size() == last_signals.size() + 1);

        assert(signals.back() == signal);

        last_signals.push_back(signal);

        assert(signals == last_signals);

    }

    if (exp_state == ThresholdState::STARTED) {

        // double check that stats.possible is sane

        if (blocks_sig >= dep.threshold - 1) assert(last_stats.possible);

    }

    // mine the final block

    bool signal = (signalling_mask >> (period % 32)) & 1;

    if (signal) ++blocks_sig;

    CBlockIndex* current_block = blocks.mine_block(signal);

    assert(checker.Condition(current_block->nVersion) == signal);

    const BIP9Stats stats = checker.GetStateStatisticsFor(current_block);

    assert(stats.period == period);

    assert(stats.threshold == dep.threshold);

    assert(stats.elapsed == period);

    assert(stats.count == blocks_sig);

    assert(stats.possible == (stats.count + period >= stats.elapsed + dep.threshold));

    // More interesting is whether the state changed.

    const ThresholdState state = checker.GetStateFor(current_block);

    const int since = checker.GetStateSinceHeightFor(current_block);

    // since is straightforward:

    assert(since % period == 0);

    assert(0 <= since && since <= current_block->nHeight + 1);

    if (state == exp_state) {

        assert(since == exp_since);

    } else {

        assert(since == current_block->nHeight + 1);

    }

    // state is where everything interesting is

    switch (state) {

    case ThresholdState::DEFINED:

        assert(since == 0);

        assert(exp_state == ThresholdState::DEFINED);

        assert(current_block->GetMedianTimePast() < dep.nStartTime);

        break;

    case ThresholdState::STARTED:

        assert(current_block->GetMedianTimePast() >= dep.nStartTime);

        if (exp_state == ThresholdState::STARTED) {

            assert(blocks_sig < dep.threshold);

            assert(current_block->GetMedianTimePast() < dep.nTimeout);

        } else {

            assert(exp_state == ThresholdState::DEFINED);

        }

        break;

    case ThresholdState::LOCKED_IN:

        if (exp_state == ThresholdState::LOCKED_IN) {

            assert(current_block->nHeight + 1 < dep.min_activation_height);

        } else {

            assert(exp_state == ThresholdState::STARTED);

            assert(blocks_sig >= dep.threshold);

        }

        break;

    case ThresholdState::ACTIVE:

        assert(always_active_test || dep.min_activation_height <= current_block->nHeight + 1);

        assert(exp_state == ThresholdState::ACTIVE || exp_state == ThresholdState::LOCKED_IN);

        break;

    case ThresholdState::FAILED:

        assert(never_active_test || current_block->GetMedianTimePast() >= dep.nTimeout);

        if (exp_state == ThresholdState::STARTED) {

            assert(blocks_sig < dep.threshold);

        } else {

            assert(exp_state == ThresholdState::FAILED);

        }

        break;

    default:

        assert(false);

    }

    if (blocks.size() >= period * max_periods) {

        // we chose the timeout (and block times) so that by the time we have this many blocks it's all over

        assert(state == ThresholdState::ACTIVE || state == ThresholdState::FAILED);

    }

    if (always_active_test) {

        // "always active" has additional restrictions

        assert(state == ThresholdState::ACTIVE);

        assert(exp_state == ThresholdState::ACTIVE);

        assert(since == 0);

    } else if (never_active_test) {

        // "never active" does too

        assert(state == ThresholdState::FAILED);

        assert(exp_state == ThresholdState::FAILED);

        assert(since == 0);

    } else {

        // for signalled deployments, the initial state is always DEFINED

        assert(since > 0 || state == ThresholdState::DEFINED);

        assert(exp_since > 0 || exp_state == ThresholdState::DEFINED);

    }

}

} // namespace