// Copyright (c) 2020-2022 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 <pow.h>

#include <primitives/block.h>

#include <test/fuzz/FuzzedDataProvider.h>

#include <test/fuzz/fuzz.h>

#include <test/fuzz/util.h>

#include <util/chaintype.h>

#include <util/check.h>

#include <util/overflow.h>

#include <cstdint>

#include <optional>

#include <string>

#include <vector>

void initialize_pow()

{

    SelectParams(ChainType::MAIN);

}

FUZZ_TARGET(pow, .init = initialize_pow)

{

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

    const Consensus::Params& consensus_params = Params().GetConsensus();

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

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

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

    LIMITED_WHILE(fuzzed_data_provider.remaining_bytes() > 0, 10000) {

        const std::optional<CBlockHeader> block_header = ConsumeDeserializable<CBlockHeader>(fuzzed_data_provider);

        if (!block_header) {

            continue;

        }

        CBlockIndex& current_block{

            *blocks.emplace_back(std::make_unique<CBlockIndex>(*block_header))};

        {

            CBlockIndex* previous_block = blocks.empty() ? nullptr : PickValue(fuzzed_data_provider, blocks).get();

            const int current_height = (previous_block != nullptr && previous_block->nHeight != std::numeric_limits<int>::max()) ? previous_block->nHeight + 1 : 0;

            if (fuzzed_data_provider.ConsumeBool()) {

                current_block.pprev = previous_block;

            }

            if (fuzzed_data_provider.ConsumeBool()) {

                current_block.nHeight = current_height;

            }

            if (fuzzed_data_provider.ConsumeBool()) {

                const uint32_t seconds = current_height * consensus_params.nPowTargetSpacing;

                if (!AdditionOverflow(fixed_time, seconds)) {

                    current_block.nTime = fixed_time + seconds;

                }

            }

            if (fuzzed_data_provider.ConsumeBool()) {

                current_block.nBits = fixed_bits;

            }

            if (fuzzed_data_provider.ConsumeBool()) {

                current_block.nChainWork = previous_block != nullptr ? previous_block->nChainWork + GetBlockProof(*previous_block) : arith_uint256{0};

            } else {

                current_block.nChainWork = ConsumeArithUInt256(fuzzed_data_provider);

            }

        }

        {

            (void)GetBlockProof(current_block);

            (void)CalculateNextWorkRequired(&current_block, fuzzed_data_provider.ConsumeIntegralInRange<int64_t>(0, std::numeric_limits<int64_t>::max()), consensus_params);

            if (current_block.nHeight != std::numeric_limits<int>::max() && current_block.nHeight - (consensus_params.DifficultyAdjustmentInterval() - 1) >= 0) {

                (void)GetNextWorkRequired(&current_block, &(*block_header), consensus_params);

            }

        }

        {

            const auto& to = PickValue(fuzzed_data_provider, blocks);

            const auto& from = PickValue(fuzzed_data_provider, blocks);

            const auto& tip = PickValue(fuzzed_data_provider, blocks);

            try {

                (void)GetBlockProofEquivalentTime(*to, *from, *tip, consensus_params);

            } catch (const uint_error&) {

            }

        }

        {

            const std::optional<uint256> hash = ConsumeDeserializable<uint256>(fuzzed_data_provider);

            if (hash) {

                (void)CheckProofOfWorkImpl(*hash, fuzzed_data_provider.ConsumeIntegral<unsigned int>(), consensus_params);

            }

        }

    }

}

FUZZ_TARGET(pow_transition, .init = initialize_pow)

{

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

    const Consensus::Params& consensus_params{Params().GetConsensus()};

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

    const uint32_t old_time{fuzzed_data_provider.ConsumeIntegral<uint32_t>()};

    const uint32_t new_time{fuzzed_data_provider.ConsumeIntegral<uint32_t>()};

    const int32_t version{fuzzed_data_provider.ConsumeIntegral<int32_t>()};

    uint32_t nbits{fuzzed_data_provider.ConsumeIntegral<uint32_t>()};

    const arith_uint256 pow_limit = UintToArith256(consensus_params.powLimit);

    arith_uint256 old_target;

    old_target.SetCompact(nbits);

    if (old_target > pow_limit) {

        nbits = pow_limit.GetCompact();

    }

    // Create one difficulty adjustment period worth of headers

    for (int height = 0; height < consensus_params.DifficultyAdjustmentInterval(); ++height) {

        CBlockHeader header;

        header.nVersion = version;

        header.nTime = old_time;

        header.nBits = nbits;

        if (height == consensus_params.DifficultyAdjustmentInterval() - 1) {

            header.nTime = new_time;

        }

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

        current_block->pprev = blocks.empty() ? nullptr : blocks.back().get();

        current_block->nHeight = height;

        blocks.emplace_back(std::move(current_block));

    }

    auto last_block{blocks.back().get()};

    unsigned int new_nbits{GetNextWorkRequired(last_block, nullptr, consensus_params)};

    Assert(PermittedDifficultyTransition(consensus_params, last_block->nHeight + 1, last_block->nBits, new_nbits));

}