// Copyright (c) 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 <policy/feerate.h>

#include <policy/policy.h>

#include <primitives/transaction.h>

#include <test/fuzz/FuzzedDataProvider.h>

#include <test/fuzz/fuzz.h>

#include <test/fuzz/util.h>

#include <test/util/setup_common.h>

#include <wallet/coinselection.h>

#include <numeric>

#include <span>

#include <vector>

namespace wallet {

static void AddCoin(const CAmount& value, int n_input, int n_input_bytes, int locktime, std::vector<COutput>& coins, CFeeRate fee_rate)

{

    CMutableTransaction tx;

    tx.vout.resize(n_input + 1);

    tx.vout[n_input].nValue = value;

    tx.nLockTime = locktime; // all transactions get different hashes

    coins.emplace_back(COutPoint(tx.GetHash(), n_input), tx.vout.at(n_input), /*depth=*/0, n_input_bytes, /*solvable=*/true, /*safe=*/true, /*time=*/0, /*from_me=*/true, fee_rate);

}

// Randomly distribute coins to instances of OutputGroup

static void GroupCoins(FuzzedDataProvider& fuzzed_data_provider, const std::vector<COutput>& coins, const CoinSelectionParams& coin_params, bool positive_only, std::vector<OutputGroup>& output_groups)

{

    auto output_group = OutputGroup(coin_params);

    bool valid_outputgroup{false};

    for (auto& coin : coins) {

        if (!positive_only || (positive_only && coin.GetEffectiveValue() > 0)) {

            output_group.Insert(std::make_shared<COutput>(coin), /*ancestors=*/0, /*descendants=*/0);

        }

        // If positive_only was specified, nothing was inserted, leading to an empty output group

        // that would be invalid for the BnB algorithm

        valid_outputgroup = !positive_only || output_group.GetSelectionAmount() > 0;

        if (valid_outputgroup && fuzzed_data_provider.ConsumeBool()) {

            output_groups.push_back(output_group);

            output_group = OutputGroup(coin_params);

            valid_outputgroup = false;

        }

    }

    if (valid_outputgroup) output_groups.push_back(output_group);

}

static CAmount CreateCoins(FuzzedDataProvider& fuzzed_data_provider, std::vector<COutput>& utxo_pool, CoinSelectionParams& coin_params, int& next_locktime)

{

    CAmount total_balance{0};

    LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), 10000)

    {

        const int n_input{fuzzed_data_provider.ConsumeIntegralInRange<int>(0, 10)};

        const int n_input_bytes{fuzzed_data_provider.ConsumeIntegralInRange<int>(41, 10000)};

        const CAmount amount{fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(1, MAX_MONEY)};

        if (total_balance + amount >= MAX_MONEY) {

            break;

        }

        AddCoin(amount, n_input, n_input_bytes, ++next_locktime, utxo_pool, coin_params.m_effective_feerate);

        total_balance += amount;

    }

    return total_balance;

}

static SelectionResult ManualSelection(std::vector<COutput>& utxos, const CAmount& total_amount, const bool& subtract_fee_outputs)

{

    SelectionResult result(total_amount, SelectionAlgorithm::MANUAL);

    std::set<std::shared_ptr<COutput>> utxo_pool;

    for (const auto& utxo : utxos) {

        utxo_pool.insert(std::make_shared<COutput>(utxo));

    }

    result.AddInputs(utxo_pool, subtract_fee_outputs);

    return result;

}

// Returns true if the result contains an error and the message is not empty

static bool HasErrorMsg(const util::Result<SelectionResult>& res) { return !util::ErrorString(res).empty(); }

FUZZ_TARGET(coin_grinder)

{

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

    std::vector<COutput> utxo_pool;

    const CAmount target{fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(1, MAX_MONEY)};

    FastRandomContext fast_random_context{ConsumeUInt256(fuzzed_data_provider)};

    CoinSelectionParams coin_params{fast_random_context};

    coin_params.m_subtract_fee_outputs = fuzzed_data_provider.ConsumeBool();

    coin_params.m_long_term_feerate = CFeeRate{ConsumeMoney(fuzzed_data_provider, /*max=*/COIN)};

    coin_params.m_effective_feerate = CFeeRate{ConsumeMoney(fuzzed_data_provider, /*max=*/COIN)};

    coin_params.change_output_size = fuzzed_data_provider.ConsumeIntegralInRange<int>(10, 1000);

    coin_params.change_spend_size = fuzzed_data_provider.ConsumeIntegralInRange<int>(10, 1000);

    coin_params.m_cost_of_change= coin_params.m_effective_feerate.GetFee(coin_params.change_output_size) + coin_params.m_long_term_feerate.GetFee(coin_params.change_spend_size);

    coin_params.m_change_fee = coin_params.m_effective_feerate.GetFee(coin_params.change_output_size);

    // For other results to be comparable to SRD, we must align the change_target with SRD’s hardcoded behavior

    coin_params.m_min_change_target = CHANGE_LOWER + coin_params.m_change_fee;

    // Create some coins

    CAmount total_balance{0};

    CAmount max_spendable{0};

    int next_locktime{0};

    LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), 10000)

    {

        const int n_input{fuzzed_data_provider.ConsumeIntegralInRange<int>(0, 10)};

        const int n_input_bytes{fuzzed_data_provider.ConsumeIntegralInRange<int>(41, 10000)};

        const CAmount amount{fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(1, MAX_MONEY)};

        if (total_balance + amount >= MAX_MONEY) {

            break;

        }

        AddCoin(amount, n_input, n_input_bytes, ++next_locktime, utxo_pool, coin_params.m_effective_feerate);

        total_balance += amount;

        CAmount eff_value = amount - coin_params.m_effective_feerate.GetFee(n_input_bytes);

        max_spendable += eff_value;

    }

    std::vector<OutputGroup> group_pos;

    GroupCoins(fuzzed_data_provider, utxo_pool, coin_params, /*positive_only=*/true, group_pos);

    // Run coinselection algorithms

    auto result_cg = CoinGrinder(group_pos, target, coin_params.m_min_change_target, MAX_STANDARD_TX_WEIGHT);

    if (target + coin_params.m_min_change_target > max_spendable || HasErrorMsg(result_cg)) return; // We only need to compare algorithms if CoinGrinder has a solution

    assert(result_cg);

    if (!result_cg->GetAlgoCompleted()) return; // Bail out if CoinGrinder solution is not optimal

    auto result_srd = SelectCoinsSRD(group_pos, target, coin_params.m_change_fee, fast_random_context, MAX_STANDARD_TX_WEIGHT);

    if (result_srd && result_srd->GetChange(CHANGE_LOWER, coin_params.m_change_fee) > 0) { // exclude any srd solutions that don’t have change, err on excluding

        assert(result_srd->GetWeight() >= result_cg->GetWeight());

    }

    auto result_knapsack = KnapsackSolver(group_pos, target, coin_params.m_min_change_target, fast_random_context, MAX_STANDARD_TX_WEIGHT);

    if (result_knapsack && result_knapsack->GetChange(CHANGE_LOWER, coin_params.m_change_fee) > 0) { // exclude any knapsack solutions that don’t have change, err on excluding

        assert(result_knapsack->GetWeight() >= result_cg->GetWeight());

    }

}

FUZZ_TARGET(coin_grinder_is_optimal)

{

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

    FastRandomContext fast_random_context{ConsumeUInt256(fuzzed_data_provider)};

    CoinSelectionParams coin_params{fast_random_context};

    coin_params.m_subtract_fee_outputs = false;

    // Set effective feerate up to MAX_MONEY sats per 1'000'000 vB (2'100'000'000 sat/vB = 21'000 BTC/kvB).

    coin_params.m_effective_feerate = CFeeRate{ConsumeMoney(fuzzed_data_provider, MAX_MONEY), 1'000'000};

    coin_params.m_min_change_target = ConsumeMoney(fuzzed_data_provider);

    // Create some coins

    CAmount max_spendable{0};

    int next_locktime{0};

    static constexpr unsigned max_output_groups{16};

    std::vector<OutputGroup> group_pos;

    LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), max_output_groups)

    {

        // With maximum m_effective_feerate and n_input_bytes = 1'000'000, input_fee <= MAX_MONEY.

        const int n_input_bytes{fuzzed_data_provider.ConsumeIntegralInRange<int>(1, 1'000'000)};

        // Only make UTXOs with positive effective value

        const CAmount input_fee = coin_params.m_effective_feerate.GetFee(n_input_bytes);

        // Ensure that each UTXO has at least an effective value of 1 sat

        const CAmount eff_value{fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(1, MAX_MONEY + group_pos.size() - max_spendable - max_output_groups)};

        const CAmount amount{eff_value + input_fee};

        std::vector<COutput> temp_utxo_pool;

        AddCoin(amount, /*n_input=*/0, n_input_bytes, ++next_locktime, temp_utxo_pool, coin_params.m_effective_feerate);

        max_spendable += eff_value;

        auto output_group = OutputGroup(coin_params);

        output_group.Insert(std::make_shared<COutput>(temp_utxo_pool.at(0)), /*ancestors=*/0, /*descendants=*/0);

        group_pos.push_back(output_group);

    }

    size_t num_groups = group_pos.size();

    assert(num_groups <= max_output_groups);

    // Only choose targets below max_spendable

    const CAmount target{fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(1, std::max(CAmount{1}, max_spendable - coin_params.m_min_change_target))};

    // Brute force optimal solution

    CAmount best_amount{MAX_MONEY};

    int best_weight{std::numeric_limits<int>::max()};

    for (uint32_t pattern = 1; (pattern >> num_groups) == 0; ++pattern) {

        CAmount subset_amount{0};

        int subset_weight{0};

        for (unsigned i = 0; i < num_groups; ++i) {

            if ((pattern >> i) & 1) {

                subset_amount += group_pos[i].GetSelectionAmount();

                subset_weight += group_pos[i].m_weight;

            }

        }

        if ((subset_amount >= target + coin_params.m_min_change_target) && (subset_weight < best_weight || (subset_weight == best_weight && subset_amount < best_amount))) {

            best_weight = subset_weight;

            best_amount = subset_amount;

        }

    }

    if (best_weight < std::numeric_limits<int>::max()) {

        // Sufficient funds and acceptable weight: CoinGrinder should find at least one solution

        int high_max_selection_weight = fuzzed_data_provider.ConsumeIntegralInRange<int>(best_weight, std::numeric_limits<int>::max());

        auto result_cg = CoinGrinder(group_pos, target, coin_params.m_min_change_target, high_max_selection_weight);

        assert(result_cg);

        assert(result_cg->GetWeight() <= high_max_selection_weight);

        assert(result_cg->GetSelectedEffectiveValue() >= target + coin_params.m_min_change_target);

        assert(best_weight < result_cg->GetWeight() || (best_weight == result_cg->GetWeight() && best_amount <= result_cg->GetSelectedEffectiveValue()));

        if (result_cg->GetAlgoCompleted()) {

            // If CoinGrinder exhausted the search space, it must return the optimal solution

            assert(best_weight == result_cg->GetWeight());

            assert(best_amount == result_cg->GetSelectedEffectiveValue());

        }

    }

    // CoinGrinder cannot ever find a better solution than the brute-forced best, or there is none in the first place

    int low_max_selection_weight = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, best_weight - 1);

    auto result_cg = CoinGrinder(group_pos, target, coin_params.m_min_change_target, low_max_selection_weight);

    // Max_weight should have been exceeded, or there were insufficient funds

    assert(!result_cg);

}

enum class CoinSelectionAlgorithm {

    BNB,

    SRD,

    KNAPSACK,

};

template<CoinSelectionAlgorithm Algorithm>

void FuzzCoinSelectionAlgorithm(std::span<const uint8_t> buffer) {

    SeedRandomStateForTest(SeedRand::ZEROS);

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

    std::vector<COutput> utxo_pool;

    const CFeeRate long_term_fee_rate{ConsumeMoney(fuzzed_data_provider, /*max=*/COIN)};

    const CFeeRate effective_fee_rate{ConsumeMoney(fuzzed_data_provider, /*max=*/COIN)};

    // Discard feerate must be at least dust relay feerate

    const CFeeRate discard_fee_rate{fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(DUST_RELAY_TX_FEE, COIN)};

    const CAmount target{fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(1, MAX_MONEY)};

    const bool subtract_fee_outputs{fuzzed_data_provider.ConsumeBool()};

    FastRandomContext fast_random_context{ConsumeUInt256(fuzzed_data_provider)};

    CoinSelectionParams coin_params{fast_random_context};

    coin_params.m_subtract_fee_outputs = subtract_fee_outputs;

    coin_params.m_long_term_feerate = long_term_fee_rate;

    coin_params.m_effective_feerate = effective_fee_rate;

    coin_params.change_output_size = fuzzed_data_provider.ConsumeIntegralInRange(1, MAX_SCRIPT_SIZE);

    coin_params.m_change_fee = effective_fee_rate.GetFee(coin_params.change_output_size);

    coin_params.m_discard_feerate = discard_fee_rate;

    coin_params.change_spend_size = fuzzed_data_provider.ConsumeIntegralInRange<int>(41, 1000);

    const auto change_spend_fee{coin_params.m_discard_feerate.GetFee(coin_params.change_spend_size)};

    coin_params.m_cost_of_change = coin_params.m_change_fee + change_spend_fee;

    CScript change_out_script = CScript() << std::vector<unsigned char>(coin_params.change_output_size, OP_TRUE);

    const auto dust{GetDustThreshold(CTxOut{/*nValueIn=*/0, change_out_script}, coin_params.m_discard_feerate)};

    coin_params.min_viable_change = std::max(change_spend_fee + 1, dust);

    int next_locktime{0};

    CAmount total_balance{CreateCoins(fuzzed_data_provider, utxo_pool, coin_params, next_locktime)};

    std::vector<OutputGroup> group_pos;

    GroupCoins(fuzzed_data_provider, utxo_pool, coin_params, /*positive_only=*/true, group_pos);

    int max_selection_weight = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, std::numeric_limits<int>::max());

    std::optional<SelectionResult> result;

    if constexpr (Algorithm == CoinSelectionAlgorithm::BNB) {

        if (!coin_params.m_subtract_fee_outputs) {

            auto result_bnb = SelectCoinsBnB(group_pos, target, coin_params.m_cost_of_change, max_selection_weight);

            if (result_bnb) {

                result = *result_bnb;

                assert(result_bnb->GetChange(coin_params.min_viable_change, coin_params.m_change_fee) == 0);

                assert(result_bnb->GetSelectedValue() >= target);

                assert(result_bnb->GetWeight() <= max_selection_weight);

                (void)result_bnb->GetShuffledInputVector();

                (void)result_bnb->GetInputSet();

            }

        }

    }

    if constexpr (Algorithm == CoinSelectionAlgorithm::SRD) {

        auto result_srd = SelectCoinsSRD(group_pos, target, coin_params.m_change_fee, fast_random_context, max_selection_weight);

        if (result_srd) {

            result = *result_srd;

            assert(result_srd->GetSelectedValue() >= target);

            assert(result_srd->GetChange(CHANGE_LOWER, coin_params.m_change_fee) > 0);

            assert(result_srd->GetWeight() <= max_selection_weight);

            result_srd->SetBumpFeeDiscount(ConsumeMoney(fuzzed_data_provider));

            result_srd->RecalculateWaste(coin_params.min_viable_change, coin_params.m_cost_of_change, coin_params.m_change_fee);

            (void)result_srd->GetShuffledInputVector();

            (void)result_srd->GetInputSet();

        }

    }

    if constexpr (Algorithm == CoinSelectionAlgorithm::KNAPSACK) {

        std::vector<OutputGroup> group_all;

        GroupCoins(fuzzed_data_provider, utxo_pool, coin_params, /*positive_only=*/false, group_all);

        for (const OutputGroup& group : group_all) {

            const CoinEligibilityFilter filter{fuzzed_data_provider.ConsumeIntegral<int>(), fuzzed_data_provider.ConsumeIntegral<int>(), fuzzed_data_provider.ConsumeIntegral<uint64_t>()};

            (void)group.EligibleForSpending(filter);

        }

        CAmount change_target{GenerateChangeTarget(target, coin_params.m_change_fee, fast_random_context)};

        auto result_knapsack = KnapsackSolver(group_all, target, change_target, fast_random_context, max_selection_weight);

        // If the total balance is sufficient for the target and we are not using

        // effective values, Knapsack should always find a solution (unless the selection exceeded the max tx weight).

        if (total_balance >= target && subtract_fee_outputs && !HasErrorMsg(result_knapsack)) {

            assert(result_knapsack);

        }

        if (result_knapsack) {

            result = *result_knapsack;

            assert(result_knapsack->GetSelectedValue() >= target);

            assert(result_knapsack->GetWeight() <= max_selection_weight);

            result_knapsack->SetBumpFeeDiscount(ConsumeMoney(fuzzed_data_provider));

            result_knapsack->RecalculateWaste(coin_params.min_viable_change, coin_params.m_cost_of_change, coin_params.m_change_fee);

            (void)result_knapsack->GetShuffledInputVector();

            (void)result_knapsack->GetInputSet();

        }

    }

    std::vector<COutput> utxos;

    CAmount new_total_balance{CreateCoins(fuzzed_data_provider, utxos, coin_params, next_locktime)};

    if (new_total_balance > 0) {

        std::set<std::shared_ptr<COutput>> new_utxo_pool;

        for (const auto& utxo : utxos) {

            new_utxo_pool.insert(std::make_shared<COutput>(utxo));

        }

        if (result) {

            const auto weight{result->GetWeight()};

            result->AddInputs(new_utxo_pool, subtract_fee_outputs);

            assert(result->GetWeight() > weight);

        }

    }

    std::vector<COutput> manual_inputs;

    CAmount manual_balance{CreateCoins(fuzzed_data_provider, manual_inputs, coin_params, next_locktime)};

    if (manual_balance == 0) return;

    auto manual_selection{ManualSelection(manual_inputs, manual_balance, coin_params.m_subtract_fee_outputs)};

    if (result) {

        const CAmount old_target{result->GetTarget()};

        const std::set<std::shared_ptr<COutput>> input_set{result->GetInputSet()};

        const int old_weight{result->GetWeight()};

        result->Merge(manual_selection);

        assert(result->GetInputSet().size() == input_set.size() + manual_inputs.size());

        assert(result->GetTarget() == old_target + manual_selection.GetTarget());

        assert(result->GetWeight() == old_weight + manual_selection.GetWeight());

    }

}

Unexecuted instantiation: _ZN6wallet26FuzzCoinSelectionAlgorithmILNS_22CoinSelectionAlgorithmE0EEEvSt4spanIKhLm18446744073709551615EE

Unexecuted instantiation: _ZN6wallet26FuzzCoinSelectionAlgorithmILNS_22CoinSelectionAlgorithmE1EEEvSt4spanIKhLm18446744073709551615EE

Unexecuted instantiation: _ZN6wallet26FuzzCoinSelectionAlgorithmILNS_22CoinSelectionAlgorithmE2EEEvSt4spanIKhLm18446744073709551615EE

FUZZ_TARGET(coinselection_bnb) {

    FuzzCoinSelectionAlgorithm<CoinSelectionAlgorithm::BNB>(buffer);

}

FUZZ_TARGET(coinselection_srd) {

    FuzzCoinSelectionAlgorithm<CoinSelectionAlgorithm::SRD>(buffer);

}

FUZZ_TARGET(coinselection_knapsack) {

    FuzzCoinSelectionAlgorithm<CoinSelectionAlgorithm::KNAPSACK>(buffer);

}

} // namespace wallet