// Copyright (c) 2016-2022 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/rbf.h>

#include <consensus/amount.h>

#include <kernel/mempool_entry.h>

#include <policy/feerate.h>

#include <primitives/transaction.h>

#include <sync.h>

#include <tinyformat.h>

#include <txmempool.h>

#include <uint256.h>

#include <util/check.h>

#include <util/moneystr.h>

#include <util/rbf.h>

#include <limits>

#include <vector>

#include <compare>

RBFTransactionState IsRBFOptIn(const CTransaction& tx, const CTxMemPool& pool)

{

    AssertLockHeld(pool.cs);

    // First check the transaction itself.

    if (SignalsOptInRBF(tx)) {

        return RBFTransactionState::REPLACEABLE_BIP125;

    }

    // If this transaction is not in our mempool, then we can't be sure

    // we will know about all its inputs.

    if (!pool.exists(GenTxid::Txid(tx.GetHash()))) {

        return RBFTransactionState::UNKNOWN;

    }

    // If all the inputs have nSequence >= maxint-1, it still might be

    // signaled for RBF if any unconfirmed parents have signaled.

    const auto& entry{*Assert(pool.GetEntry(tx.GetHash()))};

    auto ancestors{pool.AssumeCalculateMemPoolAncestors(__func__, entry, CTxMemPool::Limits::NoLimits(),

                                                        /*fSearchForParents=*/false)};

    for (CTxMemPool::txiter it : ancestors) {

        if (SignalsOptInRBF(it->GetTx())) {

            return RBFTransactionState::REPLACEABLE_BIP125;

        }

    }

    return RBFTransactionState::FINAL;

}

RBFTransactionState IsRBFOptInEmptyMempool(const CTransaction& tx)

{

    // If we don't have a local mempool we can only check the transaction itself.

    return SignalsOptInRBF(tx) ? RBFTransactionState::REPLACEABLE_BIP125 : RBFTransactionState::UNKNOWN;

}

std::optional<std::string> GetEntriesForConflicts(const CTransaction& tx,

                                                  CTxMemPool& pool,

                                                  const CTxMemPool::setEntries& iters_conflicting,

                                                  CTxMemPool::setEntries& all_conflicts)

{

    AssertLockHeld(pool.cs);

    const uint256 txid = tx.GetHash();

    uint64_t nConflictingCount = 0;

    for (const auto& mi : iters_conflicting) {

        nConflictingCount += mi->GetCountWithDescendants();

        // Rule #5: don't consider replacing more than MAX_REPLACEMENT_CANDIDATES

        // entries from the mempool. This potentially overestimates the number of actual

        // descendants (i.e. if multiple conflicts share a descendant, it will be counted multiple

        // times), but we just want to be conservative to avoid doing too much work.

        if (nConflictingCount > MAX_REPLACEMENT_CANDIDATES) {

            return strprintf("rejecting replacement %s; too many potential replacements (%d > %d)",

                             txid.ToString(),

                             nConflictingCount,

                             MAX_REPLACEMENT_CANDIDATES);

        }

    }

    // Calculate the set of all transactions that would have to be evicted.

    for (CTxMemPool::txiter it : iters_conflicting) {

        pool.CalculateDescendants(it, all_conflicts);

    }

    return std::nullopt;

}

std::optional<std::string> HasNoNewUnconfirmed(const CTransaction& tx,

                                               const CTxMemPool& pool,

                                               const CTxMemPool::setEntries& iters_conflicting)

{

    AssertLockHeld(pool.cs);

    std::set<uint256> parents_of_conflicts;

    for (const auto& mi : iters_conflicting) {

        for (const CTxIn& txin : mi->GetTx().vin) {

            parents_of_conflicts.insert(txin.prevout.hash);

        }

    }

    for (unsigned int j = 0; j < tx.vin.size(); j++) {

        // Rule #2: We don't want to accept replacements that require low feerate junk to be

        // mined first.  Ideally we'd keep track of the ancestor feerates and make the decision

        // based on that, but for now requiring all new inputs to be confirmed works.

        //

        // Note that if you relax this to make RBF a little more useful, this may break the

        // CalculateMempoolAncestors RBF relaxation which subtracts the conflict count/size from the

        // descendant limit.

        if (!parents_of_conflicts.count(tx.vin[j].prevout.hash)) {

            // Rather than check the UTXO set - potentially expensive - it's cheaper to just check

            // if the new input refers to a tx that's in the mempool.

            if (pool.exists(GenTxid::Txid(tx.vin[j].prevout.hash))) {

                return strprintf("replacement %s adds unconfirmed input, idx %d",

                                 tx.GetHash().ToString(), j);

            }

        }

    }

    return std::nullopt;

}

std::optional<std::string> EntriesAndTxidsDisjoint(const CTxMemPool::setEntries& ancestors,

                                                   const std::set<Txid>& direct_conflicts,

                                                   const uint256& txid)

{

    for (CTxMemPool::txiter ancestorIt : ancestors) {

        const Txid& hashAncestor = ancestorIt->GetTx().GetHash();

        if (direct_conflicts.count(hashAncestor)) {

            return strprintf("%s spends conflicting transaction %s",

                             txid.ToString(),

                             hashAncestor.ToString());

        }

    }

    return std::nullopt;

}

std::optional<std::string> PaysMoreThanConflicts(const CTxMemPool::setEntries& iters_conflicting,

                                                 CFeeRate replacement_feerate,

                                                 const uint256& txid)

{

    for (const auto& mi : iters_conflicting) {

        // Don't allow the replacement to reduce the feerate of the mempool.

        //

        // We usually don't want to accept replacements with lower feerates than what they replaced

        // as that would lower the feerate of the next block. Requiring that the feerate always be

        // increased is also an easy-to-reason about way to prevent DoS attacks via replacements.

        //

        // We only consider the feerates of transactions being directly replaced, not their indirect

        // descendants. While that does mean high feerate children are ignored when deciding whether

        // or not to replace, we do require the replacement to pay more overall fees too, mitigating

        // most cases.

        CFeeRate original_feerate(mi->GetModifiedFee(), mi->GetTxSize());

        if (replacement_feerate <= original_feerate) {

            return strprintf("rejecting replacement %s; new feerate %s <= old feerate %s",

                             txid.ToString(),

                             replacement_feerate.ToString(),

                             original_feerate.ToString());

        }

    }

    return std::nullopt;

}

std::optional<std::string> PaysForRBF(CAmount original_fees,

                                      CAmount replacement_fees,

                                      size_t replacement_vsize,

                                      CFeeRate relay_fee,

                                      const uint256& txid)

{

    // Rule #3: The replacement fees must be greater than or equal to fees of the

    // transactions it replaces, otherwise the bandwidth used by those conflicting transactions

    // would not be paid for.

    if (replacement_fees < original_fees) {

        return strprintf("rejecting replacement %s, less fees than conflicting txs; %s < %s",

                         txid.ToString(), FormatMoney(replacement_fees), FormatMoney(original_fees));

    }

    // Rule #4: The new transaction must pay for its own bandwidth. Otherwise, we have a DoS

    // vector where attackers can cause a transaction to be replaced (and relayed) repeatedly by

    // increasing the fee by tiny amounts.

    CAmount additional_fees = replacement_fees - original_fees;

    if (additional_fees < relay_fee.GetFee(replacement_vsize)) {

        return strprintf("rejecting replacement %s, not enough additional fees to relay; %s < %s",

                         txid.ToString(),

                         FormatMoney(additional_fees),

                         FormatMoney(relay_fee.GetFee(replacement_vsize)));

    }

    return std::nullopt;

}

std::optional<std::pair<DiagramCheckError, std::string>> ImprovesFeerateDiagram(CTxMemPool::ChangeSet& changeset)

{

    // Require that the replacement strictly improves the mempool's feerate diagram.

    const auto chunk_results{changeset.CalculateChunksForRBF()};

    if (!chunk_results.has_value()) {

        return std::make_pair(DiagramCheckError::UNCALCULABLE, util::ErrorString(chunk_results).original);

    }

    if (!std::is_gt(CompareChunks(chunk_results.value().second, chunk_results.value().first))) {

        return std::make_pair(DiagramCheckError::FAILURE, "insufficient feerate: does not improve feerate diagram");

    }

    return std::nullopt;

}