text: // Copyright (c) 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 <consensus/validation.h>
  #include <interfaces/chain.h>
  #include <policy/policy.h>
  #include <util/check.h>
  #include <util/fees.h>
  #include <util/moneystr.h>
  #include <util/rbf.h>
  #include <util/translation.h>
  #include <wallet/coincontrol.h>
  #include <wallet/fees.h>
  #include <wallet/receive.h>
  #include <wallet/spend.h>
  #include <wallet/transaction.h>
  #include <wallet/wallet.h>
  
  using interfaces::FoundBlock;
  
  static constexpr size_t OUTPUT_GROUP_MAX_ENTRIES{100};
  
  std::string COutput::ToString() const
  {
      return strprintf("COutput(%s, %d, %d) [%s]", tx->GetHash().ToString(), i, nDepth, FormatMoney(tx->tx->vout[i].nValue));
  }
  
  int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, bool use_max_sig)
  {
      CMutableTransaction txn;
      txn.vin.push_back(CTxIn(COutPoint()));
      if (!wallet->DummySignInput(txn.vin[0], txout, use_max_sig)) {
          return -1;
      }
      return GetVirtualTransactionInputSize(txn.vin[0]);
  }
  
  // txouts needs to be in the order of tx.vin
  TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts, bool use_max_sig)
  {
      CMutableTransaction txNew(tx);
      if (!wallet->DummySignTx(txNew, txouts, use_max_sig)) {
          return TxSize{-1, -1};
      }
      CTransaction ctx(txNew);
      int64_t vsize = GetVirtualTransactionSize(ctx);
      int64_t weight = GetTransactionWeight(ctx);
      return TxSize{vsize, weight};
  }
  
  TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, bool use_max_sig)
  {
      std::vector<CTxOut> txouts;
      for (const CTxIn& input : tx.vin) {
          const auto mi = wallet->mapWallet.find(input.prevout.hash);
          // Can not estimate size without knowing the input details
          if (mi == wallet->mapWallet.end()) {
              return TxSize{-1, -1};
          }
          assert(input.prevout.n < mi->second.tx->vout.size());
          txouts.emplace_back(mi->second.tx->vout[input.prevout.n]);
      }
      return CalculateMaximumSignedTxSize(tx, wallet, txouts, use_max_sig);
  }
  
  void CWallet::AvailableCoins(std::vector<COutput>& vCoins, const CCoinControl* coinControl, const CAmount& nMinimumAmount, const CAmount& nMaximumAmount, const CAmount& nMinimumSumAmount, const uint64_t nMaximumCount) const
  {
      AssertLockHeld(cs_wallet);
  
      vCoins.clear();
      CAmount nTotal = 0;
      // Either the WALLET_FLAG_AVOID_REUSE flag is not set (in which case we always allow), or we default to avoiding, and only in the case where
      // a coin control object is provided, and has the avoid address reuse flag set to false, do we allow already used addresses
      bool allow_used_addresses = !IsWalletFlagSet(WALLET_FLAG_AVOID_REUSE) || (coinControl && !coinControl->m_avoid_address_reuse);
      const int min_depth = {coinControl ? coinControl->m_min_depth : DEFAULT_MIN_DEPTH};
      const int max_depth = {coinControl ? coinControl->m_max_depth : DEFAULT_MAX_DEPTH};
      const bool only_safe = {coinControl ? !coinControl->m_include_unsafe_inputs : true};
  
      std::set<uint256> trusted_parents;
      for (const auto& entry : mapWallet)
      {
          const uint256& wtxid = entry.first;
          const CWalletTx& wtx = entry.second;
  
          if (!chain().checkFinalTx(*wtx.tx)) {
              continue;
          }
  
          if (wtx.IsImmatureCoinBase())
              continue;
  
          int nDepth = wtx.GetDepthInMainChain();
          if (nDepth < 0)
              continue;
  
          // We should not consider coins which aren't at least in our mempool
          // It's possible for these to be conflicted via ancestors which we may never be able to detect
          if (nDepth == 0 && !wtx.InMempool())
              continue;
  
          bool safeTx = IsTrusted(wtx, trusted_parents);
  
          // We should not consider coins from transactions that are replacing
          // other transactions.
          //
          // Example: There is a transaction A which is replaced by bumpfee
          // transaction B. In this case, we want to prevent creation of
          // a transaction B' which spends an output of B.
          //
          // Reason: If transaction A were initially confirmed, transactions B
          // and B' would no longer be valid, so the user would have to create
          // a new transaction C to replace B'. However, in the case of a
          // one-block reorg, transactions B' and C might BOTH be accepted,
          // when the user only wanted one of them. Specifically, there could
          // be a 1-block reorg away from the chain where transactions A and C
          // were accepted to another chain where B, B', and C were all
          // accepted.
          if (nDepth == 0 && wtx.mapValue.count("replaces_txid")) {
              safeTx = false;
          }
  
          // Similarly, we should not consider coins from transactions that
          // have been replaced. In the example above, we would want to prevent
          // creation of a transaction A' spending an output of A, because if
          // transaction B were initially confirmed, conflicting with A and
          // A', we wouldn't want to the user to create a transaction D
          // intending to replace A', but potentially resulting in a scenario
          // where A, A', and D could all be accepted (instead of just B and
          // D, or just A and A' like the user would want).
          if (nDepth == 0 && wtx.mapValue.count("replaced_by_txid")) {
              safeTx = false;
          }
  
          if (only_safe && !safeTx) {
              continue;
          }
  
          if (nDepth < min_depth || nDepth > max_depth) {
              continue;
          }
  
          for (unsigned int i = 0; i < wtx.tx->vout.size(); i++) {
              // Only consider selected coins if add_inputs is false
              if (coinControl && !coinControl->m_add_inputs && !coinControl->IsSelected(COutPoint(entry.first, i))) {
                  continue;
              }
  
              if (wtx.tx->vout[i].nValue < nMinimumAmount || wtx.tx->vout[i].nValue > nMaximumAmount)
                  continue;
  
              if (coinControl && coinControl->HasSelected() && !coinControl->fAllowOtherInputs && !coinControl->IsSelected(COutPoint(entry.first, i)))
                  continue;
  
              if (IsLockedCoin(entry.first, i))
                  continue;
  
              if (IsSpent(wtxid, i))
                  continue;
  
              isminetype mine = IsMine(wtx.tx->vout[i]);
  
              if (mine == ISMINE_NO) {
                  continue;
              }
  
              if (!allow_used_addresses && IsSpentKey(wtxid, i)) {
                  continue;
              }
  
              std::unique_ptr<SigningProvider> provider = GetSolvingProvider(wtx.tx->vout[i].scriptPubKey);
  
              bool solvable = provider ? IsSolvable(*provider, wtx.tx->vout[i].scriptPubKey) : false;
              bool spendable = ((mine & ISMINE_SPENDABLE) != ISMINE_NO) || (((mine & ISMINE_WATCH_ONLY) != ISMINE_NO) && (coinControl && coinControl->fAllowWatchOnly && solvable));
  
              vCoins.push_back(COutput(&wtx, i, nDepth, spendable, solvable, safeTx, (coinControl && coinControl->fAllowWatchOnly)));
  
              // Checks the sum amount of all UTXO's.
              if (nMinimumSumAmount != MAX_MONEY) {
                  nTotal += wtx.tx->vout[i].nValue;
  
                  if (nTotal >= nMinimumSumAmount) {
                      return;
                  }
              }
  
              // Checks the maximum number of UTXO's.
              if (nMaximumCount > 0 && vCoins.size() >= nMaximumCount) {
                  return;
              }
          }
      }
  }
  
  CAmount CWallet::GetAvailableBalance(const CCoinControl* coinControl) const
  {
      LOCK(cs_wallet);
  
      CAmount balance = 0;
      std::vector<COutput> vCoins;
      AvailableCoins(vCoins, coinControl);
      for (const COutput& out : vCoins) {
          if (out.fSpendable) {
              balance += out.tx->tx->vout[out.i].nValue;
          }
      }
      return balance;
  }
  
  const CTxOut& CWallet::FindNonChangeParentOutput(const CTransaction& tx, int output) const
  {
      AssertLockHeld(cs_wallet);
      const CTransaction* ptx = &tx;
      int n = output;
      while (IsChange(ptx->vout[n]) && ptx->vin.size() > 0) {
          const COutPoint& prevout = ptx->vin[0].prevout;
          auto it = mapWallet.find(prevout.hash);
          if (it == mapWallet.end() || it->second.tx->vout.size() <= prevout.n ||
              !IsMine(it->second.tx->vout[prevout.n])) {
              break;
          }
          ptx = it->second.tx.get();
          n = prevout.n;
      }
      return ptx->vout[n];
  }
  
  std::map<CTxDestination, std::vector<COutput>> CWallet::ListCoins() const
  {
      AssertLockHeld(cs_wallet);
  
      std::map<CTxDestination, std::vector<COutput>> result;
      std::vector<COutput> availableCoins;
  
      AvailableCoins(availableCoins);
  
      for (const COutput& coin : availableCoins) {
          CTxDestination address;
          if ((coin.fSpendable || (IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS) && coin.fSolvable)) &&
              ExtractDestination(FindNonChangeParentOutput(*coin.tx->tx, coin.i).scriptPubKey, address)) {
              result[address].emplace_back(std::move(coin));
          }
      }
  
      std::vector<COutPoint> lockedCoins;
      ListLockedCoins(lockedCoins);
      // Include watch-only for LegacyScriptPubKeyMan wallets without private keys
      const bool include_watch_only = GetLegacyScriptPubKeyMan() && IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
      const isminetype is_mine_filter = include_watch_only ? ISMINE_WATCH_ONLY : ISMINE_SPENDABLE;
      for (const COutPoint& output : lockedCoins) {
          auto it = mapWallet.find(output.hash);
          if (it != mapWallet.end()) {
              int depth = it->second.GetDepthInMainChain();
              if (depth >= 0 && output.n < it->second.tx->vout.size() &&
                  IsMine(it->second.tx->vout[output.n]) == is_mine_filter
              ) {
                  CTxDestination address;
                  if (ExtractDestination(FindNonChangeParentOutput(*it->second.tx, output.n).scriptPubKey, address)) {
                      result[address].emplace_back(
                          &it->second, output.n, depth, true /* spendable */, true /* solvable */, false /* safe */);
                  }
              }
          }
      }
  
      return result;
  }
  
  std::vector<OutputGroup> CWallet::GroupOutputs(const std::vector<COutput>& outputs, const CoinSelectionParams& coin_sel_params, const CoinEligibilityFilter& filter, bool positive_only) const
  {
      std::vector<OutputGroup> groups_out;
  
      if (!coin_sel_params.m_avoid_partial_spends) {
          // Allowing partial spends  means no grouping. Each COutput gets its own OutputGroup.
          for (const COutput& output : outputs) {
              // Skip outputs we cannot spend
              if (!output.fSpendable) continue;
  
              size_t ancestors, descendants;
              chain().getTransactionAncestry(output.tx->GetHash(), ancestors, descendants);
              CInputCoin input_coin = output.GetInputCoin();
  
              // Make an OutputGroup containing just this output
              OutputGroup group{coin_sel_params};
              group.Insert(input_coin, output.nDepth, output.tx->IsFromMe(ISMINE_ALL), ancestors, descendants, positive_only);
  
              // Check the OutputGroup's eligibility. Only add the eligible ones.
              if (positive_only && group.GetSelectionAmount() <= 0) continue;
              if (group.m_outputs.size() > 0 && group.EligibleForSpending(filter)) groups_out.push_back(group);
          }
          return groups_out;
      }
  
      // We want to combine COutputs that have the same scriptPubKey into single OutputGroups
      // except when there are more than OUTPUT_GROUP_MAX_ENTRIES COutputs grouped in an OutputGroup.
      // To do this, we maintain a map where the key is the scriptPubKey and the value is a vector of OutputGroups.
      // For each COutput, we check if the scriptPubKey is in the map, and if it is, the COutput's CInputCoin is added
      // to the last OutputGroup in the vector for the scriptPubKey. When the last OutputGroup has
      // OUTPUT_GROUP_MAX_ENTRIES CInputCoins, a new OutputGroup is added to the end of the vector.
      std::map<CScript, std::vector<OutputGroup>> spk_to_groups_map;
      for (const auto& output : outputs) {
          // Skip outputs we cannot spend
          if (!output.fSpendable) continue;
  
          size_t ancestors, descendants;
          chain().getTransactionAncestry(output.tx->GetHash(), ancestors, descendants);
          CInputCoin input_coin = output.GetInputCoin();
          CScript spk = input_coin.txout.scriptPubKey;
  
          std::vector<OutputGroup>& groups = spk_to_groups_map[spk];
  
          if (groups.size() == 0) {
              // No OutputGroups for this scriptPubKey yet, add one
              groups.emplace_back(coin_sel_params);
          }
  
          // Get the last OutputGroup in the vector so that we can add the CInputCoin to it
          // A pointer is used here so that group can be reassigned later if it is full.
          OutputGroup* group = &groups.back();
  
          // Check if this OutputGroup is full. We limit to OUTPUT_GROUP_MAX_ENTRIES when using -avoidpartialspends
          // to avoid surprising users with very high fees.
          if (group->m_outputs.size() >= OUTPUT_GROUP_MAX_ENTRIES) {
              // The last output group is full, add a new group to the vector and use that group for the insertion
              groups.emplace_back(coin_sel_params);
              group = &groups.back();
          }
  
          // Add the input_coin to group
          group->Insert(input_coin, output.nDepth, output.tx->IsFromMe(ISMINE_ALL), ancestors, descendants, positive_only);
      }
  
      // Now we go through the entire map and pull out the OutputGroups
      for (const auto& spk_and_groups_pair: spk_to_groups_map) {
          const std::vector<OutputGroup>& groups_per_spk= spk_and_groups_pair.second;
  
          // Go through the vector backwards. This allows for the first item we deal with being the partial group.
          for (auto group_it = groups_per_spk.rbegin(); group_it != groups_per_spk.rend(); group_it++) {
              const OutputGroup& group = *group_it;
  
              // Don't include partial groups if there are full groups too and we don't want partial groups
              if (group_it == groups_per_spk.rbegin() && groups_per_spk.size() > 1 && !filter.m_include_partial_groups) {
                  continue;
              }
  
              // Check the OutputGroup's eligibility. Only add the eligible ones.
              if (positive_only && group.GetSelectionAmount() <= 0) continue;
              if (group.m_outputs.size() > 0 && group.EligibleForSpending(filter)) groups_out.push_back(group);
          }
      }
  
      return groups_out;
  }
  
  bool CWallet::AttemptSelection(const CAmount& nTargetValue, const CoinEligibilityFilter& eligibility_filter, std::vector<COutput> coins,
                                   std::set<CInputCoin>& setCoinsRet, CAmount& nValueRet, const CoinSelectionParams& coin_selection_params) const
  {
      setCoinsRet.clear();
      nValueRet = 0;
  
      // Note that unlike KnapsackSolver, we do not include the fee for creating a change output as BnB will not create a change output.
      std::vector<OutputGroup> positive_groups = GroupOutputs(coins, coin_selection_params, eligibility_filter, true /* positive_only */);
      if (SelectCoinsBnB(positive_groups, nTargetValue, coin_selection_params.m_cost_of_change, setCoinsRet, nValueRet)) {
          return true;
      }
      // The knapsack solver has some legacy behavior where it will spend dust outputs. We retain this behavior, so don't filter for positive only here.
      std::vector<OutputGroup> all_groups = GroupOutputs(coins, coin_selection_params, eligibility_filter, false /* positive_only */);
      // While nTargetValue includes the transaction fees for non-input things, it does not include the fee for creating a change output.
      // So we need to include that for KnapsackSolver as well, as we are expecting to create a change output.
      return KnapsackSolver(nTargetValue + coin_selection_params.m_change_fee, all_groups, setCoinsRet, nValueRet);
  }
  
  bool CWallet::SelectCoins(const std::vector<COutput>& vAvailableCoins, const CAmount& nTargetValue, std::set<CInputCoin>& setCoinsRet, CAmount& nValueRet, const CCoinControl& coin_control, CoinSelectionParams& coin_selection_params) const
  {
      std::vector<COutput> vCoins(vAvailableCoins);
      CAmount value_to_select = nTargetValue;
  
      // coin control -> return all selected outputs (we want all selected to go into the transaction for sure)
      if (coin_control.HasSelected() && !coin_control.fAllowOtherInputs)
      {
          for (const COutput& out : vCoins)
          {
              if (!out.fSpendable)
                   continue;
              nValueRet += out.tx->tx->vout[out.i].nValue;
              setCoinsRet.insert(out.GetInputCoin());
          }
          return (nValueRet >= nTargetValue);
      }
  
      // calculate value from preset inputs and store them
      std::set<CInputCoin> setPresetCoins;
      CAmount nValueFromPresetInputs = 0;
  
      std::vector<COutPoint> vPresetInputs;
      coin_control.ListSelected(vPresetInputs);
      for (const COutPoint& outpoint : vPresetInputs)
      {
          std::map<uint256, CWalletTx>::const_iterator it = mapWallet.find(outpoint.hash);
          if (it != mapWallet.end())
          {
              const CWalletTx& wtx = it->second;
              // Clearly invalid input, fail
              if (wtx.tx->vout.size() <= outpoint.n) {
                  return false;
              }
              // Just to calculate the marginal byte size
              CInputCoin coin(wtx.tx, outpoint.n, wtx.GetSpendSize(outpoint.n, false));
              nValueFromPresetInputs += coin.txout.nValue;
              if (coin.m_input_bytes <= 0) {
                  return false; // Not solvable, can't estimate size for fee
              }
              coin.effective_value = coin.txout.nValue - coin_selection_params.m_effective_feerate.GetFee(coin.m_input_bytes);
              if (coin_selection_params.m_subtract_fee_outputs) {
                  value_to_select -= coin.txout.nValue;
              } else {
                  value_to_select -= coin.effective_value;
              }
              setPresetCoins.insert(coin);
          } else {
              return false; // TODO: Allow non-wallet inputs
          }
      }
  
      // remove preset inputs from vCoins so that Coin Selection doesn't pick them.
      for (std::vector<COutput>::iterator it = vCoins.begin(); it != vCoins.end() && coin_control.HasSelected();)
      {
          if (setPresetCoins.count(it->GetInputCoin()))
              it = vCoins.erase(it);
          else
              ++it;
      }
  
      unsigned int limit_ancestor_count = 0;
      unsigned int limit_descendant_count = 0;
      chain().getPackageLimits(limit_ancestor_count, limit_descendant_count);
      const size_t max_ancestors = (size_t)std::max<int64_t>(1, limit_ancestor_count);
      const size_t max_descendants = (size_t)std::max<int64_t>(1, limit_descendant_count);
      const bool fRejectLongChains = gArgs.GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS);
  
      // form groups from remaining coins; note that preset coins will not
      // automatically have their associated (same address) coins included
      if (coin_control.m_avoid_partial_spends && vCoins.size() > OUTPUT_GROUP_MAX_ENTRIES) {
          // Cases where we have 101+ outputs all pointing to the same destination may result in
          // privacy leaks as they will potentially be deterministically sorted. We solve that by
          // explicitly shuffling the outputs before processing
          Shuffle(vCoins.begin(), vCoins.end(), FastRandomContext());
      }
  
      // Coin Selection attempts to select inputs from a pool of eligible UTXOs to fund the
      // transaction at a target feerate. If an attempt fails, more attempts may be made using a more
      // permissive CoinEligibilityFilter.
      const bool res = [&] {
          // Pre-selected inputs already cover the target amount.
          if (value_to_select <= 0) return true;
  
          // If possible, fund the transaction with confirmed UTXOs only. Prefer at least six
          // confirmations on outputs received from other wallets and only spend confirmed change.
          if (AttemptSelection(value_to_select, CoinEligibilityFilter(1, 6, 0), vCoins, setCoinsRet, nValueRet, coin_selection_params)) return true;
          if (AttemptSelection(value_to_select, CoinEligibilityFilter(1, 1, 0), vCoins, setCoinsRet, nValueRet, coin_selection_params)) return true;
  
          // Fall back to using zero confirmation change (but with as few ancestors in the mempool as
          // possible) if we cannot fund the transaction otherwise.
          if (m_spend_zero_conf_change) {
              if (AttemptSelection(value_to_select, CoinEligibilityFilter(0, 1, 2), vCoins, setCoinsRet, nValueRet, coin_selection_params)) return true;
              if (AttemptSelection(value_to_select, CoinEligibilityFilter(0, 1, std::min((size_t)4, max_ancestors/3), std::min((size_t)4, max_descendants/3)),
                                     vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
                  return true;
              }
              if (AttemptSelection(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2),
                                     vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
                  return true;
              }
              // If partial groups are allowed, relax the requirement of spending OutputGroups (groups
              // of UTXOs sent to the same address, which are obviously controlled by a single wallet)
              // in their entirety.
              if (AttemptSelection(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1, true /* include_partial_groups */),
                                     vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
                  return true;
              }
              // Try with unsafe inputs if they are allowed. This may spend unconfirmed outputs
              // received from other wallets.
              if (coin_control.m_include_unsafe_inputs
                  && AttemptSelection(value_to_select,
                      CoinEligibilityFilter(0 /* conf_mine */, 0 /* conf_theirs */, max_ancestors-1, max_descendants-1, true /* include_partial_groups */),
                      vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
                  return true;
              }
              // Try with unlimited ancestors/descendants. The transaction will still need to meet
              // mempool ancestor/descendant policy to be accepted to mempool and broadcasted, but
              // OutputGroups use heuristics that may overestimate ancestor/descendant counts.
              if (!fRejectLongChains && AttemptSelection(value_to_select,
                                        CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max(), std::numeric_limits<uint64_t>::max(), true /* include_partial_groups */),
                                        vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
                  return true;
              }
          }
          // Coin Selection failed.
          return false;
      }();
  
      // AttemptSelection clears setCoinsRet, so add the preset inputs from coin_control to the coinset
      util::insert(setCoinsRet, setPresetCoins);
  
      // add preset inputs to the total value selected
      nValueRet += nValueFromPresetInputs;
  
      return res;
  }
  
  static bool IsCurrentForAntiFeeSniping(interfaces::Chain& chain, const uint256& block_hash)
  {
      if (chain.isInitialBlockDownload()) {
          return false;
      }
      constexpr int64_t MAX_ANTI_FEE_SNIPING_TIP_AGE = 8 * 60 * 60; // in seconds
      int64_t block_time;
      CHECK_NONFATAL(chain.findBlock(block_hash, FoundBlock().time(block_time)));
      if (block_time < (GetTime() - MAX_ANTI_FEE_SNIPING_TIP_AGE)) {
          return false;
      }
      return true;
  }
  
  /**
   * Return a height-based locktime for new transactions (uses the height of the
   * current chain tip unless we are not synced with the current chain
   */
  static uint32_t GetLocktimeForNewTransaction(interfaces::Chain& chain, const uint256& block_hash, int block_height)
  {
      uint32_t locktime;
      // Discourage fee sniping.
      //
      // For a large miner the value of the transactions in the best block and
      // the mempool can exceed the cost of deliberately attempting to mine two
      // blocks to orphan the current best block. By setting nLockTime such that
      // only the next block can include the transaction, we discourage this
      // practice as the height restricted and limited blocksize gives miners
      // considering fee sniping fewer options for pulling off this attack.
      //
      // A simple way to think about this is from the wallet's point of view we
      // always want the blockchain to move forward. By setting nLockTime this
      // way we're basically making the statement that we only want this
      // transaction to appear in the next block; we don't want to potentially
      // encourage reorgs by allowing transactions to appear at lower heights
      // than the next block in forks of the best chain.
      //
      // Of course, the subsidy is high enough, and transaction volume low
      // enough, that fee sniping isn't a problem yet, but by implementing a fix
      // now we ensure code won't be written that makes assumptions about
      // nLockTime that preclude a fix later.
      if (IsCurrentForAntiFeeSniping(chain, block_hash)) {
          locktime = block_height;
  
          // Secondly occasionally randomly pick a nLockTime even further back, so
          // that transactions that are delayed after signing for whatever reason,
          // e.g. high-latency mix networks and some CoinJoin implementations, have
          // better privacy.
          if (GetRandInt(10) == 0)
              locktime = std::max(0, (int)locktime - GetRandInt(100));
      } else {
          // If our chain is lagging behind, we can't discourage fee sniping nor help
          // the privacy of high-latency transactions. To avoid leaking a potentially
          // unique "nLockTime fingerprint", set nLockTime to a constant.
          locktime = 0;
      }
      assert(locktime < LOCKTIME_THRESHOLD);
      return locktime;
  }
  
  bool CWallet::CreateTransactionInternal(
          const std::vector<CRecipient>& vecSend,
          CTransactionRef& tx,
          CAmount& nFeeRet,
          int& nChangePosInOut,
          bilingual_str& error,
          const CCoinControl& coin_control,
          FeeCalculation& fee_calc_out,
          bool sign)
  {
      AssertLockHeld(cs_wallet);
  
      CMutableTransaction txNew; // The resulting transaction that we make
      txNew.nLockTime = GetLocktimeForNewTransaction(chain(), GetLastBlockHash(), GetLastBlockHeight());
  
      CoinSelectionParams coin_selection_params; // Parameters for coin selection, init with dummy
      coin_selection_params.m_avoid_partial_spends = coin_control.m_avoid_partial_spends;
  
      CAmount recipients_sum = 0;
      const OutputType change_type = TransactionChangeType(coin_control.m_change_type ? *coin_control.m_change_type : m_default_change_type, vecSend);
      ReserveDestination reservedest(this, change_type);
      unsigned int outputs_to_subtract_fee_from = 0; // The number of outputs which we are subtracting the fee from
      for (const auto& recipient : vecSend) {
          recipients_sum += recipient.nAmount;
  
          if (recipient.fSubtractFeeFromAmount) {
              outputs_to_subtract_fee_from++;
              coin_selection_params.m_subtract_fee_outputs = true;
          }
      }
  
      // Create change script that will be used if we need change
      // TODO: pass in scriptChange instead of reservedest so
      // change transaction isn't always pay-to-xcbc-address
      CScript scriptChange;
  
      // coin control: send change to custom address
      if (!std::get_if<CNoDestination>(&coin_control.destChange)) {
          scriptChange = GetScriptForDestination(coin_control.destChange);
      } else { // no coin control: send change to newly generated address
          // Note: We use a new key here to keep it from being obvious which side is the change.
          //  The drawback is that by not reusing a previous key, the change may be lost if a
          //  backup is restored, if the backup doesn't have the new private key for the change.
          //  If we reused the old key, it would be possible to add code to look for and
          //  rediscover unknown transactions that were written with keys of ours to recover
          //  post-backup change.
  
          // Reserve a new key pair from key pool. If it fails, provide a dummy
          // destination in case we don't need change.
          CTxDestination dest;
          std::string dest_err;
          if (!reservedest.GetReservedDestination(dest, true, dest_err)) {
              error = strprintf(_("Transaction needs a change address, but we can't generate it. %s"), dest_err);
          }
          scriptChange = GetScriptForDestination(dest);
          // A valid destination implies a change script (and
          // vice-versa). An empty change script will abort later, if the
          // change keypool ran out, but change is required.
          CHECK_NONFATAL(IsValidDestination(dest) != scriptChange.empty());
      }
      CTxOut change_prototype_txout(0, scriptChange);
      coin_selection_params.change_output_size = GetSerializeSize(change_prototype_txout);
  
      // Get size of spending the change output
      int change_spend_size = CalculateMaximumSignedInputSize(change_prototype_txout, this);
      // If the wallet doesn't know how to sign change output, assume p2sh-p2wpkh
      // as lower-bound to allow BnB to do it's thing
      if (change_spend_size == -1) {
          coin_selection_params.change_spend_size = DUMMY_NESTED_P2WPKH_INPUT_SIZE;
      } else {
          coin_selection_params.change_spend_size = (size_t)change_spend_size;
      }
  
      // Set discard feerate
      coin_selection_params.m_discard_feerate = GetDiscardRate(*this);
  
      // Get the fee rate to use effective values in coin selection
      FeeCalculation feeCalc;
      coin_selection_params.m_effective_feerate = GetMinimumFeeRate(*this, coin_control, &feeCalc);
      // Do not, ever, assume that it's fine to change the fee rate if the user has explicitly
      // provided one
      if (coin_control.m_feerate && coin_selection_params.m_effective_feerate > *coin_control.m_feerate) {
          error = strprintf(_("Fee rate (%s) is lower than the minimum fee rate setting (%s)"), coin_control.m_feerate->ToString(FeeEstimateMode::SAT_VB), coin_selection_params.m_effective_feerate.ToString(FeeEstimateMode::SAT_VB));
          return false;
      }
      if (feeCalc.reason == FeeReason::FALLBACK && !m_allow_fallback_fee) {
          // eventually allow a fallback fee
          error = _("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
          return false;
      }
  
      // Get long term estimate
      CCoinControl cc_temp;
      cc_temp.m_confirm_target = chain().estimateMaxBlocks();
      coin_selection_params.m_long_term_feerate = GetMinimumFeeRate(*this, cc_temp, nullptr);
  
      // Calculate the cost of change
      // Cost of change is the cost of creating the change output + cost of spending the change output in the future.
      // For creating the change output now, we use the effective feerate.
      // For spending the change output in the future, we use the discard feerate for now.
      // So cost of change = (change output size * effective feerate) + (size of spending change output * discard feerate)
      coin_selection_params.m_change_fee = coin_selection_params.m_effective_feerate.GetFee(coin_selection_params.change_output_size);
      coin_selection_params.m_cost_of_change = coin_selection_params.m_discard_feerate.GetFee(coin_selection_params.change_spend_size) + coin_selection_params.m_change_fee;
  
      // vouts to the payees
      if (!coin_selection_params.m_subtract_fee_outputs) {
          coin_selection_params.tx_noinputs_size = 11; // Static vsize overhead + outputs vsize. 4 nVersion, 4 nLocktime, 1 input count, 1 output count, 1 witness overhead (dummy, flag, stack size)
      }
      for (const auto& recipient : vecSend)
      {
          CTxOut txout(recipient.nAmount, recipient.scriptPubKey);
  
          // Include the fee cost for outputs.
          if (!coin_selection_params.m_subtract_fee_outputs) {
              coin_selection_params.tx_noinputs_size += ::GetSerializeSize(txout, PROTOCOL_VERSION);
          }
  
          if (IsDust(txout, chain().relayDustFee()))
          {
              error = _("Transaction amount too small");
              return false;
          }
          txNew.vout.push_back(txout);
      }
  
      // Include the fees for things that aren't inputs, excluding the change output
      const CAmount not_input_fees = coin_selection_params.m_effective_feerate.GetFee(coin_selection_params.tx_noinputs_size);
      CAmount selection_target = recipients_sum + not_input_fees;
  
      // Get available coins
      std::vector<COutput> vAvailableCoins;
      AvailableCoins(vAvailableCoins, &coin_control, 1, MAX_MONEY, MAX_MONEY, 0);
  
      // Choose coins to use
      CAmount inputs_sum = 0;
      std::set<CInputCoin> setCoins;
      if (!SelectCoins(vAvailableCoins, /* nTargetValue */ selection_target, setCoins, inputs_sum, coin_control, coin_selection_params))
      {
          error = _("Insufficient funds");
          return false;
      }
  
      // Always make a change output
      // We will reduce the fee from this change output later, and remove the output if it is too small.
      const CAmount change_and_fee = inputs_sum - recipients_sum;
      assert(change_and_fee >= 0);
      CTxOut newTxOut(change_and_fee, scriptChange);
  
      if (nChangePosInOut == -1)
      {
          // Insert change txn at random position:
          nChangePosInOut = GetRandInt(txNew.vout.size()+1);
      }
      else if ((unsigned int)nChangePosInOut > txNew.vout.size())
      {
          error = _("Change index out of range");
          return false;
      }
  
      assert(nChangePosInOut != -1);
      auto change_position = txNew.vout.insert(txNew.vout.begin() + nChangePosInOut, newTxOut);
  
      // Shuffle selected coins and fill in final vin
      std::vector<CInputCoin> selected_coins(setCoins.begin(), setCoins.end());
      Shuffle(selected_coins.begin(), selected_coins.end(), FastRandomContext());
  
      // Note how the sequence number is set to non-maxint so that
      // the nLockTime set above actually works.
      //
      // BIP125 defines opt-in RBF as any nSequence < maxint-1, so
      // we use the highest possible value in that range (maxint-2)
      // to avoid conflicting with other possible uses of nSequence,
      // and in the spirit of "smallest possible change from prior
      // behavior."
      const uint32_t nSequence = coin_control.m_signal_bip125_rbf.value_or(m_signal_rbf) ? MAX_BIP125_RBF_SEQUENCE : (CTxIn::SEQUENCE_FINAL - 1);
      for (const auto& coin : selected_coins) {
          txNew.vin.push_back(CTxIn(coin.outpoint, CScript(), nSequence));
      }
  
      // Calculate the transaction fee
      TxSize tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), this, coin_control.fAllowWatchOnly);
      int nBytes = tx_sizes.vsize;
      if (nBytes < 0) {
          error = _("Signing transaction failed");
          return false;
      }
      nFeeRet = coin_selection_params.m_effective_feerate.GetFee(nBytes);
  
      // Subtract fee from the change output if not subtracting it from recipient outputs
      CAmount fee_needed = nFeeRet;
      if (!coin_selection_params.m_subtract_fee_outputs) {
          change_position->nValue -= fee_needed;
      }
  
      // We want to drop the change to fees if:
      // 1. The change output would be dust
      // 2. The change is within the (almost) exact match window, i.e. it is less than or equal to the cost of the change output (cost_of_change)
      CAmount change_amount = change_position->nValue;
      if (IsDust(*change_position, coin_selection_params.m_discard_feerate) || change_amount <= coin_selection_params.m_cost_of_change)
      {
          nChangePosInOut = -1;
          change_amount = 0;
          txNew.vout.erase(change_position);
  
          // Because we have dropped this change, the tx size and required fee will be different, so let's recalculate those
          tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), this, coin_control.fAllowWatchOnly);
          nBytes = tx_sizes.vsize;
          fee_needed = coin_selection_params.m_effective_feerate.GetFee(nBytes);
      }
  
      // The only time that fee_needed should be less than the amount available for fees (in change_and_fee - change_amount) is when
      // we are subtracting the fee from the outputs. If this occurs at any other time, it is a bug.
      assert(coin_selection_params.m_subtract_fee_outputs || fee_needed <= change_and_fee - change_amount);
  
      // Update nFeeRet in case fee_needed changed due to dropping the change output
      if (fee_needed <= change_and_fee - change_amount) {
          nFeeRet = change_and_fee - change_amount;
      }
  
      // Reduce output values for subtractFeeFromAmount
      if (coin_selection_params.m_subtract_fee_outputs) {
          CAmount to_reduce = fee_needed + change_amount - change_and_fee;
          int i = 0;
          bool fFirst = true;
          for (const auto& recipient : vecSend)
          {
              if (i == nChangePosInOut) {
                  ++i;
              }
              CTxOut& txout = txNew.vout[i];
  
              if (recipient.fSubtractFeeFromAmount)
              {
                  txout.nValue -= to_reduce / outputs_to_subtract_fee_from; // Subtract fee equally from each selected recipient
  
                  if (fFirst) // first receiver pays the remainder not divisible by output count
                  {
                      fFirst = false;
                      txout.nValue -= to_reduce % outputs_to_subtract_fee_from;
                  }
  
                  // Error if this output is reduced to be below dust
                  if (IsDust(txout, chain().relayDustFee())) {
                      if (txout.nValue < 0) {
                          error = _("The transaction amount is too small to pay the fee");
                      } else {
                          error = _("The transaction amount is too small to send after the fee has been deducted");
                      }
                      return false;
                  }
              }
              ++i;
          }
          nFeeRet = fee_needed;
      }
  
      // Give up if change keypool ran out and change is required
      if (scriptChange.empty() && nChangePosInOut != -1) {
          return false;
      }
  
      if (sign && !SignTransaction(txNew)) {
          error = _("Signing transaction failed");
          return false;
      }
  
      // Return the constructed transaction data.
      tx = MakeTransactionRef(std::move(txNew));
  
      // Limit size
      if ((sign && GetTransactionWeight(*tx) > MAX_STANDARD_TX_WEIGHT) ||
          (!sign && tx_sizes.weight > MAX_STANDARD_TX_WEIGHT))
      {
          error = _("Transaction too large");
          return false;
      }
  
      if (nFeeRet > m_default_max_tx_fee) {
          error = TransactionErrorString(TransactionError::MAX_FEE_EXCEEDED);
          return false;
      }
  
      if (gArgs.GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS)) {
          // Lastly, ensure this tx will pass the mempool's chain limits
          if (!chain().checkChainLimits(tx)) {
              error = _("Transaction has too long of a mempool chain");
              return false;
          }
      }
  
      // Before we return success, we assume any change key will be used to prevent
      // accidental re-use.
      reservedest.KeepDestination();
      fee_calc_out = feeCalc;
  
      WalletLogPrintf("Fee Calculation: Fee:%d Bytes:%u Tgt:%d (requested %d) Reason:\"%s\" Decay %.5f: Estimation: (%g - %g) %.2f%% %.1f/(%.1f %d mem %.1f out) Fail: (%g - %g) %.2f%% %.1f/(%.1f %d mem %.1f out)\n",
                nFeeRet, nBytes, feeCalc.returnedTarget, feeCalc.desiredTarget, StringForFeeReason(feeCalc.reason), feeCalc.est.decay,
                feeCalc.est.pass.start, feeCalc.est.pass.end,
                (feeCalc.est.pass.totalConfirmed + feeCalc.est.pass.inMempool + feeCalc.est.pass.leftMempool) > 0.0 ? 100 * feeCalc.est.pass.withinTarget / (feeCalc.est.pass.totalConfirmed + feeCalc.est.pass.inMempool + feeCalc.est.pass.leftMempool) : 0.0,
                feeCalc.est.pass.withinTarget, feeCalc.est.pass.totalConfirmed, feeCalc.est.pass.inMempool, feeCalc.est.pass.leftMempool,
                feeCalc.est.fail.start, feeCalc.est.fail.end,
                (feeCalc.est.fail.totalConfirmed + feeCalc.est.fail.inMempool + feeCalc.est.fail.leftMempool) > 0.0 ? 100 * feeCalc.est.fail.withinTarget / (feeCalc.est.fail.totalConfirmed + feeCalc.est.fail.inMempool + feeCalc.est.fail.leftMempool) : 0.0,
                feeCalc.est.fail.withinTarget, feeCalc.est.fail.totalConfirmed, feeCalc.est.fail.inMempool, feeCalc.est.fail.leftMempool);
      return true;
  }
  
  bool CWallet::CreateTransaction(
          const std::vector<CRecipient>& vecSend,
          CTransactionRef& tx,
          CAmount& nFeeRet,
          int& nChangePosInOut,
          bilingual_str& error,
          const CCoinControl& coin_control,
          FeeCalculation& fee_calc_out,
          bool sign)
  {
      if (vecSend.empty()) {
          error = _("Transaction must have at least one recipient");
          return false;
      }
  
      if (std::any_of(vecSend.cbegin(), vecSend.cend(), [](const auto& recipient){ return recipient.nAmount < 0; })) {
          error = _("Transaction amounts must not be negative");
          return false;
      }
  
      LOCK(cs_wallet);
  
      int nChangePosIn = nChangePosInOut;
      Assert(!tx); // tx is an out-param. TODO change the return type from bool to tx (or nullptr)
      bool res = CreateTransactionInternal(vecSend, tx, nFeeRet, nChangePosInOut, error, coin_control, fee_calc_out, sign);
      // try with avoidpartialspends unless it's enabled already
      if (res && nFeeRet > 0 /* 0 means non-functional fee rate estimation */ && m_max_aps_fee > -1 && !coin_control.m_avoid_partial_spends) {
          CCoinControl tmp_cc = coin_control;
          tmp_cc.m_avoid_partial_spends = true;
          CAmount nFeeRet2;
          CTransactionRef tx2;
          int nChangePosInOut2 = nChangePosIn;
          bilingual_str error2; // fired and forgotten; if an error occurs, we discard the results
          if (CreateTransactionInternal(vecSend, tx2, nFeeRet2, nChangePosInOut2, error2, tmp_cc, fee_calc_out, sign)) {
              // if fee of this alternative one is within the range of the max fee, we use this one
              const bool use_aps = nFeeRet2 <= nFeeRet + m_max_aps_fee;
              WalletLogPrintf("Fee non-grouped = %lld, grouped = %lld, using %s\n", nFeeRet, nFeeRet2, use_aps ? "grouped" : "non-grouped");
              if (use_aps) {
                  tx = tx2;
                  nFeeRet = nFeeRet2;
                  nChangePosInOut = nChangePosInOut2;
              }
          }
      }
      return res;
  }
  
  bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl coinControl)
  {
      std::vector<CRecipient> vecSend;
  
      // Turn the txout set into a CRecipient vector.
      for (size_t idx = 0; idx < tx.vout.size(); idx++) {
          const CTxOut& txOut = tx.vout[idx];
          CRecipient recipient = {txOut.scriptPubKey, txOut.nValue, setSubtractFeeFromOutputs.count(idx) == 1};
          vecSend.push_back(recipient);
      }
  
      coinControl.fAllowOtherInputs = true;
  
      for (const CTxIn& txin : tx.vin) {
          coinControl.Select(txin.prevout);
      }
  
      // Acquire the locks to prevent races to the new locked unspents between the
      // CreateTransaction call and LockCoin calls (when lockUnspents is true).
      LOCK(cs_wallet);
  
      CTransactionRef tx_new;
      FeeCalculation fee_calc_out;
      if (!CreateTransaction(vecSend, tx_new, nFeeRet, nChangePosInOut, error, coinControl, fee_calc_out, false)) {
          return false;
      }
  
      if (nChangePosInOut != -1) {
          tx.vout.insert(tx.vout.begin() + nChangePosInOut, tx_new->vout[nChangePosInOut]);
      }
  
      // Copy output sizes from new transaction; they may have had the fee
      // subtracted from them.
      for (unsigned int idx = 0; idx < tx.vout.size(); idx++) {
          tx.vout[idx].nValue = tx_new->vout[idx].nValue;
      }
  
      // Add new txins while keeping original txin scriptSig/order.
      for (const CTxIn& txin : tx_new->vin) {
          if (!coinControl.IsSelected(txin.prevout)) {
              tx.vin.push_back(txin);
  
          }
          if (lockUnspents) {
              LockCoin(txin.prevout);
          }
  
      }
  
      return true;
  }
  