// Copyright (c) 2009-2010 Satoshi Nakamoto

// Copyright (c) 2009-2022 The Bitcoin Core developers

// Distributed under the MIT software license, see the accompanying

// file COPYING or http://www.opensource.org/licenses/mit-license.php.

// NOTE: This file is intended to be customised by the end user, and includes only local node policy logic

#include <policy/policy.h>

#include <coins.h>

#include <consensus/amount.h>

#include <consensus/consensus.h>

#include <consensus/validation.h>

#include <policy/feerate.h>

#include <primitives/transaction.h>

#include <script/interpreter.h>

#include <script/script.h>

#include <script/solver.h>

#include <serialize.h>

#include <span.h>

#include <algorithm>

#include <cstddef>

#include <vector>

CAmount GetDustThreshold(const CTxOut& txout, const CFeeRate& dustRelayFeeIn)

{

    // "Dust" is defined in terms of dustRelayFee,

    // which has units satoshis-per-kilobyte.

    // If you'd pay more in fees than the value of the output

    // to spend something, then we consider it dust.

    // A typical spendable non-segwit txout is 34 bytes big, and will

    // need a CTxIn of at least 148 bytes to spend:

    // so dust is a spendable txout less than

    // 182*dustRelayFee/1000 (in satoshis).

    // 546 satoshis at the default rate of 3000 sat/kvB.

    // A typical spendable segwit P2WPKH txout is 31 bytes big, and will

    // need a CTxIn of at least 67 bytes to spend:

    // so dust is a spendable txout less than

    // 98*dustRelayFee/1000 (in satoshis).

    // 294 satoshis at the default rate of 3000 sat/kvB.

    if (txout.scriptPubKey.IsUnspendable())

        return 0;

    size_t nSize = GetSerializeSize(txout);

    int witnessversion = 0;

    std::vector<unsigned char> witnessprogram;

    // Note this computation is for spending a Segwit v0 P2WPKH output (a 33 bytes

    // public key + an ECDSA signature). For Segwit v1 Taproot outputs the minimum

    // satisfaction is lower (a single BIP340 signature) but this computation was

    // kept to not further reduce the dust level.

    // See discussion in https://github.com/bitcoin/bitcoin/pull/22779 for details.

    if (txout.scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram)) {

        // sum the sizes of the parts of a transaction input

        // with 75% segwit discount applied to the script size.

        nSize += (32 + 4 + 1 + (107 / WITNESS_SCALE_FACTOR) + 4);

    } else {

        nSize += (32 + 4 + 1 + 107 + 4); // the 148 mentioned above

    }

    return dustRelayFeeIn.GetFee(nSize);

}

bool IsDust(const CTxOut& txout, const CFeeRate& dustRelayFeeIn)

{

    return (txout.nValue < GetDustThreshold(txout, dustRelayFeeIn));

}

bool IsStandard(const CScript& scriptPubKey, const std::optional<unsigned>& max_datacarrier_bytes, TxoutType& whichType)

{

    std::vector<std::vector<unsigned char> > vSolutions;

    whichType = Solver(scriptPubKey, vSolutions);

    if (whichType == TxoutType::NONSTANDARD) {

        return false;

    } else if (whichType == TxoutType::MULTISIG) {

        unsigned char m = vSolutions.front()[0];

        unsigned char n = vSolutions.back()[0];

        // Support up to x-of-3 multisig txns as standard

        if (n < 1 || n > 3)

            return false;

        if (m < 1 || m > n)

            return false;

    } else if (whichType == TxoutType::NULL_DATA) {

        if (!max_datacarrier_bytes || scriptPubKey.size() > *max_datacarrier_bytes) {

            return false;

        }

    }

    return true;

}

bool IsStandardTx(const CTransaction& tx, const std::optional<unsigned>& max_datacarrier_bytes, bool permit_bare_multisig, const CFeeRate& dust_relay_fee, std::string& reason)

{

    if (tx.version > TX_MAX_STANDARD_VERSION || tx.version < 1) {

        reason = "version";

        return false;

    }

    // Extremely large transactions with lots of inputs can cost the network

    // almost as much to process as they cost the sender in fees, because

    // computing signature hashes is O(ninputs*txsize). Limiting transactions

    // to MAX_STANDARD_TX_WEIGHT mitigates CPU exhaustion attacks.

    unsigned int sz = GetTransactionWeight(tx);

    if (sz > MAX_STANDARD_TX_WEIGHT) {

        reason = "tx-size";

        return false;

    }

    for (const CTxIn& txin : tx.vin)

    {

        // Biggest 'standard' txin involving only keys is a 15-of-15 P2SH

        // multisig with compressed keys (remember the MAX_SCRIPT_ELEMENT_SIZE byte limit on

        // redeemScript size). That works out to a (15*(33+1))+3=513 byte

        // redeemScript, 513+1+15*(73+1)+3=1627 bytes of scriptSig, which

        // we round off to 1650(MAX_STANDARD_SCRIPTSIG_SIZE) bytes for

        // some minor future-proofing. That's also enough to spend a

        // 20-of-20 CHECKMULTISIG scriptPubKey, though such a scriptPubKey

        // is not considered standard.

        if (txin.scriptSig.size() > MAX_STANDARD_SCRIPTSIG_SIZE) {

            reason = "scriptsig-size";

            return false;

        }

        if (!txin.scriptSig.IsPushOnly()) {

            reason = "scriptsig-not-pushonly";

            return false;

        }

    }

    unsigned int nDataOut = 0;

    TxoutType whichType;

    for (const CTxOut& txout : tx.vout) {

        if (!::IsStandard(txout.scriptPubKey, max_datacarrier_bytes, whichType)) {

            reason = "scriptpubkey";

            return false;

        }

        if (whichType == TxoutType::NULL_DATA)

            nDataOut++;

        else if ((whichType == TxoutType::MULTISIG) && (!permit_bare_multisig)) {

            reason = "bare-multisig";

            return false;

        } else if (IsDust(txout, dust_relay_fee)) {

            reason = "dust";

            return false;

        }

    }

    // only one OP_RETURN txout is permitted

    if (nDataOut > 1) {

        reason = "multi-op-return";

        return false;

    }

    return true;

}

/**

 * Check transaction inputs to mitigate two

 * potential denial-of-service attacks:

 *

 * 1. scriptSigs with extra data stuffed into them,

 *    not consumed by scriptPubKey (or P2SH script)

 * 2. P2SH scripts with a crazy number of expensive

 *    CHECKSIG/CHECKMULTISIG operations

 *

 * Why bother? To avoid denial-of-service attacks; an attacker

 * can submit a standard HASH... OP_EQUAL transaction,

 * which will get accepted into blocks. The redemption

 * script can be anything; an attacker could use a very

 * expensive-to-check-upon-redemption script like:

 *   DUP CHECKSIG DROP ... repeated 100 times... OP_1

 *

 * Note that only the non-witness portion of the transaction is checked here.

 */

bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)

{

    if (tx.IsCoinBase()) {

        return true; // Coinbases don't use vin normally

    }

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

        const CTxOut& prev = mapInputs.AccessCoin(tx.vin[i].prevout).out;

        std::vector<std::vector<unsigned char> > vSolutions;

        TxoutType whichType = Solver(prev.scriptPubKey, vSolutions);

        if (whichType == TxoutType::NONSTANDARD || whichType == TxoutType::WITNESS_UNKNOWN) {

            // WITNESS_UNKNOWN failures are typically also caught with a policy

            // flag in the script interpreter, but it can be helpful to catch

            // this type of NONSTANDARD transaction earlier in transaction

            // validation.

            return false;

        } else if (whichType == TxoutType::SCRIPTHASH) {

            std::vector<std::vector<unsigned char> > stack;

            // convert the scriptSig into a stack, so we can inspect the redeemScript

            if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker(), SigVersion::BASE))

                return false;

            if (stack.empty())

                return false;

            CScript subscript(stack.back().begin(), stack.back().end());

            if (subscript.GetSigOpCount(true) > MAX_P2SH_SIGOPS) {

                return false;

            }

        }

    }

    return true;

}

bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)

{

    if (tx.IsCoinBase())

        return true; // Coinbases are skipped

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

    {

        // We don't care if witness for this input is empty, since it must not be bloated.

        // If the script is invalid without witness, it would be caught sooner or later during validation.

        if (tx.vin[i].scriptWitness.IsNull())

            continue;

        const CTxOut &prev = mapInputs.AccessCoin(tx.vin[i].prevout).out;

        // get the scriptPubKey corresponding to this input:

        CScript prevScript = prev.scriptPubKey;

        // witness stuffing detected

        if (prevScript.IsPayToAnchor()) {

            return false;

        }

        bool p2sh = false;

        if (prevScript.IsPayToScriptHash()) {

            std::vector <std::vector<unsigned char> > stack;

            // If the scriptPubKey is P2SH, we try to extract the redeemScript casually by converting the scriptSig

            // into a stack. We do not check IsPushOnly nor compare the hash as these will be done later anyway.

            // If the check fails at this stage, we know that this txid must be a bad one.

            if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker(), SigVersion::BASE))

                return false;

            if (stack.empty())

                return false;

            prevScript = CScript(stack.back().begin(), stack.back().end());

            p2sh = true;

        }

        int witnessversion = 0;

        std::vector<unsigned char> witnessprogram;

        // Non-witness program must not be associated with any witness

        if (!prevScript.IsWitnessProgram(witnessversion, witnessprogram))

            return false;

        // Check P2WSH standard limits

        if (witnessversion == 0 && witnessprogram.size() == WITNESS_V0_SCRIPTHASH_SIZE) {

            if (tx.vin[i].scriptWitness.stack.back().size() > MAX_STANDARD_P2WSH_SCRIPT_SIZE)

                return false;

            size_t sizeWitnessStack = tx.vin[i].scriptWitness.stack.size() - 1;

            if (sizeWitnessStack > MAX_STANDARD_P2WSH_STACK_ITEMS)

                return false;

            for (unsigned int j = 0; j < sizeWitnessStack; j++) {

                if (tx.vin[i].scriptWitness.stack[j].size() > MAX_STANDARD_P2WSH_STACK_ITEM_SIZE)

                    return false;

            }

        }

        // Check policy limits for Taproot spends:

        // - MAX_STANDARD_TAPSCRIPT_STACK_ITEM_SIZE limit for stack item size

        // - No annexes

        if (witnessversion == 1 && witnessprogram.size() == WITNESS_V1_TAPROOT_SIZE && !p2sh) {

            // Taproot spend (non-P2SH-wrapped, version 1, witness program size 32; see BIP 341)

            Span stack{tx.vin[i].scriptWitness.stack};

            if (stack.size() >= 2 && !stack.back().empty() && stack.back()[0] == ANNEX_TAG) {

                // Annexes are nonstandard as long as no semantics are defined for them.

                return false;

            }

            if (stack.size() >= 2) {

                // Script path spend (2 or more stack elements after removing optional annex)

                const auto& control_block = SpanPopBack(stack);

                SpanPopBack(stack); // Ignore script

                if (control_block.empty()) return false; // Empty control block is invalid

                if ((control_block[0] & TAPROOT_LEAF_MASK) == TAPROOT_LEAF_TAPSCRIPT) {

                    // Leaf version 0xc0 (aka Tapscript, see BIP 342)

                    for (const auto& item : stack) {

                        if (item.size() > MAX_STANDARD_TAPSCRIPT_STACK_ITEM_SIZE) return false;

                    }

                }

            } else if (stack.size() == 1) {

                // Key path spend (1 stack element after removing optional annex)

                // (no policy rules apply)

            } else {

                // 0 stack elements; this is already invalid by consensus rules

                return false;

            }

        }

    }

    return true;

}

int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost, unsigned int bytes_per_sigop)

{

    return (std::max(nWeight, nSigOpCost * bytes_per_sigop) + WITNESS_SCALE_FACTOR - 1) / WITNESS_SCALE_FACTOR;

}

int64_t GetVirtualTransactionSize(const CTransaction& tx, int64_t nSigOpCost, unsigned int bytes_per_sigop)

{

    return GetVirtualTransactionSize(GetTransactionWeight(tx), nSigOpCost, bytes_per_sigop);

}

int64_t GetVirtualTransactionInputSize(const CTxIn& txin, int64_t nSigOpCost, unsigned int bytes_per_sigop)

{

    return GetVirtualTransactionSize(GetTransactionInputWeight(txin), nSigOpCost, bytes_per_sigop);

}