blvm-consensus 0.1.12

//! Signature operation counting functions
//!
//! Implements consensus's sigop counting for block validation.
//! Sigops are counted to enforce MAX_BLOCK_SIGOPS_COST limit (80,000).
//!
//! Reference: consensus `tx_verify.cpp` and `script.cpp`

use crate::error::Result;
use crate::opcodes::*;
use crate::segwit::Witness;
use crate::types::*;
use crate::utxo_overlay::UtxoLookup;
use blvm_spec_lock::spec_locked;

/// Maximum number of public keys in a multisig (for sigop counting)
/// This is used when we can't accurately determine the number from the script
const MAX_PUBKEYS_PER_MULTISIG: u32 = 20;

/// Witness scale factor for sigop cost calculation
/// Legacy sigops count as 4x their actual number in sigop cost
const WITNESS_SCALE_FACTOR: u64 = 4;

/// Count sigops in a script (legacy counting)
///
/// Counts OP_CHECKSIG, OP_CHECKSIGVERIFY, OP_CHECKMULTISIG, OP_CHECKMULTISIGVERIFY.
/// Matches consensus's CScript::GetSigOpCount(bool fAccurate).
///
/// Uses GetOp-style iteration: each call to the loop body reads one opcode and
/// advances past any associated push data, exactly like consensus's GetOp().
///
/// # Arguments
/// * `script` - Script to count sigops in
/// * `accurate` - If true, use OP_1-OP_16 before OP_CHECKMULTISIG to determine key count
///
/// # Returns
/// Number of sigops in the script
#[spec_locked("5.2.2")]
pub fn count_sigops_in_script(script: &ByteString, accurate: bool) -> u32 {
    let mut count = 0u32;
    let mut last_opcode: Option<u8> = None;
    let mut i = 0;

    while i < script.len() {
        let opcode = script[i];

        // Skip past push data (matches consensus's GetOp)
        if opcode > 0 && opcode < OP_PUSHDATA1 {
            // Direct push: opcode IS the length (1-75 bytes)
            let len = opcode as usize;
            last_opcode = Some(opcode);
            i += 1 + len;
            continue;
        } else if opcode == OP_PUSHDATA1 {
            // OP_PUSHDATA1: next byte is length
            if i + 1 >= script.len() {
                break;
            }
            let len = script[i + 1] as usize;
            last_opcode = Some(opcode);
            i += 2 + len;
            continue;
        } else if opcode == OP_PUSHDATA2 {
            // OP_PUSHDATA2: next 2 bytes (little-endian) are length
            if i + 2 >= script.len() {
                break;
            }
            let len = u16::from_le_bytes([script[i + 1], script[i + 2]]) as usize;
            last_opcode = Some(opcode);
            i += 3 + len;
            continue;
        } else if opcode == OP_PUSHDATA4 {
            // OP_PUSHDATA4: next 4 bytes (little-endian) are length
            if i + 4 >= script.len() {
                break;
            }
            let len =
                u32::from_le_bytes([script[i + 1], script[i + 2], script[i + 3], script[i + 4]])
                    as usize;
            last_opcode = Some(opcode);
            i += 5 + len;
            continue;
        }

        // OP_CHECKSIG and OP_CHECKSIGVERIFY count as 1 sigop each
        if opcode == OP_CHECKSIG || opcode == OP_CHECKSIGVERIFY {
            count = count.saturating_add(1);
        }
        // OP_CHECKMULTISIG and OP_CHECKMULTISIGVERIFY count as multiple sigops
        else if opcode == OP_CHECKMULTISIG || opcode == OP_CHECKMULTISIGVERIFY {
            if accurate {
                // If accurate mode and previous opcode is OP_1-OP_16, use that number
                if let Some(prev_op) = last_opcode {
                    if (OP_1..=OP_16).contains(&prev_op) {
                        // OP_1 = 0x51, OP_16 = 0x60
                        // Decode: OP_N = N - 0x50
                        let n = (prev_op - OP_1 + 1) as u32;
                        count = count.saturating_add(n);
                    } else {
                        count = count.saturating_add(MAX_PUBKEYS_PER_MULTISIG);
                    }
                } else {
                    count = count.saturating_add(MAX_PUBKEYS_PER_MULTISIG);
                }
            } else {
                // Not accurate: assume maximum
                count = count.saturating_add(MAX_PUBKEYS_PER_MULTISIG);
            }
        }

        last_opcode = Some(opcode);
        i += 1;
    }

    count
}

/// Count sigops in a tapscript per BIP 342 (`CountTapscriptSigOps`).
///
/// Used for **per-tapscript validation weight** during script execution. This must **not** be folded
/// into block `MAX_BLOCK_SIGOPS_COST`: Bitcoin Core `WitnessSigOps` only counts witness **v0**; v1
/// (Taproot) contributes **0** to that total.
#[spec_locked("11.2.8")]
pub fn count_tapscript_sigops(script: &ByteString) -> u32 {
    let mut count = 0u32;
    let mut i = 0;

    while i < script.len() {
        let opcode = script[i];

        if opcode > 0 && opcode < OP_PUSHDATA1 {
            let len = opcode as usize;
            i += 1 + len;
            continue;
        } else if opcode == OP_PUSHDATA1 {
            if i + 1 >= script.len() {
                break;
            }
            let len = script[i + 1] as usize;
            i += 2 + len;
            continue;
        } else if opcode == OP_PUSHDATA2 {
            if i + 2 >= script.len() {
                break;
            }
            let len = u16::from_le_bytes([script[i + 1], script[i + 2]]) as usize;
            i += 3 + len;
            continue;
        } else if opcode == OP_PUSHDATA4 {
            if i + 4 >= script.len() {
                break;
            }
            let len =
                u32::from_le_bytes([script[i + 1], script[i + 2], script[i + 3], script[i + 4]])
                    as usize;
            i += 5 + len;
            continue;
        }

        if opcode == OP_CHECKSIG || opcode == OP_CHECKSIGVERIFY || opcode == OP_CHECKSIGADD {
            count = count.saturating_add(1);
        }
        i += 1;
    }
    count
}

/// Check if a script is P2SH (Pay-to-Script-Hash) — Orange Paper 5.2.1 IsP2SH
///
/// P2SH scripts have the format: OP_HASH160 (0xa9) <20-byte-hash> OP_EQUAL (0x87)
#[spec_locked("5.2.1")]
pub fn is_pay_to_script_hash(script: &[u8]) -> bool {
    script.len() == 23
        && script[0] == OP_HASH160  // OP_HASH160
        && script[1] == 0x14  // Push 20 bytes
        && script[22] == OP_EQUAL // OP_EQUAL
}

/// Extract redeem script from P2SH scriptSig
///
/// For P2SH, the scriptSig pushes the redeem script. We need to extract
/// the last push data item from scriptSig.
/// Orange Paper 5.2.1: P2SH scriptSig must contain only pushes; last push = redeem script.
#[spec_locked("5.2.1")]
fn extract_redeem_script_from_scriptsig(script_sig: &ByteString) -> Option<ByteString> {
    let mut i = 0;
    let mut last_data: Option<ByteString> = None;

    while i < script_sig.len() {
        let opcode = script_sig[i];

        if opcode <= OP_PUSHDATA4 {
            // Push data opcode
            let (len, advance) = if opcode < OP_PUSHDATA1 {
                // Direct push: opcode is the length
                let len = opcode as usize;
                (len, 1)
            } else if opcode == OP_PUSHDATA1 {
                // OP_PUSHDATA1
                if i + 1 >= script_sig.len() {
                    return None;
                }
                let len = script_sig[i + 1] as usize;
                (len, 2)
            } else if opcode == OP_PUSHDATA2 {
                // OP_PUSHDATA2
                if i + 2 >= script_sig.len() {
                    return None;
                }
                let len = u16::from_le_bytes([script_sig[i + 1], script_sig[i + 2]]) as usize;
                (len, 3)
            } else if opcode == OP_PUSHDATA4 {
                // OP_PUSHDATA4
                if i + 4 >= script_sig.len() {
                    return None;
                }
                let len = u32::from_le_bytes([
                    script_sig[i + 1],
                    script_sig[i + 2],
                    script_sig[i + 3],
                    script_sig[i + 4],
                ]) as usize;
                (len, 5)
            } else {
                // Other push opcodes (OP_1NEGATE, OP_RESERVED, OP_1-OP_16)
                (0, 1)
            };

            if i + advance + len > script_sig.len() {
                return None;
            }

            last_data = Some(script_sig[i + advance..i + advance + len].to_vec());
            i += advance + len;
        } else if (OP_1..=OP_16).contains(&opcode) {
            // OP_1 to OP_16: push single byte
            last_data = Some(vec![opcode - OP_N_BASE]); // Convert OP_N to value N
            i += 1;
        } else {
            // Other opcode: not a push, invalid for P2SH
            return None;
        }
    }

    last_data
}

/// Get legacy sigop count from transaction
///
/// Counts sigops in scriptSig and scriptPubKey of all inputs and outputs.
/// Matches consensus's GetLegacySigOpCount().
///
/// # Arguments
/// * `tx` - Transaction to count sigops in
///
/// # Returns
/// Total number of legacy sigops
#[spec_locked("5.2.2")]
pub fn get_legacy_sigop_count(tx: &Transaction) -> u32 {
    let mut count = 0u32;

    // Count sigops in all input scriptSigs
    for input in &tx.inputs {
        count = count.saturating_add(count_sigops_in_script(&input.script_sig, false));
    }

    // Count sigops in all output scriptPubKeys
    for output in &tx.outputs {
        count = count.saturating_add(count_sigops_in_script(&output.script_pubkey, false));
    }

    count
}

/// Get P2SH sigop count from transaction
///
/// Counts sigops in P2SH redeem scripts. Only counts sigops for outputs
/// that are P2SH (Pay-to-Script-Hash).
/// Matches consensus's GetP2SHSigOpCount().
///
/// # Arguments
/// * `tx` - Transaction to count sigops in
/// * `utxo_lookup` - UTXO lookup (UtxoSet or UtxoOverlay)
///
/// # Returns
/// Total number of P2SH sigops
#[spec_locked("5.2.2")]
pub fn get_p2sh_sigop_count<U: UtxoLookup>(tx: &Transaction, utxo_lookup: &U) -> Result<u32> {
    // Coinbase transactions have no P2SH sigops
    use crate::transaction::is_coinbase;
    if is_coinbase(tx) {
        return Ok(0);
    }

    let mut count = 0u32;

    for input in &tx.inputs {
        // Get the UTXO (scriptPubKey) for this input
        if let Some(utxo) = utxo_lookup.get(&input.prevout) {
            // Check if this is a P2SH output
            if is_pay_to_script_hash(utxo.script_pubkey.as_ref()) {
                // Extract redeem script from scriptSig
                if let Some(redeem_script) = extract_redeem_script_from_scriptsig(&input.script_sig)
                {
                    // Count sigops in redeem script (use accurate counting)
                    count = count.saturating_add(count_sigops_in_script(&redeem_script, true));
                }
            }
        }
    }

    Ok(count)
}

/// Count witness sigops in transaction
///
/// Counts sigops in witness scripts for SegWit transactions.
/// P2WPKH: 1 sigop; P2WSH: count in witness script; P2TR: count in tapscript.
///
/// # Arguments
/// * `tx` - Transaction
/// * `witnesses` - Witness data for each input (slice of Witness vectors)
/// * `utxo_lookup` - UTXO lookup (UtxoSet or UtxoOverlay)
/// * `flags` - Script verification flags
///
/// # Returns
/// Number of witness sigops
#[spec_locked("11.1")]
pub(crate) fn count_witness_sigops<U: UtxoLookup>(
    tx: &Transaction,
    witnesses: &[Witness],
    utxo_lookup: &U,
    flags: u32,
) -> Result<u64> {
    use crate::transaction::is_coinbase;

    // SegWit flag must be enabled
    if (flags & 0x800) == 0 {
        return Ok(0);
    }

    if is_coinbase(tx) {
        return Ok(0);
    }

    let mut count = 0u64;

    for (i, input) in tx.inputs.iter().enumerate() {
        if let Some(utxo) = utxo_lookup.get(&input.prevout) {
            let script_pubkey = &utxo.script_pubkey;

            // P2WPKH: OP_0 <20-byte-hash>
            if script_pubkey.len() == 22 && script_pubkey[0] == OP_0 && script_pubkey[1] == 0x14 {
                // P2WPKH has 1 sigop (the CHECKSIG in the witness script)
                if let Some(witness) = witnesses.get(i) {
                    if !witness.is_empty() {
                        count = count.saturating_add(1);
                    }
                }
            }
            // P2WSH: OP_0 <32-byte-hash>
            else if script_pubkey.len() == 34
                && script_pubkey[0] == OP_0
                && script_pubkey[1] == 0x20
            {
                // P2WSH: count sigops in witness script
                if let Some(witness) = witnesses.get(i) {
                    if let Some(witness_script) = witness.last() {
                        count = count
                            .saturating_add(count_sigops_in_script(witness_script, true) as u64);
                    }
                }
            }
            // P2TR (witness v1): do **not** add tapscript sigops here.
            // Bitcoin Core `WitnessSigOps` only handles version 0; v1 returns 0.
            // BIP 342 enforces signature-related limits via tapscript validation weight during
            // execution, not `MAX_BLOCK_SIGOPS_COST`. Counting tapscript ops here overstates the
            // block total and rejects mined mainnet blocks (e.g. heavy tapscript spends).
        }
    }

    Ok(count)
}

/// Legacy sigop count with accurate OP_CHECKMULTISIG (OP_1..OP_16 = 1..16, else 20).
/// Used for BIP54 per-tx 2500 limit to match Core's GetSigOpCount(fAccurate=true).
#[spec_locked("5.2.2")]
pub fn get_legacy_sigop_count_accurate(tx: &Transaction) -> u32 {
    let mut count = 0u32;
    for input in &tx.inputs {
        count = count.saturating_add(count_sigops_in_script(&input.script_sig, true));
    }
    for output in &tx.outputs {
        count = count.saturating_add(count_sigops_in_script(&output.script_pubkey, true));
    }
    count
}

/// Get total transaction sigop count (BIP54 limit).
///
/// Sum of legacy + P2SH + witness sigop counts (same accounting as BIP16).
/// Used to enforce per-transaction limit of 2500 sigops after BIP54 activation.
pub fn get_transaction_sigop_count<U: UtxoLookup>(
    tx: &Transaction,
    utxo_lookup: &U,
    witnesses: Option<&[Witness]>,
    flags: u32,
) -> Result<u64> {
    let legacy = get_legacy_sigop_count(tx) as u64;
    let p2sh = get_p2sh_sigop_count(tx, utxo_lookup)? as u64;
    let witness = witnesses
        .map(|w| count_witness_sigops(tx, w, utxo_lookup, flags))
        .unwrap_or(Ok(0))?;
    Ok(legacy.saturating_add(p2sh).saturating_add(witness))
}

/// BIP54 per-tx sigop count: legacy (accurate) + P2SH + witness.
/// Matches Core's CheckSigopsBIP54 (GetSigOpCount(scriptSig, true) for legacy).
pub fn get_transaction_sigop_count_for_bip54<U: UtxoLookup>(
    tx: &Transaction,
    utxo_lookup: &U,
    witnesses: Option<&[Witness]>,
    flags: u32,
) -> Result<u64> {
    let legacy = get_legacy_sigop_count_accurate(tx) as u64;
    let p2sh = get_p2sh_sigop_count(tx, utxo_lookup)? as u64;
    let witness = witnesses
        .map(|w| count_witness_sigops(tx, w, utxo_lookup, flags))
        .unwrap_or(Ok(0))?;
    Ok(legacy.saturating_add(p2sh).saturating_add(witness))
}

/// Get total transaction sigop cost
///
/// Calculates total sigop cost for a transaction, including:
/// - Legacy sigops × 4 (witness scale factor)
/// - P2SH sigops × 4 (if P2SH enabled)
/// - Witness sigops (actual count, not scaled)
///
/// Matches consensus's GetTransactionSigOpCost().
///
/// # Arguments
/// * `tx` - Transaction to count sigops in
/// * `utxo_set` - UTXO set to lookup inputs
/// * `witness` - Witness data for this transaction (one Witness per input)
/// * `flags` - Script verification flags
///
/// # Returns
/// Total sigop cost
#[spec_locked("5.2.2")]
pub fn get_transaction_sigop_cost<U: UtxoLookup>(
    tx: &Transaction,
    utxo_lookup: &U,
    witness: Option<&Witness>,
    flags: u32,
) -> Result<u64> {
    let witness_slices = witness.map(std::slice::from_ref);
    get_transaction_sigop_cost_with_witness_slices(tx, utxo_lookup, witness_slices, flags)
}

/// Same as get_transaction_sigop_cost but accepts pre-fetched UTXOs in input order.
/// Avoids redundant overlay lookups when caller already has UTXO data.
#[spec_locked("5.2.2")]
pub fn get_transaction_sigop_cost_with_utxos(
    tx: &Transaction,
    utxos: &[Option<&UTXO>],
    witnesses: Option<&[Witness]>,
    flags: u32,
) -> Result<u64> {
    let legacy_count = get_legacy_sigop_count(tx) as u64;
    let mut total_cost = legacy_count.saturating_mul(WITNESS_SCALE_FACTOR);

    use crate::transaction::is_coinbase;
    if is_coinbase(tx) {
        return Ok(total_cost);
    }

    if (flags & 0x01) != 0 {
        let mut p2sh_count = 0u32;
        for (input, utxo_opt) in tx.inputs.iter().zip(utxos.iter()) {
            if let Some(utxo) = utxo_opt {
                if is_pay_to_script_hash(utxo.script_pubkey.as_ref()) {
                    if let Some(redeem_script) =
                        extract_redeem_script_from_scriptsig(&input.script_sig)
                    {
                        p2sh_count =
                            p2sh_count.saturating_add(count_sigops_in_script(&redeem_script, true));
                    }
                }
            }
        }
        total_cost = total_cost
            .saturating_add(p2sh_count.saturating_mul(WITNESS_SCALE_FACTOR as u32) as u64);
    }

    if let Some(witnesses) = witnesses {
        if (flags & 0x800) != 0 {
            for (i, (input, utxo_opt)) in tx.inputs.iter().zip(utxos.iter()).enumerate() {
                if let Some(utxo) = utxo_opt {
                    let script_pubkey = utxo.script_pubkey.as_ref();
                    if script_pubkey.len() == 22
                        && script_pubkey[0] == OP_0
                        && script_pubkey[1] == 0x14
                    {
                        if let Some(witness) = witnesses.get(i) {
                            if !witness.is_empty() {
                                total_cost = total_cost.saturating_add(1);
                            }
                        }
                    } else if script_pubkey.len() == 34
                        && script_pubkey[0] == OP_0
                        && script_pubkey[1] == 0x20
                    {
                        if let Some(witness) = witnesses.get(i) {
                            if let Some(witness_script) = witness.last() {
                                total_cost = total_cost.saturating_add(count_sigops_in_script(
                                    witness_script,
                                    true,
                                )
                                    as u64);
                            }
                        }
                    }
                    // P2TR / witness v1: witness sigop cost is 0 for block limit (match Core WitnessSigOps).
                }
            }
        }
    }

    Ok(total_cost)
}

/// Same as get_transaction_sigop_cost but accepts per-input witness slices directly.
/// Avoids flattening witness data in block validation hot path.
#[spec_locked("5.2.2")]
pub fn get_transaction_sigop_cost_with_witness_slices<U: UtxoLookup>(
    tx: &Transaction,
    utxo_lookup: &U,
    witnesses: Option<&[Witness]>,
    flags: u32,
) -> Result<u64> {
    // Legacy sigops × witness scale factor
    let legacy_count = get_legacy_sigop_count(tx) as u64;
    let mut total_cost = legacy_count.saturating_mul(WITNESS_SCALE_FACTOR);

    use crate::transaction::is_coinbase;
    if is_coinbase(tx) {
        return Ok(total_cost);
    }

    // P2SH sigops × witness scale factor (if P2SH enabled)
    if (flags & 0x01) != 0 {
        // SCRIPT_VERIFY_P2SH flag enabled
        let p2sh_count = get_p2sh_sigop_count(tx, utxo_lookup)? as u64;
        total_cost = total_cost.saturating_add(p2sh_count.saturating_mul(WITNESS_SCALE_FACTOR));
    }

    // Witness sigops (actual count, not scaled)
    if let Some(witnesses) = witnesses {
        let witness_count = count_witness_sigops(tx, witnesses, utxo_lookup, flags)?;
        total_cost = total_cost.saturating_add(witness_count);
    }

    Ok(total_cost)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_count_sigops_checksig() {
        // Script with OP_CHECKSIG
        let script = vec![OP_1, OP_1, OP_CHECKSIG]; // OP_1, OP_1, OP_CHECKSIG
        assert_eq!(count_sigops_in_script(&script, false), 1);
    }

    #[test]
    fn test_count_sigops_checksigverify() {
        // Script with OP_CHECKSIGVERIFY
        let script = vec![OP_1, OP_1, OP_CHECKSIGVERIFY]; // OP_1, OP_1, OP_CHECKSIGVERIFY
        assert_eq!(count_sigops_in_script(&script, false), 1);
    }

    #[test]
    fn test_count_sigops_multisig() {
        // Script with OP_CHECKMULTISIG (defaults to 20)
        let script = vec![OP_1, OP_2, OP_CHECKMULTISIG]; // OP_1, OP_2, OP_CHECKMULTISIG
        assert_eq!(count_sigops_in_script(&script, false), 20);

        // Accurate mode: use OP_2 value (2 sigops)
        assert_eq!(count_sigops_in_script(&script, true), 2);
    }

    #[test]
    fn test_get_legacy_sigop_count() {
        let tx = Transaction {
            version: 1,
            inputs: vec![TransactionInput {
                prevout: OutPoint {
                    hash: [0; 32].into(),
                    index: 0,
                },
                script_sig: vec![OP_1, OP_CHECKSIG], // OP_1, OP_CHECKSIG
                sequence: 0xffffffff,
            }]
            .into(),
            outputs: vec![TransactionOutput {
                value: 1000,
                script_pubkey: vec![OP_1, OP_CHECKSIGVERIFY].into(), // OP_1, OP_CHECKSIGVERIFY
            }]
            .into(),
            lock_time: 0,
        };

        assert_eq!(get_legacy_sigop_count(&tx), 2);
    }

    #[test]
    fn test_is_pay_to_script_hash() {
        // Valid P2SH script: OP_HASH160 <20 bytes> OP_EQUAL
        let mut p2sh_script = vec![OP_HASH160, 0x14]; // OP_HASH160, push 20
        p2sh_script.extend_from_slice(&[0u8; 20]);
        p2sh_script.push(OP_EQUAL); // OP_EQUAL

        assert!(is_pay_to_script_hash(&p2sh_script));

        // Invalid: wrong length
        assert!(!is_pay_to_script_hash(&vec![OP_HASH160, 0x14]));

        // Invalid: not P2SH format
        let p2pkh = vec![OP_DUP, OP_HASH160, 0x14]; // OP_DUP OP_HASH160
        assert!(!is_pay_to_script_hash(&p2pkh));
    }

    // ==========================================================================
    // REGRESSION TESTS: Push data must not be counted as sigops (block 310357 fix)
    // ==========================================================================
    // These tests prevent regression of the bug where bytes inside push data
    // (e.g., 0xAC = OP_CHECKSIG) were incorrectly counted as sigops.
    // This caused valid blocks to be rejected with "sigop cost exceeds maximum".

    #[test]
    fn test_pushdata1_containing_checksig_byte_not_counted() {
        // OP_PUSHDATA1 <len=3> <0xAC 0xAC 0xAC>
        // The 0xAC bytes are push DATA, not OP_CHECKSIG opcodes.
        // Sigop count must be 0.
        let script = vec![OP_PUSHDATA1, 0x03, OP_CHECKSIG, OP_CHECKSIG, OP_CHECKSIG];
        assert_eq!(
            count_sigops_in_script(&script, false),
            0,
            "Push data containing 0xAC must NOT be counted as sigops"
        );
    }

    #[test]
    fn test_pushdata2_containing_checksig_byte_not_counted() {
        // OP_PUSHDATA2 <len=4 as u16 LE> <0xAC 0xAD 0xAE 0xAF>
        // These are push DATA bytes, not opcodes.
        let script = vec![
            OP_PUSHDATA2,
            0x04,
            0x00,
            OP_CHECKSIG,
            OP_CHECKSIGVERIFY,
            OP_CHECKMULTISIG,
            OP_CHECKMULTISIGVERIFY,
        ];
        assert_eq!(
            count_sigops_in_script(&script, false),
            0,
            "Push data containing sigop-like bytes must NOT be counted"
        );
    }

    #[test]
    fn test_pushdata4_containing_checksig_byte_not_counted() {
        // OP_PUSHDATA4 <len=2 as u32 LE> <0xAC 0xAC>
        let script = vec![
            OP_PUSHDATA4,
            0x02,
            0x00,
            0x00,
            0x00,
            OP_CHECKSIG,
            OP_CHECKSIG,
        ];
        assert_eq!(
            count_sigops_in_script(&script, false),
            0,
            "OP_PUSHDATA4 data containing 0xAC must NOT be counted"
        );
    }

    #[test]
    fn test_direct_push_containing_checksig_byte_not_counted() {
        // Direct push: opcode 0x05 means "push next 5 bytes"
        // Data contains OP_CHECKSIG byte which must NOT be counted.
        let script = vec![
            0x05,
            OP_CHECKSIG,
            OP_CHECKSIG,
            OP_CHECKSIG,
            OP_CHECKSIG,
            OP_CHECKSIG,
        ];
        assert_eq!(
            count_sigops_in_script(&script, false),
            0,
            "Direct push data containing 0xAC must NOT be counted as sigops"
        );
    }

    #[test]
    fn test_push_data_then_real_checksig() {
        // Direct push of 3 bytes (containing 0xAC), then a REAL OP_CHECKSIG
        // Only the real OP_CHECKSIG (after push data) should count.
        let script = vec![0x03, OP_CHECKSIG, OP_CHECKSIG, OP_CHECKSIG, OP_CHECKSIG]; // push 3, data, then OP_CHECKSIG
        assert_eq!(
            count_sigops_in_script(&script, false),
            1,
            "Only real OP_CHECKSIG after push data should count"
        );
    }

    #[test]
    fn test_pushdata1_then_real_multisig() {
        // OP_PUSHDATA1 <len=2> <OP_CHECKSIG OP_CHECKSIG> then OP_2 OP_CHECKMULTISIG
        // The OP_CHECKSIG bytes in push data don't count. Only the real OP_CHECKMULTISIG counts.
        let script = vec![
            OP_PUSHDATA1,
            0x02,
            OP_CHECKSIG,
            OP_CHECKSIG,
            OP_2,
            OP_CHECKMULTISIG,
        ];
        // Inaccurate mode: multisig = 20
        assert_eq!(
            count_sigops_in_script(&script, false),
            20,
            "Only real OP_CHECKMULTISIG should count (inaccurate=20)"
        );
        // Accurate mode: OP_2 before OP_CHECKMULTISIG = 2
        assert_eq!(
            count_sigops_in_script(&script, true),
            2,
            "Accurate mode: OP_2 before OP_CHECKMULTISIG = 2 sigops"
        );
    }

    #[test]
    fn test_empty_script_zero_sigops() {
        let script: Vec<u8> = vec![];
        assert_eq!(count_sigops_in_script(&script, false), 0);
        assert_eq!(count_sigops_in_script(&script, true), 0);
    }

    #[test]
    fn test_truncated_pushdata1_does_not_panic() {
        // OP_PUSHDATA1 at end of script (no length byte)
        let script = vec![OP_PUSHDATA1];
        assert_eq!(count_sigops_in_script(&script, false), 0);
    }

    #[test]
    fn test_truncated_pushdata2_does_not_panic() {
        // OP_PUSHDATA2 with only 1 of 2 length bytes
        let script = vec![OP_PUSHDATA2, 0x01];
        assert_eq!(count_sigops_in_script(&script, false), 0);
    }

    #[test]
    fn test_truncated_pushdata4_does_not_panic() {
        // OP_PUSHDATA4 with only 3 of 4 length bytes
        let script = vec![OP_PUSHDATA4, 0x01, 0x00, 0x00];
        assert_eq!(count_sigops_in_script(&script, false), 0);
    }

    #[test]
    fn test_large_push_data_with_many_checksig_bytes() {
        // Simulate a realistic script where push data contains many OP_CHECKSIG bytes
        // This is the kind of script that caused the block 310357 failure.
        // OP_PUSHDATA2 <len=100 as u16 LE> <100 bytes of OP_CHECKSIG>
        let mut script = vec![OP_PUSHDATA2, 100, 0x00]; // OP_PUSHDATA2, length=100
        script.extend_from_slice(&[OP_CHECKSIG; 100]); // 100 bytes of OP_CHECKSIG data
        assert_eq!(
            count_sigops_in_script(&script, false),
            0,
            "100 bytes of OP_CHECKSIG in push data must count as 0 sigops"
        );
    }

    #[test]
    fn test_multiple_sigop_opcodes() {
        // OP_CHECKSIG OP_CHECKSIG OP_CHECKSIGVERIFY
        let script = vec![0xac, 0xac, 0xad];
        assert_eq!(count_sigops_in_script(&script, false), 3);
    }

    #[test]
    fn test_multisig_accurate_op_16() {
        // OP_16 (0x60) OP_CHECKMULTISIG
        let script = vec![0x60, 0xae];
        assert_eq!(count_sigops_in_script(&script, true), 16);
    }

    #[test]
    fn test_multisig_accurate_op_1() {
        // OP_1 (0x51) OP_CHECKMULTISIG
        let script = vec![0x51, 0xae];
        assert_eq!(count_sigops_in_script(&script, true), 1);
    }

    /// Prefetched-UTXO sigop cost must match overlay-based counting (used on assume-valid path).
    /// P2TR witness does not contribute to legacy block sigop cost (`WitnessSigOps` v1 = 0 in Core).
    #[test]
    fn get_transaction_sigop_cost_with_utxos_matches_witness_slices_p2tr_excluded_from_block_cost()
    {
        use crate::segwit::Witness;

        let prev = OutPoint {
            hash: [7u8; 32].into(),
            index: 0,
        };
        let mut spk = vec![OP_1, 0x20];
        spk.extend_from_slice(&[9u8; 32]);

        let utxo = UTXO {
            value: 50_000,
            script_pubkey: spk.into(),
            height: 700_000,
            is_coinbase: false,
        };

        let mut set: UtxoSet = Default::default();
        utxo_set_insert(&mut set, prev, utxo);

        let tapscript = vec![OP_CHECKSIG];
        let witness_two: Witness = vec![tapscript.clone(), vec![0u8; 32]];
        let witness_three: Witness = vec![tapscript, vec![0x50], vec![0u8; 32]];

        let tx = Transaction {
            version: 2,
            inputs: vec![TransactionInput {
                prevout: prev,
                script_sig: vec![],
                sequence: 0xffffffff,
            }]
            .into(),
            outputs: vec![TransactionOutput {
                value: 10_000,
                script_pubkey: vec![OP_0].into(),
            }]
            .into(),
            lock_time: 0,
        };

        let flags = 0x800 | 0x8000 | 0x01;
        let uref = set.get(&prev).map(|a| a.as_ref());
        let utxo_refs: Vec<Option<&UTXO>> = vec![uref];

        for witnesses in [&witness_two, &witness_three] {
            let w = vec![witnesses.clone()];
            let with_slices = get_transaction_sigop_cost_with_witness_slices(
                &tx,
                &set,
                Some(w.as_slice()),
                flags,
            )
            .unwrap();
            let with_utxos =
                get_transaction_sigop_cost_with_utxos(&tx, &utxo_refs, Some(w.as_slice()), flags)
                    .unwrap();
            assert_eq!(
                with_utxos, with_slices,
                "sigop cost must match between utxo prefetch and overlay lookup"
            );
            assert_eq!(
                with_slices, 0,
                "tapscript in P2TR witness must not add to block sigop cost"
            );
        }
    }
}