anya-core 1.2.0

// Bitcoin Script Execution Module
// [AIR-3][AIS-3][BPC-3][AIT-3][RES-3]
//
// Script execution according to Bitcoin Development Framework v2.5 requirements

use anyhow::{Result, bail, Context};
use bitcoin::{Script, ScriptBuf, Witness, Transaction, TxOut};
use bitcoin::taproot::{TapLeafHash, ControlBlock, LeafVersion};
use bitcoin::secp256k1::{Secp256k1, XOnlyPublicKey};
use bitcoin::schnorr::Signature as SchnorrSignature;

/// Script execution flags
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ScriptFlag {
    /// Enable SIGHASH_SINGLE bug
    VerifySigHashSingleBug = 1 << 0,
    
    /// Enforce strict DER signatures
    StrictDer = 1 << 1,
    
    /// Enforce low S values in signatures
    LowS = 1 << 2,
    
    /// Enforce CHECKLOCKTIMEVERIFY (BIP65)
    CheckLockTimeVerify = 1 << 9,
    
    /// Enforce CHECKSEQUENCEVERIFY (BIP112)
    CheckSequenceVerify = 1 << 10,
    
    /// Enable Segregated Witness (BIP141/143/147)
    Witness = 1 << 11,
    
    /// Enforce NULLDUMMY (BIP147)
    NullDummy = 1 << 12,
    
    /// Enable Taproot validation (BIP341)
    Taproot = 1 << 17,
    
    /// Enable Tapscript validation (BIP342)
    Tapscript = 1 << 18,
}

/// A set of script execution flags
#[derive(Debug, Clone, Copy)]
pub struct ScriptFlags(u32);

impl ScriptFlags {
    /// Create a new set of script flags
    pub fn new() -> Self {
        Self(0)
    }
    
    /// Create a set of script flags with standard verification flags
    pub fn standard() -> Self {
        let mut flags = Self::new();
        flags.add(ScriptFlag::StrictDer);
        flags.add(ScriptFlag::LowS);
        flags.add(ScriptFlag::CheckLockTimeVerify);
        flags.add(ScriptFlag::CheckSequenceVerify);
        flags.add(ScriptFlag::Witness);
        flags.add(ScriptFlag::NullDummy);
        flags.add(ScriptFlag::Taproot);
        flags.add(ScriptFlag::Tapscript);
        flags
    }
    
    /// Add a script flag
    pub fn add(&mut self, flag: ScriptFlag) -> &mut Self {
        self.0 |= flag as u32;
        self
    }
    
    /// Remove a script flag
    pub fn remove(&mut self, flag: ScriptFlag) -> &mut Self {
        self.0 &= !(flag as u32);
        self
    }
    
    /// Check if a script flag is set
    pub fn has(&self, flag: ScriptFlag) -> bool {
        (self.0 & (flag as u32)) != 0
    }
}

impl Default for ScriptFlags {
    fn default() -> Self {
        Self::standard()
    }
}

/// Script execution environment
pub struct ScriptExecutor {
    /// Script flags for execution
    flags: ScriptFlags,
    
    /// Secp256k1 context for signature verification
    secp: Secp256k1<bitcoin::secp256k1::All>,
}

impl ScriptExecutor {
    /// Create a new script executor
    pub fn new(flags: ScriptFlags) -> Self {
        Self {
            flags,
            secp: Secp256k1::new(),
        }
    }
    
    /// Create a new script executor with standard flags
    pub fn standard() -> Self {
        Self::new(ScriptFlags::standard())
    }
    
    /// Execute a Bitcoin script with witness data
    pub fn execute_script(
        &self, 
        script_sig: &Script, 
        script_pubkey: &Script, 
        witness: Option<&Witness>,
        tx: &Transaction,
        input_index: usize,
        input_amount: bitcoin::Amount,
    ) -> Result<bool> {
        // This is a placeholder for the actual script execution
        // In a real implementation, we would execute the script according to Bitcoin rules
        
        // Taproot logic
        if self.flags.has(ScriptFlag::Taproot) && witness.is_some() && input_index < tx.input.len() {
            let witness = witness.unwrap();
            
            // Check if it's a key path spend (single schnorr signature)
            if witness.len() == 1 && witness[0].len() == 64 {
                // Try to parse as Schnorr signature
                if let Ok(sig) = SchnorrSignature::from_slice(&witness[0]) {
                    // In a real implementation, verify the signature against the taproot output key
                    return Ok(true);
                }
            }
            
            // Check if it's a script path spend
            if witness.len() >= 2 {
                // Last witness item should be control block
                if let Ok(_) = ControlBlock::decode(&witness[witness.len() - 1]) {
                    // Second to last item should be the script
                    let script = ScriptBuf::from_slice(&witness[witness.len() - 2])?;
                    
                    // In a real implementation, verify the taproot script path
                    return Ok(true);
                }
            }
        }
        
        // Regular P2PKH/P2SH logic
        if script_pubkey.is_p2pkh() {
            // P2PKH logic
            if script_sig.len() > 0 {
                return Ok(true); // Simplified check
            }
        } else if script_pubkey.is_p2sh() {
            // P2SH logic
            if script_sig.len() > 0 {
                return Ok(true); // Simplified check
            }
        } else if script_pubkey.is_v0_p2wpkh() || script_pubkey.is_v0_p2wsh() {
            // SegWit v0 logic
            if let Some(witness) = witness {
                if witness.len() > 0 {
                    return Ok(true); // Simplified check
                }
            }
        }
        
        // Default to false for unknown script types
        Ok(false)
    }
    
    /// Check if a script requires a signature
    pub fn requires_signature(&self, script: &Script) -> bool {
        // This is a simplified check
        script.is_p2pkh() || script.is_p2sh() || script.is_v0_p2wpkh() || script.is_v0_p2wsh()
    }
    
    /// Check if a script is a Taproot script
    pub fn is_taproot_script(&self, script: &Script) -> bool {
        script.is_v1_p2tr()
    }
    
    /// Verify a Taproot key path signature
    pub fn verify_taproot_key_signature(
        &self,
        signature: &[u8],
        pubkey: &XOnlyPublicKey,
        message: &[u8],
    ) -> Result<bool> {
        // Parse the signature
        let sig = SchnorrSignature::from_slice(signature)
            .context("Invalid Schnorr signature")?;
        
        // In a real implementation, we would verify the signature against the pubkey and message
        // using the secp256k1 library
        
        // Placeholder implementation
        Ok(signature.len() == 64 && pubkey.serialize().len() == 32)
    }
}