ddk-dlc 1.1.2

//! Module for working with DLC inputs

use bitcoin::{Amount, EcdsaSighashType, OutPoint, ScriptBuf, Transaction, Witness};
use secp256k1_zkp::{ecdsa::Signature, PublicKey, Secp256k1, SecretKey, Signing, Verification};

use crate::{util::finalize_sig, Error, TxInputInfo};

#[derive(Clone, Debug, PartialEq, Eq)]
#[cfg_attr(feature = "use-serde", derive(serde::Serialize, serde::Deserialize))]
/// Contains information about a DLC input to be used in a funding transaction.
pub struct DlcInputInfo {
    /// The transaction of the funding transaction.
    pub fund_tx: Transaction,
    /// The output index of the funding transaction.
    pub fund_vout: u32,
    /// The local funding public key.
    pub local_fund_pubkey: PublicKey,
    /// The remote funding public key.
    pub remote_fund_pubkey: PublicKey,
    /// The amount of the funding transaction.
    pub fund_amount: Amount,
    /// The maximum witness length of the funding transaction.
    pub max_witness_len: usize,
    /// The serial id of the funding transaction.
    pub input_serial_id: u64,
    /// The contract id referenced
    pub contract_id: [u8; 32],
}

impl From<&DlcInputInfo> for TxInputInfo {
    fn from(val: &DlcInputInfo) -> Self {
        TxInputInfo {
            outpoint: OutPoint::new(val.fund_tx.compute_txid(), val.fund_vout),
            max_witness_len: val.max_witness_len,
            redeem_script: ScriptBuf::new(),
            serial_id: val.input_serial_id,
        }
    }
}

/// Calculate weight of DLC inputs for fee estimation
pub fn get_dlc_inputs_weight(dlc_inputs: &[DlcInputInfo]) -> usize {
    dlc_inputs
        .iter()
        .map(|dlc_input| {
            // P2WSH 2-of-2 multisig weight
            36 * 4 + 4 + 4 * 4 + dlc_input.max_witness_len
        })
        .sum()
}

/// Calculate total amount from DLC inputs
pub fn calculate_total_dlc_input_amount(dlc_inputs: &[DlcInputInfo]) -> Amount {
    dlc_inputs.iter().map(|input| input.fund_amount).sum()
}

/// Create the funding script for a DLC input
pub fn create_dlc_input_funding_script(dlc_input: &DlcInputInfo) -> ScriptBuf {
    crate::make_funding_redeemscript(&dlc_input.local_fund_pubkey, &dlc_input.remote_fund_pubkey)
}

/// Create a signature for a DLC funding input
pub fn create_dlc_funding_input_signature<C: Signing>(
    secp: &Secp256k1<C>,
    fund_transaction: &Transaction,
    input_index: usize,
    dlc_input: &DlcInputInfo,
    privkey: &SecretKey,
) -> Result<Vec<u8>, Error> {
    let funding_script = create_dlc_input_funding_script(dlc_input);
    let sig_hash_msg = super::util::get_sig_hash_msg(
        fund_transaction,
        input_index,
        &funding_script,
        dlc_input.fund_amount,
    )?;
    let signature = secp.sign_ecdsa_low_r(&sig_hash_msg, privkey);
    Ok(finalize_sig(&signature, EcdsaSighashType::All))
}

/// Verify a DLC funding input signature
pub fn verify_dlc_funding_input_signature<V: Verification>(
    secp: &Secp256k1<V>,
    fund_transaction: &Transaction,
    input_index: usize,
    dlc_input: &DlcInputInfo,
    signature: Vec<u8>,
    pubkey: &PublicKey,
) -> Result<(), Error> {
    let funding_script = create_dlc_input_funding_script(dlc_input);

    // Parse DER signature instead of compact
    let signature = if signature.len() == 64 {
        Signature::from_compact(&signature)?
    } else {
        // Remove sighash type byte and parse DER
        let sig_bytes = &signature[..signature.len() - 1];
        Signature::from_der(sig_bytes)?
    };

    super::verify_tx_input_sig(
        secp,
        &signature,
        fund_transaction,
        input_index,
        &funding_script,
        dlc_input.fund_amount,
        pubkey,
    )
}

/// Combine both parties' signatures for a DLC input
pub fn combine_dlc_input_signatures(
    dlc_input: &DlcInputInfo,
    my_signature: &Vec<u8>,
    other_signature: &Vec<u8>,
    my_pubkey: &PublicKey,
    other_pubkey: &PublicKey,
) -> Witness {
    let funding_script = create_dlc_input_funding_script(dlc_input);

    // Order signatures based on pubkey order
    let (first_sig, second_sig) = if my_pubkey <= other_pubkey {
        (my_signature, other_signature)
    } else {
        (other_signature, my_signature)
    };

    let mut witness = Witness::new();
    witness.push([]);
    witness.push(first_sig);
    witness.push(second_sig);
    witness.push(funding_script.to_bytes());

    witness
}