From 74bb611851d0913a6f1164404b6be742d2bf0ec4 Mon Sep 17 00:00:00 2001
From: conduition <conduition@proton.me>
Date: Thu, 29 Feb 2024 05:23:55 +0000
Subject: [PATCH] reusable method for computing funding output

---
 src/contract/mod.rs       | 14 +++++++++++++-
 src/spend_info/funding.rs | 13 +++++++++----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/src/contract/mod.rs b/src/contract/mod.rs
index ee14271..7380f12 100644
--- a/src/contract/mod.rs
+++ b/src/contract/mod.rs
@@ -2,7 +2,7 @@ pub(crate) mod fees;
 pub(crate) mod outcome;
 pub(crate) mod split;
 
-use bitcoin::{transaction::InputWeightPrediction, Amount, FeeRate};
+use bitcoin::{transaction::InputWeightPrediction, Amount, FeeRate, TxOut};
 use secp::Point;
 
 use crate::{
@@ -10,6 +10,7 @@ use crate::{
     errors::Error,
     oracles::EventAnnouncment,
     parties::{MarketMaker, Player},
+    spend_info::FundingSpendInfo,
 };
 
 use std::collections::{BTreeMap, BTreeSet};
@@ -92,6 +93,17 @@ pub struct WinCondition {
 }
 
 impl ContractParameters {
+    /// Returns the transaction output which the funding transaction should pay to.
+    ///
+    /// Avoid overusing this method, as it recomputes the aggregated key every time
+    /// it is invoked. Instead, prefer
+    /// [`TicketedDLC::funding_output`][crate::TicketedDLC::funding_output].
+    pub fn funding_output(&self) -> Result<TxOut, Error> {
+        let spend_info =
+            FundingSpendInfo::new(&self.market_maker, &self.players, self.funding_value)?;
+        Ok(spend_info.funding_output())
+    }
+
     pub(crate) fn outcome_output_value(&self) -> Result<Amount, Error> {
         let input_weights = [InputWeightPrediction::P2TR_KEY_DEFAULT_SIGHASH];
         let fee = fees::fee_calc_safe(self.fee_rate, input_weights, [P2TR_SCRIPT_PUBKEY_SIZE])?;
diff --git a/src/spend_info/funding.rs b/src/spend_info/funding.rs
index 0cc67f6..4ec2ca4 100644
--- a/src/spend_info/funding.rs
+++ b/src/spend_info/funding.rs
@@ -42,6 +42,14 @@ impl FundingSpendInfo {
         &self.key_agg_ctx
     }
 
+    /// Returns the transaction output which the funding transaction should pay to.
+    pub(crate) fn funding_output(&self) -> TxOut {
+        TxOut {
+            script_pubkey: self.script_pubkey(),
+            value: self.funding_value,
+        }
+    }
+
     /// Returns the TX locking script for funding the ticketed DLC multisig.
     pub(crate) fn script_pubkey(&self) -> ScriptBuf {
         // This is safe because the musig key aggregation formula prevents
@@ -56,10 +64,7 @@ impl FundingSpendInfo {
         &self,
         outcome_tx: &Transaction,
     ) -> Result<TapSighash, bitcoin::sighash::Error> {
-        let funding_prevouts = [TxOut {
-            script_pubkey: self.script_pubkey(),
-            value: self.funding_value,
-        }];
+        let funding_prevouts = [self.funding_output()];
 
         SighashCache::new(outcome_tx).taproot_key_spend_signature_hash(
             0,