From a0e9815779be38127ce077a2f0580c2c1a2ffa74 Mon Sep 17 00:00:00 2001
From: Polybius93 <adam.daniel.puskas@polybius-studios.com>
Date: Thu, 21 Nov 2024 12:34:39 +0100
Subject: [PATCH] feat: modify protocol fee calculation by dropping decimal
 points

---
 package.json                               |  2 +-
 src/functions/bitcoin/bitcoin-functions.ts |  4 ++--
 tests/unit/bitcoin-functions.test.ts       | 25 ++++++++++++++++++++++
 3 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/package.json b/package.json
index f8d0446..6e0ef4c 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "type": "module",
   "name": "dlc-btc-lib",
-  "version": "2.4.16",
+  "version": "2.4.17",
   "description": "This library provides a comprehensive set of interfaces and functions for minting dlcBTC tokens on supported blockchains.",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
diff --git a/src/functions/bitcoin/bitcoin-functions.ts b/src/functions/bitcoin/bitcoin-functions.ts
index 381af8e..1dfbbea 100644
--- a/src/functions/bitcoin/bitcoin-functions.ts
+++ b/src/functions/bitcoin/bitcoin-functions.ts
@@ -39,8 +39,8 @@ const ECDSA_PUBLIC_KEY_LENGTH = 33;
 const bip32 = BIP32Factory(ellipticCurveCryptography);
 
 export function getFeeAmount(bitcoinAmount: number, feeBasisPoints: number): number {
-  const feePercentage = new Decimal(feeBasisPoints).dividedBy(100);
-  return new Decimal(bitcoinAmount).times(feePercentage.dividedBy(100)).toNumber();
+  const feePercentage = new Decimal(feeBasisPoints).dividedBy(10000);
+  return new Decimal(bitcoinAmount).times(feePercentage).trunc().toNumber();
 }
 
 /**
diff --git a/tests/unit/bitcoin-functions.test.ts b/tests/unit/bitcoin-functions.test.ts
index 82cf91e..5ddc1ea 100644
--- a/tests/unit/bitcoin-functions.test.ts
+++ b/tests/unit/bitcoin-functions.test.ts
@@ -7,11 +7,13 @@ import {
   deriveUnhardenedPublicKey,
   ecdsaPublicKeyToSchnorr,
   finalizeUserInputs,
+  getFeeAmount,
   getFeeRecipientAddress,
   getInputIndicesByScript,
   getScriptMatchingOutputFromTransaction,
   getUnspendableKeyCommittedToUUID,
 } from '../../src/functions/bitcoin/bitcoin-functions';
+import { shiftValue, unshiftValue } from '../../src/utilities';
 import {
   TEST_TESTNET_ATTESTOR_EXTENDED_GROUP_PUBLIC_KEY_1,
   TEST_TESTNET_ATTESTOR_UNHARDENED_DERIVED_PUBLIC_KEY_1,
@@ -257,4 +259,27 @@ describe('Bitcoin Functions', () => {
       expect(result).toBeUndefined();
     });
   });
+
+  describe('getFeeAmount', () => {
+    test('calculates correct fee for whole numbers', () => {
+      expect(getFeeAmount(1000000, 50)).toBe(5000);
+      expect(getFeeAmount(1000000, 25)).toBe(2500);
+    });
+
+    test('handles small fee basis points', () => {
+      expect(getFeeAmount(1000000, 1)).toBe(100);
+      expect(getFeeAmount(2000000, 1)).toBe(200);
+    });
+
+    test('handles typical fee calculations', () => {
+      expect(getFeeAmount(1500000, 15)).toBe(2250);
+      expect(getFeeAmount(2000000, 25)).toBe(5000);
+    });
+
+    test('properly drops decimals', () => {
+      expect(getFeeAmount(1008584578, 15)).toBe(1512876);
+      expect(getFeeAmount(1234567, 15)).toBe(1851); // 1234567 * 15 / 10000 = 1851.8505 -> 1851
+      expect(getFeeAmount(9876543, 23)).toBe(22716); // 9876543 * 23 / 10000 = 22716.0489 -> 22716
+    });
+  });
 });