From c119561bdb6c4213e93c88ad5e74608ddc3b722d Mon Sep 17 00:00:00 2001
From: Ryan Ghods <ralxzryan@gmail.com>
Date: Tue, 2 Jan 2024 17:35:18 -0800
Subject: [PATCH] fix basis points rounding (#1344)

* fix basis points rounding

* fix

* use bigints

* fix

* improve fn names
---
 src/constants.ts   |  7 ++++---
 src/sdk.ts         | 20 +++++++++-----------
 src/utils/utils.ts | 27 +++++++++++++++++++++++----
 3 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/src/constants.ts b/src/constants.ts
index ab6055113..ec38ac974 100644
--- a/src/constants.ts
+++ b/src/constants.ts
@@ -1,12 +1,13 @@
-import { ethers } from "ethers";
+import { FixedNumber, ZeroAddress } from "ethers";
 
-export const INVERSE_BASIS_POINT = 10_000; // 100 basis points per 1%
+export const FIXED_NUMBER_100 = FixedNumber.fromValue(100);
+export const INVERSE_BASIS_POINT = 10_000n; // 100 basis points per 1%
 export const MAX_EXPIRATION_MONTHS = 1;
 
 export const API_BASE_MAINNET = "https://api.opensea.io";
 export const API_BASE_TESTNET = "https://testnets-api.opensea.io";
 
-export const DEFAULT_ZONE = ethers.ZeroAddress;
+export const DEFAULT_ZONE = ZeroAddress;
 export const ENGLISH_AUCTION_ZONE_MAINNETS =
   "0x110b2b128a9ed1be5ef3232d8e4e41640df5c2cd";
 export const ENGLISH_AUCTION_ZONE_TESTNETS =
diff --git a/src/sdk.ts b/src/sdk.ts
index e80d2bc4a..7b235ae77 100644
--- a/src/sdk.ts
+++ b/src/sdk.ts
@@ -54,10 +54,11 @@ import {
   hasErrorCode,
   getAssetItemType,
   getAddressAfterRemappingSharedStorefrontAddressToLazyMintAdapterAddress,
-  feesToBasisPoints,
   requireValidProtocol,
   getWETHAddress,
   isTestChain,
+  basisPointsForFee,
+  totalBasisPointsForFees,
 } from "./utils/utils";
 
 /**
@@ -244,12 +245,9 @@ export class OpenSeaSDK {
 
   private getAmountWithBasisPointsApplied = (
     amount: bigint,
-    basisPoints: number,
+    basisPoints: bigint,
   ): string => {
-    return (
-      (amount * BigInt(basisPoints)) /
-      BigInt(INVERSE_BASIS_POINT)
-    ).toString();
+    return ((amount * basisPoints) / INVERSE_BASIS_POINT).toString();
   };
 
   private async getFees({
@@ -266,10 +264,10 @@ export class OpenSeaSDK {
     endAmount?: bigint;
   }): Promise<ConsiderationInputItem[]> {
     const collectionFees = collection.fees;
-    const collectionFeesBasisPoints = feesToBasisPoints(collectionFees);
+    const collectionFeesBasisPoints = totalBasisPointsForFees(collectionFees);
     const sellerBasisPoints = INVERSE_BASIS_POINT - collectionFeesBasisPoints;
 
-    const getConsiderationItem = (basisPoints: number, recipient?: string) => {
+    const getConsiderationItem = (basisPoints: bigint, recipient?: string) => {
       return {
         token: paymentTokenAddress,
         amount: this.getAmountWithBasisPointsApplied(startAmount, basisPoints),
@@ -288,7 +286,7 @@ export class OpenSeaSDK {
     }
     for (const fee of collectionFees) {
       considerationItems.push(
-        getConsiderationItem(fee.fee * 100, fee.recipient),
+        getConsiderationItem(basisPointsForFee(fee), fee.recipient),
       );
     }
     return considerationItems;
@@ -1106,10 +1104,10 @@ export class OpenSeaSDK {
 
     // Validation
     if (startAmount == null || startAmountWei < 0) {
-      throw new Error(`Starting price must be a number >= 0`);
+      throw new Error("Starting price must be a number >= 0");
     }
     if (isEther && orderSide === OrderSide.BID) {
-      throw new Error(`Offers must use wrapped ETH or an ERC-20 token.`);
+      throw new Error("Offers must use wrapped ETH or an ERC-20 token.");
     }
     if (priceDiffWei < 0) {
       throw new Error(
diff --git a/src/utils/utils.ts b/src/utils/utils.ts
index 42a5daedf..336844655 100644
--- a/src/utils/utils.ts
+++ b/src/utils/utils.ts
@@ -2,11 +2,12 @@ import {
   CROSS_CHAIN_SEAPORT_V1_5_ADDRESS,
   ItemType,
 } from "@opensea/seaport-js/lib/constants";
-import { ethers } from "ethers";
+import { ethers, FixedNumber } from "ethers";
 import {
   MAX_EXPIRATION_MONTHS,
   SHARED_STOREFRONT_LAZY_MINT_ADAPTER_CROSS_CHAIN_ADDRESS,
   SHARED_STOREFRONT_ADDRESSES,
+  FIXED_NUMBER_100,
 } from "../constants";
 import {
   Chain,
@@ -224,9 +225,27 @@ export const getAddressAfterRemappingSharedStorefrontAddressToLazyMintAdapterAdd
  * @param fees The fees to sum up
  * @returns sum of basis points
  */
-export const feesToBasisPoints = (fees: Fee[]): number => {
-  const feeBasisPoints = fees.map((fee) => fee.fee * 100);
-  return feeBasisPoints.reduce((sum, basisPoints) => basisPoints + sum, 0);
+export const totalBasisPointsForFees = (fees: Fee[]): bigint => {
+  const feeBasisPoints = fees.map((fee) => basisPointsForFee(fee));
+  const totalBasisPoints = feeBasisPoints.reduce(
+    (sum, basisPoints) => basisPoints + sum,
+    0n,
+  );
+  return totalBasisPoints;
+};
+
+/**
+ * Converts a fee to its basis points representation.
+ * @param fee The fee to convert
+ * @returns the basis points
+ */
+export const basisPointsForFee = (fee: Fee): bigint => {
+  return BigInt(
+    FixedNumber.fromString(fee.fee.toString())
+      .mul(FIXED_NUMBER_100)
+      .toFormat(0) // format to 0 decimal places to convert to bigint
+      .toString(),
+  );
 };
 
 /**