From 2f7a765b8b84eef978ab06940455523ce5293a20 Mon Sep 17 00:00:00 2001
From: jsy1218 <91580504+jsy1218@users.noreply.github.com>
Date: Thu, 7 Sep 2023 15:24:26 -0700
Subject: [PATCH] Add fee-on-transfer token fees fields (#83)

* Token construct supports FOT fees

* Fix code style issues with Prettier

* delete .idea folders

---------

Co-authored-by: Siyu Jiang <siyu.jiang@CORN-Siyu-217.local>
Co-authored-by: Lint Action <lint-action@samuelmeuli.com>
---
 src/entities/token.test.ts |  9 +++++++++
 src/entities/token.ts      | 22 +++++++++++++++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/entities/token.test.ts b/src/entities/token.test.ts
index e3c36f1d..58a8e196 100644
--- a/src/entities/token.test.ts
+++ b/src/entities/token.test.ts
@@ -1,4 +1,5 @@
 import { Token } from './token'
+import { BigNumber } from '@ethersproject/bignumber'
 
 describe('Token', () => {
   const ADDRESS_ONE = '0x0000000000000000000000000000000000000001'
@@ -20,6 +21,14 @@ describe('Token', () => {
     it('fails with non-integer decimals', () => {
       expect(() => new Token(3, ADDRESS_ONE, 1.5).address).toThrow('DECIMALS')
     })
+    it('fails with negative FOT fees', () => {
+      expect(
+        () => new Token(3, ADDRESS_ONE, 18, undefined, undefined, undefined, BigNumber.from(-1), undefined)
+      ).toThrow('NON-NEGATIVE FOT FEES')
+      expect(
+        () => new Token(3, ADDRESS_ONE, 18, undefined, undefined, undefined, undefined, BigNumber.from(-1))
+      ).toThrow('NON-NEGATIVE FOT FEES')
+    })
   })
 
   describe('#constructor with bypassChecksum = true', () => {
diff --git a/src/entities/token.ts b/src/entities/token.ts
index 590f0290..3c1d8581 100644
--- a/src/entities/token.ts
+++ b/src/entities/token.ts
@@ -1,3 +1,4 @@
+import { BigNumber } from '@ethersproject/bignumber'
 import invariant from 'tiny-invariant'
 import { checkValidAddress, validateAndParseAddress } from '../utils/validateAndParseAddress'
 import { BaseCurrency } from './baseCurrency'
@@ -15,6 +16,13 @@ export class Token extends BaseCurrency {
    */
   public readonly address: string
 
+  /**
+   * Relevant for fee-on-transfer (FOT) token taxes,
+   * Not every ERC20 token is FOT token, so this field is optional
+   */
+  public readonly buyFeeBps?: BigNumber
+  public readonly sellFeeBps?: BigNumber
+
   /**
    *
    * @param chainId {@link BaseCurrency#chainId}
@@ -23,6 +31,8 @@ export class Token extends BaseCurrency {
    * @param symbol {@link BaseCurrency#symbol}
    * @param name {@link BaseCurrency#name}
    * @param bypassChecksum If true it only checks for length === 42, startsWith 0x and contains only hex characters
+   * @param buyFeeBps Buy fee tax for FOT tokens, in basis points
+   * @param sellFeeBps Sell fee tax for FOT tokens, in basis points
    */
   public constructor(
     chainId: number,
@@ -30,7 +40,9 @@ export class Token extends BaseCurrency {
     decimals: number,
     symbol?: string,
     name?: string,
-    bypassChecksum?: boolean
+    bypassChecksum?: boolean,
+    buyFeeBps?: BigNumber,
+    sellFeeBps?: BigNumber
   ) {
     super(chainId, decimals, symbol, name)
     if (bypassChecksum) {
@@ -38,6 +50,14 @@ export class Token extends BaseCurrency {
     } else {
       this.address = validateAndParseAddress(address)
     }
+    if (buyFeeBps) {
+      invariant(buyFeeBps.gte(BigNumber.from(0)), 'NON-NEGATIVE FOT FEES')
+    }
+    if (sellFeeBps) {
+      invariant(sellFeeBps.gte(BigNumber.from(0)), 'NON-NEGATIVE FOT FEES')
+    }
+    this.buyFeeBps = buyFeeBps
+    this.sellFeeBps = sellFeeBps
   }
 
   /**