fix(lp fee): correct the computation of the realized LP fee

Author: moodysalem

src/utils/prices.test.ts

@@ -0,0 +1,40 @@
+import { ChainId, JSBI, Pair, Route, Token, TokenAmount, Trade, TradeType } from '@uniswap/sdk'
+import { computeTradePriceBreakdown } from './prices'
+
+describe('prices', () => {
+  const token1 = new Token(ChainId.MAINNET, '0x0000000000000000000000000000000000000001', 18)
+  const token2 = new Token(ChainId.MAINNET, '0x0000000000000000000000000000000000000002', 18)
+  const token3 = new Token(ChainId.MAINNET, '0x0000000000000000000000000000000000000003', 18)
+
+  const pair12 = new Pair(new TokenAmount(token1, JSBI.BigInt(10000)), new TokenAmount(token2, JSBI.BigInt(20000)))
+  const pair23 = new Pair(new TokenAmount(token2, JSBI.BigInt(20000)), new TokenAmount(token3, JSBI.BigInt(30000)))
+
+  describe('computeTradePriceBreakdown', () => {
+    it('returns undefined for undefined', () => {
+      expect(computeTradePriceBreakdown(undefined)).toEqual({
+        priceImpactWithoutFee: undefined,
+        realizedLPFee: undefined
+      })
+    })
+
+    it('correct realized lp fee for single hop', () => {
+      expect(
+        computeTradePriceBreakdown(
+          new Trade(new Route([pair12], token1), new TokenAmount(token1, JSBI.BigInt(1000)), TradeType.EXACT_INPUT)
+        ).realizedLPFee
+      ).toEqual(new TokenAmount(token1, JSBI.BigInt(3)))
+    })
+
+    it('correct realized lp fee for double hop', () => {
+      expect(
+        computeTradePriceBreakdown(
+          new Trade(
+            new Route([pair12, pair23], token1),
+            new TokenAmount(token1, JSBI.BigInt(1000)),
+            TradeType.EXACT_INPUT
+          )
+        ).realizedLPFee
+      ).toEqual(new TokenAmount(token1, JSBI.BigInt(5)))
+    })
+  })
+})

src/utils/prices.ts

@@ -18,7 +18,7 @@ export function computeTradePriceBreakdown(
     : ONE_HUNDRED_PERCENT.subtract(
         trade.route.pairs.reduce<Fraction>(
           (currentFee: Fraction): Fraction => currentFee.multiply(INPUT_FRACTION_AFTER_FEE),
-          INPUT_FRACTION_AFTER_FEE
+          ONE_HUNDRED_PERCENT
         )
       )