fix(twap): allow creating orders with 100% slippage (cowprotocol#3897)

apps/cowswap-frontend/src/modules/twap/state/twapOrderAtom.ts

@@ -1,5 +1,6 @@
 import { atom } from 'jotai'
 
+import { FractionUtils } from '@cowprotocol/common-utils'
 import { walletInfoAtom } from '@cowprotocol/wallet'
 import { CurrencyAmount, Token } from '@uniswap/sdk-core'
 
@@ -38,7 +39,9 @@ export const twapSlippageAdjustedBuyAmount = atom<CurrencyAmount<Token> | null>(
   const slippage = get(twapOrderSlippageAtom)
 
   const slippageAmount = outputCurrencyAmount.multiply(slippage)
-  return outputCurrencyAmount.subtract(slippageAmount) as CurrencyAmount<Token>
+  const buyAmount = outputCurrencyAmount.subtract(slippageAmount) as CurrencyAmount<Token>
+
+  return FractionUtils.amountToAtLeastOneWei(buyAmount)
 })
 
 export const twapOrderAtom = atom<TWAPOrder | null>((get) => {

apps/cowswap-frontend/src/modules/twap/utils/twapOrderToStruct.ts

@@ -1,17 +1,18 @@
 import { NATIVE_CURRENCY_ADDRESS } from '@cowprotocol/common-const'
-import { getIsNativeToken } from '@cowprotocol/common-utils'
+import { FractionUtils, getIsNativeToken } from '@cowprotocol/common-utils'
 
 import { TWAPOrder, TWAPOrderStruct } from '../types'
 
 export function twapOrderToStruct(order: TWAPOrder): TWAPOrderStruct {
   const buyToken = order.buyAmount.currency
+  const minPartLimit = FractionUtils.amountToAtLeastOneWei(order.buyAmount.divide(order.numOfParts))
 
   return {
     sellToken: order.sellAmount.currency.address,
     buyToken: getIsNativeToken(buyToken) ? NATIVE_CURRENCY_ADDRESS : buyToken.address,
     receiver: order.receiver,
     partSellAmount: order.sellAmount.divide(order.numOfParts).quotient.toString(),
-    minPartLimit: order.buyAmount.divide(order.numOfParts).quotient.toString(),
+    minPartLimit: minPartLimit.quotient.toString(),
     t0: order.startTime,
     n: order.numOfParts,
     t: order.timeInterval,

libs/common-utils/src/fractionUtils.ts

@@ -143,4 +143,13 @@ export class FractionUtils {
 
     return new Fraction(JSBI.BigInt(numerator), JSBI.BigInt(denominator))
   }
+
+  /**
+   * When an amount equals zero, return 1 wei, otherwise return amount
+   *
+   * @param amount
+   */
+  static amountToAtLeastOneWei(amount: CurrencyAmount<Token>): CurrencyAmount<Token> {
+    return JSBI.EQ(amount.quotient, 0) ? CurrencyAmount.fromRawAmount(amount.currency, 1) : amount
+  }
 }