feat: calculate amountOutMin to minimize slippage

app/src/store/cart.ts

@@ -20,6 +20,7 @@ import {
 import {
   BigNumber,
   BigNumberish,
+  BytesLike,
   Contract,
   ContractTransaction,
   hexDataSlice,
@@ -193,7 +194,7 @@ export default function useCartStore() {
    */
   async function checkout() {
     const { signer, userAddress } = useWalletStore();
-    const { swaps, donations, deadline } = cartDonationInputs.value;
+    const { swaps, donations, deadline } = await getCartDonationInputs();
     const manager = new Contract(GRANT_ROUND_MANAGER_ADDRESS, GRANT_ROUND_MANAGER_ABI, signer.value);
     const getInputToken = (swap: SwapSummary) => getAddress(hexDataSlice(swap.path, 0, 20));
 
@@ -224,42 +225,20 @@ export default function useCartStore() {
     clearCart();
   }
 
-  // --- Getters ---
-  /**
-   * @notice Returns true if the provided grantId is in the cart, false otherwise
-   * @param grantId Grant ID to check
-   */
-  function isInCart(grantId: BigNumberish): boolean {
-    const grantIds = lsCart.value.map((item) => item.grantId);
-    return grantIds.includes(toString(grantId));
-  }
-
-  /**
-   * @notice Convert a cart into an array of objects summarizing the cart info, with human-readable values
-   * @returns Object where keys are token addresses, values are total amount of that token in cart
-   */
-  const cartSummary = computed((): Record<keyof typeof SUPPORTED_TOKENS_MAPPING, number> => {
-    const output: Record<keyof typeof SUPPORTED_TOKENS_MAPPING, number> = {};
-    for (const item of cart.value) {
-      const tokenAddress = item.contributionToken.address;
-      if (tokenAddress in output) output[tokenAddress] += item.contributionAmount;
-      else output[tokenAddress] = item.contributionAmount;
-    }
-    return output;
-  });
-
   /**
    * @notice Takes an array of cart items and returns inputs needed for the GrantRoundManager.donate() method
    */
-  const cartDonationInputs = computed((): { swaps: SwapSummary[]; donations: Donation[]; deadline: number } => {
+  async function getCartDonationInputs(): Promise<{ swaps: SwapSummary[]; donations: Donation[]; deadline: number }> {
     // Get the swaps array
-    const swaps: SwapSummary[] = Object.keys(cartSummary.value).map((tokenAddress) => {
+    const swapPromises = Object.keys(cartSummary.value).map(async (tokenAddress) => {
       const decimals = SUPPORTED_TOKENS_MAPPING[tokenAddress].decimals;
       const amountIn = parseUnits(String(cartSummary.value[tokenAddress]), decimals);
-      const amountOutMin = '1'; // TODO improve this
       const path = SWAP_PATHS[<keyof typeof SWAP_PATHS>tokenAddress];
+      // Use Uniswap's Quoter.sol to get amountOutMin, unless the path indicates so swap is required
+      const amountOutMin = path.length === 42 ? amountIn : await quoteExactInput(path, amountIn);
       return { amountIn, amountOutMin, path };
     });
+    const swaps = <SwapSummary[]>await Promise.all(swapPromises);
 
     // Get the donations array
     const donations: Donation[] = cart.value.map((item) => {
@@ -284,6 +263,30 @@ export default function useCartStore() {
     const now = new Date().getTime();
     const nowPlus20Minutes = new Date(now + 20 * 60 * 1000).getTime();
     return { swaps, donations: fixDonationRoundingErrors(donations), deadline: Math.floor(nowPlus20Minutes / 1000) };
+  }
+
+  // --- Getters ---
+  /**
+   * @notice Returns true if the provided grantId is in the cart, false otherwise
+   * @param grantId Grant ID to check
+   */
+  function isInCart(grantId: BigNumberish): boolean {
+    const grantIds = lsCart.value.map((item) => item.grantId);
+    return grantIds.includes(toString(grantId));
+  }
+
+  /**
+   * @notice Convert a cart into an array of objects summarizing the cart info, with human-readable values
+   * @returns Object where keys are token addresses, values are total amount of that token in cart
+   */
+  const cartSummary = computed((): Record<keyof typeof SUPPORTED_TOKENS_MAPPING, number> => {
+    const output: Record<keyof typeof SUPPORTED_TOKENS_MAPPING, number> = {};
+    for (const item of cart.value) {
+      const tokenAddress = item.contributionToken.address;
+      if (tokenAddress in output) output[tokenAddress] += item.contributionAmount;
+      else output[tokenAddress] = item.contributionAmount;
+    }
+    return output;
   });
 
   /**
@@ -297,14 +300,13 @@ export default function useCartStore() {
     return summary.slice(0, -3); // trim the trailing ` + ` from the string
   });
 
+  // Only export additional items as they are needed outside the store
   return {
     // Store
     // WARNING: Be careful -- the `cart` ref is directly exposed so it can be edited by v-model, so just make
     // sure to call `updateCart()` with the appropriate inputs whenever the `cart` ref is modified
     cart,
     // Getters
-    cartDonationInputs,
-    cartSummary,
     cartSummaryString,
     // Mutations
     addToCart,
@@ -317,6 +319,8 @@ export default function useCartStore() {
   };
 }
 
+// --- Pure functions (not reliant on state) ---
+
 /**
  * @notice Takes an array of donation data, and adjusts the ratios so they sum to 1e18 for each set of tokens
  * @dev For each token, we adjust the first item in the cart to force the sum to be 100%. The adjustments will only
@@ -343,3 +347,16 @@ function fixDonationRoundingErrors(donations: Donation[]) {
 
   return donations;
 }
+
+/**
+ * @notice Returns the amountOutMin expected for a given trade assuming 0.5% slippage
+ * @param path Swap path
+ * @param amountIn Swap input amount, as a full integer
+ */
+async function quoteExactInput(path: BytesLike, amountIn: BigNumberish): Promise<BigNumber> {
+  const { provider } = useWalletStore();
+  const abi = ['function quoteExactInput(bytes memory path, uint256 amountIn) external view returns (uint256 amountOut)']; // prettier-ignore
+  const quoter = new Contract('0xb27308f9F90D607463bb33eA1BeBb41C27CE5AB6', abi, provider.value);
+  const amountOut = await quoter.quoteExactInput(path, amountIn);
+  return amountOut.mul(995).div(1000); // multiplying by 995/1000 is equivalent to 0.5% slippage
+}

app/src/utils/ethers.ts

@@ -15,13 +15,17 @@
  * Read more at https://github.com/vitejs/vite/issues/731
  */
 
-export type { BigNumberish } from 'ethers';
+// --- Types ---
+export type { BigNumberish } from '@ethersproject/bignumber';
+export type { ContractTransaction } from '@ethersproject/contracts';
+export type { BytesLike } from '@ethersproject/bytes';
+export type { Network } from '@ethersproject/networks';
+
+// --- Methods and classes ---
 export { getAddress, isAddress } from '@ethersproject/address';
 export { BigNumber } from '@ethersproject/bignumber';
 export { hexDataSlice } from '@ethersproject/bytes';
 export { Contract } from '@ethersproject/contracts';
-export type { ContractTransaction } from '@ethersproject/contracts';
-export type { Network } from '@ethersproject/networks';
 export { JsonRpcProvider, JsonRpcSigner, Web3Provider } from '@ethersproject/providers';
 export { commify, formatUnits, parseUnits } from '@ethersproject/units';
 export { MaxUint256 } from '@ethersproject/constants';