Build across 0xNothing.

npm install viem

import { createPublicClient, defineChain, http } from "viem";

export const litvmTestnet = defineChain({
  id: 4441,
  name: "LitVM LiteForge",
  nativeCurrency: { name: "zkLTC", symbol: "zkLTC", decimals: 18 },
  rpcUrls: {
    default: { http: ["https://liteforge.rpc.caldera.xyz/infra-partner-http"] },
  },
  blockExplorers: {
    default: { name: "LiteForge Explorer", url: "https://liteforge.explorer.caldera.xyz" },
  },
});

export const publicClient = createPublicClient({
  chain: litvmTestnet,
  transport: http(),
});

export const contracts = {
  pixel: "0x33A32b9b2BEe864f9e42BFa39cA7BDC72f655988",
  pixelMarketplace: "0x13337cadA78d53C90E3c0EcE44C17c467C1a86F4",
  nusd: "0x5317e21aba902c6c7087a84457bc02fFe99604d1",
  pump: "0x4a0eaf310e3659aa9b360fd44e90208c31dbe0e2",
  fiRouter: "0x7b17035A4aC3A32f2A18a16e2F43A5f8C66275b0",
  fiFactory: "0xe33fE815c2e12DC83b69397CeD12b09849Fa9C0D",
  wzkLtc: "0xE93d4373CE1eDA3df6c3Ab7ed3ab07A07aA5939F",
  nbtc: "0x0CBc1e968db77885DCa648D7bD0e80fCc94cB9Cf",
  neth: "0xD504bB9430d94ccFF87e12e94fd6C0074D0E8aCb",
} as const;

import { parseAbi, type Address, type PublicClient, type WalletClient } from "viem";

const routerAbi = parseAbi([
  "function getAmountsOut(uint256 amountIn, address[] path) view returns (uint256[] amounts)",
  "function swapExactTokensForTokens(uint256 amountIn, uint256 amountOutMin, address[] path, address to, uint256 deadline) returns (uint256[] amounts)",
]);

const erc20Abi = parseAbi([
  "function allowance(address owner, address spender) view returns (uint256)",
  "function approve(address spender, uint256 amount) returns (bool)",
]);

type Quote = { path: Address[]; amountOut: bigint };

export async function swapErc20(params: {
  publicClient: PublicClient;
  walletClient: WalletClient;
  account: Address;
  tokenIn: Address;
  tokenOut: Address;
  amountIn: bigint;
  slippageBps?: bigint;
}) {
  const {
    publicClient,
    walletClient,
    account,
    tokenIn,
    tokenOut,
    amountIn,
    slippageBps = 50n,
  } = params;

  if (await walletClient.getChainId() !== 4441) {
    throw new Error("Switch wallet to LitVM chain 4441");
  }
  if (amountIn <= 0n || slippageBps < 0n || slippageBps >= 10_000n) {
    throw new Error("Invalid swap parameters");
  }

  const paths: Address[][] = [[tokenIn, tokenOut]];
  const usesNusd =
    tokenIn.toLowerCase() === contracts.nusd.toLowerCase() ||
    tokenOut.toLowerCase() === contracts.nusd.toLowerCase();
  if (!usesNusd) paths.push([tokenIn, contracts.nusd, tokenOut]);

  const quotes = await Promise.all(paths.map(async (path): Promise<Quote | undefined> => {
    try {
      const amounts = await publicClient.readContract({
        address: contracts.fiRouter,
        abi: routerAbi,
        functionName: "getAmountsOut",
        args: [amountIn, path],
      });
      return { path, amountOut: amounts.at(-1)! };
    } catch {
      return undefined;
    }
  }));

  const best = quotes
    .filter((quote): quote is Quote => Boolean(quote))
    .sort((a, b) => a.amountOut === b.amountOut ? 0 : a.amountOut > b.amountOut ? -1 : 1)[0];
  if (!best) throw new Error("No executable 0xFi route");

  const amountOutMin = best.amountOut * (10_000n - slippageBps) / 10_000n;
  const allowance = await publicClient.readContract({
    address: tokenIn,
    abi: erc20Abi,
    functionName: "allowance",
    args: [account, contracts.fiRouter],
  });

  if (allowance < amountIn) {
    const approval = await publicClient.simulateContract({
      account,
      address: tokenIn,
      abi: erc20Abi,
      functionName: "approve",
      args: [contracts.fiRouter, amountIn],
    });
    const approvalHash = await walletClient.writeContract(approval.request);
    const approvalReceipt = await publicClient.waitForTransactionReceipt({ hash: approvalHash });
    if (approvalReceipt.status !== "success") throw new Error("Approval reverted");
  }

  const deadline = BigInt(Math.floor(Date.now() / 1_000) + 20 * 60);
  const simulation = await publicClient.simulateContract({
    account,
    address: contracts.fiRouter,
    abi: routerAbi,
    functionName: "swapExactTokensForTokens",
    args: [amountIn, amountOutMin, best.path, account, deadline],
  });
  const hash = await walletClient.writeContract(simulation.request);
  const receipt = await publicClient.waitForTransactionReceipt({ hash });
  if (receipt.status !== "success") throw new Error("0xFi swap reverted");

  return { hash, receipt, path: best.path, quotedOut: best.amountOut, amountOutMin };
}

const nusdAbi = parseAbi([
  "function quoteMint(uint256 collateralWei) view returns (uint256 amountNusd)",
  "function mintAtOracle(uint256 minNusdOut, address recipient) payable returns (uint256 amountNusd)",
  "function quoteRedeem(uint256 amountNusd) view returns (uint256 collateralOutWei)",
  "function redeemAtOracle(uint256 amountNusd, uint256 minCollateralOutWei, address recipient) returns (uint256 collateralOutWei)",
]);

const minimumOut = (quote: bigint, slippageBps = 50n) =>
  quote * (10_000n - slippageBps) / 10_000n;

// Native zkLTC to NUSD
const quotedNusd = await publicClient.readContract({
  address: contracts.nusd,
  abi: nusdAbi,
  functionName: "quoteMint",
  args: [zkLtcIn],
});
const mint = await publicClient.simulateContract({
  account,
  address: contracts.nusd,
  abi: nusdAbi,
  functionName: "mintAtOracle",
  args: [minimumOut(quotedNusd), account],
  value: zkLtcIn,
});

// NUSD to native zkLTC. No ERC-20 approval is required.
const quotedZkLtc = await publicClient.readContract({
  address: contracts.nusd,
  abi: nusdAbi,
  functionName: "quoteRedeem",
  args: [nusdIn],
});
const redeem = await publicClient.simulateContract({
  account,
  address: contracts.nusd,
  abi: nusdAbi,
  functionName: "redeemAtOracle",
  args: [nusdIn, minimumOut(quotedZkLtc), account],
});

Build a complete 0xFi swap integration for an existing Next.js TypeScript app.

Target network
- Network: LitVM LiteForge Testnet
- Chain ID: 4441
- Native asset: zkLTC, 18 decimals
- RPC: https://liteforge.rpc.caldera.xyz/infra-partner-http
- Explorer: https://liteforge.explorer.caldera.xyz

Pinned contracts
- NUSD / OracleNUSD: 0x5317e21aba902c6c7087a84457bc02fFe99604d1
- WzkLTC: 0xE93d4373CE1eDA3df6c3Ab7ed3ab07A07aA5939F
- 0xFi Factory: 0xe33fE815c2e12DC83b69397CeD12b09849Fa9C0D
- 0xFi Router: 0x7b17035A4aC3A32f2A18a16e2F43A5f8C66275b0

Implementation requirements
- Use viem and the wallet layer already installed by the app. Do not add a server-side signer.
- Create typed chain config, minimal ABIs, quote service, transaction service, React hook, and accessible swap UI.
- Accept bigint amounts internally. Read token decimals, balance, and allowance over RPC.
- For ERC-20 routes, probe [tokenIn, tokenOut] and [tokenIn, NUSD, tokenOut]. Choose the successful quote with the largest final output.
- Use getAmountsOut for executable AMM quotes. It already includes LP fees, protocol fees, route surcharge, and price impact.
- Use swapExactTokensForTokens for ERC-20 pairs.
- Use swapExactNativeForTokens when input is native zkLTC. The path must start with WzkLTC and the transaction must send value.
- Use swapExactTokensForNative when output is native zkLTC. The path must end with WzkLTC.
- For the exact zkLTC/NUSD route, use quoteMint plus mintAtOracle, or quoteRedeem plus redeemAtOracle. Do not route this exact pair through the AMM.
- Request exact ERC-20 approval only when allowance is insufficient. Wait for the approval receipt before the swap.
- Apply user-controlled slippage in basis points. Never use zero minimum output.
- Use a short deadline, simulate every write, wait for the final receipt, and reject reverted receipts.
- Verify chain ID 4441 before every write. Keep enough zkLTC for gas.
- Show route, fee summary, quoted output, minimum received, price impact, recipient, pending state, transaction hash, and actionable errors.
- Requote after token, amount, account, chain, or block-relevant state changes.
- Use Goldsky only for history and charts. Never use indexed reserves for an executable quote.
- Reject unsupported fee-on-transfer tokens and repeated or zero-address paths.

Required delivery
- Return complete files with no placeholders or omitted sections.
- Include loading, empty, wrong-network, approval, signing, confirming, success, and error states.
- Include unit tests for route selection, slippage math, native path rules, allowance branching, and failed simulation.
- Mark the integration as testnet-only. Do not describe it as audited or mainnet-ready.

const INDEXERS = {
  pixelMarketplace: "https://api.goldsky.com/api/public/project_cmr0mev6548fr01xtd92rc135/subgraphs/marketplace/1.0.1/gn",
  pump: "https://api.goldsky.com/api/public/project_cmqmpust19i8v01t595z8hpq4/subgraphs/zeroxpump-testnet/staging/gn",
  fi: "https://api.goldsky.com/api/public/project_cms8vgtcn6a6z01r5fo87d6im/subgraphs/zeroxfi-testnet/staging/gn",
} as const;

export async function queryIndexer<T>(endpoint: string, query: string, variables = {}) {
  const response = await fetch(endpoint, {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify({ query, variables }),
  });
  if (!response.ok) throw new Error("Indexer HTTP " + response.status);
  const payload = await response.json();
  if (payload.errors?.length) throw new Error(payload.errors[0].message);
  return payload.data as T;
}