Ethereum para Desenvolvedores Web: Smart Contracts Sem o Hype

interface Transaction {
  // Quem recebe esta transação — um endereço EOA ou de contrato
  to: string; // Endereço hex de 20 bytes, ou null para deploy de contrato
  // Quanto ETH enviar (em wei)
  value: bigint; // Pode ser 0n para chamadas puras de contrato
  // Dados de chamada de função codificados, ou vazio para transferências simples de ETH
  data: string; // Bytes codificados em hex, "0x" para transferências simples
  // Contador sequencial, previne ataques de replay
  nonce: number; // Deve ser exatamente igual ao nonce atual do remetente
  // Limite de gas — máximo de gas que esta tx pode consumir
  gasLimit: bigint;
  // Parâmetros de taxa EIP-1559
  maxFeePerGas: bigint;
  maxPriorityFeePerGas: bigint;
  // Identificador de chain (1 = mainnet, 11155111 = Sepolia, 137 = Polygon)
  chainId: number;
}

import { ethers } from "ethers";
 
const provider = new ethers.JsonRpcProvider("https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY");
const wallet = new ethers.Wallet("0xYOUR_PRIVATE_KEY", provider);
 
const tx = await wallet.sendTransaction({
  to: "0xRecipientAddress...",
  value: ethers.parseEther("0.1"), // Converte "0.1" para wei (100000000000000000n)
});
 
console.log("Tx hash:", tx.hash);
 
// Esperar pela inclusão em um bloco
const receipt = await tx.wait();
console.log("Block number:", receipt.blockNumber);
console.log("Gas used:", receipt.gasUsed.toString());
console.log("Status:", receipt.status); // 1 = sucesso, 0 = revert

import { createWalletClient, http, parseEther } from "viem";
import { mainnet } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";
 
const account = privateKeyToAccount("0xYOUR_PRIVATE_KEY");
 
const client = createWalletClient({
  account,
  chain: mainnet,
  transport: http("https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY"),
});
 
const hash = await client.sendTransaction({
  to: "0xRecipientAddress...",
  value: parseEther("0.1"),
});
 
console.log("Tx hash:", hash);

const ERC20_ABI = [
  // Funções somente leitura (view/pure — sem custo de gas quando chamadas externamente)
  "function name() view returns (string)",
  "function symbol() view returns (string)",
  "function decimals() view returns (uint8)",
  "function totalSupply() view returns (uint256)",
  "function balanceOf(address owner) view returns (uint256)",
  "function allowance(address owner, address spender) view returns (uint256)",
 
  // Funções que mudam estado (requerem transação, custam gas)
  "function transfer(address to, uint256 amount) returns (bool)",
  "function approve(address spender, uint256 amount) returns (bool)",
  "function transferFrom(address from, address to, uint256 amount) returns (bool)",
 
  // Eventos (emitidos durante execução, armazenados em logs de transação)
  "event Transfer(address indexed from, address indexed to, uint256 value)",
  "event Approval(address indexed owner, address indexed spender, uint256 value)",
] as const;

import { ethers } from "ethers";
 
const iface = new ethers.Interface(ERC20_ABI);
 
// Codificar uma chamada de função
const calldata = iface.encodeFunctionData("transfer", ["0xBobAddress...", 1000000n]);
console.log(calldata);
// 0xa9059cbb000000000000000000000000bob...000000000000000000000000000f4240
 
// Decodificar calldata de volta para nome da função e args
const decoded = iface.parseTransaction({ data: calldata });
console.log(decoded.name); // "transfer"
console.log(decoded.args[0]); // "0xBobAddress..."
console.log(decoded.args[1]); // 1000000n (BigInt)
 
// Decodificar dados de retorno de uma função
const returnData = "0x0000000000000000000000000000000000000000000000000000000000000001";
const result = iface.decodeFunctionResult("transfer", returnData);
console.log(result[0]); // true

// Lendo o slot de armazenamento 0 de um contrato
const slot0 = await provider.getStorage("0xContractAddress...", 0);
console.log(slot0); // Valor hex bruto de 32 bytes

// Escutando eventos Transfer em tempo real com ethers.js
const contract = new ethers.Contract(tokenAddress, ERC20_ABI, provider);
 
contract.on("Transfer", (from, to, value, event) => {
  console.log(`${from} -> ${to}: ${ethers.formatUnits(value, 18)} tokens`);
  console.log("Block:", event.log.blockNumber);
  console.log("Tx hash:", event.log.transactionHash);
});
 
// Consultando eventos históricos
const filter = contract.filters.Transfer(null, "0xMyAddress..."); // from=qualquer, to=específico
const events = await contract.queryFilter(filter, 19000000, 19100000); // intervalo de blocos
 
for (const event of events) {
  console.log("From:", event.args.from);
  console.log("Value:", event.args.value.toString());
}

import { createPublicClient, http, parseAbiItem } from "viem";
import { mainnet } from "viem/chains";
 
const client = createPublicClient({
  chain: mainnet,
  transport: http("https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY"),
});
 
// Logs históricos
const logs = await client.getLogs({
  address: "0xTokenAddress...",
  event: parseAbiItem("event Transfer(address indexed from, address indexed to, uint256 value)"),
  args: {
    to: "0xMyAddress...",
  },
  fromBlock: 19000000n,
  toBlock: 19100000n,
});
 
for (const log of logs) {
  console.log("From:", log.args.from);
  console.log("To:", log.args.to);
  console.log("Value:", log.args.value);
}
 
// Observação em tempo real
const unwatch = client.watchEvent({
  address: "0xTokenAddress...",
  event: parseAbiItem("event Transfer(address indexed from, address indexed to, uint256 value)"),
  onLogs: (logs) => {
    for (const log of logs) {
      console.log(`Transfer: ${log.args.from} -> ${log.args.to}`);
    }
  },
});
 
// Chame unwatch() para parar de escutar

// Isso é o que sua biblioteca faz por baixo
const response = await fetch("https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    jsonrpc: "2.0",
    id: 1,
    method: "eth_call",
    params: [
      {
        to: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48", // USDC
        data: "0x70a08231000000000000000000000000d8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
        // balanceOf(vitalik.eth)
      },
      "latest",
    ],
  }),
});
 
const result = await response.json();
console.log(result);
// { jsonrpc: "2.0", id: 1, result: "0x000000000000000000000000000000000000000000000000000000174876e800" }

import { ethers } from "ethers";
 
// ethers.js v6 fallback provider
const provider = new ethers.FallbackProvider([
  {
    provider: new ethers.JsonRpcProvider("https://eth-mainnet.g.alchemy.com/v2/KEY1"),
    priority: 1,
    stallTimeout: 2000,
    weight: 2,
  },
  {
    provider: new ethers.JsonRpcProvider("https://mainnet.infura.io/v3/KEY2"),
    priority: 2,
    stallTimeout: 2000,
    weight: 1,
  },
]);

import { ethers } from "ethers";
 
const provider = new ethers.JsonRpcProvider("https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY");
 
// Interface ERC-20 — apenas as funções de leitura
const erc20 = new ethers.Contract(
  "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48", // USDC
  [
    "function name() view returns (string)",
    "function symbol() view returns (string)",
    "function decimals() view returns (uint8)",
    "function totalSupply() view returns (uint256)",
    "function balanceOf(address) view returns (uint256)",
  ],
  provider, // Nota: provider, não signer. Somente leitura.
);
 
const [name, symbol, decimals, totalSupply] = await Promise.all([
  erc20.name(),
  erc20.symbol(),
  erc20.decimals(),
  erc20.totalSupply(),
]);
 
console.log(`${name} (${symbol})`); // "USD Coin (USDC)"
console.log(`Decimals: ${decimals}`); // 6 (NÃO 18!)
console.log(`Total supply: ${ethers.formatUnits(totalSupply, decimals)}`);
 
// Verificar o saldo de um endereço específico
const balance = await erc20.balanceOf("0xSomeAddress...");
console.log(`Balance: ${ethers.formatUnits(balance, decimals)} USDC`);

import { ethers } from "ethers";
 
// Conectar a um nó
const provider = new ethers.JsonRpcProvider("https://...");
 
// Consultas básicas
const blockNumber = await provider.getBlockNumber();
const balance = await provider.getBalance("0xAddress...");
const block = await provider.getBlock(blockNumber);
const txCount = await provider.getTransactionCount("0xAddress...");

// De uma chave privada (lado servidor, scripts)
const wallet = new ethers.Wallet("0xPrivateKey...", provider);
 
// De uma carteira de navegador (lado cliente)
const browserProvider = new ethers.BrowserProvider(window.ethereum);
const signer = await browserProvider.getSigner();
 
// Obter o endereço
const address = await signer.getAddress();

const usdc = new ethers.Contract(USDC_ADDRESS, ERC20_ABI, provider);
 
// Ler (gratuito, retorna valor diretamente)
const balance = await usdc.balanceOf("0xSomeAddress...");
// balance é um bigint: 1000000000n (1000 USDC com 6 decimais)
 
// Para escrever, conecte com um signer
const usdcWithSigner = usdc.connect(signer);
 
// Escrever (custa gas, retorna TransactionResponse)
const tx = await usdcWithSigner.transfer("0xRecipient...", 1000000n);
const receipt = await tx.wait(); // Esperar pela inclusão no bloco
 
if (receipt.status === 0) {
  throw new Error("Transaction reverted");
}

// Sem TypeChain — sem verificação de tipos
const balance = await contract.balanceOf("0x...");
// balance é 'any'. Sem autocomplete. Fácil de usar errado.
 
// Com TypeChain — type safety completo
import { USDC__factory } from "./typechain";
 
const usdc = USDC__factory.connect(USDC_ADDRESS, provider);
const balance = await usdc.balanceOf("0x...");
// balance é BigNumber. Autocomplete funciona. Erros de tipo capturados em compile time.

// WebSocket para eventos em tempo real
const wsProvider = new ethers.WebSocketProvider("wss://eth-mainnet.g.alchemy.com/v2/YOUR_KEY");
 
const contract = new ethers.Contract(USDC_ADDRESS, ERC20_ABI, wsProvider);
 
// Escutar todos os eventos Transfer
contract.on("Transfer", (from, to, value, event) => {
  console.log(`Transfer: ${from} -> ${to}`);
  console.log(`Amount: ${ethers.formatUnits(value, 6)} USDC`);
});
 
// Escutar transferências PARA um endereço específico
const filter = contract.filters.Transfer(null, "0xMyAddress...");
contract.on(filter, (from, to, value) => {
  console.log(`Incoming transfer: ${ethers.formatUnits(value, 6)} USDC from ${from}`);
});
 
// Limpar quando terminar
contract.removeAllListeners();

// wagmi.config.ts
import { createConfig, http } from "wagmi";
import { mainnet, sepolia } from "wagmi/chains";
import { injected, walletConnect } from "wagmi/connectors";
 
export const config = createConfig({
  chains: [mainnet, sepolia],
  connectors: [injected(), walletConnect({ projectId: "YOUR_WALLETCONNECT_PROJECT_ID" })],
  transports: {
    [mainnet.id]: http("https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY"),
    [sepolia.id]: http("https://eth-sepolia.g.alchemy.com/v2/YOUR_KEY"),
  },
});

// app/providers.tsx
"use client";
 
import { WagmiProvider } from "wagmi";
import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
import { config } from "./wagmi.config";
 
const queryClient = new QueryClient();
 
export function Providers({ children }: { children: React.ReactNode }) {
  return (
    <WagmiProvider config={config}>
      <QueryClientProvider client={queryClient}>
        {children}
      </QueryClientProvider>
    </WagmiProvider>
  );
}

"use client";
 
import { useReadContract } from "wagmi";
import { formatUnits } from "viem";
 
const ERC20_ABI = [
  {
    name: "balanceOf",
    type: "function",
    stateMutability: "view",
    inputs: [{ name: "owner", type: "address" }],
    outputs: [{ name: "balance", type: "uint256" }],
  },
] as const;
 
function TokenBalance({ address }: { address: `0x${string}` }) {
  const { data: balance, isLoading, error } = useReadContract({
    address: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48", // USDC
    abi: ERC20_ABI,
    functionName: "balanceOf",
    args: [address],
  });
 
  if (isLoading) return <span>Carregando...</span>;
  if (error) return <span>Erro: {error.message}</span>;
 
  // balance é tipado como bigint porque a ABI diz uint256
  return <span>{formatUnits(balance ?? 0n, 6)} USDC</span>;
}

"use client";
 
import { useWriteContract, useWaitForTransactionReceipt } from "wagmi";
import { parseUnits } from "viem";
 
function SendTokens() {
  const { writeContract, data: hash, isPending, error } = useWriteContract();
 
  const { isLoading: isConfirming, isSuccess } = useWaitForTransactionReceipt({
    hash,
  });
 
  function handleSend() {
    writeContract({
      address: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
      abi: ERC20_ABI,
      functionName: "transfer",
      args: [
        "0xRecipientAddress...",
        parseUnits("100", 6), // 100 USDC
      ],
    });
  }
 
  return (
    <div>
      <button onClick={handleSend} disabled={isPending}>
        {isPending ? "Confirme na carteira..." : "Enviar 100 USDC"}
      </button>
 
      {hash && <p>Transação: {hash}</p>}
      {isConfirming && <p>Aguardando confirmação...</p>}
      {isSuccess && <p>Transferência confirmada!</p>}
      {error && <p>Erro: {error.message}</p>}
    </div>
  );
}

"use client";
 
import { useWatchContractEvent } from "wagmi";
import { useState } from "react";
import { formatUnits } from "viem";
 
interface TransferEvent {
  from: string;
  to: string;
  value: string;
}
 
function LiveTransfers() {
  const [transfers, setTransfers] = useState<TransferEvent[]>([]);
 
  useWatchContractEvent({
    address: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
    abi: ERC20_ABI,
    eventName: "Transfer",
    onLogs(logs) {
      const newTransfers = logs.map((log) => ({
        from: log.args.from as string,
        to: log.args.to as string,
        value: formatUnits(log.args.value as bigint, 6),
      }));
      setTransfers((prev) => [...newTransfers, ...prev].slice(0, 50));
    },
  });
 
  return (
    <ul>
      {transfers.map((t, i) => (
        <li key={i}>
          {t.from.slice(0, 8)}... → {t.to.slice(0, 8)}...: {t.value} USDC
        </li>
      ))}
    </ul>
  );
}

interface EIP1193Provider {
  request(args: { method: string; params?: unknown[] }): Promise<unknown>;
  on(event: string, handler: (...args: unknown[]) => void): void;
  removeListener(event: string, handler: (...args: unknown[]) => void): void;
}

// Interação de baixo nível com carteira (você não deveria fazer isso diretamente, mas é útil entender)
 
// Solicitar acesso à conta
const accounts = await window.ethereum.request({
  method: "eth_requestAccounts",
});
console.log("Connected address:", accounts[0]);
 
// Obter a chain atual
const chainId = await window.ethereum.request({
  method: "eth_chainId",
});
console.log("Chain ID:", parseInt(chainId, 16)); // "0x1" -> 1 (mainnet)
 
// Escutar mudanças de conta (usuário troca contas no MetaMask)
window.ethereum.on("accountsChanged", (accounts: string[]) => {
  if (accounts.length === 0) {
    console.log("Carteira desconectada");
  } else {
    console.log("Trocou para:", accounts[0]);
  }
});
 
// Escutar mudanças de chain (usuário troca de rede)
window.ethereum.on("chainChanged", (chainId: string) => {
  // A abordagem recomendada é recarregar a página
  window.location.reload();
});

// Descobrindo todas as carteiras disponíveis
interface EIP6963ProviderDetail {
  info: {
    uuid: string;
    name: string;
    icon: string;
    rdns: string; // Nome de domínio reverso, ex: "io.metamask"
  };
  provider: EIP1193Provider;
}
 
const wallets: EIP6963ProviderDetail[] = [];
 
window.addEventListener("eip6963:announceProvider", (event: CustomEvent) => {
  wallets.push(event.detail);
});
 
// Solicitar que todas as carteiras se anunciem
window.dispatchEvent(new Event("eip6963:requestProvider"));
 
// Agora 'wallets' contém todas as carteiras instaladas com seus nomes e ícones
// Você pode mostrar uma UI de seleção de carteira

import { walletConnect } from "wagmi/connectors";
 
const connector = walletConnect({
  projectId: "YOUR_PROJECT_ID", // Obtenha em cloud.walletconnect.com
  showQrModal: true,
});

"use client";
 
import { useAccount, useSwitchChain } from "wagmi";
import { mainnet } from "wagmi/chains";
 
function NetworkGuard({ children }: { children: React.ReactNode }) {
  const { chain } = useAccount();
  const { switchChain, isPending } = useSwitchChain();
 
  if (!chain) return <p>Por favor conecte sua carteira</p>;
 
  if (chain.id !== mainnet.id) {
    return (
      <div>
        <p>Por favor mude para Ethereum Mainnet</p>
        <button
          onClick={() => switchChain({ chainId: mainnet.id })}
          disabled={isPending}
        >
          {isPending ? "Trocando..." : "Trocar Rede"}
        </button>
      </div>
    );
  }
 
  return <>{children}</>;
}

{
  "name": "Cool NFT #42",
  "description": "Um NFT muito legal",
  "image": "ipfs://QmImageHash...",
  "attributes": [
    { "trait_type": "Background", "value": "Blue" },
    { "trait_type": "Rarity", "value": "Legendary" }
  ]
}

function ipfsToHttp(uri: string): string {
  if (uri.startsWith("ipfs://")) {
    const cid = uri.replace("ipfs://", "");
    return `https://ipfs.io/ipfs/${cid}`;
    // Ou use um gateway dedicado:
    // return `https://YOUR_PROJECT.mypinata.cloud/ipfs/${cid}`;
  }
  return uri;
}
 
// Buscando metadados de NFT
async function getNftMetadata(contractAddress: string, tokenId: bigint, provider: ethers.Provider) {
  const contract = new ethers.Contract(
    contractAddress,
    ["function tokenURI(uint256 tokenId) view returns (string)"],
    provider,
  );
 
  const tokenUri = await contract.tokenURI(tokenId);
  const httpUri = ipfsToHttp(tokenUri);
 
  const response = await fetch(httpUri);
  const metadata = await response.json();
 
  return {
    name: metadata.name,
    description: metadata.description,
    image: ipfsToHttp(metadata.image),
    attributes: metadata.attributes,
  };
}

// Upload para Pinata
async function pinToIpfs(file: File): Promise<string> {
  const formData = new FormData();
  formData.append("file", file);
 
  const response = await fetch("https://api.pinata.cloud/pinning/pinFileToIPFS", {
    method: "POST",
    headers: {
      Authorization: `Bearer ${PINATA_JWT}`,
    },
    body: formData,
  });
 
  const result = await response.json();
  return `ipfs://${result.IpfsHash}`; // Retorna CID
}

# Schema do subgraph (schema.graphql)
type Transfer @entity {
  id: Bytes!
  from: Bytes!
  to: Bytes!
  value: BigInt!
  blockNumber: BigInt!
  timestamp: BigInt!
}
 
type Account @entity {
  id: Bytes!
  balance: BigInt!
  transfersFrom: [Transfer!]! @derivedFrom(field: "from")
  transfersTo: [Transfer!]! @derivedFrom(field: "to")
}

// Consultando um subgraph do seu frontend
const SUBGRAPH_URL = "https://api.studio.thegraph.com/query/YOUR_ID/YOUR_SUBGRAPH/v0.0.1";
 
async function getRecentTransfers(address: string) {
  const query = `
    query GetTransfers($address: Bytes!) {
      transfers(
        where: { from: $address }
        orderBy: blockNumber
        orderDirection: desc
        first: 100
      ) {
        id
        from
        to
        value
        blockNumber
        timestamp
      }
    }
  `;
 
  const response = await fetch(SUBGRAPH_URL, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ query, variables: { address } }),
  });
 
  const { data } = await response.json();
  return data.transfers;
}

// Alchemy: Obter todos os saldos de tokens ERC-20 para um endereço
const response = await fetch(`https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY`, {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    jsonrpc: "2.0",
    id: 1,
    method: "alchemy_getTokenBalances",
    params: ["0xAddress...", "erc20"],
  }),
});
 
// Retorna TODOS os saldos de tokens ERC-20 em uma chamada
// vs. escanear o balanceOf() de todo possível contrato ERC-20

// Alchemy: Obter todos os NFTs de um endereço
const response = await fetch(`https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY/getNFTs?owner=0xAddress...`);
 
const { ownedNfts } = await response.json();
for (const nft of ownedNfts) {
  console.log(`${nft.title} - ${nft.contract.address}#${nft.tokenId}`);
}

// ERRADO — perda silenciosa de precisão
const balance = 1000000000000000000; // 1 ETH em wei
const double = balance * 2;
console.log(double); // 2000000000000000000 — parece certo, mas...
 
const largeBalance = 99999999999999999999; // ~100 ETH
console.log(largeBalance); // 100000000000000000000 — ERRADO! Arredondado para cima.
console.log(largeBalance === 100000000000000000000); // true — corrupção de dados
 
// CORRETO — use BigInt
const balance = 1000000000000000000n;
const double = balance * 2n;
console.log(double.toString()); // "2000000000000000000" — correto
 
const largeBalance = 99999999999999999999n;
console.log(largeBalance.toString()); // "99999999999999999999" — correto

import { formatUnits, parseUnits } from "viem";
 
// Exibição: BigInt → string legível
const weiAmount = 1500000000000000000n; // 1.5 ETH
const display = formatUnits(weiAmount, 18); // "1.5"
 
// Input: string legível → BigInt
const userInput = "1.5";
const wei = parseUnits(userInput, 18); // 1500000000000000000n
 
// USDC tem 6 decimais, não 18
const usdcAmount = 100000000n; // 100 USDC
const usdcDisplay = formatUnits(usdcAmount, 6); // "100.0"

// O usuário pode rejeitar qualquer prompt de carteira
try {
  const tx = await writeContract({
    address: contractAddress,
    abi: ERC20_ABI,
    functionName: "approve",
    args: [spenderAddress, amount],
  });
} catch (error) {
  if (error.code === 4001) {
    // Usuário rejeitou a transação na carteira
    // Isso é normal — não é um erro para reportar
    showToast("Transação cancelada");
  } else if (error.code === -32603) {
    // Erro interno JSON-RPC — frequentemente significa que a transação reverteria
    showToast("Transação falharia. Verifique seu saldo.");
  } else {
    // Erro inesperado
    console.error("Erro na transação:", error);
    showToast("Algo deu errado. Por favor tente novamente.");
  }
}

// Verificação defensiva de chain
import { useAccount, useChainId } from "wagmi";
 
function useRequireChain(requiredChainId: number) {
  const chainId = useChainId();
  const { isConnected } = useAccount();
 
  if (!isConnected) {
    return { ready: false, error: "Por favor conecte sua carteira" };
  }
 
  if (chainId !== requiredChainId) {
    return {
      ready: false,
      error: `Por favor mude para ${getChainName(requiredChainId)}. Você está na ${getChainName(chainId)}.`,
    };
  }
 
  return { ready: true, error: null };
}

// Definindo tolerância de slippage em um swap estilo Uniswap
const amountOutMin = (expectedOutput * 995n) / 1000n; // 0.5% de tolerância de slippage
 
// Usando um deadline para prevenir transações pendentes de longa duração
const deadline = BigInt(Math.floor(Date.now() / 1000) + 60 * 20); // 20 minutos
 
await router.swapExactTokensForTokens(
  amountIn,
  amountOutMin, // Output mínimo aceitável — reverte se receberíamos menos
  [tokenA, tokenB],
  userAddress,
  deadline, // Reverte se não executar em 20 minutos
);

// Usando Flashbots Protect como seu endpoint RPC
const provider = new ethers.JsonRpcProvider("https://rpc.flashbots.net");

async function formatTokenAmount(tokenAddress: string, rawAmount: bigint, provider: ethers.Provider): Promise<string> {
  const contract = new ethers.Contract(
    tokenAddress,
    ["function decimals() view returns (uint8)", "function symbol() view returns (string)"],
    provider,
  );
 
  const [decimals, symbol] = await Promise.all([contract.decimals(), contract.symbol()]);
 
  return `${ethers.formatUnits(rawAmount, decimals)} ${symbol}`;
}
 
// formatTokenAmount(USDC, 1000000n, provider) → "1.0 USDC"
// formatTokenAmount(WETH, 1000000000000000000n, provider) → "1.0 WETH"
// formatTokenAmount(WBTC, 100000000n, provider) → "1.0 WBTC"

import { createPublicClient, http, decodeFunctionResult } from "viem";
 
async function simulateAndGetError(client: ReturnType<typeof createPublicClient>, tx: object) {
  try {
    await client.call({
      account: tx.from,
      to: tx.to,
      data: tx.data,
      value: tx.value,
    });
    return null; // Sem erro — transação teria sucesso
  } catch (error) {
    // Decodificar o motivo da reversão
    if (error.data) {
      // Strings de revert comuns
      if (error.data.startsWith("0x08c379a0")) {
        // Error(string) — revert padrão com mensagem
        const reason = decodeAbiParameters([{ type: "string" }], `0x${error.data.slice(10)}`);
        return `Revert: ${reason[0]}`;
      }
    }
    return error.message;
  }
}

"use client";
 
import { useAccount, useConnect, useDisconnect, useReadContract, useWriteContract, useWaitForTransactionReceipt } from "wagmi";
import { injected } from "wagmi/connectors";
import { formatUnits, parseUnits } from "viem";
import { useState } from "react";
 
const USDC_ADDRESS = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48";
 
const USDC_ABI = [
  {
    name: "balanceOf",
    type: "function",
    stateMutability: "view",
    inputs: [{ name: "account", type: "address" }],
    outputs: [{ name: "", type: "uint256" }],
  },
  {
    name: "transfer",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "to", type: "address" },
      { name: "amount", type: "uint256" },
    ],
    outputs: [{ name: "", type: "bool" }],
  },
] as const;
 
export function TokenDashboard() {
  const { address, isConnected } = useAccount();
  const { connect } = useConnect();
  const { disconnect } = useDisconnect();
 
  const [recipient, setRecipient] = useState("");
  const [amount, setAmount] = useState("");
 
  // Ler saldo — só roda quando address está definido
  const { data: balance, refetch: refetchBalance } = useReadContract({
    address: USDC_ADDRESS,
    abi: USDC_ABI,
    functionName: "balanceOf",
    args: address ? [address] : undefined,
    query: { enabled: !!address },
  });
 
  // Escrita: transferir tokens
  const {
    writeContract,
    data: txHash,
    isPending: isSigning,
    error: writeError,
  } = useWriteContract();
 
  // Esperar pela confirmação
  const { isLoading: isConfirming, isSuccess } = useWaitForTransactionReceipt({
    hash: txHash,
  });
 
  // Rebuscar saldo após confirmação
  if (isSuccess) {
    refetchBalance();
  }
 
  if (!isConnected) {
    return (
      <button onClick={() => connect({ connector: injected() })}>
        Conectar Carteira
      </button>
    );
  }
 
  return (
    <div>
      <p>Conectado: {address}</p>
      <p>
        Saldo USDC:{" "}
        {balance !== undefined ? formatUnits(balance, 6) : "Carregando..."}
      </p>
 
      <div>
        <input
          placeholder="Endereço do destinatário (0x...)"
          value={recipient}
          onChange={(e) => setRecipient(e.target.value)}
        />
        <input
          placeholder="Quantidade (ex: 100)"
          value={amount}
          onChange={(e) => setAmount(e.target.value)}
        />
        <button
          onClick={() => {
            writeContract({
              address: USDC_ADDRESS,
              abi: USDC_ABI,
              functionName: "transfer",
              args: [recipient as `0x${string}`, parseUnits(amount, 6)],
            });
          }}
          disabled={isSigning || isConfirming}
        >
          {isSigning
            ? "Confirme na carteira..."
            : isConfirming
              ? "Confirmando..."
              : "Enviar USDC"}
        </button>
      </div>
 
      {writeError && <p style={{ color: "red" }}>{writeError.message}</p>}
      {isSuccess && <p style={{ color: "green" }}>Transferência confirmada!</p>}
      {txHash && (
        <a
          href={`https://etherscan.io/tx/${txHash}`}
          target="_blank"
          rel="noopener noreferrer"
        >
          Ver no Etherscan
        </a>
      )}
 
      <button onClick={() => disconnect()}>Desconectar</button>
    </div>
  );
}