const V2_ROUTER = '0xC7ca845B8302346e1C7227f03bb9EFb35ecD51fe'; // Mainnet

await tokenA.approve(V2_ROUTER, amountA);
await tokenB.approve(V2_ROUTER, amountB);

const V2_ROUTER_ABI = [
  'function addLiquidity(address tokenA, address tokenB, uint256 amountADesired, uint256 amountBDesired, uint256 amountAMin, uint256 amountBMin, address to, uint256 deadline) returns (uint256 amountA, uint256 amountB, uint256 liquidity)',
  'function addLiquidityETH(address token, uint256 amountTokenDesired, uint256 amountTokenMin, uint256 amountETHMin, address to, uint256 deadline) payable returns (uint256 amountToken, uint256 amountETH, uint256 liquidity)'
];

const router = new ethers.Contract(V2_ROUTER, V2_ROUTER_ABI, signer);
const deadline = Math.floor(Date.now() / 1000) + 1200; // 20 minutes

// ERC-20 / ERC-20 pair
const tx = await router.addLiquidity(
  tokenA.target,
  tokenB.target,
  amountADesired,
  amountBDesired,
  amountADesired * 99n / 100n,  // 1% slippage
  amountBDesired * 99n / 100n,
  userAddress,
  deadline
);

const tx = await router.addLiquidityETH(
  tokenAddress,
  amountTokenDesired,
  amountTokenDesired * 99n / 100n,
  amountKASDesired * 99n / 100n,
  userAddress,
  deadline,
  { value: amountKASDesired }
);

const lpToken = new ethers.Contract(pairAddress, ERC20_ABI, signer);
await lpToken.approve(V2_ROUTER, lpAmount);

const REMOVE_ABI = [
  'function removeLiquidity(address tokenA, address tokenB, uint256 liquidity, uint256 amountAMin, uint256 amountBMin, address to, uint256 deadline) returns (uint256 amountA, uint256 amountB)',
  'function removeLiquidityETH(address token, uint256 liquidity, uint256 amountTokenMin, uint256 amountETHMin, address to, uint256 deadline) returns (uint256 amountToken, uint256 amountETH)'
];

const router = new ethers.Contract(V2_ROUTER, REMOVE_ABI, signer);

// ERC-20 / ERC-20 pair
const tx = await router.removeLiquidity(
  tokenA,
  tokenB,
  lpAmount,
  0,  // amountAMin (set to 0 for simplicity; use slippage in production)
  0,  // amountBMin
  userAddress,
  deadline
);

const tx = await router.removeLiquidityETH(
  tokenAddress,
  lpAmount,
  0,
  0,
  userAddress,
  deadline
);

const PAIR_ABI = [
  'function getReserves() view returns (uint112, uint112, uint32)',
  'function token0() view returns (address)'
];

const pair = new ethers.Contract(pairAddress, PAIR_ABI, provider);
const [reserve0, reserve1] = await pair.getReserves();
const token0 = await pair.token0();

// If you want to deposit amountA of tokenA:
const isToken0 = tokenA.toLowerCase() === token0.toLowerCase();
const amountB = isToken0
  ? (amountA * reserve1) / reserve0
  : (amountA * reserve0) / reserve1;