Swapping - Fixed Input

1
const { decimalsToken1 } = await getTokenDecimals(
2
  client,
3
  testnetPair,
4
);
5
// We define the amount of tokens that we would like to get out (in token1 units)
6
const amountOut = 1000n * 10n ** BigInt(decimalsToken1);
7
console.log("Desired amount Out ", amountOut);

1
Desired amount Out  1000000000000000000000n

1
/**
2
 * Helper: quote required token0 for a fixed token1 output.
3
 */
4
async function quoteAmountsIn(
5
  pair: `0x${string}`,
6
  amountOut: bigint,
7
  path: `0x${string}`[],
8
) {
9
  return await client.readContract({
10
    address: pair,
11
    abi: stableSwapAbi,
12
    functionName: 'getAmountsIn',
13
    args: [amountOut, path],
14
  });
15
}

1
const [amountInMax] = await quoteAmountsIn(
2
  PAIR_AUSD_CTK,
3
  amountOut,
4
  [TOKEN0_AUSD, TOKEN1_CTK],
5
);
6
7
console.log('Quoted amountInMax (raw AUSD):', amountInMax)

1
Quoted amountInMax (raw AUSD): 1000200000

1
/**
2
 * Give `pair` permission to spend `amount` of `tokenToApprove`.
3
 * Returns the transaction hash of the on-chain approval.
4
 */
5
async function approveAllowance(
6
  tokenToApprove: `0x${string}`,
7
  pair: `0x${string}`,
8
  amount: bigint,
9
) {
10
  // 1) Dry-run to catch reverts & obtain gas estimate
11
  const { request } = await client.simulateContract({
12
    address: tokenToApprove,
13
    abi: ausdImplementationAbi, // standard ERC-20 ABI
14
    functionName: "approve",
15
    args: [pair, amount],
16
  });
17
18
  // 2) Send the real transaction
19
  return await client.writeContract(request);
20
}

1
console.log(
2
  `Approving contract ${TESTNET_PAIR_AUSD_CTK} to spend ${amountInMax} units of token ${inputTokenAddress}...`,
3
);
4
const approveAllowanceTxHash = await approveAllowance(
5
  inputTokenAddress,
6
  TESTNET_PAIR_AUSD_CTK,
7
  amountInMax,
8
);
9
console.log("Approve transaction hash:", approveAllowanceTxHash);

1
Approving pair to spend 1000200000 units of AUSD...
2
Approve transaction hash: 0x1d166bbc9ce4e0ba3000a42aa22360c14cb8a8ba8007d137915a3922e304e0f4

1
console.log("Executing swapTokensForExactTokens...");
2
const { request: swapRequest } = await client.simulateContract({
3
  address: TESTNET_PAIR_AUSD_CTK,
4
  abi: stableSwapAbi,
5
  functionName: "swapTokensForExactTokens",
6
  args: [amountOut, amountInMax, swapPath, callerAddress, BigInt(deadline)],
7
});
8
const swapRequestTxHash = await client.writeContract(swapRequest);
9
console.log("Swap transaction hash:", swapRequestTxHash);

1
Executing swapTokensForExactTokens...
2
Swap transaction hash: 0x5d27ab73a4759720aedd71b32075366a427c8ce21220cd9910b6352715550c3a