Adding liqudity to DEX

Let's create a new file liquidity.ts in the actions folder and start implementing a function to mint / provide liquidity:

// file: src/liquidity.ts

export const mint = async (
  state: DexState,
  { caller, input: { amountIn0, amountIn1 } }: DexAction
): Promise<ContractResult> => {};
// We will put the logic of token deposits here

The parameters amountIn0 and amountIn1 specify how much tokens are we going to deposit. Before we transfer the tokens let's first record who is making the deposit. For simplicity, we will implement the simplest version that will allow only a single liquidity provider.

if (state.liquidityProvider == null) {
  state.liquidityProvider = caller;
} else {
  throw new ContractError('Burn liquidity first before adding it again');
}

In the contract's state, we define a variable called liqudityProvider that keeps the current liquidity provider. It's only possible to set up the provider when the value is empty (null). Otherwise, the contract will throw an error.

Next, we will write the code that will transfer the tokens from the provider's wallet to the contract. We use the ERC20 token standard that is defined in the Warp's provided WRC library. Although the contract code is written in RUST we could seamlessly communicate with it from the typescript code.

📣 Warp contracts are fully interoperable regardless of the language they are implemented in.

if (amountIn0 > 0) {
  const token0TransferResult = await SmartWeave.contracts.write(state.token0, {
    function: 'transferFrom',
    from: caller,
    to: SmartWeave.contract.id,
    amount: amountIn0,
  });
  
  state.reserve0 += amountIn0;
}

In the code above, we're changing a state of an external ERC20 contract. Therefore, we use the built-in SmartWeave.contracts.write method (one of two possible internal calls) to pass as parameters the address of an external contract, function name, and a list of arguments. Note that if the internal write will fail, the contract evaluation will automatically throw a ContractError - there's no need to manually check the result of the internal write. In case everything is fine, we update the state variable that keeps the size of the reserve.

We also need to implement a very similar logic to transfer the second token:

if (amountIn1 > 0) {
  await SmartWeave.contracts.write(state.token1, {
    function: 'transferFrom',
    from: caller,
    to: SmartWeave.contract.id,
    amount: amountIn1,
  });
  state.reserve1 += amountIn1;
}

The final and very important step is to return the state variable allowing Warp to properly update the contract's state.

return { state };