4. Deploying BMC Smart contract

4.1 Deploying BMC Smart contract to Klaytn Testnet

After successfully testing the functionalities of our BMC smart contract, let’s proceed to deploy to the Klaytn Testnet Baobab in the following steps:

Step 1 - Creating a .env file

Now create your .env file in the project folder. This file helps us load environment variables from a .env file into process.env.

Paste this command in your terminal to create a .env file

touch .env

After creating your file, lets configure our .env file to look like this:

BAOBAB_URL= "Your RPC URL"
PRIVATE_KEY= "your private key copied from metamask wallet"

Step 2 - Setting up Hardhat Configs

Paste this configurations in your hardhat.config.js file

require("@nomicfoundation/hardhat-toolbox");
require("dotenv").config();
const BAOBAB_URL = process.env.BAOBAB_URL;
const PRIVATE_KEY = process.env.PRIVATE_KEY;
/** @type import('hardhat/config').HardhatUserConfig */
module.exports = {
  solidity: "0.8.18",
  defaultNetwork: "hardhat",
  networks: {
    baobab: {
      url: BAOBAB_URL,
      accounts: [PRIVATE_KEY],
    }
  }
};

Step 3 - Creating deployment scripts

To create a new deployment script that deploys this smart contract to a specified network, create a new file scripts/deploy.js and paste in the code below:

const hre = require("hardhat");
async function main() {
  const BuyMeACoffee = await hre.ethers.getContractFactory("BuyMeACoffee");
  const buyMeACoffe = await BuyMeACoffee.deploy();
  await buyMeACoffe.deployed();
  console.log(`BuyMeACoffee Contract Address`, buyMeACoffe.address);
}
// We recommend this pattern to be able to use async/await everywhere
// and properly handle errors.
main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

Now that we have our configurations all set, let’s deploy to Klaytn Testnet Baobab by running the command below:

npx hardhat run scripts/deploy.js --network baobab

Once the contract deploys successfully, your terminal should look like this:

BuyMeACoffee Contract Address 0x0bEd1ed7B205d8c18e38A20b5BaB6e265A96d1AC

Congratulations on deploying your BMC smart contract on Klaytn Baobab Network! You can verify this transaction on Klaytnscope by pasting your address in the search field.

4.2 Interacting with BMC Smart Contract

In this section, you will learn how to use hardhat scripts to withdraw the coffee tips sent into the smart contract. To get started, create a new file withdraw.js in your scripts folder and paste the code below:

const hre = require("hardhat");

// contract address of BMC Contract
const buyMeACoffeAddress = "Paste BMC contract address";

// address of the contract deployer
// useful when calling the withdrawCoffeTips() function
// ensure that this address is the SAME address as the original contract deployer
const deployerAddress = "Paste deployer address";
// get the balance of a specified address
async function getBalance(address) {
    const balanceBigInt = await hre.ethers.provider.getBalance(address);
    return hre.ethers.utils.formatEther(balanceBigInt)
}

async function main() {

  // initialize the deployerAddress to a signer object
  // this will be useful when calling the withdrawCoffeTips() to the owner address
  const signer = await hre.ethers.getSigner(deployerAddress);

  // instantiate the BMC contract
  const BuyMeACoffee = await hre.ethers.getContractAt("BuyMeACoffee", buyMeACoffeAddress, signer);

  const balanceBefore = await getBalance(signer.address);
  const contractBalance = await getBalance(BuyMeACoffee.address);
  console.log(`Owner balance before withdrawing tips: ${balanceBefore} KLAY`);
  console.log(`Contract balance before withdrawing tips:  ${contractBalance} KLAY`);

    // Withdraw funds if there are funds to withdraw.
    if (contractBalance !== "0.0") {
        console.log("withdrawing funds..")
        const withdrawCoffeTxn = await BuyMeACoffee.withdrawCoffeTips();
        await withdrawCoffeTxn.wait();
        // check owner's balance after withdrawing coffee tips
        const balanceAfter = await getBalance(signer.address);
        console.log(`Owner balance after withdrawing tips ${balanceAfter} KLAY`);
      } else {
        console.log("no funds to withdraw!");
      }
}
// We recommend this pattern to be able to use async/await everywhere
// and properly handle errors.
main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

As you can see from the code above, having instantiated the BMC contract, the scripts will execute the withdrawCoffeTips function only when the contract balance is greater than zero. Makes sense right?

Yes! In the event where the contract has no funds, it prints "No funds to withdraw" hence saving us some gas from contract invocation.

To see this in action, lets run the script below:

npx hardhat run scripts/withdraw.js --network baobab

On successful execution of the scripts, your terminal should look like this:

Ayomitans-MacBook-Pro:smart-contract oxpampam$ npx hardhat run scripts/withdraw.js --network baobab
Owner balance before withdrawing tips: 155.8337532 KLAY
Contract balance before withdrawing tips:  2.0 KLAY
withdrawing funds..
Owner balance after withdrawing tips 157.83298835 KLAY

You can see from the output that the owner balance increased by 2 KLAY after withdrawing the coffee tips.

Now that we have our contract deployed and all functionalities tested, it is time to build out the frontend.

The frontend will bring the BMC functionality to live i.e we can now visualize how we interact with the BMC smart contract.