# Payments In this Tutorial, we will be building a simple payment project where we get to donate to a smart contract using the `RWA` token. ### Step 1: DOWNLOAD THE STARTERKITS Download the starter kits below to get started in building fundme projects {% embed url="" %} follow the guidlines on the [README.md](https://github.com/xendfinance/assetchain-starterkits/blob/main/README.md) file to get your starter kits ready. ### Step 2: WRITING OUR FUNDME CONTRACT Now that our environment is set up, on to more exciting stuff: *writing our smart contract code* Open up the `hardhat` project in your favorite editor (we like [VSCode](https://code.visualstudio.com/)). Smart contracts are written in a language called Solidity which is what we will use to write our NFT.sol smart contract.‌ Navigate to the `contracts` folder and create a new file called `FundMe.sol` Below is our smart contract code, Copy and paste the contents below into your `FundMe.sol` file. ```solidity //SPDX-License-Identifier: MIT pragma solidity >=0.8.0 <0.9.0; contract FundMe { address public owner; uint256 public totalDonations; address[] donators; mapping(address => uint256) public donations; event DonationReceived(address donor, uint256 amount); event FundsWithdrawn(address owner, uint256 amount); modifier onlyOwner() { require(msg.sender == owner, "Only owner can perform this action"); _; } constructor() { owner = msg.sender; } function donate() external payable { require(msg.value > 0, "Donation amount should be greater than zero"); donations[msg.sender] += msg.value; totalDonations += msg.value; donators.push(msg.sender); emit DonationReceived(msg.sender, msg.value); } function withdrawFunds() external onlyOwner { uint256 amount = address(this).balance; require(amount > 0, "No funds to withdraw"); payable(owner).transfer(amount); emit FundsWithdrawn(owner, amount); } function getDonationDetails(address _donor) external view returns (uint256) { return donations[_donor]; } } ``` So, what does this code *do* exactly? Let’s break it down, line-by-line. 1. **License Declaration(**`// SPDX-License-Identifier: MIT` ): Specifies the software license for the code, which is the MIT license in this case. 2. **Pragma Directive(**`pragma solidity >=0.8.0 <0.9.0;` ): Specifies the version of Solidity compiler that can compile this contract, which should be any version from 0.8.0 up to, but not including, 0.9.0. 3. **Contract Declaration(**`contract FundMe`): Declares the start of a smart contract named `FundMe`. 4. **State Variables**: * `address public owner;`: Stores the address of the contract owner and makes it publicly accessible. * `uint256 public totalDonations;`: Stores the total amount of donations received and makes it publicly accessible. * `address[] donators;`: Stores a list of addresses that have donated. * `mapping(address => uint256) public donations;`: Maps donor addresses to the amount they have donated and makes it publicly accessible. 5. **Events**: * `event DonationReceived(address donor, uint256 amount);`: Declares an event that is emitted when a donation is received, including the donor's address and the donation amount. * `event FundsWithdrawn(address owner, uint256 amount);`: Declares an event that is emitted when funds are withdrawn, including the owner's address and the withdrawn amount. 6. **Modifier**: `modifier onlyOwner()` * `require(msg.sender == owner, "Only owner can perform this action");`: Ensures that the function using this modifier can only be called by the contract owner. * `_;`: Placeholder that represents the function's body where the modifier is applied. 7. **Constructor**: `constructor()` * `owner = msg.sender;`: Sets the owner of the contract to the address that deploys the contract. 8. **Function to Donate**: `function donate()` * `external payable`: A function declared as `external` can only be called from outside the contract and When a function is marked as `payable`, it can receive `RWA token`, and the value sent with the transaction (in Wei) can be accessed using `msg.value`. * `require(msg.value > 0, "Donation amount should be greater than zero");`: Ensures that the donation amount is greater than zero. * `donations[msg.sender] += msg.value;`: Updates the donation amount for the sender's address. * `totalDonations += msg.value;`: Increases the total donations by the amount sent. * `donators.push(msg.sender);`: Adds the donor's address to the list of donators. * `emit DonationReceived(msg.sender, msg.value);`: Emits the `DonationReceived` event. 9. **Function to Withdraw Funds**: `function withdrawFunds()` * `external onlyOwner` : A function declared as `external` can only be called from outside the contract and when a function is marked `onlyOwner` It ensures that only the owner of the contract can call this function. * `uint256 amount = address(this).balance;`: Retrieves the contract's current balance. * `require(amount > 0, "No funds to withdraw");`: Ensures that there are funds available to withdraw. * `payable(owner).transfer(amount);`: Transfers the contract's balance to the owner's address. * `emit FundsWithdrawn(owner, amount);`: Emits the `FundsWithdrawn` event. 10. **Function to Get Donation Details**: `function getDonationDetails(address _donor) external view returns (uint256)` * `return donations[_donor];`: Returns the donation amount for the specified donor address. ### STEP 3: UPDATE OUR DEPLOYMENT SCRIPTS Navigate to the `deploy/00_deploy_your_contract.ts` folder , adding the following contents to it: ```typescript import { HardhatRuntimeEnvironment } from "hardhat/types"; import { DeployFunction } from "hardhat-deploy/types"; /** * Deploys a contract named "YourContract" using the deployer account and * constructor arguments set to the deployer address * * @param hre HardhatRuntimeEnvironment object. */ const deployYourContract: DeployFunction = async function (hre: HardhatRuntimeEnvironment) { /* When deploying to live networks (e.g `yarn deploy --network assetchain_testnet`), the deployer account should have sufficient balance to pay for the gas fees for contract creation. You can generate a random account with `yarn generate` which will fill DEPLOYER_PRIVATE_KEY with a random private key in the .env file (then used on hardhat.config.ts) You can run the `yarn account` command to check your balance in every network. */ const { deployer } = await hre.getNamedAccounts(); const { deploy } = hre.deployments; await deploy("FundMe", { from: deployer, // Contract constructor arguments log: true, // autoMine: can be passed to the deploy function to make the deployment process faster on local networks by // automatically mining the contract deployment transaction. There is no effect on live networks. autoMine: true, }); // Get the deployed contract to interact with it after deploying. // const yourContract = await hre.ethers.getContract("Greeter", deployer); }; export default deployYourContract; // Tags are useful if you have multiple deploy files and only want to run one of them. // e.g. yarn deploy --tags Greeter deployYourContract.tags = ["FundMe"]; ``` ### STEP 4: DEPLOY OUR CONTRACT We’re finally ready to deploy our smart contract! Navigate back to the root of your hardhat project directory, and in the command line run: ``` yarn deploy --network assetchain_testnet ``` You should then see something like: `"FundMe" at 0xcaa32C250fbC0cDd13A09c385e33b83e7D3e15F7` {% hint style="success" %} Congratulations! Your Fundme contract is successfully depolyed on Asset Chain Blockchain. {% endhint %} If we go to the [Asset Chain explorer ](https://testnet.assetchain.org/)and search for our contract address or transaction hash. we should be able to see that it has been deployed successfully. {% embed url="" %} updated codebase for the smart contract {% endembed %} ### STEP 5: BUILDING OUR FRONTEND AND INTERACTING WITH OUR FRONTEND coming soon.... Below are link to preview project {% embed url="" %} ### STEP 5: ASSIGNMENT coming soon.... if you have questions, join our [Telegram](https://t.me/XendFinanceDevs) and say hello 👋. We're Active!