# Deploy Smart Contracts with Foundry

#### Prerequisites

* Install **Foundry**:

  ```bash
  curl -L <https://foundry.paradigm.xyz> | bash
  foundryup
  ```
* **Node.js & npm** (for optional frontend)
* **Hela Node/Web3 Gateway** running locally or using testnet RPC URL
* **Wallet (Metamask)** configured to connect to Hela RPC

**Check the version:**

```jsx
forge --version
```

### Initialize Foundry Project:

Let’s create a new project:

```bash
forge init hello-hela
cd hello-hela
```

Inside this folder, you now have:

* `src/` → your contracts
* `test/` → your tests

## Write the Smart Contract:

We’ll create a simple **SplitWise app,** a contract where friends can track and settle debts.

Create :(`src/SplitWise.sol`)

```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

contract SplitWise {
    mapping(address => mapping(address => int256)) public debts;

    event ExpenseAdded(address indexed payer, address indexed to, uint256 amount);
    event DebtCleared(address indexed from, address indexed to, uint256 amount);

    // Record an expense
    function addExpense(address friend, uint256 amount) public {
        debts[friend][msg.sender] -= int256(amount);
        debts[msg.sender][friend] += int256(amount);

        emit ExpenseAdded(msg.sender, friend, amount);
    }

    // Check balance between two friends
    function checkBalance(address friend) public view returns (int256) {
        return debts[msg.sender][friend];
    }

    // Clear a debt
    function clearDebt(address friend, uint256 amount) public {
        require(debts[msg.sender][friend] >= int256(amount), "Not enough debt!");
        debts[msg.sender][friend] -= int256(amount);
        debts[friend][msg.sender] += int256(amount);

        emit DebtCleared(msg.sender, friend, amount);
    }
}
```

### Write a Simple Test  (`test/SplitWise.t.sol`)

Tests are super important to confirm things work before spending gas.

```solidity
pragma solidity ^0.8.9;

import "forge-std/Test.sol";
import "../src/SplitWise.sol";

contract SplitWiseTest is Test {
    SplitWise splitwise;
    address alice = address(1);
    address bob = address(2);

    function setUp() public {
        splitwise = new SplitWise();
    }

    function testAddExpense() public {
        vm.prank(alice);
        splitwise.addExpense(bob, 100);

        int256 balance = splitwise.checkBalance(bob);
        assertEq(balance, 100);
    }
}
```

Run the tests:

```bash
forge test
```

***

### Deploy to HeLa

Open `foundry.toml` and add your Hela testnet endpoint:

```toml
[rpc_endpoints]
hela = "<https://rpc.testnet.hela.xyz>"  # replace with actual endpoint
```

Deploy with:

```bash
forge create --rpc-url hela --private-key <YOUR_PRIVATE_KEY> src/SplitWise.sol:SplitWise
```

#### Interact with Your Contract

* Add an expense:

  ```bash
  cast send <CONTRACT_ADDRESS> "addExpense(address,uint256)" <FRIEND_ADDR> 100 --rpc-url hela --private-key <KEY>

  ```
* Check balance:

  ```bash
  cast call <CONTRACT_ADDRESS> "checkBalance(address)" <FRIEND_ADDR> --rpc-url hela

  ```

You’ll see a number:

* Positive → your friend owes you
* Negative → you owe them

## Support :&#x20;

If you encounter any issues during setup or require assistance, please join the [**HeLa Developer Community**](https://discord.gg/NEBtTztJCj) for direct support and guidance.