Vending Machine Smart Contract

This is a smart contract for a Vending Machine where users can purchase a certain ERC-20 token using USDC, USDT or MATIC (native token of Polygon Network). The contract also supports withdrawal of the ERC-20 tokens in exchange for USDC, USDT or MATIC.

Prerequisites

This contract uses the following dependencies from OpenZeppelin and Chainlink:

"@openzeppelin/contracts/token/ERC20/IERC20.sol";
"@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
"@openzeppelin/contracts/security/ReentrancyGuard.sol";
"@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

Contract details:

• owner: the address of the contract owner.

• USDCAddress: the address of the USDC token.

• USDTAddress: the address of the USDC token.

• ERC20Address: the address of the ERC-20 token to be purchased.

• ERC20ToUSDCRate: the conversion rate from the ERC-20 token to USDC in %.

• minimumPurchaseAmount: the minimum amount of ERC-20 token that can be purchased at a time.

• priceFeedUSDC: Chainlink Price Feed Contract address for the USDC/USD pair.

• priceFeedUSDT: Chainlink Price Feed Contract address for the USDT/USD pair.

• priceFeedMATIC: Chainlink Price Feed Contract address for the MATIC/USD pair.

The contract has the following functions:

• getLatestUSDCPrice(): returns the latest price of USDC in USD (Chainlink).
• getLatestMATICPrice(): returns the latest price of MATIC in USD (Chainlink).
• convertToStable(uint256 _TokenAmount): converts the given _TokenAmount of ERC-20 token to stable coin(USDT/USDC).
• convertFromStable(uint256 USDC): converts the given stable coin(USDT/USDC) amount to ERC-20 token.
• getVendingMATICBalance(): returns the balance of MATIC in the contract.
• checkPurchaseAmount(uint256 _TokenAmount): modifier to check if the _TokenAmount is greater than or equal to the minimumPurchaseAmount.
• sufficientTokenFunds(address fundsOwner, uint256 _TokenAmount): modifier to check if the fundsOwner has sufficient ERC-20 tokens for the _TokenAmount.
• purchaseForStable(uint256 _TokenAmount, address _stableAddress): allows the user to purchase ERC-20 token in exchange for stable coin(USDT/USDC).
• purchaseForUSDC(uint256 _TokenAmount): allows the user to purchase ERC-20 token in exchange for USDC using purchaseForStable with USDC address.
• purchaseForUSDT(uint256 _TokenAmount): allows the user to purchase ERC-20 token in exchange for USDT using purchaseForStable with USDT address.
• purchaseForMATIC(): allows the user to purchase ERC-20 token in exchange for MATIC.
• withdrawStable(uint256 _TokenAmount, address _stableAddress): allows the user to withdraw stable coin(USDT/USDC) tokens in exchange for ERC-20.
• withdrawUSDC(uint256 _TokenAmount): allows the user to withdraw USDC tokens in exchange for ERC-20 using withdrawStable with USDC address.
• withdrawUSDT(uint256 _TokenAmount): allows the user to withdraw USDT tokens in exchange for ERC-20 using withdrawStable with USDT address.
• withdrawMATIC(uint256 _TokenAmount): allows the user to withdraw MATIC tokens in exchange for ERC-20.
• withdrawOwnerStable(uint256 _TokenAmount, address _stableAddress, address _withdrawAddress): allows the owner to withdraw stable coin(USDT/USDC) tokens from Vending Machine Balance.
• withdrawOwnerUSDC(uint256 _TokenAmount): allows the owner to withdraw USDC tokens from Vending Machine Balance using withdrawOwnerStable with USDC address.
• withdrawOwnerUSDT(uint256 _TokenAmount): allows the owner to withdraw USDT tokens from Vending Machine Balance using withdrawOwnerStable with USDT address.
• withdrawOwnerMATIC(uint256 _TokenAmount): allows the owner to withdraw MATIC tokens from Vending Machine Balance.

Usage

Install the dependencies:

yarn;

To use this contract, you need to deploy it on the Polygon Network. You can also use it as a template to create similar contracts on other networks (you need to work with decimals). You can find sample deploy scripts scripts/deploy-vending.ts, scripts/deploy-token.ts and .env.example. Please fill Alchemy url and private keys first if you want to deploy the contracts. The contract constructor takes the following parameters:

• _USDCAddress: the address of the USDC token.
• _USDTAddress: the address of the USDT token.
• _ERC20Address: the address of the ERC-20 token to be purchased.
• _ERC20ToUSDCRate: the conversion rate from the ERC-20 token to USDC.
• _minimumPurchaseAmount: the minimum amount of ERC-20 token that can be purchased at a time.
• _priceFeedUSDC: (Chainlink) Price Feed Contract address for the USDC/USD pair.
• _priceFeedUSDT: (Chainlink) Price Feed Contract address for the USDT/USD pair.
• _priceFeedMATIC: (Chainlink) Price Feed Contract address for the MATIC/USD pair.

Testing

You can find chai test for all base functions in tests/vending-machine.test.ts and run it with following command:

npx hardhat test