## Introduction to Remix Buy Me A Coffee Smart Contract This lesson is part of the Cyfrin Updraft Vyper course. We will be exploring the Buy Me a Coffee smart contract. The code for this lesson is available on the following GitHub repo: ```bash https://github.com/Cyfrin/remix-buy-me-a-coffee-cu ``` We will be building a simple smart contract that allows people to send you money based on a price that we set. In this case, we'll be using a price of $50. We will also explore a withdrawal function that allows the owner of the contract to withdraw the funds. We will be using Remix and the Tenderly virtual network for this lesson. We will explore the following code: ```python # pragma version 0.4.1 # pragma enable-decimals """ @license MIT @title A sample buy-me-a-coffee contract @author You! @notice This contract is for creating a sample funding contract """ # We'll learn a new way to do interfaces later... interface AggregatorV3Interface: def decimals() -> uint8: view def description() -> String[1000]: view def version() -> uint256: view def getRoundData(roundId: uint80) -> (uint80, int256, uint256, uint256, uint80): view def latestRoundData() -> (uint80, int256, uint256, uint256, uint80): view # minimum USD decimals: public(constant(decimal)) = 50.0 MINIMUM_USD: public(constant(uint256)) = 50 * (10**18) PRECISION: constant(uint256) = 1 * (10**18) OWNER: public(immutable(address)) funders: public(DynArray[address], 100) address_to_amount_funded: public(HashMap[address, uint256]) price_feed: public(AggregatorV3Interface) @deploy def __init__(price_feed: address): self.price_feed = AggregatorV3Interface(price_feed) OWNER = msg.sender @internal def _only_owner(): assert msg.sender == OWNER, "Not the contract owner!" @external @payable def fund(): usd_value_of_eth: uint256 = self.get_eth_to_usd_rate(self.price_feed, msg.value) assert usd_value_of_eth >= MINIMUM_USD, "You need to spend more ETH!!" self.address_to_amount_funded[msg.sender] += msg.value self.funders.append(msg.sender) @external def withdraw(): self._only_owner() for funder: address in self.funders: self.address_to_amount_funded[funder] = 0 self.funders = [] send(OWNER, self.balance) @internal @view def get_eth_to_usd_rate(price_feed: AggregatorV3Interface, eth_amount: uint256) -> uint256: # Check the conversion rate a: uint80 = 0 b: int256 = 0 c: uint256 = 0 d: uint256 = 0 e: uint80 = 0 (a, b, c, d, e) = staticcall(price_feed.latestRoundData()) # We know the price has 8 decimals, so we need to add 1 + eth_amount: uint256 = convert(int256, (10**18) * (b * (10**-8))) # return eth_amount: uint256 = convert(int256, price * eth_amount) price: int256 = 0 return price: int256 ``` We can compile and deploy this smart contract in Remix. Remix allows us to interact with our smart contract to fund it with our test ETH and then withdraw those funds as well. We can use Tenderly to see the balance of our deployed smart contract.