Smart Contract Challenge

Adapted from https://github.com/edgeandnode/contracts-challenge/tree/exercise-5

Introduction and logistics

Congratulations on making it to this stage in the process! This challenge is designed to test your software engineering skills applied to smart contracts development. Below are some instructions for a coding challenge that involves writing a smart contract and interacting with it.

You can work on a private GitHub repo and then share it with anirudh2, severiano-sisneros, and tmigone GitHub users. Document and validate your work in any ways you think work best. Feel free to send any questions that come up while doing the exercise. We recommend not spending more than 4 hours in this exercise, partial submissions are okay.

We hope you find this task enjoyable, and appreciate the time and effort you put into this.

Good luck!

The Challenge

1) Setup a project and create a contract

Context

ETHPaymentEscrow allows "Service Providers" to stake some ETH to provide an off-chain service and collect payments from a "Payer". Payers must previously deposit funds in the ETHPaymentEscrow contract as escrow. Payers can then sign Vouchers (using an EIP-712 signed message) and send them off-chain to the Service Provider. The Service Provider can then post the Voucher on-chain to collect the payment.

Requirements

• Service Providers must stake at least 0.00001 ETH to participate, and must have staked for at least 1 hour before being eligible to collect payments.
• Service Providers use the stake(...) function to stake ETH.
• Payers use the deposit(...) function to deposit ETH into the escrow
• Service Providers use the collect(...) function to collect a payment, sending an EIP-712 signed message as proof that the Payer authorized the payment.
• The Voucher must specify who is authorized to collect, the amount of ETH to pay, and any other fields you consider useful.

Example:

Let say we have user Alice, a Service Provider that sells bananas, and Bob, a customer or Payer that wants bananas.

Alice stakes 0.0001 ETH on the ETHPaymentEscrow contract. Bob deposits 0.001 ETH in the ETHPaymentEscrow contract.

Alice provides the service (ships some bananas to Bob), and Bob gives Alice a signed voucher to collect 0.0005 ETH as payment. Alice collects the payment by posting the voucher to the ETHPaymentEscrow contract. 0.0005 ETH are sent from Bob's escrow account on ETHPaymentEscrow to Alice's address.

Goal

Design and code a contract for ETHPaymentEscrow, feel free to ask any clarifying questions or to make all the assumptions you need to move forward. Bonus points for thinking about the most gas-efficient implementation you can.

Please use Solidity, but you can use any development tools you prefer: Foundry, Hardhat, OpenZeppelin contracts, etc.

A template contract showing an implementation of the stake() function is available here.

Useful resources:

• OpenZeppelin Contracts documentation: https://docs.openzeppelin.com/contracts/4.x/
• OpenZeppelin's EIP-712: https://docs.openzeppelin.com/contracts/5.x/api/utils#EIP712
• Solidity Docs: https://docs.soliditylang.org/en/v0.8.19
• Hardhat getting started: https://hardhat.org/hardhat-runner/docs/getting-started
• Foundry getting started: https://book.getfoundry.sh/getting-started/installation

2) Deploy your contract

Deploy the contract to any Ethereum testnet of your preference. Keep record of the deployed address. If you need testnet ETH, you can use a Sepolia faucet like this one or send us your address and we can send you some.

Bonus:

• Verify the contract in Etherscan

3) Interact with the contract

Create scripts (or Hardhat tasks) to stake some ETH, deposit ETH into the escrow, generate a voucher and collect a payment.