HW07: Patreon

Problem statement

Implement a smart contract for supporting an artist.

• The contract is created by the contributor and it stores the address of the artist.
• The contract can only receive funds upon creation.
• The artist can withdraw the money in 52 installments (i.e. weekly for one year).

Example scenario

Alice creates a contract with 52 ether initial balance to support Bob, the artist. For the next 52 weeks, Bob can make a single withdrawal of at most 1 ether every week.

Contract interface

• constructor: function Patreon(address artist) payable

  • The creator of the contract (msg.sender) is the contributor.
  • artist is the artist.
  • Any funds sent are stored in the contract.

• withdraw: function withdraw(uint256 amount)

  • Sends amount wei to the sender of the transaction.
  • Succeeds only if the sender is the artist, the amount is not over the weekly withdraw limit, and at least one week has passed since the last withdrawal.

• fallback: function () payable

  • This transaction should never succeed, i.e. after creation, we will not allow sending additional ether to the contract. (Caveat: the contract can still receive ether if another contract calls selfdestruct with our contract's address. You do not need to handle this case here.)

Contract skeleton

pragma solidity ^0.4.21;

contract Patreon {

    // <contract_variables>

    // </contract_variables>

    function Patreon(address artist) public payable {
        // TODO
    }

    function withdraw(uint256 amount) public {
        // TODO
    }

    function () public payable {
        // TODO
    }

}