HW04: Family wealth management

Problem statement

Implement a smart contract for shared wealth management for families.

• The contract should store the addresses of two parents and one child.
• The contract should store the funds of the family in ether.
• Only the parents and the child can access the funds.
• There is a limit of 1 ether for single withdraws by parents.
• Any withdraws by the child must first be approved by the parents.

Example scenario

Alice and Bob create a contract with 10 ether initial balance, giving access to their daughter, Claire. Every time they receive their salary, they transfer it to the contract.

Every time they need money, they withdraw money from the contract, knowing that Alice and Bob can only withdraw 1 ether at a time. When Claire needs 0.1 ether, first one of the parents approves a withdrawal with a maximum amount of 0.1 ether, then Claire can withdraw the amount.

Contract interface

• constructor: function WealthManager(address parent2, address child) payable

  • The creator of the contract (msg.sender) is the first parent.
  • parent2 is the second parent.
  • child is the child.

• withdraw: function withdraw(uint256 amount)

  • Sends amount wei to the sender of the transaction.
  • Succeeds only if the sender is one of the parents and amount is not over the associated withdraw limit, or the sender is the child and the withdrawal has been approved/signed by one of the parents.

• sign: sign(uint256 maxAmount)

  • Approves a single withdraw of at most maxAmount wei for the child.
  • Succeeds only if the sender is one of the parents.
  • Overwrites any previous approvals that have not been withdrawn (i.e. at any point in time, at most one withdrawal can be approved for the child).

• fallback: function () payable

  • Receives ether from any address.

Contract skeleton

pragma solidity ^0.4.21;

contract WealthManager {

    // <contract_variables>

    // </contract_variables>

    function WealthManager(address parent2, address child) public payable {
        // TODO
    }

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

    function sign(uint256 maxAmount) public {
        // TODO
    }

    function () public payable {
        // TODO
    }

}