CharityChallenge.sol

pragma solidity ^0.4.18;

contract CharityChallenge {
    
    address public charity;

    // Milestones correspond to notable levels of funds raised,
    // in terms the number of meals afforded for the 96 homeless
    // youths (at ~ $3/meal and $700/eth)

    // We will need the exchange rate to connect to meal prices.
    uint public eth_usd;

    uint[5] public milestones = [
        2100,                           // 1 week
        8400,                           // 1 month
        25200,                          // 3 months
        50400,                           // 6 months
        100800                          // 1 year
    ];


    uint public end_block;


    function CharityChallenge(
        address _charity, 
        uint _eth_usd,
        uint _duration
    ) public {
        charity = _charity;
        eth_usd = _eth_usd;
        end_block = block.number + _duration;
    }
    
    struct Donor {
        address addr;
        string message;
        uint8[3] rgb;
    }
    
    Donor[100] public leaderboard;
    
    mapping (address => uint) public donations;
    
    function claim (uint i, string message, uint8[3] rgb) public {
        require (i < leaderboard.length);
        if (donations[leaderboard[i].addr] < donations[msg.sender]) {
            leaderboard[i] = Donor({
                addr: msg.sender,
                message: message,
                rgb: rgb
            });
            Stamp(msg.sender, i);
        }
    }
    

    function () payable public {
        require (block.number < end_block);
        charity.transfer(msg.value);
        donations[msg.sender] += msg.value;
        Donation(msg.sender, msg.value);
    } 
    
    
    event Donation (address indexed from, uint amount);
    event Stamp (address indexed from, uint index);
}