Doubler

pragma solidity ^0.2.0;

contract Doubler {
    struct Participant {
        address etherAddress;
        uint amount;
    }

    Participant[] public participants;

    uint public payoutIdx = 0;
    uint public collectedFees;
    uint public balance;

    address public owner;

    function Doubler() {
        owner = msg.sender;
    }

    function() {
        enter();
    }

    function enter() {
        if (msg.value < 1 ether) {
            msg.sender.send(msg.value);
            return;
        }

        uint idx = participants.length;
        participants.length += 1;
        participants[idx].etherAddress = msg.sender;
        participants[idx].amount = msg.value;

        if (idx == 0) {
            collectedFees += msg.value;
        } else {
            collectedFees += msg.value / 10;
            balance += msg.value;
        }

        while (balance > participants[payoutIdx].amount * 2) {
            uint payout = participants[payoutIdx].amount * 2 - participants[payoutIdx].amount / 10;
            participants[payoutIdx].etherAddress.send(payout);
            balance -= participants[payoutIdx].amount * 2;
            payoutIdx++;
        }
    }

    function collectFees() {
        if (msg.sender != owner) return;
        if (collectedFees == 0) return;
        owner.send(collectedFees);
        collectedFees = 0;
    }

    function setOwner(address _owner) {
        if (msg.sender != owner) return;
        owner = _owner;
    }
}