Lottery Contract

lottery.sol

pragma solidity ^0.4.0;

contract Casino {
    
    uint private start;
    
    uint private buyPeriod = 1000;
    uint private verifyPeriod = 100;
    uint private checkPeriod = 100;
    
    mapping(address => uint) private _tickets;
    mapping(address => uint) private _winnings;

    address[] _entries;
    address[] _verified;

    uint private winnerSeed;
    bool private hasWinner;
    address private winner;
    
    function Casino()
        public {
        start = block.timestamp;    
    }
    
    /**
     * This should NOT be part of the contract!!
     */
    function unsafeEntry(uint number, uint salt) 
        public
        payable
        returns (bool) {
        return buyTicket(generateHash(number, salt));
    }
    
    function generateHash(uint number, uint salt)
        public
        pure
        returns (uint) {
        return uint(keccak256(number + salt));
    }
    
    function buyTicket(uint hash)
        public
        payable
        returns (bool) {
        // Within the timeframe
        require(block.timestamp < start+buyPeriod);
        // Correct amount
        require(1 ether == msg.value);
        // 1 entry per address
        require(_tickets[msg.sender] == 0);
        _tickets[msg.sender] = hash;
        _entries.push(msg.sender);
        return true;
    }
    
    function verifyTicket(uint number, uint salt)
        public
        returns (bool) {
        // Within the timeframe
        require(block.timestamp >= start+buyPeriod);
        require(block.timestamp < start+buyPeriod+verifyPeriod);
        // Has a valid entry
        require(_tickets[msg.sender] > 0);
        // Validate hash
        require(salt > number);
        require(generateHash(number, salt) == _tickets[msg.sender]);
        winnerSeed = winnerSeed ^ salt ^ uint(msg.sender);
        _verified.push(msg.sender);
    }
    
    function checkWinner()
        public
        returns (bool) {
        // Within the timeframe
        require(block.timestamp >= start+buyPeriod+verifyPeriod);
        require(block.timestamp < start+buyPeriod+verifyPeriod+checkPeriod);
        if (!hasWinner) {
            winner = _verified[winnerSeed % _verified.length];
            _winnings[winner] = _verified.length-10 ether;
            hasWinner = true;
        }
        return msg.sender == winner;
    }
    
    function claim()
        public {
        // Has winnings to claim
        require(_winnings[msg.sender] > 0);
        uint claimAmount = _winnings[msg.sender];
        _winnings[msg.sender] = 0;
        msg.sender.transfer(claimAmount);        
    }
}