SafeMath.sol

library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    assert(c / a == b); 
    return c;
  }
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b; 
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}
contract TimeLock {
    using SafeMath for uint; // use the library for uint type
    mapping(address => uint256) public balances;
    mapping(address => uint256) public lockTime;
    
    function deposit() public payable {
        balances[msg.sender] = balances[msg.sender].add(msg.value);
        lockTime[msg.sender] = now.add(1 weeks);
    }
    
    function increaseLockTime(uint256 _secondsToIncrease) public {
        lockTime[msg.sender] = lockTime[msg.sender].add(_secondsToIncrease);
    }
    
    function withdraw() public {
        require(balances[msg.sender] > 0);
        require(now > lockTime[msg.sender]);
        balances[msg.sender] = 0;
        msg.sender.transfer(balances[msg.sender]);
    }
}