HODL.sol

contract HODL {
  uint256 amount;
  uint releaseAt;
  uint createdAt;
  address owner;

  modifier canRelease() {
      // 当前时间超过了 HODL 期限即可取款
      // 或者 7 天内后悔了
      require(now > releaseAt || (now - createdAt < 7 days));
      _;
  }

  modifier isOwner() {
      require(msg.sender == owner);
      _;
  }

  function HODL(uint256 n) public payable {
    require(msg.value > 0);
    require(n > 30);

    // 别让用户手抖输入太多钱或者太大的值
    require(msg.value < 100 ether);
    require(n < 365 * 5);

    releaseAt = now + n * 1 days;
    createdAt = now;
    owner = msg.sender;
    amount = msg.value;
  }

  function getBalance() public returns(uint256) {
      return this.balance;
  }

  function withdraw() public isOwner canRelease {
    require(this.balance > 0);
    // 原路退款
    owner.send(amount);
  }
}