contract VELOStakingPool is LPTokenWrapper, IRewardDistributionRecipient {
    IERC20 public velo;
    uint256 public duration; 

    uint256 public starttime; 
    uint256 public periodFinish = 0;
    uint256 public rewardRate = 0;
    uint256 public lastUpdateTime;
    uint256 public rewardPerTokenStored;
    mapping(address => uint256) public userRewardPerTokenPaid;
    mapping(address => uint256) public rewards;

    event RewardAdded(uint256 reward);
    event Staked(address indexed user, uint256 amount);
    event Withdrawn(address indexed user, uint256 amount);
    event RewardPaid(address indexed user, uint256 reward);


    constructor(address _velo, 
		address _erc20_token_address,
		uint256 _starttime,
		uint256 _duration) public 
    LPTokenWrapper(_erc20_token_address)
    {
      velo = IERC20(_velo);
      starttime = _starttime;
      duration = _duration;
    }

    modifier checkStart() {
        require(block.timestamp >= starttime,"not start");
        _;
    }

    modifier updateReward(address account) {
        rewardPerTokenStored = rewardPerToken();
        lastUpdateTime = lastTimeRewardApplicable();
        if (account != address(0)) {
            rewards[account] = earned(account);
            userRewardPerTokenPaid[account] = rewardPerTokenStored;
        }
        _;
    }


    function lastTimeRewardApplicable() public view returns (uint256) {
        return Math.min(block.timestamp, periodFinish);
    }

    function rewardPerToken() public view returns (uint256) {
        if (totalSupply() == 0) {
            return rewardPerTokenStored;
        }
        return
            rewardPerTokenStored.add(
                lastTimeRewardApplicable()
                    .sub(lastUpdateTime)
                    .mul(rewardRate)
                    .mul(1e18)
                    .div(totalSupply())
            );
    }

    function earned(address account) public view returns (uint256) {
        return
            balanceOf(account)
                .mul(rewardPerToken().sub(userRewardPerTokenPaid[account]))
                .div(1e18)
                .add(rewards[account]);
    }

    // stake visibility is public as overriding LPTokenWrapper's stake() function
    function stake(uint256 amount) public updateReward(msg.sender) checkStart {
        require(amount > 0, "Cannot stake 0");
        super.stake(amount);
        emit Staked(msg.sender, amount);
    }

    function withdraw(uint256 amount) public updateReward(msg.sender) checkStart {
        require(amount > 0, "Cannot withdraw 0");
        super.withdraw(amount);
        emit Withdrawn(msg.sender, amount);
    }

    function exit() external {
        withdraw(balanceOf(msg.sender));
        getReward();
    }

    function getReward() public updateReward(msg.sender) checkStart {
        uint256 reward = earned(msg.sender);
        if (reward > 0) {
            rewards[msg.sender] = 0;
            uint256 scalingFactor = VELO(address(velo)).velosScalingFactor();
            uint256 trueReward = reward.mul(scalingFactor).div(10**18);
            velo.safeTransfer(msg.sender, trueReward);
            emit RewardPaid(msg.sender, trueReward);
        }
    }

    function notifyRewardAmount(uint256 reward)
        external
        onlyRewardDistribution
        updateReward(address(0))
    {
        if (block.timestamp > starttime) {
          if (block.timestamp >= periodFinish) {
              rewardRate = reward.div(duration);
          } else {
              uint256 remaining = periodFinish.sub(block.timestamp);
              uint256 leftover = remaining.mul(rewardRate);
              rewardRate = reward.add(leftover).div(duration);
          }
          lastUpdateTime = block.timestamp;
          periodFinish = block.timestamp.add(duration);
          emit RewardAdded(reward);
        } else {
          rewardRate = reward.div(duration);
          lastUpdateTime = starttime;
          periodFinish = starttime.add(duration);
          emit RewardAdded(reward);
        }
    }
}
function stake(uint256 amount) public updateReward(msg.sender) checkStart {
        require(amount > 0, "Cannot stake 0");
        super.stake(amount);
        emit Staked(msg.sender, amount);
    }
// stake visibility is public as overriding LPTokenWrapper's stake() function