testDistribute.sol

/*
 * References:
 *   1. https://uploads-ssl.webflow.com/5ad71ffeb79acc67c8bcdaba/5ad8d1193a40977462982470_scalable-reward-distribution-paper.pdf
 *   2. https://eips.ethereum.org/EIPS/eip-1973
 */

pragma solidity 0.4.24;

contract Test {
    // using SafeMath for uint256;

    uint256 public totalStaking = 0;
    mapping (address => uint256) public staking;
    mapping (address => uint256) public rewards;

    function deposit() payable public {
        staking[msg.sender] += msg.value;
        totalStaking += msg.value;
    }

    function distribute() payable public {
        uint256 reward = msg.value;
        if (totalStaking == 0) {
            return;
        }
        
        // TODO: distribute reward to user base on pass block number
    }
    function () payable public {
       distribute();
    }

    function claimReward() public {
        address user = msg.sender;
        uint256 reward = rewards[user];
        if (reward > 0) {
            user.transfer(reward);  // use Address.sendValue
        }
    }
    function withdraw() public {
        address user = msg.sender;
        uint256 deposited = staking[user];
        staking[user] = 0;

        user.transfer(deposited);
    }


    /*
     * Tips:
     * 1. add SafeMath and Address
     * 2. mul 10e18 for totalReward, div 10e18 for reward
     */
}

(likewise you can emit an event when the user withdraws, so you can calculate when the deposit starts and when the deposit ends, and disburse according to the staked duration - if qualified, for example).

@Enigmatic331 thank you.