DeferredEquityPlan.sol

pragma solidity ^0.5.0;

// lvl 3: equity plan
contract DeferredEquityPlan {
    address human_resources;

    address payable employee; // bob
    bool active = true; // this employee is active at the start of the contract

    uint total_shares = 1000;
    uint annual_distribution = 250;

    uint start_time = now; // permanently store the time this contract was initialized
    
    uint public unlock_time = start_time + 365; 

    uint public distributed_shares; // starts at 0

    constructor(address payable _employee) public {
        human_resources = msg.sender;
        employee = _employee;
    }

    function distribute() public {
        require(msg.sender == human_resources || msg.sender == employee, "You are not authorized to execute this contract.");
        require(active == true, "Contract not active.");

        require(unlock_time <= now, "Shares are not ready to be vested.");

        require(distributed_shares <= total_shares, "All shares are vested.");

        unlock_time += 365;

        distributed_shares = ((now - start_time) / 365 * annual_distribution);

        if (distributed_shares > 1000) {
            distributed_shares = 1000;
        }
    }

    function deactivate() public {
        require(msg.sender == human_resources || msg.sender == employee, "You are not authorized to deactivate this contract.");
        active = false;
    }

    function() external payable {
        revert("Do not send Ether to this contract!");
    }
}