Work agreement and taxes smart contracts

WorkAgreement.sol

pragma solidity ^0.4.11;

contract TaxAuthority {
    address public owner;
    mapping (address => uint) public taxesCollected;

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

    function TaxAuthority() {
        owner = msg.sender;
    }

    function getBalance() constant returns (uint balance) {
        return this.balance;
    }

    function pay() payable {
        taxesCollected[msg.sender] += msg.value;
    }

    function withdraw(uint amount) onlyOwner {
        if (amount == 0 || amount > this.balance) {
            revert();
        }
        msg.sender.transfer(amount);
    }
}

contract WorkAgreement {
    address public employer;

    address public employee;
    uint public salaryPerPayPeriod;
    uint public payPeriodLengthInBlocks;
    uint public numPayPeriods;
    uint public numBufferPayPeriods;
    uint public startBlock;

    uint public endBlock;
    uint public lastWithdrawlBlock;

    uint public taxPercentage;

    modifier onlyEmployer() {
        require(msg.sender == employer);
        _;
    }

    modifier onlyEmployee() {
        require(msg.sender == employee);
        _;
    }

    function WorkAgreement(
        address _employee,
        uint _salaryPerPayPeriod,
        uint _payPeriodLengthInBlocks,
        uint _numPayPeriods,
        uint _numBufferPayPeriods,
        uint _startBlock
    )
        payable
    {
        if (
            msg.value == 0 ||
            _salaryPerPayPeriod == 0 ||
            _payPeriodLengthInBlocks == 0 ||
            _numPayPeriods == 0 ||
            _startBlock == 0 ||
            msg.value < _salaryPerPayPeriod * _numBufferPayPeriods ||
            msg.value > _salaryPerPayPeriod * _numPayPeriods ||
            _numBufferPayPeriods > _numPayPeriods
        ) {
            revert();
        }
        employer = msg.sender;
        employee = _employee;
        salaryPerPayPeriod = _salaryPerPayPeriod;
        payPeriodLengthInBlocks = _payPeriodLengthInBlocks;
        numPayPeriods = _numPayPeriods;
        numBufferPayPeriods = _numBufferPayPeriods;
        startBlock = _startBlock;
        lastWithdrawlBlock = _startBlock;
    }

    function deposit() payable onlyEmployer returns(uint newBalance) {
        if (
            this.balance > numPayPeriods * salaryPerPayPeriod ||
            (block.number > endBlock && endBlock > 0)
        ) {
            revert();
        }
        return this.balance;
    }

    function getBalance() constant returns(uint) {
        return this.balance;
    }

    function setEndBlock(uint blockNumber) onlyEmployer {
        if (endBlock < block.number) {
            revert();
        }
        endBlock = blockNumber;
    }

    function setTaxPercentage(uint percentage) onlyEmployee {
        if (percentage == taxPercentage || percentage > 100) {
            revert();
        }
        taxPercentage = percentage;
    }

    function triggerSeverance() onlyEmployee {
        if (this.balance >= numBufferPayPeriods * salaryPerPayPeriod) {
            revert();
        }
        employee.transfer(this.balance);
    }

    function withdraw() onlyEmployee {
        uint blocksSinceWithdrawl = block.number - lastWithdrawlBlock;
        uint payPeriodsSinceWithdrawl = blocksSinceWithdrawl / payPeriodLengthInBlocks;

        if (payPeriodsSinceWithdrawl < 1) {
            revert();
        }

        lastWithdrawlBlock = block.number;

        uint paymentAmount = payPeriodsSinceWithdrawl * salaryPerPayPeriod;
        uint taxedAmount = paymentAmount * taxPercentage / 100;
        uint paymentAmountAfterTaxes = paymentAmount - taxedAmount;

        employee.transfer(paymentAmountAfterTaxes);
        // taxAuthority.pay(taxedAmount);
    }
}