Assignment #3

pragma solidity ^0.4.14;

import './SafeMath.sol';
import './Ownable.sol';

contract Payroll is Ownable {
    struct Employee {
        address id;
        uint salary;
        uint lastPayday;
    }
    
    uint constant payDuration = 10 seconds;
    
    uint totalSalary = 0 ether; 
    mapping(address => Employee) public employees;
    
    modifier employeeExist (address employeeId){
        var employee = employees[employeeId];
        assert(employee.id != 0x0);
        _;
    }
    
    //only employee have access to update payment address
    modifier onlyEmployee (address employeeId) {
        require(msg.sender == employees[employeeId].id);
        _;
      }
    
    function _partialPaid(Employee employee) private {
        uint payment = employee.salary * (now - employee.lastPayday) / payDuration;
        // employee.id.transfer(payment);
    }
    
    function addEmployee(address employeeId, uint salary) onlyOwner {
        var employee = employees[employeeId];
        assert(employee.id == 0x0);
        employees[employeeId] = Employee(employeeId,salary * 1 ether,now);
        totalSalary += employees[employeeId].salary;
    }
    
    function removeEmployee(address employeeId) onlyOwner employeeExist(employeeId) {
        var employee = employees[employeeId]; 
        _partialPaid(employee);
        totalSalary -= employees[employeeId].salary;
        delete employees[employeeId];
    }
    
    //update salary
    function changeEmployeeSalary(address employeeId, uint salary) onlyOwner employeeExist(employeeId){
        var employee = employees[employeeId];
        
        _partialPaid(employee);
        
        totalSalary -= employees[employeeId].salary;
        employees[employeeId].salary = salary * 1 ether;
        employees[employeeId].lastPayday = now;
        
        totalSalary += employees[employeeId].salary;
    }
    
    //update address
    function changePaymentAddress (address employeeId, address employeeIdNew) onlyEmployee (employeeId) employeeExist(employeeId){
        var employee = employees[employeeId];
        
        _partialPaid(employee);
        
        employees[employeeIdNew] = Employee(employeeIdNew,employees[employeeId].salary,now);
        delete employees[employeeId];
    }
    
    function addFund() payable returns (uint) {
        return this.balance;
    }
    
    function calculateRunway() returns (uint) {
        return this.balance / totalSalary;
    }
    
    function hasEnoughFund() returns (bool) {
        return calculateRunway() > 0;
    }
    
    function checkEmployee(address employeeId) returns(uint salary, uint lastPayday){
        var employee = employees[employeeId];
        salary = employee.salary;
        lastPayday = employee.lastPayday;
    }
    
    function getPaid() employeeExist(msg.sender){
        var employee = employees[msg.sender];
        
        uint nextPayday = employee.lastPayday + payDuration;
        assert(nextPayday < now);

        employees[msg.sender].lastPayday = nextPayday;
        employee.id.transfer(employee.salary);
    }
}