Hi !
I need a review on the token and ICO smart contract, i also need help because I can't test the contract on the Remix virtual machine (I can't buy tokens on the VM), if someone can test the contract and tell me what they think please 
Contract:
pragma solidity ^0.5.7;
interface ERC20Interface {
function transfer(address to, uint tokens) external returns (bool success);
function transferFrom(address from, address to, uint tokens) external returns (bool success);
function balanceOf(address tokenOwner) external view returns (uint balance);
function approve(address spender, uint tokens) external returns (bool success);
function allowance(address tokenOwner, address spender) external view returns (uint remaining);
function totalSupply() external view returns (uint);
event Transfer(address indexed from, address indexed to, uint tokens);
event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}
contract ERC20Token is ERC20Interface {
string public name;
string public symbol;
uint8 public decimals;
uint public totalSupply;
mapping(address => uint) public balances;
mapping(address => mapping(address => uint)) public allowed;
constructor(
string memory _name,
string memory _symbol,
uint8 _decimals,
uint _totalSupply)
public {
name = _name;
symbol = _symbol;
decimals = _decimals;
totalSupply = _totalSupply;
balances[msg.sender] = _totalSupply;
}
function transfer(address to, uint value) public returns(bool) {
require(balances[msg.sender] >= value);
balances[msg.sender] -= value;
balances[to] += value;
emit Transfer(msg.sender, to, value);
return true;
}
function transferFrom(address from, address to, uint value) public returns(bool) {
uint allowance = allowed[from][msg.sender];
require(balances[msg.sender] >= value && allowance >= value);
allowed[from][msg.sender] -= value;
balances[msg.sender] -= value;
balances[to] += value;
emit Transfer(msg.sender, to, value);
return true;
}
function approve(address spender, uint value) public returns(bool) {
require(spender != msg.sender);
allowed[msg.sender][spender] = value;
emit Approval(msg.sender, spender, value);
return true;
}
function allowance(address owner, address spender) public view returns(uint) {
return allowed[owner][spender];
}
function balanceOf(address owner) public view returns(uint) {
return balances[owner];
}
}
contract ICO {
struct Sale {
address investor;
uint quantity;
}
Sale[] public sales;
mapping(address => bool) public investors;
address public token;
address public admin;
uint public end;
uint public price;
uint public availableTokens;
uint public minPurchase;
uint public maxPurchase;
bool public released;
constructor(
string memory _name,
string memory _symbol,
uint8 _decimals,
uint _totalSupply)
public {
token = address(new ERC20Token(
_name,
_symbol,
_decimals,
_totalSupply
));
admin = msg.sender;
}
function start(
uint duration,
uint _price,
uint _availableTokens,
uint _minPurchase,
uint _maxPurchase)
external
onlyAdmin()
icoNotActive() {
require(duration > 0, 'duration should be > 0');
uint totalSupply = ERC20Token(token).totalSupply();
require(_availableTokens > 0 && _availableTokens <= totalSupply, 'totalSupply should be > 0 and <= totalSupply');
require(_minPurchase > 0, '_minPurchase should > 0');
require(_maxPurchase > 0 && _maxPurchase <= _availableTokens, '_maxPurchase should be > 0 and <= _availableTokens');
end = duration + now;
price = _price;
availableTokens = _availableTokens;
minPurchase = _minPurchase;
maxPurchase = _maxPurchase;
}
function whitelist(address investor)
external
onlyAdmin() {
investors[investor] = true;
}
function buy()
payable
('
}
function release()
external
onlyAdmin()
icoEnded()
tokensNotReleased() {
ERC20Token tokenInstance = ERC20Token(token);
for(uint i = 0; i < sales.length; i++) {
Sale storage sale = sales[i];
tokenInstance.transfer(sale.investor, sale.quantity);
}
}
function withdraw(
address payable to,
uint amount)
external
onlyAdmin()
icoEnded()
tokensReleased() {
to.transfer(amount);
}
modifier icoActive() {
require(end > 0 && now < end && availableTokens > 0, "ICO must be active");
_;
}
modifier icoNotActive() {
require(end == 0, 'ICO should not be active');
_;
}
modifier icoEnded() {
require(end > 0 && (now >= end || availableTokens == 0), 'ICO must have ended');
_;
}
modifier tokensNotReleased() {
require(released == false, 'Tokens must NOT have been released');
_;
}
modifier tokensReleased() {
require(released == true, 'Tokens must have been released');
_;
}
modifier onlyInvestors() {
require(investors[msg.sender] == true, 'only investors');
_;
}
modifier onlyAdmin() {
require(msg.sender == admin, 'only admin');
_;
}
}