pragma solidity ^0.5.16;

import "../interfaces/IERC20.sol";
import "../SafeDecimalMath.sol";

contract WETH is IERC20 {
    using SafeMath for uint256;

    string public name = "Wrapped Ether";
    string public symbol = "WETH";
    uint8 public decimals = 18;

    uint256 private _totalSupply;

    event Approval(address indexed src, address indexed guy, uint wad);
    event Transfer(address indexed src, address indexed dst, uint wad);
    event Deposit(address indexed dst, uint wad);
    event Withdrawal(address indexed src, uint wad);

    mapping(address => uint) public balanceOf;
    mapping(address => mapping(address => uint)) public allowance;

    function() external payable {
        deposit();
    }

    function deposit() public payable {
        balanceOf[msg.sender] += msg.value;
        _totalSupply = _totalSupply.add(msg.value);
        emit Deposit(msg.sender, msg.value);
    }

    function withdraw(uint wad) public {
        require(balanceOf[msg.sender] >= wad);
        balanceOf[msg.sender] -= wad;
        _totalSupply = _totalSupply.sub(wad);
        msg.sender.transfer(wad);
        emit Withdrawal(msg.sender, wad);
    }

    function totalSupply() public view returns (uint) {
        // Using _totalSupply instead of balanceOf[this]
        // as it would cause error in OVM compile
        // return address(this).balance;
        return _totalSupply;
    }

    function approve(address guy, uint wad) public returns (bool) {
        allowance[msg.sender][guy] = wad;
        emit Approval(msg.sender, guy, wad);
        return true;
    }

    function transfer(address dst, uint wad) public returns (bool) {
        return transferFrom(msg.sender, dst, wad);
    }

    function transferFrom(
        address src,
        address dst,
        uint wad
    ) public returns (bool) {
        require(balanceOf[src] >= wad);

        if (src != msg.sender && allowance[src][msg.sender] != uint(-1)) {
            require(allowance[src][msg.sender] >= wad);
            allowance[src][msg.sender] -= wad;
        }

        balanceOf[src] -= wad;
        balanceOf[dst] += wad;

        emit Transfer(src, dst, wad);

        return true;
    }
}