// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";

// The Skatosphere is full of rewards and treasure.
// This contract handles swapping to and from xGovernanceToken <> GovernanceToken
contract Skatosphere is ERC20 {
    using SafeMath for uint256;
    IERC20 public govToken;

    // Define the Skatosphere token contract
    constructor(
      string memory _name,
      string memory _symbol,
      IERC20 _govToken
    ) public ERC20(_name, _symbol) {
        govToken = _govToken;
    }

    // Locks GovernanceToken and mints xGovernanceToken
    function enter(uint256 _amount) public {
        // Gets the amount of GovernanceToken locked in the contract
        uint256 totalGovernanceToken = govToken.balanceOf(address(this));
        // Gets the amount of xGovernanceToken in existence
        uint256 totalShares = totalSupply();
        // If no xGovernanceToken exists, mint it 1:1 to the amount put in
        if (totalShares == 0 || totalGovernanceToken == 0) {
            _mint(msg.sender, _amount);
        }
        // Calculate and mint the amount of xGovernanceToken the GovernanceToken is worth. The ratio will change overtime, as xGovernanceToken is burned/minted and GovernanceToken deposited + gained from fees / withdrawn.
        else {
            uint256 what = _amount.mul(totalShares).div(totalGovernanceToken);
            _mint(msg.sender, what);
        }
        // Lock the GovernanceToken in the contract
        govToken.transferFrom(msg.sender, address(this), _amount);
    }

    // Unclocks the staked + gained GovernanceToken and burns xGovernanceToken
    function leave(uint256 _share) public {
        // Gets the amount of xGovernanceToken in existence
        uint256 totalShares = totalSupply();
        // Calculates the amount of GovernanceToken the xGovernanceToken is worth
        uint256 what =
            _share.mul(govToken.balanceOf(address(this))).div(totalShares);
        _burn(msg.sender, _share);
        govToken.transfer(msg.sender, what);
    }
}