contract CurveExchangeAdapter is GSNRecipient {
    using SafeMath for uint256;
    
    IERC20 RENBTC;
    IERC20 WBTC;
    IERC20 curveToken;

    ICurveExchange public exchange;  
    IGatewayRegistry public registry;

    event Mint(uint256 mintValue);
    event Burn(uint256 burnValue);

    constructor(ICurveExchange _exchange, IGatewayRegistry _registry, IERC20 _wbtc) public {
        exchange = _exchange;
        registry = _registry;
        RENBTC = registry.getTokenBySymbol("BTC");
        WBTC = _wbtc;
        address curveTokenAddress = 0x49849C98ae39Fff122806C06791Fa73784FB3675;
        curveToken = IERC20(curveTokenAddress);
        
        // Approve exchange.
        require(RENBTC.approve(address(exchange), uint256(-1)));
        require(WBTC.approve(address(exchange), uint256(-1)));
    }
    
    // GSN Support
    function acceptRelayedCall(
        address,
        address,
        bytes calldata,
        uint256,
        uint256,
        uint256,
        uint256,
        bytes calldata,
        uint256
    ) external view returns (uint256, bytes memory) {
        return _approveRelayedCall();
    }
    
    function _preRelayedCall(bytes memory context) internal returns (bytes32) {
    }
    
    function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal {
    }
    
    function mintThenSwap(
        uint256 _minExchangeRate,
        uint256 _newMinExchangeRate,
        uint256 slippage,
        address payable _wbtcDestination,
        uint256 _amount,
        bytes32 _nHash,
        bytes calldata _sig
    ) external {
        // Mint renBTC tokens
        bytes32 pHash = keccak256(abi.encode(_minExchangeRate, slippage, _wbtcDestination));
        uint256 mintedAmount = registry.getGatewayBySymbol("BTC").mint(pHash, _amount, _nHash, _sig);

        emit Mint(mintedAmount);
        
        // Get price
        uint256 dy = exchange.get_dy(0, 1, mintedAmount);
        uint256 rate = dy.mul(1e8).div(mintedAmount);
        slippage = 1e4 - slippage;
        uint256 min_dy = mintedAmount.mul(rate).div(1e8).mul(slippage).div(1e4);
        
        // Price is OK
        if (rate >= _newMinExchangeRate) {
            uint256 startWbtcBalance = WBTC.balanceOf(address(this));
            exchange.exchange(0, 1, mintedAmount, min_dy);

            uint256 endWbtcBalance = WBTC.balanceOf(address(this));
            uint256 wbtcBought = endWbtcBalance.sub(startWbtcBalance);
        
            //Send proceeds to the User
            require(WBTC.transfer(_wbtcDestination, wbtcBought));
        } else {
            //Send renBTC to the User instead
            require(RENBTC.transfer(_wbtcDestination, mintedAmount));
        }
    }

    function mintThenDeposit(address payable _wbtcDestination, uint256 _amount, uint256[2] calldata amounts, uint256 min_mint_amount, uint256 new_min_mint_amount, bytes32 _nHash, bytes calldata _sig) external {
        // Mint renBTC tokens
        bytes32 pHash = keccak256(abi.encode(_wbtcDestination, amounts, min_mint_amount));
        //use actual _amount the user sent
        uint256 mintedAmount = registry.getGatewayBySymbol("BTC").mint(pHash, _amount, _nHash, _sig);

        emit Mint(mintedAmount);

        //set renBTC to actual minted amount in case the user sent less BTC to Ren
        uint256[2] memory receivedAmounts = amounts;
        receivedAmounts[0] = mintedAmount;
        uint256 calc_token_amount = exchange.calc_token_amount(amounts, true);
        if(calc_token_amount >= new_min_mint_amount) {
            require(WBTC.transferFrom(msg.sender, address(this), receivedAmounts[1]));
            uint256 curveBalanceBefore = curveToken.balanceOf(address(this));
            exchange.add_liquidity(receivedAmounts, 0);
            uint256 curveBalanceAfter = curveToken.balanceOf(address(this));
            uint256 curveAmount = curveBalanceAfter.sub(curveBalanceBefore);
            require(curveAmount >= new_min_mint_amount);
            require(curveToken.transfer(msg.sender, curveAmount));
        }
        else {
            require(RENBTC.transfer(_wbtcDestination, mintedAmount));
        }
    }

    function removeLiquidityThenBurn(bytes calldata _btcDestination, uint256 amount, uint256[2] calldata min_amounts) external {
        uint256 startRenbtcBalance = RENBTC.balanceOf(address(this));
        uint256 startWbtcBalance = WBTC.balanceOf(address(this));
        require(curveToken.transferFrom(msg.sender, address(this), amount));
        exchange.remove_liquidity(amount, min_amounts);
        uint256 endRenbtcBalance = RENBTC.balanceOf(address(this));
        uint256 endWbtcBalance = WBTC.balanceOf(address(this));
        uint256 wbtcWithdrawn = endWbtcBalance.sub(startWbtcBalance);
        require(WBTC.transfer(msg.sender, wbtcWithdrawn));
        uint256 renbtcWithdrawn = endRenbtcBalance.sub(startRenbtcBalance);

        // Burn and send proceeds to the User
        uint256 burnAmount = registry.getGatewayBySymbol("BTC").burn(_btcDestination, renbtcWithdrawn);
        emit Burn(burnAmount);
    }

    function removeLiquidityImbalanceThenBurn(bytes calldata _btcDestination, uint256[2] calldata amounts, uint256 max_burn_amount) external {
        uint256 startRenbtcBalance = RENBTC.balanceOf(address(this));
        uint256 startWbtcBalance = WBTC.balanceOf(address(this));
        uint256 _tokens = curveToken.balanceOf(msg.sender);
        if(_tokens > max_burn_amount) { 
            _tokens = max_burn_amount;
        }
        require(curveToken.transferFrom(msg.sender, address(this), _tokens));
        exchange.remove_liquidity_imbalance(amounts, max_burn_amount.mul(101).div(100));
        _tokens = curveToken.balanceOf(address(this));
        require(curveToken.transfer(msg.sender, _tokens));
        uint256 endRenbtcBalance = RENBTC.balanceOf(address(this));
        uint256 endWbtcBalance = WBTC.balanceOf(address(this));
        uint256 renbtcWithdrawn = endRenbtcBalance.sub(startRenbtcBalance);
        uint256 wbtcWithdrawn = endWbtcBalance.sub(startWbtcBalance);
        require(WBTC.transfer(msg.sender, wbtcWithdrawn));

        // Burn and send proceeds to the User
        uint256 burnAmount = registry.getGatewayBySymbol("BTC").burn(_btcDestination, renbtcWithdrawn);
        emit Burn(burnAmount);
    }

    //always removing in renBTC, else use normal method
    function removeLiquidityOneCoinThenBurn(bytes calldata _btcDestination, uint256 _token_amounts, uint256 min_amount) external {
        uint256 startRenbtcBalance = RENBTC.balanceOf(address(this));
        require(curveToken.transferFrom(msg.sender, address(this), _token_amounts));
        exchange.remove_liquidity_one_coin(_token_amounts, 0, min_amount);
        uint256 endRenbtcBalance = RENBTC.balanceOf(address(this));
        uint256 renbtcWithdrawn = endRenbtcBalance.sub(startRenbtcBalance);

        // Burn and send proceeds to the User
        uint256 burnAmount = registry.getGatewayBySymbol("BTC").burn(_btcDestination, renbtcWithdrawn);
        emit Burn(burnAmount);
    }
    
    function swapThenBurn(bytes calldata _btcDestination, uint256 _amount, uint256 _minRenbtcAmount) external {
        require(WBTC.transferFrom(msg.sender, address(this), _amount));
        uint256 startRenbtcBalance = RENBTC.balanceOf(address(this));
        exchange.exchange(1, 0, _amount, _minRenbtcAmount);
        uint256 endRenbtcBalance = RENBTC.balanceOf(address(this));
        uint256 renbtcBought = endRenbtcBalance.sub(startRenbtcBalance);
        
        // Burn and send proceeds to the User
        uint256 burnAmount = registry.getGatewayBySymbol("BTC").burn(_btcDestination, renbtcBought);
        emit Burn(burnAmount);
    }
}
function removeLiquidityOneCoinThenBurn(bytes calldata _btcDestination, uint256 _token_amounts, uint256 min_amount) external {
        uint256 startRenbtcBalance = RENBTC.balanceOf(address(this));
        require(curveToken.transferFrom(msg.sender, address(this), _token_amounts));
        exchange.remove_liquidity_one_coin(_token_amounts, 0, min_amount);
        uint256 endRenbtcBalance = RENBTC.balanceOf(address(this));
        uint256 renbtcWithdrawn = endRenbtcBalance.sub(startRenbtcBalance);

        // Burn and send proceeds to the User
        uint256 burnAmount = registry.getGatewayBySymbol("BTC").burn(_btcDestination, renbtcWithdrawn);
        emit Burn(burnAmount);
    }
//always removing in renBTC, else use normal method