ScdMcdMigration.sol

pragma solidity 0.5.12;

import { JoinLike, ManagerLike, SaiTubLike, VatLike } from "./Interfaces.sol";

contract ScdMcdMigration {
    SaiTubLike                  public tub;
    VatLike                     public vat;
    ManagerLike                 public cdpManager;
    JoinLike                    public saiJoin;
    JoinLike                    public wethJoin;
    JoinLike                    public daiJoin;

    constructor(
        address tub_,           // SCD tub contract address
        address cdpManager_,    // MCD manager contract address
        address saiJoin_,       // MCD SAI collateral adapter contract address
        address wethJoin_,      // MCD ETH collateral adapter contract address
        address daiJoin_        // MCD DAI adapter contract address
    ) public {
        tub = SaiTubLike(tub_);
        cdpManager = ManagerLike(cdpManager_);
        vat = VatLike(cdpManager.vat());
        saiJoin = JoinLike(saiJoin_);
        wethJoin = JoinLike(wethJoin_);
        daiJoin = JoinLike(daiJoin_);

        require(wethJoin.gem() == tub.gem(), "non-matching-weth");
        require(saiJoin.gem() == tub.sai(), "non-matching-sai");

        tub.gov().approve(address(tub), uint(-1));
        tub.skr().approve(address(tub), uint(-1));
        tub.sai().approve(address(tub), uint(-1));
        tub.sai().approve(address(saiJoin), uint(-1));
        wethJoin.gem().approve(address(wethJoin), uint(-1));
        daiJoin.dai().approve(address(daiJoin), uint(-1));
        vat.hope(address(daiJoin));
    }

    function add(uint x, uint y) internal pure returns (uint z) {
        require((z = x + y) >= x, "add-overflow");
    }

    function sub(uint x, uint y) internal pure returns (uint z) {
        require((z = x - y) <= x, "sub-underflow");
    }

    function mul(uint x, uint y) internal pure returns (uint z) {
        require(y == 0 || (z = x * y) / y == x, "mul-overflow");
    }

    function toInt(uint x) internal pure returns (int y) {
        y = int(x);
        require(y >= 0, "int-overflow");
    }

    // Function to swap SAI to DAI
    // This function is to be used by users that want to get new DAI in exchange of old one (aka SAI)
    // wad amount has to be <= the value pending to reach the debt ceiling (the minimum between general and ilk one)
    function swapSaiToDai(
        uint wad
    ) external {
        // Get wad amount of SAI from user's wallet:
        saiJoin.gem().transferFrom(msg.sender, address(this), wad);
        // Join the SAI wad amount to the `vat`:
        saiJoin.join(address(this), wad);
        // Lock the SAI wad amount to the CDP and generate the same wad amount of DAI
        vat.frob(saiJoin.ilk(), address(this), address(this), address(this), toInt(wad), toInt(wad));
        // Send DAI wad amount as a ERC20 token to the user's wallet
        daiJoin.exit(msg.sender, wad);
    }

    // Function to swap DAI to SAI
    // This function is to be used by users that want to get SAI in exchange of DAI
    // wad amount has to be <= the amount of SAI locked (and DAI generated) in the migration contract SAI CDP
    function swapDaiToSai(
        uint wad
    ) external {
        // Get wad amount of DAI from user's wallet:
        daiJoin.dai().transferFrom(msg.sender, address(this), wad);
        // Join the DAI wad amount to the vat:
        daiJoin.join(address(this), wad);
        // Payback the DAI wad amount and unlocks the same value of SAI collateral
        vat.frob(saiJoin.ilk(), address(this), address(this), address(this), -toInt(wad), -toInt(wad));
        // Send SAI wad amount as a ERC20 token to the user's wallet
        saiJoin.exit(msg.sender, wad);
    }

    // Function to migrate a SCD CDP to MCD one (needs to be used via a proxy so the code can be kept simpler). Check MigrationProxyActions.sol code for usage.
    // In order to use migrate function, SCD CDP debtAmt needs to be <= SAI previously deposited in the SAI CDP * (100% - Collateralization Ratio)
    function migrate(
        bytes32 cup
    ) external returns (uint cdp) {
        // Get values
        uint debtAmt = tub.tab(cup);    // CDP SAI debt
        uint pethAmt = tub.ink(cup);    // CDP locked collateral
        uint ethAmt = tub.bid(pethAmt); // CDP locked collateral equiv in ETH

        // Take SAI out from MCD SAI CDP. For this operation is necessary to have a very low collateralization ratio
        // This is not actually a problem as this ilk will only be accessed by this migration contract,
        // which will make sure to have the amounts balanced out at the end of the execution.
        vat.frob(
            bytes32(saiJoin.ilk()),
            address(this),
            address(this),
            address(this),
            -toInt(debtAmt),
            0
        );
        saiJoin.exit(address(this), debtAmt); // SAI is exited as a token

        // Shut SAI CDP and gets WETH back
        tub.shut(cup);      // CDP is closed using the SAI just exited and the MKR previously sent by the user (via the proxy call)
        tub.exit(pethAmt);  // Converts PETH to WETH

        // Open future user's CDP in MCD
        cdp = cdpManager.open(wethJoin.ilk(), address(this));

        // Join WETH to Adapter
        wethJoin.join(cdpManager.urns(cdp), ethAmt);

        // Lock WETH in future user's CDP and generate debt to compensate the SAI used to paid the SCD CDP
        (, uint rate,,,) = vat.ilks(wethJoin.ilk());
        cdpManager.frob(
            cdp,
            toInt(ethAmt),
            toInt(mul(debtAmt, 10 ** 27) / rate + 1) // To avoid rounding issues we add an extra wei of debt
        );
        // Move DAI generated to migration contract (to recover the used funds)
        cdpManager.move(cdp, address(this), mul(debtAmt, 10 ** 27));
        // Re-balance MCD SAI migration contract's CDP
        vat.frob(
            bytes32(saiJoin.ilk()),
            address(this),
            address(this),
            address(this),
            0,
            -toInt(debtAmt)
        );

        // Set ownership of CDP to the user
        cdpManager.give(cdp, msg.sender);
    }
}