fix flashswap sell logic; add back swapcore interface

contracts/fund/PrimaryMarketV5.sol

@@ -163,6 +163,39 @@ contract PrimaryMarketV5 is IPrimaryMarketV5, ReentrancyGuard, ITrancheIndexV2,
         underlying = _getRedemption(inQ - feeQ);
     }
 
+    /// @notice Calculate the amount of QUEEN that can be redeemed for at least the given amount
+    ///         of underlying tokens.
+    /// @dev The return value may not be the minimum solution due to rounding errors.
+    /// @param minUnderlying Minimum received underlying amount
+    /// @return inQ QUEEN amount that should be redeemed
+    function getRedemptionForUnderlying(
+        uint256 minUnderlying
+    ) external view override returns (uint256 inQ) {
+        // Assume:
+        //   minUnderlying * fundEquivalentTotalQ = a * fundUnderlying - b
+        //   a * 1e18 = c * (1e18 - redemptionFeeRate) + d
+        // where
+        //   a, b, c, d are integers
+        //   0 <= b < fundUnderlying
+        //   0 <= d < 1e18 - redemeptionFeeRate
+        // Then
+        //   inQAfterFee = a
+        //   inQ = c
+        //   getRedemption(inQ).underlying
+        //     = floor((c - floor(c * redemptionFeeRate / 1e18)) * fundUnderlying / fundEquivalentTotalQ)
+        //     = floor(ceil(c * (1e18 - redemptionFeeRate) / 1e18) * fundUnderlying / fundEquivalentTotalQ)
+        //     = floor(((c * (1e18 - redemptionFeeRate) + d) / 1e18) * fundUnderlying / fundEquivalentTotalQ)
+        //     = floor(a * fundUnderlying / fundEquivalentTotalQ)
+        //     => floor((a * fundUnderlying - b) / fundEquivalentTotalQ)
+        //     = minUnderlying
+        uint256 fundUnderlying = IFundV3(fund).getTotalUnderlying();
+        uint256 fundEquivalentTotalQ = IFundV3(fund).getEquivalentTotalQ();
+        uint256 inQAfterFee = minUnderlying.mul(fundEquivalentTotalQ).add(fundUnderlying - 1).div(
+            fundUnderlying
+        );
+        return inQAfterFee.divideDecimal(1e18 - redemptionFeeRate);
+    }
+
     /// @notice Calculate the result of a split.
     /// @param inQ QUEEN amount to be split
     /// @return outB Received BISHOP amount

contracts/fund/WstETHPrimaryMarketRouter.sol

@@ -9,8 +9,9 @@ import "../interfaces/IPrimaryMarketV5.sol";
 import "../interfaces/IFundV3.sol";
 import "../interfaces/IWstETH.sol";
 import "../interfaces/ITrancheIndexV2.sol";
+import "../interfaces/IStableSwap.sol";
 
-contract WstETHPrimaryMarketRouter is ITrancheIndexV2 {
+contract WstETHPrimaryMarketRouter is IStableSwapCore, ITrancheIndexV2 {
     using SafeERC20 for IERC20;
 
     IPrimaryMarketV5 public immutable primaryMarket;
@@ -28,6 +29,51 @@ contract WstETHPrimaryMarketRouter is ITrancheIndexV2 {
         _tokenB = fund_.tokenB();
     }
 
+    /// @dev Get redemption with StableSwap getQuoteOut interface.
+    function getQuoteOut(uint256 baseIn) external view override returns (uint256 quoteOut) {
+        (quoteOut, ) = primaryMarket.getRedemption(baseIn);
+    }
+
+    /// @dev Get creation for QUEEN with StableSwap getQuoteIn interface.
+    function getQuoteIn(uint256 baseOut) external view override returns (uint256 quoteIn) {
+        quoteIn = primaryMarket.getCreationForQ(baseOut);
+    }
+
+    /// @dev Get creation with StableSwap getBaseOut interface.
+    function getBaseOut(uint256 quoteIn) external view override returns (uint256 baseOut) {
+        baseOut = primaryMarket.getCreation(quoteIn);
+    }
+
+    /// @dev Get redemption for underlying with StableSwap getBaseIn interface.
+    function getBaseIn(uint256 quoteOut) external view override returns (uint256 baseIn) {
+        baseIn = primaryMarket.getRedemptionForUnderlying(quoteOut);
+    }
+
+    /// @dev Create QUEEN with StableSwap buy interface.
+    ///      Underlying should have already been sent to this contract
+    function buy(
+        uint256 version,
+        uint256 baseOut,
+        address recipient,
+        bytes calldata
+    ) external override returns (uint256 realBaseOut) {
+        uint256 routerQuoteBalance = IERC20(_wstETH).balanceOf(address(this));
+        IERC20(_wstETH).safeTransfer(address(primaryMarket), routerQuoteBalance);
+        realBaseOut = primaryMarket.create(recipient, baseOut, version);
+    }
+
+    /// @dev Redeem QUEEN with StableSwap sell interface.
+    ///      QUEEN should have already been sent to this contract
+    function sell(
+        uint256 version,
+        uint256 quoteOut,
+        address recipient,
+        bytes calldata
+    ) external override returns (uint256 realQuoteOut) {
+        uint256 routerBaseBalance = fund.trancheBalanceOf(TRANCHE_Q, address(this));
+        realQuoteOut = primaryMarket.redeem(recipient, routerBaseBalance, quoteOut, version);
+    }
+
     function create(
         address recipient,
         bool needWrap,

contracts/interfaces/IPrimaryMarketV5.sol

@@ -10,6 +10,8 @@ interface IPrimaryMarketV5 {
 
     function getRedemption(uint256 inQ) external view returns (uint256 underlying, uint256 fee);
 
+    function getRedemptionForUnderlying(uint256 minUnderlying) external view returns (uint256 inQ);
+
     function getSplit(uint256 inQ) external view returns (uint256 outB, uint256 outR);
 
     function getSplitForR(uint256 minOutR) external view returns (uint256 inQ, uint256 outB);

contracts/swap/FlashSwapRouterV3.sol

@@ -159,9 +159,12 @@ contract FlashSwapRouterV3 is ITranchessSwapCallee, ITrancheIndexV2, Ownable {
                     version
                 );
                 // Redeem or swap QUEEN for underlying
+                uint256 underlyingAmount = IStableSwapCoreInternalRevertExpected(
+                    queenSwapOrPrimaryMarketRouter
+                ).getQuoteOut(outQ);
                 uint256 totalQuoteAmount = IStableSwapCoreInternalRevertExpected(
                     queenSwapOrPrimaryMarketRouter
-                ).sell(version, 0, address(this), "");
+                ).sell(version, underlyingAmount, address(this), "");
                 // Send back quote asset to tranchess swap
                 IERC20(tokenQuote).safeTransfer(msg.sender, quoteAmount);
                 // Send the rest of quote asset to user

test/flashSwapRouterV3.ts

@@ -118,7 +118,7 @@ describe("FlashSwapRouterV3", function () {
             BigNumber.from(1).shl(256).sub(1),
             true
         );
-        const PrimaryMarketRouter = await ethers.getContractFactory("PrimaryMarketRouter");
+        const PrimaryMarketRouter = await ethers.getContractFactory("WstETHPrimaryMarketRouter");
         const primaryMarketRouter = await PrimaryMarketRouter.connect(owner).deploy(
             primaryMarket.address
         );
@@ -183,7 +183,7 @@ describe("FlashSwapRouterV3", function () {
         await steth.approve(wsteth.address, initWstETH);
         await wsteth.wrap(initWstETH);
         await wsteth.approve(primaryMarketRouter.address, initWstETH);
-        await primaryMarketRouter.create(owner.address, initWstETH, 0, 0);
+        await primaryMarketRouter.create(owner.address, false, initWstETH, 0, 0);
         await primaryMarket.split(owner.address, initQ, 0);
         await fund.trancheApprove(TRANCHE_B, swapRouter.address, LP_B, 0);
         await steth.mint(owner.address, LP_STETH);