Add FlashSwapRouterV3Helper

contracts/swap/FlashSwapRouterV3Helper.sol

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+pragma solidity >=0.6.10 <0.8.0;
+
+import "./FlashSwapRouterV3.sol";
+
+contract FlashSwapRouterV3Helper {
+    FlashSwapRouterV3 public immutable flashSwapRouter;
+
+    constructor(address flashSwapRouter_) public {
+        flashSwapRouter = FlashSwapRouterV3(flashSwapRouter_);
+    }
+
+    /// @dev Only meant for an off-chain client to call with eth_call.
+    ///      When inQuote does not increase monotonically with outR,
+    ///      this function does not guarantee to return the optimal solution.
+    function getBuyRFromQuote(
+        IFundV5 fund,
+        bool needWrap,
+        address queenSwapOrPrimaryMarketRouter,
+        address tokenQuote,
+        uint256 minOutR,
+        uint256 maxOutR,
+        uint256 inQuote
+    ) external returns (uint256 outR) {
+        while (minOutR < maxOutR - 1) {
+            uint256 midOutR = minOutR / 2 + maxOutR / 2;
+            (bool success, bytes memory data) = address(flashSwapRouter).call(
+                abi.encodeWithSelector(
+                    FlashSwapRouterV3.getBuyR.selector,
+                    fund,
+                    needWrap,
+                    queenSwapOrPrimaryMarketRouter,
+                    tokenQuote,
+                    midOutR
+                )
+            );
+            if (success) {
+                (uint256 quoteDelta, ) = abi.decode(data, (uint256, uint256));
+                if (quoteDelta <= inQuote) {
+                    minOutR = midOutR;
+                    continue;
+                }
+            }
+            maxOutR = midOutR;
+        }
+        return minOutR;
+    }
+}