Add view method to estimate swaps outputs

contracts/adapters/BaseUniswapAdapter.sol

@@ -42,6 +42,48 @@ contract BaseUniswapAdapter {
     uniswapRouter = _uniswapRouter;
   }
 
+  /**
+ * @dev Given an input asset amount, returns the maximum output amount of the other asset
+ * @param amountIn Amount of reserveIn
+ * @param reserveIn Address of the asset to be swap from
+ * @param reserveOut Address of the asset to be swap to
+ * @return uint256 amountOut
+ */
+  function getAmountOut(uint256 amountIn, address reserveIn, address reserveOut)
+  public
+  view
+  returns (uint256)
+  {
+    address[] memory path = new address[](2);
+    path[0] = reserveIn;
+    path[1] = reserveOut;
+
+    uint256[] memory amounts = uniswapRouter.getAmountsOut(amountIn, path);
+
+    return amounts[1];
+  }
+
+  /**
+   * @dev Returns the minimum input asset amount required to buy the given output asset amount
+   * @param amountOut Amount of reserveOut
+   * @param reserveIn Address of the asset to be swap from
+   * @param reserveOut Address of the asset to be swap to
+   * @return uint256 amountIn
+   */
+  function getAmountIn(uint256 amountOut, address reserveIn, address reserveOut)
+  public
+  view
+  returns (uint256)
+  {
+    address[] memory path = new address[](2);
+    path[0] = reserveIn;
+    path[1] = reserveOut;
+
+    uint256[] memory amounts = uniswapRouter.getAmountsIn(amountOut, path);
+
+    return amounts[0];
+  }
+
   /**
    * @dev Swaps an `amountToSwap` of an asset to another
    * @param assetToSwapFrom Origin asset
@@ -191,7 +233,27 @@ contract BaseUniswapAdapter {
   }
 
   /**
-   * @dev Take action with the swap left overs as configured in the parameters
+   * @dev Pull the ATokens from the user
+   * @param reserve address of the asset
+   * @param user address
+   * @param amount of tokens to be transferred to the contract
+   */
+  function pullAToken(
+    address reserve,
+    address user,
+    uint256 amount
+  ) internal {
+    address reserveAToken = getAToken(reserve);
+
+    // transfer from user to adapter
+    IERC20(reserveAToken).safeTransferFrom(user, address(this), amount);
+
+    // withdraw reserve
+    pool.withdraw(reserve, amount);
+  }
+
+  /**
+   * @dev Pull the ATokens from the user and use them to repay the flashloan
    * @param reserve address of the asset
    * @param user address
    * @param flashLoanDebt need to be repaid
@@ -201,13 +263,7 @@ contract BaseUniswapAdapter {
     address user,
     uint256 flashLoanDebt
   ) internal {
-    address reserveAToken = getAToken(reserve);
+    pullAToken(reserve, user, flashLoanDebt);
-
-    // transfer from user to adapter
-    IERC20(reserveAToken).safeTransferFrom(user, address(this), flashLoanDebt);
-
-    // withdraw reserve
-    pool.withdraw(reserve, flashLoanDebt);
 
     // Repay flashloan
     IERC20(reserve).approve(address(pool), flashLoanDebt);

contracts/interfaces/IUniswapV2Router02.sol

@@ -17,4 +17,8 @@ interface IUniswapV2Router02 {
     address to,
     uint deadline
   ) external returns (uint256[] memory amounts);
+
+  function getAmountsOut(uint amountIn, address[] calldata path) external view returns (uint[] memory amounts);
+
+  function getAmountsIn(uint amountOut, address[] calldata path) external view returns (uint[] memory amounts);
 }

contracts/mocks/swap/MockUniswapV2Router02.sol

@@ -8,6 +8,8 @@ import {MintableERC20} from '../tokens/MintableERC20.sol';
 contract MockUniswapV2Router02 is IUniswapV2Router02 {
   uint256 internal _amountToReturn;
   uint256 internal _amountToSwap;
+  mapping(address => mapping(address => mapping(uint256 => uint256))) internal _amountsIn;
+  mapping(address => mapping(address => mapping(uint256 => uint256))) internal _amountsOut;
 
   function setAmountToReturn(uint256 amount) public {
     _amountToReturn = amount;
@@ -35,8 +37,8 @@ contract MockUniswapV2Router02 is IUniswapV2Router02 {
   }
 
   function swapTokensForExactTokens(
-    uint amountOut,
+    uint /* amountOut */,
-    uint amountInMax,
+    uint /* amountInMax */,
     address[] calldata path,
     address to,
     uint /* deadline */
@@ -50,4 +52,26 @@ contract MockUniswapV2Router02 is IUniswapV2Router02 {
     amounts[0] = _amountToSwap;
     amounts[1] = _amountToReturn;
   }
+
+  function setAmountOut(uint amountIn, address reserveIn, address reserveOut, uint amountOut) public {
+    _amountsOut[reserveIn][reserveOut][amountIn] = amountOut;
+  }
+
+  function setAmountIn(uint amountOut, address reserveIn, address reserveOut, uint amountIn) public {
+    _amountsIn[reserveIn][reserveOut][amountOut] = amountIn;
+  }
+
+  function getAmountsOut(uint amountIn, address[] calldata path) external view override returns (uint[] memory) {
+    uint256[] memory amounts = new uint256[](2);
+    amounts[0] = amountIn;
+    amounts[1] = _amountsOut[path[0]][path[1]][amountIn];
+    return amounts;
+  }
+
+  function getAmountsIn(uint amountOut, address[] calldata path) external view override returns (uint[] memory) {
+    uint256[] memory amounts = new uint256[](2);
+    amounts[0] = _amountsIn[path[0]][path[1]][amountOut];
+    amounts[1] = amountOut;
+    return amounts;
+  }
 }