feat: delegatecall to executor in SwapExecutionDispatcher

foundry/src/SwapExecutionDispatcher.sol

@@ -1,6 +1,10 @@
 // SPDX-License-Identifier: UNLICENSED
 pragma solidity ^0.8.28;
 
+import "@interfaces/ISwapExecutor.sol";
+
+error SwapExecutionDispatcher__UnapprovedExecutor();
+
 /**
  * @title SwapExecutionDispatcher - Dispatch swap execution to external contracts
  * @author PropellerHeads Devs
@@ -10,8 +14,61 @@ pragma solidity ^0.8.28;
  *  be called using delegatecall so they can share state with the main
  *  contract if needed.
  *
- *  Note Executor contracts need to implement the ISwapExecutor interface
+ *  Note Executor contracts need to implement the ISwapExecutor interface unless
+ *  an alternate selector is specified.
  */
 contract SwapExecutionDispatcher {
     mapping(address => bool) public swapExecutors;
+
+    /**
+     * @dev Calls an executor, assumes swap.protocolData contains
+     *  token addresses if required by the executor.
+     */
+    function _callSwapExecutor(
+        uint8 exchange,
+        uint256 amount,
+        bytes calldata data
+    ) internal returns (uint256 calculatedAmount) {
+        address executor;
+        bytes4 decodedSelector;
+        bytes memory protocolData;
+
+        (executor, decodedSelector, protocolData) =
+            _decodeExecutorAndSelector(data);
+
+        bytes4 selector = decodedSelector == bytes4(0)
+            ? ISwapExecutor.swap.selector
+            : decodedSelector;
+
+        if (!swapExecutors[executor]){
+            revert SwapExecutionDispatcher__UnapprovedExecutor();
+        }
+
+        (bool success, bytes memory result) = executor.delegatecall(
+            abi.encodeWithSelector(selector, amount, protocolData)
+        );
+
+        if (!success) {
+            revert(
+                string(
+                    result.length > 0
+                        ? result
+                        : abi.encodePacked("Swap execution failed")
+                )
+            );
+        }
+
+        calculatedAmount = abi.decode(result, (uint256));
+    }
+
+    function _decodeExecutorAndSelector(bytes calldata data)
+        internal
+        pure
+        returns (address executor, bytes4 selector, bytes memory protocolData)
+    {
+        require(data.length >= 24, "Invalid data length");
+        executor = address(uint160(bytes20(data[:20])));
+        selector = bytes4(data[20:24]);
+        protocolData = data[24:];
+    }
 }