feat: Perform staticcall to CallbackVerifier

foundry/src/CallbackVerificationDispatcher.sol

@@ -1,5 +1,10 @@
 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.8.0;
+pragma solidity ^0.8.28;
+
+import "@interfaces/ICallbackVerifier.sol";
+
+error CallbackVerificationDispatcher__UnapprovedVerifier();
+error CallbackVerificationDispatcher__NonContractVerifier();
 
 /**
  * @title Dispatch callback verification to external contracts
@@ -12,4 +17,63 @@ pragma solidity ^0.8.0;
  */
 contract CallbackVerificationDispatcher {
     mapping(address => bool) public callbackVerifiers;
+
+    /**
+     * @dev Calls a callback verifier. This should revert if the callback verification fails.
+     */
+    // slither-disable-next-line dead-code
+    function _callVerifyCallback(bytes calldata data)
+        internal
+        returns (
+            uint256 amountOwed,
+            uint256 amountReceived,
+            address tokenOwed,
+            uint16 dataOffset
+        )
+    {
+        address verifier;
+        bytes4 decodedSelector;
+        bytes memory verifierData;
+
+        (verifier, decodedSelector, verifierData) =
+            _decodeVerifierAndSelector(data);
+
+        if (!callbackVerifiers[verifier]) {
+            revert CallbackVerificationDispatcher__UnapprovedVerifier();
+        }
+
+        bytes4 selector = decodedSelector == bytes4(0)
+            ? ICallbackVerifier.verifyCallback.selector
+            : decodedSelector;
+
+        address sender = msg.sender;
+
+        // slither-disable-next-line low-level-calls
+        (bool success, bytes memory result) = verifier.staticcall(
+            abi.encodeWithSelector(selector, sender, verifierData)
+        );
+
+        if (!success) {
+            if (result.length > 0) {
+                revert(string(result));
+            } else {
+                revert("Callback verification failed");
+            }
+        }
+
+        (amountOwed, amountReceived, tokenOwed, dataOffset) =
+            abi.decode(result, (uint256, uint256, address, uint16));
+    }
+
+    // slither-disable-next-line dead-code
+    function _decodeVerifierAndSelector(bytes calldata data)
+        internal
+        pure
+        returns (address verifier, bytes4 selector, bytes memory verifierData)
+    {
+        require(data.length >= 20, "Invalid data length");
+        verifier = address(uint160(bytes20(data[:20])));
+        selector = bytes4(data[20:24]);
+        verifierData = data[24:];
+    }
 }