add liquidate callback function

contracts/OverlayV1Market.sol

@@ -8,6 +8,7 @@ import "./interfaces/IOverlayV1Factory.sol";
 import "./interfaces/IOverlayV1Market.sol";
 import "./interfaces/IOverlayV1Token.sol";
 import "./interfaces/feeds/IOverlayV1Feed.sol";
+import "./interfaces/callback/IOverlayMarketLiquidateCallback.sol";
 
 import "./libraries/FixedCast.sol";
 import "./libraries/FixedPoint.sol";
@@ -507,6 +508,11 @@ contract OverlayV1Market is IOverlayV1Market, Pausable {
             pos.isLong ? oiLongShares : oiShortShares
         );
 
+        // if the owner of the potision has LIQUIDATE_CALLBACK_ROLE, make a callback
+        if (ov.hasRole(LIQUIDATE_CALLBACK_ROLE, owner)) {
+            IOverlayMarketLiquidateCallback(owner).overlayMarketLiquidateCallback(positionId);
+        }
+
         // burn the pnl for the position + insurance margin
         ov.burn(cost - value + marginToBurn);
 

contracts/interfaces/IOverlayV1Token.sol

@@ -10,6 +10,7 @@ bytes32 constant GOVERNOR_ROLE = keccak256("GOVERNOR");
 bytes32 constant GUARDIAN_ROLE = keccak256("GUARDIAN");
 bytes32 constant PAUSER_ROLE = keccak256("PAUSER");
 bytes32 constant RISK_MANAGER_ROLE = keccak256("RISK_MANAGER");
+bytes32 constant LIQUIDATE_CALLBACK_ROLE = keccak256("LIQUIDATE_CALLBACK");
 
 interface IOverlayV1Token is IAccessControl, IERC20 {
     // mint/burn

contracts/interfaces/callback/IOverlayMarketLiquidateCallback.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+pragma solidity >=0.5.0;
+
+/// @title Callback for OverlayV1Market#liquidate
+interface IOverlayMarketLiquidateCallback {
+    /// @notice Called to `owner` after executing a liquidation.
+    /// amount0Delta and amount1Delta can both be 0 if no tokens were swapped.
+    /// @param positionId The positionId of the liquidated position
+    function overlayMarketLiquidateCallback(
+        uint256 positionId
+    ) external;
+}