initial commit for Pool Manager hook

contracts/ERC721PoolManager.sol

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: CC0-1.0
+// Compatible with OpenZeppelin Contracts ^5.0.0
+pragma solidity ^0.8.15;
+
+import "@openzeppelin/contracts/access/AccessControl.sol";
+
+interface DistributionPool {
+    function getUnits(address memberAddr) external view returns (uint128);
+    function updateMemberUnits(address memberAddr, uint128 newUnits) external returns (bool);
+}
+
+contract ERC721PoolManager is AccessControl {
+    bytes32 public constant MANAGER_ROLE = keccak256("MANAGER_ROLE");
+
+    address public nft;
+    DistributionPool public pool;
+
+    constructor(address _nft, DistributionPool _pool) {
+        nft = _nft;
+        pool = _pool;
+        _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
+        _grantRole(MANAGER_ROLE, msg.sender);
+    }
+
+    function setPool(DistributionPool _pool) external {
+        require(hasRole(MANAGER_ROLE, msg.sender), "ERC721PoolManager: must have manager role to set pool");
+        pool = _pool;
+    }
+
+    function setNft(address _nft) external {
+        require(hasRole(MANAGER_ROLE, msg.sender), "ERC721PoolManager: must have manager role to set NFT");
+        nft = _nft;
+    }
+
+    function updateMemberUnits(address memberAddr, uint128 newUnits) external {
+        require(hasRole(MANAGER_ROLE, msg.sender), "ERC721PoolManager: must have manager role to update units");
+        pool.updateMemberUnits(memberAddr, newUnits);
+    }
+
+    function _beforeTokenTransfer(
+        address from,
+        address to,
+        uint256,
+        uint256
+    ) external {
+        // require that the caller is the NFT contract:
+        require(msg.sender == nft, "ERC721PoolManager: caller is not the NFT contract");
+        // first adjust sender's units:
+        if (from != address(0)) {
+            uint128 senderUnits = pool.getUnits(from);
+            if (senderUnits > 0) {
+                pool.updateMemberUnits(from, senderUnits - 1);
+            }
+        }
+        // now adjust recipient's units:
+        if (to != address(0)) {
+            uint128 recipientUnits = pool.getUnits(to);
+            pool.updateMemberUnits(to, recipientUnits + 1);
+        }
+    }
+
+}
+