feat: implement admin functions contract (#16)

Author: mpetrun5

contracts/Admin.sol

@@ -0,0 +1,52 @@
+// The Licensed Work is (c) 2022 Sygma
+// SPDX-License-Identifier: LGPL-3.0-only
+pragma solidity 0.8.20;
+
+import "@openzeppelin/contracts/access/Ownable.sol";
+
+/**
+    @title Facilitates deposits and creation of deposit proposals, and deposit executions.
+    @author ChainSafe Systems.
+ */
+contract Admin is Ownable {
+    event StartKeygen();
+    event EndKeygen();
+    event KeyRefresh(string hash);
+
+    error MPCAddressAlreadySet();
+    error MPCAddressIsNotUpdatable();
+    error MPCAddressZeroAddress();
+
+    constructor() Ownable(msg.sender) {}
+
+    /**
+        @notice Once MPC address is set, this method can't be invoked anymore.
+        It's used to trigger the belonging process on the MPC side which also handles keygen function calls order.
+        @notice Only callable by owner
+     */
+    function startKeygen() external onlyOwner {
+        if (_MPCAddress != address(0)) revert MPCAddressAlreadySet();
+        emit StartKeygen();
+    }
+
+    /**
+        @notice This method can be called only once, after the MPC address is set.
+        @notice Only callable by owner.
+        @param MPCAddress Address that will be set as MPC address.
+     */
+    function endKeygen(address MPCAddress) external onlyOwner {
+        if(MPCAddress == address(0)) revert MPCAddressZeroAddress();
+        if (_MPCAddress != address(0)) revert MPCAddressIsNotUpdatable();
+        _MPCAddress = MPCAddress;
+        emit EndKeygen();
+    }
+
+    /**
+        @notice It's used to trigger the refresh process on the MPC side.
+        @notice Only callable by owner
+        @param hash Topology hash which prevents changes during refresh process.
+     */
+    function refreshKey(string memory hash) external onlyOwner {
+        emit KeyRefresh(hash);
+    }
+}