aave-protocol-v2/contracts/libraries/aave-upgradeability/BaseImmutableAdminUpgradeabilityProxy.sol

// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.6.8;

import '../../dependencies/openzeppelin/upgradeability/BaseUpgradeabilityProxy.sol';

/**
 * @title BaseImmutableAdminUpgradeabilityProxy
 * @author Aave, inspired by the OpenZeppelin upgradeability proxy pattern
 * @dev This contract combines an upgradeability proxy with an authorization
 * mechanism for administrative tasks. The admin role is stored in an immutable, which
 * helps saving transactions costs
 * All external functions in this contract must be guarded by the
 * `ifAdmin` modifier. See ethereum/solidity#3864 for a Solidity
 * feature proposal that would enable this to be done automatically.
 */
contract BaseImmutableAdminUpgradeabilityProxy is BaseUpgradeabilityProxy {
  address immutable ADMIN;

  constructor(address admin) public {
    ADMIN = admin;
  }

  modifier ifAdmin() {
    if (msg.sender == ADMIN) {
      _;
    } else {
      _fallback();
    }
  }

  /**
   * @return The address of the proxy admin.
   */
  function admin() external ifAdmin returns (address) {
    return ADMIN;
  }

  /**
   * @return The address of the implementation.
   */
  function implementation() external ifAdmin returns (address) {
    return _implementation();
  }

  /**
   * @dev Upgrade the backing implementation of the proxy.
   * Only the admin can call this function.
   * @param newImplementation Address of the new implementation.
   */
  function upgradeTo(address newImplementation) external ifAdmin {
    _upgradeTo(newImplementation);
  }

  /**
   * @dev Upgrade the backing implementation of the proxy and call a function
   * on the new implementation.
   * This is useful to initialize the proxied contract.
   * @param newImplementation Address of the new implementation.
   * @param data Data to send as msg.data in the low level call.
   * It should include the signature and the parameters of the function to be called, as described in
   * https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector-and-argument-encoding.
   */
  function upgradeToAndCall(address newImplementation, bytes calldata data)
    external
    payable
    ifAdmin
  {
    _upgradeTo(newImplementation);
    (bool success, ) = newImplementation.delegatecall(data);
    require(success);
  }

  /**
   * @dev Only fall back when the sender is not the admin.
   */
  function _willFallback() internal virtual override {
    require(msg.sender != ADMIN, 'Cannot call fallback function from the proxy admin');
    super._willFallback();
  }
}