pragma solidity ^0.5.2;

/*
 * SPDX-License-Identitifer:    MIT
 */


// See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-897.md

interface ERCProxy {
    function proxyType() external pure returns (uint256 proxyTypeId);
    function implementation() external view returns (address codeAddr);
}



contract DelegateProxyForwarder {
    function delegatedFwd(address _dst, bytes memory _calldata) internal {
        // solium-disable-next-line security/no-inline-assembly
        assembly {
            let result := delegatecall(
                sub(gas, 10000),
                _dst,
                add(_calldata, 0x20),
                mload(_calldata),
                0,
                0
            )
            let size := returndatasize

            let ptr := mload(0x40)
            returndatacopy(ptr, 0, size)

            // revert instead of invalid() bc if the underlying call failed with invalid() it already wasted gas.
            // if the call returned error data, forward it
            switch result
                case 0 {
                    revert(ptr, size)
                }
                default {
                    return(ptr, size)
                }
        }
    }
    
    function isContract(address _target) internal view returns (bool) {
        if (_target == address(0)) {
            return false;
        }

        uint256 size;
        assembly {
            size := extcodesize(_target)
        }
        return size > 0;
    }
}




contract DelegateProxy is ERCProxy, DelegateProxyForwarder {
    function proxyType() external pure returns (uint256 proxyTypeId) {
        // Upgradeable proxy
        proxyTypeId = 2;
    }

    function implementation() external view returns (address);
}



contract UpgradableProxy is DelegateProxy {
    event ProxyUpdated(address indexed _new, address indexed _old);
    event OwnerUpdate(address _new, address _old);

    bytes32 constant IMPLEMENTATION_SLOT = keccak256("matic.network.proxy.implementation");
    bytes32 constant OWNER_SLOT = keccak256("matic.network.proxy.owner");

    constructor(address _proxyTo) public {
        setOwner(msg.sender);
        setImplementation(_proxyTo);
    }

    function() external payable {
        // require(currentContract != 0, "If app code has not been set yet, do not call");
        // Todo: filter out some calls or handle in the end fallback
        delegatedFwd(loadImplementation(), msg.data);
    }

    modifier onlyProxyOwner() {
        require(loadOwner() == msg.sender, "NOT_OWNER");
        _;
    }

    function owner() external view returns(address) {
        return loadOwner();
    }

    function loadOwner() internal view returns(address) {
        address _owner;
        bytes32 position = OWNER_SLOT;
        assembly {
            _owner := sload(position)
        }
        return _owner;
    }

    function implementation() external view returns (address) {
        return loadImplementation();
    }

    function loadImplementation() internal view returns(address) {
        address _impl;
        bytes32 position = IMPLEMENTATION_SLOT;
        assembly {
            _impl := sload(position)
        }
        return _impl;
    }

    function transferOwnership(address newOwner) public onlyProxyOwner {
        require(newOwner != address(0), "ZERO_ADDRESS");
        emit OwnerUpdate(newOwner, loadOwner());
        setOwner(newOwner);
    }

    function setOwner(address newOwner) private {
        bytes32 position = OWNER_SLOT;
        assembly {
            sstore(position, newOwner)
        }
    }

    function updateImplementation(address _newProxyTo) public onlyProxyOwner {
        require(_newProxyTo != address(0x0), "INVALID_PROXY_ADDRESS");
        require(isContract(_newProxyTo), "DESTINATION_ADDRESS_IS_NOT_A_CONTRACT");

        emit ProxyUpdated(_newProxyTo, loadImplementation());
        
        setImplementation(_newProxyTo);
    }

    function updateAndCall(address _newProxyTo, bytes memory data) payable public onlyProxyOwner {
        updateImplementation(_newProxyTo);

        (bool success, bytes memory returnData) = address(this).call.value(msg.value)(data);
        require(success, string(returnData));
    }

    function setImplementation(address _newProxyTo) private {
        bytes32 position = IMPLEMENTATION_SLOT;
        assembly {
            sstore(position, _newProxyTo)
        }
    }
}



contract StakeManagerProxy is UpgradableProxy {
    constructor(address _proxyTo) public UpgradableProxy(_proxyTo) {}
}

{
  "compilationTarget": {
    "StakeManagerProxy.sol": "StakeManagerProxy"
  },
  "evmVersion": "istanbul",
  "libraries": {},
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}