ImplementationA.sol

//SPDX-License-Identifier: MIT

pragma solidity ^0.8.1;

import "./Proxiable.sol";

contract ImplementationA is Proxiable {

    address public owner;
    uint public count;
    bool public initalized = false;

    function initialize() public {
        require(owner == address(0), "Already initalized");
        require(!initalized, "Already initalized");
        owner = msg.sender;
        initalized = true;
    }
    function encode() public pure returns(bytes memory ){
        return abi.encodeWithSignature("initialize()");
    }

    function increment() public {
        count++;
    }

    function updateCode(address newCode) onlyOwner public {
        updateCodeAddress(newCode);
    }

    modifier onlyOwner() {
        require(msg.sender == owner, "Only owner is allowed to perform this action");
        _;
    }
}

//SPDX-License-Identifier: MIT

pragma solidity ^0.8.1;

contract Proxy {
// Code position in storage is keccak256("PROXIABLE") = "0xc5f16f0fcc639fa48a6947836d9850f504798523bf8c9a3a87d5876cf622bcf7"
constructor( address contractLogic) {
// save the code address
assembly { // solium-disable-line
sstore(0xc5f16f0fcc639fa48a6947836d9850f504798523bf8c9a3a87d5876cf622bcf7, contractLogic)
}
}

fallback() external payable {
    assembly { // solium-disable-line
        let contractLogic := sload(0xc5f16f0fcc639fa48a6947836d9850f504798523bf8c9a3a87d5876cf622bcf7)
        calldatacopy(0x0, 0x0, calldatasize())
        let success := delegatecall(sub(gas(), 10000), contractLogic, 0x0, calldatasize(), 0, 0)
        let retSz := returndatasize()
        returndatacopy(0, 0, retSz)
        switch success
        case 0 {
            revert(0, retSz)
        }
        default {
            return(0, retSz)
        }
    }
}

}

//SPDX-License-Identifier: MIT

pragma solidity ^0.8.1;

contract Proxiable {
// Code position in storage is keccak256("PROXIABLE") = "0xc5f16f0fcc639fa48a6947836d9850f504798523bf8c9a3a87d5876cf622bcf7"

function updateCodeAddress(address newAddress) internal {
    require(
        bytes32(0xc5f16f0fcc639fa48a6947836d9850f504798523bf8c9a3a87d5876cf622bcf7) == Proxiable(newAddress).proxiableUUID(),
        "Not compatible"
    );
    assembly { // solium-disable-line
        sstore(0xc5f16f0fcc639fa48a6947836d9850f504798523bf8c9a3a87d5876cf622bcf7, newAddress)
    }
}

function proxiableUUID() public pure returns (bytes32) {
    return 0xc5f16f0fcc639fa48a6947836d9850f504798523bf8c9a3a87d5876cf622bcf7;
}

}