SupplyChain.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
...
    // 9th step in supply chain process
    function purchaseItemByRetailer(uint256 _productCode)
        public
        payable
        onlyRetailer // check _msgSender() belongs to RetailerRole
        forSaleByDistributor(_productCode)
        paidEnough(items[_productCode].productPrice)
        checkValue(_productCode, payable(_msgSender()))
    {
        address payable ownerAddressPayable = _make_payable(
            items[_productCode].distributorID
        );
        ownerAddressPayable.transfer(items[_productCode].productPrice);
        items[_productCode].ownerID = _msgSender();
        items[_productCode].retailerID = _msgSender();
        items[_productCode].itemState = State.PurchasedByRetailer;
        itemsHistory[_productCode].DTR = block.number;
        emit PurchasedByRetailer(_productCode);
    }

    // 10th step in supply chain process
    function shippedItemByDistributor(uint256 _productCode)
        public
        onlyDistributor // check _msgSender() belongs to DistributorRole
        purchasedByRetailer(_productCode)
        verifyCaller(items[_productCode].distributorID) // check _msgSender() is distributorID
    {
        items[_productCode].itemState = State.ShippedByDistributor;
        emit ShippedByDistributor(_productCode);
    }

    // 11th step in supply chain process
    function receivedItemByRetailer(uint256 _productCode)
        public
        onlyRetailer // check _msgSender() belongs to RetailerRole
        shippedByDistributor(_productCode)
        verifyCaller(items[_productCode].ownerID) // check _msgSender() is ownerID
    {
        items[_productCode].itemState = State.ReceivedByRetailer;
        emit ReceivedByRetailer(_productCode);
    }
  ...