SupplyChain.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
...

  // 4th step in supply chain process
    function shippedItemByFarmer(uint256 _productCode)
        public
        payable
        onlyFarmer // check _msgSender() belongs to FarmerRole
        purchasedByDistributor(_productCode)
        verifyCaller(items[_productCode].farmerID) // check _msgSender() is originFarmID
    {
        items[_productCode].itemState = State.ShippedByFarmer; // update state
        emit ShippedByFarmer(_productCode);
    }

    // 5th step in supply chain process
    function receivedItemByDistributor(uint256 _productCode)
        public
        onlyDistributor // check _msgSender() belongs to DistributorRole
        shippedByFarmer(_productCode)
        verifyCaller(items[_productCode].ownerID) // check _msgSender() is owner
    {
        items[_productCode].itemState = State.ReceivedByDistributor; // update state
        emit ReceivedByDistributor(_productCode);
    }
 ...