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contracts...Learning...CropsSupplyChain.sol

//SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

contract CropsSupplyChain{

    //Define variable for tracking crop batch

    struct CropBatch{
        string origin;
        string cropType;
        uint256 quantity;
        uint256 dateProduced;
        address producer;
        address[] handlers;
        address distributor;
        bool isCertified;
    }
    //Define variables for tracking certifications
    struct Certification{
        address certifier;
        string standard;
        string result;
        uint256 dateCertified;
    }
    //batch ids to crops batach information

    mapping(uint256 => CropBatch) public cropsBatches;

    //mapping for batch ids to array of certification
    mapping(uint256 => Certification[]) public certifications;

    //counter for genreating batch ids
    uint256 public batchCounter = 0;

    //event for when new crop batch is created
    event CropBatchCreated(uint256 batchId,
                                string origin,
                                string cropType,
                                uint256 quantity,
                                uint256 dateProduced,
                                address producer
                                );
    //event when crop batch is certified
    event CropBatchCertified(uint256 batchId,
                                address certifier,
                                string standard,
                                string result,
                                uint256 dateCertified);
    //function to created crop batch
    function createCropBatch(string memory _origin,
                                string memory _cropType,
                                uint256 _quantity,
                                uint256 _dateProduced
                                ) 
                                public {
            batchCounter++;
            CropBatch storage newBatch = cropsBatches[batchCounter];
            newBatch.origin = _origin;
            newBatch.cropType = _cropType;
            newBatch.quantity = _quantity;
            newBatch.dateProduced = _dateProduced;
            newBatch.producer = msg.sender;

            emit CropBatchCreated(batchCounter,_origin,_cropType,_quantity,_dateProduced,msg.sender);
        
        }
        //function for adding a handler to crop batch
        function addHandler(uint256 _batchId,address _hanlder) public{
            CropBatch storage batch = cropsBatches[_batchId];
            require(batch.producer == msg.sender || batch.distributor==msg.sender || batch.handlers[batch.handlers.length-1]== msg.sender,"Only Producer,distributor and current handler  can add a handler"); 
            batch.handlers.push(_hanlder);
        }
        //function to certifyin a crop batch

        function certifyCropBatch(uint256 _batchId,string memory _standard,string memory _result )
                                    public{
                    CropBatch storage batch = cropsBatches[_batchId];
                    require(batch.isCertified == false,"Batch is already certified");
                    require(batch.distributor == msg.sender,"Only distributor can certify a batch ");
                    certifications[_batchId].push(Certification(msg.sender,_standard,_result,block.timestamp));
                    batch.isCertified = true;
                    
                    emit CropBatchCertified(_batchId,msg.sender,_standard,_result,block.timestamp);
                }

        //function for getting the certifications for a crop 
        function getCropBatchCertifications(uint256 _batchId) public view returns(Certification[] memory){
            return certifications[_batchId];
        }

}