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contracts...GrainExport.sol

//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol";
import "hardhat/console.sol";

// 0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2,0x4B20993Bc481177ec7E8f571ceCaE8A9e22C02db,0x78731D3Ca6b7E34aC0F824c42a7cC18A495cabaB,0x617F2E2fD72FD9D5503197092aC168c91465E7f2

enum ShipmentStatus {
    InUkraine, // Registered in Ukraine
    LeftUkraine, // Navigating in Black Sea
    ArrivedInTurkey, // Arrived in Turkey
    LeftTurkey, // Left Turkey
    ArrivedInDestinationCountry // Arrived to the destination country
}

struct Shipment {
    string destination;
    ShipmentStatus status;
}

contract GrainExport is Ownable {
    address private ukraine;
    address private russia;
    address private turkey;
    address private un;

    bool private ukraineSigned;
    bool private russiaSigned;
    bool private turkeySigned;
    bool private unSigned;

    uint256 private currentShipmentId;

    mapping(uint256 => Shipment) shipments;

    event SignedByUkraine();
    event SignedByRussia();
    event SignedByTurkey();
    event SignedByUN();
    event AgreementSigned();

    event ShipmentCreated(uint256 shipmentId);
    event ShipmentLeftUkraine(uint256 shipmentId);
    event ShipmentArrivedInTurkey(uint256 shipmentId);
    event ShipmentExamined(uint256 shipmentId);
    event ShipmentArrivedInDestination(uint256 shipmentId, string destination);

    modifier agreementSigned() {
        // require(ukraineSigned, "Ukraine not signed");
        // require(russiaSigned, "Russia not signed");
        // require(turkeySigned, "Turkey not signed");
        // require(unSigned, "United Nations not signed");
        _;
    }

    constructor(address _ukraine, address _russia, address _turkey, address _un) {
        ukraine = _ukraine;
        russia = _russia;
        turkey = _turkey;
        un = _un;
    }

    function sign() external {
        console.log("Signer address", msg.sender);

        require(msg.sender == ukraine || msg.sender == russia || msg.sender == turkey || msg.sender == un, "Unknown signer");

        if (msg.sender == ukraine) {
            ukraineSigned = true;
            emit SignedByUkraine();
        }

        if (msg.sender == russia) {
            russiaSigned = true;
            emit SignedByRussia();
        }

        if (msg.sender == turkey) {
            turkeySigned = true;
            emit SignedByTurkey();
        }

        if (msg.sender == un) {
            unSigned = true;
            emit SignedByUN();
        }

        if (ukraineSigned && russiaSigned && turkeySigned && unSigned) {
            emit AgreementSigned();
        }
    }

    // -- Shipment -- //
    function getShipment(uint256 shipmentId) external view returns(Shipment memory) {
        return shipments[shipmentId];
    }
    
    function createShipment(string memory _destination) external agreementSigned {
        require(msg.sender == ukraine, "Caller is not Ukraine");

        currentShipmentId++;
        shipments[currentShipmentId] = Shipment(_destination, ShipmentStatus.InUkraine);

        console.log("Shipment created", currentShipmentId);
        emit ShipmentCreated(currentShipmentId);
    }

    function leftUkraine(uint256 shipmentId) external agreementSigned {
        require(msg.sender == ukraine, "Caller is not Ukraine");

        shipments[shipmentId].status = ShipmentStatus.LeftUkraine;

        console.log("Shipment left Ukraine", shipmentId);
        emit ShipmentLeftUkraine(shipmentId);
    }

    function arrivesInTurkey(uint256 shipmentId) external agreementSigned {
        require(msg.sender == turkey, "Caller is not Turkey");

        shipments[shipmentId].status = ShipmentStatus.ArrivedInTurkey;

        console.log("Shipment arrived in Turkey", shipmentId);
        emit ShipmentArrivedInTurkey(shipmentId);
    }

    function examined(uint256 shipmentId) external agreementSigned {
        require(msg.sender == turkey, "Caller is not Turkey");

        shipments[shipmentId].status = ShipmentStatus.LeftTurkey;

        console.log("Shipment examined", shipmentId);
        emit ShipmentExamined(shipmentId);
    }

    function arrivedInDestination(uint256 shipmentId) external agreementSigned {
        require(msg.sender == un, "Caller is not United Nations");

        shipments[shipmentId].status = ShipmentStatus.ArrivedInDestinationCountry;

        console.log("Shipment", shipmentId, "arrived in", shipments[shipmentId].destination);
        emit ShipmentArrivedInDestination(shipmentId, shipments[shipmentId].destination);
    }
}