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/*
* Create smart contract for tracking cars repair history.
* Fill up the code blocks in Solidity for:
* - getCar()
* - createCar()
* - updateKilometers()
* - transferOwnership()
*/

pragma solidity ^0.4.21;

/**
 * Contract to store the mileage of a car 
 */
contract Odometer {
    
    event Creation(
        address indexed from,
        string indexed vin
    );
    
    event Transfer(
        address indexed from,
        address indexed to,
        string indexed vin
    );
    
    struct Car {
        string vin;
        address owner;
        uint kilometers;
    }
    
    mapping (string => Car) cars;
    
    function Odometer() public {}

/**
     * Returns the current data of the given car
     */
    function getCar(string vin) public constant returns(address owner, uint kilometers) {
        /* -- Your code here -- */
        Car storage car = cars[vin];
        return (car.owner, car.kilometers);
    }
    
    /**
     * Creates a track record of a new car. 
     * Transaction will fail (and burn gas!) if the car already exists.
     */
    function createCar(string vin) public {
        /* -- Your code here -- */
        assert(cars[vin].owner == address(0));
        cars[vin] = Car({
            vin: vin,
            owner: msg.sender,
            kilometers: 0
        });
        emit Creation(msg.sender, vin);
    }

/**
    * Updates the current kilometers of the car. Transactions fails and burns gas if 
    * the new kilometer value is lower than the old one.
    */
    function updateKilometers(string vin, uint kilometers) public {
        /* -- Your code here -- */
        assert(cars[vin].kilometers < kilometers);
        assert(msg.sender == cars[vin].owner);
        cars[vin].kilometers = kilometers;
    }
    
    /**
     * Transfers the ownership of a car to a different address. 
     * Transaction fails and burns gas if the car is not owned by the caller or if the kilometers are 
     * less than the last known state. 
     */
    function transferOwnership(string vin, address owner, uint kilometers) public {
        /* -- Your code here -- */
        updateKilometers(vin, kilometers);
        cars[vin].owner = owner;
        emit Transfer(msg.sender, owner, vin);
    }
}