// A Tank holds fuel of a particular type.
class Tank {
        // Set how much this tank can hold. This is fixed for life.
    public Tank(long max,FuelType type){
        capacity = max;
        fuelType = type;
        // The tank is full to start with.
        refill();
    }

    public long getCapacity(){
        return capacity;
    }

    public FuelType getFuelType(){
        return fuelType;
    }

        // Can this tank deliver some of the amount required?
    public boolean canDeliver(){
        return getLevel() > 0;
    }

        // Deliver the required amount, if possible.
        // Return the actual amount delivered.
    public long deliver(long amount){
        long delivered = 0L;
        if(amount > 0L){
            long currentLevel = getLevel();
            if(amount <= currentLevel){
                setLevel(currentLevel-amount);
                delivered = amount;
            }
            else{
                // Deliver what we have.
                setLevel(0L);
                delivered = currentLevel;
            }
        }
        return delivered;
    }

        // Refill the tank to its full capacity.
    public void refill(){
        setLevel(getCapacity());
    }

    public long getLevel(){
        return level;
    }

    protected void setLevel(long newLevel){
        level = newLevel;
    }

    // How much the tank can hold.
    private final long capacity;
    // What sort of fuel it holds.
    private final FuelType fuelType;
    // How much is in the tank.
    private long level;
}