void TogglePlayerEnabled(bool b)
{
    playerCar.GetComponent<CarController>().enabled = b;
}
void ToggleAiCarEnabled(bool b)
{
    aiCar.GetComponent<CarController>().enabled = b;
}

public class GameManagerControl : MonoBehaviour {

public GameObject playerCar;
public GameObject aiCar;

public int sceneChangeZValue;

private string countdown = "";
private bool showCountdown = true;




// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {
    // TODO: This will change the scene when the track ends.
    //if (player.transform.position.z >= sceneChangeZValue)
    //      {

    //          SceneManager.LoadScene("race_track_lake");
    //      }

    if (showCountdown)
    {
        StartCoroutine(GetReady());
    }


}

// call this function to display countdown
IEnumerator GetReady()
{
    countdown = "3";
    TogglePlayerEnabled(false);
    ToggleAiCarEnabled(false);
    yield return new WaitForSeconds(1.5f);
    TogglePlayerEnabled(true);
    ToggleAiCarEnabled(true);

    countdown = "2";
    TogglePlayerEnabled(false);
    ToggleAiCarEnabled(false);
    yield return new WaitForSeconds(1.5f);
    TogglePlayerEnabled(true);
    ToggleAiCarEnabled(true);

    countdown = "1";
    TogglePlayerEnabled(false);
    ToggleAiCarEnabled(false);
    yield return new WaitForSeconds(1.5f);
    TogglePlayerEnabled(true);
    ToggleAiCarEnabled(true);

    countdown = "GO";
    TogglePlayerEnabled(false);
    ToggleAiCarEnabled(false);
    yield return new WaitForSeconds(1.5f);
    TogglePlayerEnabled(true);
    ToggleAiCarEnabled(true);

    showCountdown = false;
    countdown = "";
}

// GUI
void OnGUI()
{
    if (showCountdown)
    {
        GUI.color = Color.red;
        GUI.Box(new Rect(Screen.width / 2 - 100, 50, 200, 175), "GET READY");

        // display countdown
        GUI.color = Color.white;
        GUI.Box(new Rect(Screen.width / 2 - 90, 75, 180, 140), countdown);
    }
}