public class VerticalLine : MonoBehaviour
{
    [SerializeField] private Transform start = null;
    [SerializeField] private Transform end = null;

    [SerializeField] private LineItem lineItem = null;

    private LineItemPool objectPool;

    private List<LineItem> lineItems;

    public float SpawnYPosition
    {
        get
        {
            if (lineItems.Count == 0)
                return StartYPosition;

            LineItem lineItem = lineItems[lineItems.Count - 1];
            return lineItem.transform.position.y - lineItem.transform.localScale.y/2;
        }
    }

    public float EndYPosition => end.position.y;

    public float StartYPosition => start.position.y;
    void Start()
    {
        lineItems = new List<LineItem>();
        objectPool = new LineItemPool(this, lineItem, 10);
        AddLine();
    }

    public void AddLine()
    {
        lineItems.Add(objectPool.GetObject());
    }

    public void ReturnToPool(LineItem lineItem)
    {
        lineItems.Remove(lineItem);
        objectPool.ReturnObject(lineItem);
        lineItem.Initialize(objectPool.GetNewParametrs());
    }

}

public class LineItem : PoolingObject
{
    private VerticalLine verticalLine;
    [SerializeField] private MeshRenderer meshRenderer = null;

    private bool spawn = false;

    private float length;
    private int id;

    public void Initialize(VerticalLine verticalLine, LineItemParametrs parametrs)
    {
        this.verticalLine = verticalLine;
        Initialize(parametrs);
    }

    public void Initialize(LineItemParametrs parametrs)
    {
        meshRenderer.material.color = parametrs.color;
        length = parametrs.length;
        id = parametrs.id;
    }

    private void SetTransformParametrs()
    {
        transform.localScale = new Vector3(2F, length);
        transform.position = new Vector3(transform.position.x, verticalLine.SpawnYPosition - transform.localScale.y / 2);
    }

    private void Update()
    {
        if(!spawn)
            CheckLowerEdge();
        CheckHightEdge();
    }

    private void CheckLowerEdge()
    {
        if(transform.position.y - transform.localScale.y/2 > verticalLine.EndYPosition)
        {
            verticalLine.AddLine();
            spawn = true;
        }
    }

    private void CheckHightEdge()
    {
        if (transform.position.y - transform.localScale.y > verticalLine.StartYPosition)
        {
            verticalLine.ReturnToPool(this);
        }
    }

    public override void ReturnToPool()
    {
        base.ReturnToPool();
        spawn = false;
    }

    public override void GetFromPool()
    {
        base.GetFromPool();
        SetTransformParametrs();
    }
}