using UnityEngine;
class DiscountLodGroup : MonoBehaviour
{
    [SerializeField] private LODGroup targetLodGroup;

    private Vector3 rendererBoundsSize, rendererBoundsCenter;
    private Renderer[][] renderers;
    private float[] lodweights;

    //https://forum.unity.com/threads/how-lod-group-component-works-internaly-i-want-to-optimize-it.522353/
    void OnEnable()
    {
        renderers = new Renderer[targetLodGroup.lodCount][];
        lodweights = new float[targetLodGroup.lodCount];

        var lods = targetLodGroup.GetLODs();

        for (int i = 0; i < lods.Length; i++)
        {
            renderers[i] = lods[i].renderers;
            lodweights[i] = lods[i].screenRelativeTransitionHeight;
        }

        RecalculateBounds();
        targetLodGroup.enabled = false;
    }

    public void RecalculateBounds()
    {
        var bnds = renderers[0][0].bounds;

        for (int i = 0; i < renderers.Length; i++)
            for (int j = 0; j < renderers[i].Length; j++)
                bnds.Encapsulate(renderers[i][j].bounds);


        rendererBoundsCenter = bnds.center;
        rendererBoundsSize = bnds.size;
    }
    void OnDrawGizmosSelected()
    {
        Gizmos.DrawWireCube(rendererBoundsCenter, rendererBoundsSize);
    }

    void OnDisable()
    {
        targetLodGroup.enabled = true;
        for (int i = 0; i < renderers.Length; i++)
        {
            for (int j = 0; j < renderers[i].Length; j++)
            {
                renderers[i][j].forceRenderingOff = false;
            }
        }
    }

    void LateUpdate()
    {
        var cam = Camera.main;
        float size = Mathf.Max(rendererBoundsSize.x, rendererBoundsSize.y, rendererBoundsSize.z);

        float distance = Vector3.Distance(cam.transform.position, rendererBoundsCenter);
        float screenSpaceHeight = Mathf.Abs(Mathf.Atan2(size, distance) * Mathf.Rad2Deg * QualitySettings.lodBias) / cam.fieldOfView;
        Debug.Log($"{screenSpaceHeight}");

        int currentLodLevel = renderers.Length - 1;

        //todo: figure out a way not to loop twice.
        for (int i = 0; i < lodweights.Length; i++)
        {
            if (screenSpaceHeight > lodweights[i])
            {
                currentLodLevel = i;
                break;
            }
        }

        for (int i = 0; i < renderers.Length; i++)
        {
            for (int j = 0; j < renderers[i].Length; j++)
            {
                renderers[i][j].forceRenderingOff = i != currentLodLevel; //dont render if we are not current lod level
            }
        }
    }
}