using UnityEngine;

[RequireComponent(typeof(CapsuleCollider))]
public class Stepper : MonoBehaviour
{
    #region Data
    public LayerMask groundLayer;
    public float collisionBuffer, stepHeight, slopeAngle;

    private CapsuleCollider capsule;
    #endregion

    #region Unity Functions
    private void Awake()
    {
        capsule = GetComponent<CapsuleCollider>();
    }
    private void FixedUpdate()
    {
        float groundDistance = -CalculateGroundDistance();

        // This also causes the transform to snap down the stairs too
        // If you wanted to avoid this you would remove the Mathf.Abs and add a && groundDistance > 0.
        if (Mathf.Abs(groundDistance) < stepHeight)
            transform.position += new Vector3(0, groundDistance, 0);
    }
    #endregion

    #region Private Functions
    private float CalculateGroundDistance()
    {
        // Calculating global scale.
        float radius = (Mathf.Max(transform.lossyScale.x, transform.lossyScale.z) * capsule.radius) + collisionBuffer;
        float height = capsule.height * transform.lossyScale.y;

        // Caluclating global position.
        Vector3 castPosition = transform.TransformPoint(capsule.center) + new Vector3(0, radius, 0);

        if (Physics.SphereCast(castPosition, radius, Vector3.down, out RaycastHit hit, height, groundLayer)) {
            hit.distance -= height / 2;
        }

        float angle = Vector3.Angle(hit.normal, Vector3.up);
        return angle > slopeAngle ? 0 : hit.distance;
    }
    #endregion
}