using UnityEngine;

public class AxisConstrainedLookAt : MonoBehaviour
{
    public Transform target;

    public enum LocalAxis { X, Y, Z }
    public enum RotationAxis { X, Y, Z }

    [Header("Which local axis should point at the target?")]
    public LocalAxis lookAxis = LocalAxis.Z;

    [Header("Allow rotation only around this world axis")]
    public RotationAxis allowedRotationAxis = RotationAxis.Y;

    void Update()
    {
        if (target == null) return;

        Vector3 toTarget = target.position - transform.position;

        if (toTarget.sqrMagnitude < 0.0001f) return;

        // Project direction onto the allowed rotation plane
        Vector3 projectedDirection = ProjectDirection(toTarget.normalized, allowedRotationAxis);
        if (projectedDirection.sqrMagnitude < 0.0001f) return;

        // Get the desired rotation to look at the projected target direction
        Quaternion targetRotation = Quaternion.LookRotation(projectedDirection, Vector3.up);

        // Adjust rotation so the selected local axis is pointing in that direction
        Quaternion localAxisRotation = GetLocalAxisRotation(lookAxis);

        // Apply final rotation
        transform.rotation = targetRotation * Quaternion.Inverse(localAxisRotation);
    }

    private Vector3 ProjectDirection(Vector3 direction, RotationAxis axis)
    {
        switch (axis)
        {
            case RotationAxis.X:
                return Vector3.ProjectOnPlane(direction, Vector3.right);
            case RotationAxis.Y:
                return Vector3.ProjectOnPlane(direction, Vector3.up);
            case RotationAxis.Z:
                return Vector3.ProjectOnPlane(direction, Vector3.forward);
            default:
                return direction;
        }
    }

    private Quaternion GetLocalAxisRotation(LocalAxis axis)
    {
        switch (axis)
        {
            case LocalAxis.X:
                return Quaternion.LookRotation(Vector3.right, Vector3.up);
            case LocalAxis.Y:
                return Quaternion.LookRotation(Vector3.up, Vector3.forward); // alternative up
            case LocalAxis.Z:
                return Quaternion.LookRotation(Vector3.forward, Vector3.up);
            default:
                return Quaternion.identity;
        }
    }
}