using UnityEngine;

/// <summary>
/// A single radar blip spawned by <see cref="Radar"/>. Each frame it orients itself so its forward (+Z, where
/// the "Point" marker sits) faces the direction from the reference camera to a world-space target, visualising
/// the bearing camera -> target. Tracks continuously (the camera turns / the target moves) and self-destructs
/// once its lifetime elapses - or earlier if its target is destroyed. The point's base colour and size encode
/// the two things the flat radar disc can't show via position alone: <see cref="forwardGradient"/> tints it by
/// how far the target sits ahead of / behind the camera, and its scale shrinks with camera -> target distance.
/// </summary>
[DisallowMultipleComponent]
public sealed class RadarTarget : MonoBehaviour
{
    public Renderer pointRenderer;

    [Tooltip("Point tint by bearing: sampled at 0 when the target is dead ahead of the camera, at 1 when directly behind. Flip the keys for the reverse.")]
    [SerializeField] Gradient forwardGradient;
    [Tooltip("Point transform scale at the near (x) and far (y) end of pointDistanceRange.")]
    [SerializeField] Vector2 pointDistanceScale;
    [Tooltip("camera -> target distance mapped onto pointDistanceScale: x = near distance, y = far distance.")]
    [SerializeField] Vector2 pointDistanceRange;

    private Transform _target;
    private Camera _camera;
    private float _lifetime;
    private float _age;
    private bool _initialised;

    private MaterialPropertyBlock _mpb;
    private static readonly int BaseColorId = Shader.PropertyToID("_BaseColor");

    public Transform Target => _target;
    public float RemainingLifetime => Mathf.Max(0f, _lifetime - _age);

    public void Init(Transform target, Camera referenceCamera, float lifetime)
    {
        _target = target;
        _camera = referenceCamera;
        _lifetime = lifetime;
        _age = 0f;
        _initialised = true;
        Aim();
    }

    // LateUpdate so the aim uses the camera's final position/rotation for this frame.
    private void LateUpdate()
    {
        if (!_initialised) return;

        _age += Time.deltaTime;
        if (_age >= _lifetime)
        {
            Destroy(gameObject);
            return;
        }

        // The world target may despawn (e.g. a caught hider) before this blip expires - drop it, don't dangle.
        if (!_target)
        {
            Destroy(gameObject);
            return;
        }

        Aim();
    }

    private void Aim()
    {
        if (!_target || !_camera) return;
        Vector3 dir = _target.position - _camera.transform.position;
        float sqr = dir.sqrMagnitude;
        if (sqr < 1e-8f) return; // camera sitting on the target -> keep the last orientation/colour/scale

        transform.rotation = Quaternion.LookRotation(dir);

        float distance = Mathf.Sqrt(sqr);
        ApplyDistanceScale(distance);
        ApplyForwardColor(dir / distance);
    }

    // Shrinks the blip with distance: pointDistanceRange (near, far) remapped onto pointDistanceScale (near, far), clamped.
    private void ApplyDistanceScale(float distance)
    {
        if (!pointRenderer) return;
        float t = Mathf.InverseLerp(pointDistanceRange.x, pointDistanceRange.y, distance);
        float s = Mathf.Lerp(pointDistanceScale.x, pointDistanceScale.y, t);
        pointRenderer.transform.localScale = new Vector3(s, s, s);
    }

    // Tints the point's base colour by how far the target sits ahead of (0) vs directly behind (1) the camera.
    private void ApplyForwardColor(Vector3 dirNormalized)
    {
        if (!pointRenderer || forwardGradient == null) return;
        float t = Vector3.Angle(_camera.transform.forward, dirNormalized) / 180f;
        _mpb ??= new MaterialPropertyBlock();
        pointRenderer.GetPropertyBlock(_mpb);
        _mpb.SetColor(BaseColorId, forwardGradient.Evaluate(t));
        pointRenderer.SetPropertyBlock(_mpb);
    }
}