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.
///
/// On top of the radar-wide fade, each blip fades in when it spawns and fades out at the end of its life (or when
/// its world target vanishes) via its own <see cref="_fade"/> factor, so blips appear/disappear smoothly instead
/// of popping. Fade-in and fade-out speeds are independent; the factor persists across <see cref="Refresh"/> so a
/// refreshed blip is pulled back to full opacity rather than flickering to zero first.
/// </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;

    [Header("Fade")]
    [Tooltip("Per-blip fade-in speed in alpha units per second when the blip appears. e.g. 6 = ~0.17s. 0 = appear instantly.")]
    [SerializeField] float fadeInSpeed = 6f;
    [Tooltip("Per-blip fade-out speed in alpha units per second at the end of life / when the target vanishes. e.g. 4 = ~0.25s. 0 = vanish instantly.")]
    [SerializeField] float fadeOutSpeed = 4f;

    private Transform _target;
    private Camera _camera;
    private float _lifetime;
    private float _age;
    private bool _initialised;
    private float _fade;   // per-blip 0..1 ramp, multiplied on top of the radar-wide fade; persists across Refresh

    private MaterialPropertyBlock _mpb;
    private Color _pointColor = Color.white;   // last gradient-evaluated point colour; its alpha is scaled by the radar fade
    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();
        PushPointColor();
    }

    /// <summary>Restarts this blip's countdown to <paramref name="lifetime"/> seconds. Used when a ping arrives
    /// for a target this radar already tracks: the existing blip is refreshed instead of stacking a duplicate.</summary>
    public void Refresh(float lifetime)
    {
        _lifetime = lifetime;
        _age = 0f;
    }

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

        _age += Time.deltaTime;

        // Fade out at the very end of life, or immediately if the world target vanished (e.g. a caught hider)
        // instead of dangling. The fade-out window equals the time to ramp 1 -> 0 at fadeOutSpeed, so the point
        // reaches full transparency right as the lifetime elapses; then the blip destroys itself.
        float fadeOutWindow = fadeOutSpeed > 0f ? 1f / fadeOutSpeed : 0f;
        bool fadingOut = !_target || RemainingLifetime <= fadeOutWindow;

        float goal = fadingOut ? 0f : 1f;
        float speed = Mathf.Max(0f, fadingOut ? fadeOutSpeed : fadeInSpeed);
        _fade = Mathf.MoveTowards(_fade, goal, speed * Time.deltaTime);

        if (fadingOut && (speed <= 0f || _fade <= 0.0001f))
        {
            Destroy(gameObject);
            return;
        }

        Aim();            // keeps last orientation/colour if the target is gone (Aim early-returns)
        PushPointColor(); // every frame so the alpha tracks both the radar fade and this blip's own fade
    }

    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.
    // Only caches the colour here; PushPointColor writes it (with the fade applied) so the alpha can track the
    // radar fade every frame independent of when the bearing last changed.
    private void ApplyForwardColor(Vector3 dirNormalized)
    {
        if (forwardGradient == null) return;
        float t = Vector3.Angle(_camera.transform.forward, dirNormalized) / 180f;
        _pointColor = forwardGradient.Evaluate(t);
    }

    // Writes the point's _BaseColor with its alpha scaled by both the radar's shared fade factor (so blips fade in
    // step with the disc) and this blip's own fade (so it eases in on spawn and out at the end of its life).
    private void PushPointColor()
    {
        if (!pointRenderer) return;
        Color c = _pointColor;
        c.a *= (Radar.Instance ? Radar.Instance.CurrentFade : 1f) * _fade;
        _mpb ??= new MaterialPropertyBlock();
        pointRenderer.GetPropertyBlock(_mpb);
        _mpb.SetColor(BaseColorId, c);
        pointRenderer.SetPropertyBlock(_mpb);
    }
}