using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// Sole owner of the animated character's collider bake: keeps a non-convex MeshCollider in sync with
/// the SkinnedMeshRenderer's current pose every frame, independent of any paint/game mode. MeshPainter's
/// own per-frame bake sits behind its PaintingEnabled gate, so the collider would otherwise freeze in
/// player-control / insect mode. When this component is present MeshPainter delegates to it (it stops
/// baking and only borrows <see cref="BakedMesh"/> for its GPU raster path), so the deformed-pose
/// collider stays fresh for everyone - paint raycasts, physics, future seeker / line-of-sight queries.
///
/// Bakes in the renderer's LOCAL space (BakeMesh, scale = 1) - the same convention MeshPainter and
/// ConcealmentMeter use (world = transform.localToWorldMatrix). Runs at a negative execution order so
/// the collider is fresh before MeshPainter (and other consumers) read it in the same frame. Owns the
/// baked Mesh (creates + destroys it); MeshPainter never destroys a borrowed mesh.
/// </summary>
[DisallowMultipleComponent]
[DefaultExecutionOrder(-50)]
[RequireComponent(typeof(SkinnedMeshRenderer))]
public class SkinnedColliderBaker : MonoBehaviour
{
    [Min(0f)]
    [Tooltip("Seconds between collider re-bakes. 0 = every frame (matches MeshPainter's per-frame bake). " +
             "Raise it to trade collider freshness for CPU on a high-poly rig.")]
    [SerializeField] private float bakeInterval = 0f;

    /// <summary>The mesh baked from the current pose, in local space. Valid after the first bake.</summary>
    public Mesh BakedMesh => _baked;

    private SkinnedMeshRenderer _skinned;
    private MeshCollider _collider;
    private Mesh _baked;
    private float _timer;
    private readonly List<Vector3> _vbuf = new List<Vector3>(); // reused vertex scratch so the scale fixup allocates nothing per bake

    private void Awake()
    {
        _skinned = GetComponent<SkinnedMeshRenderer>();
        if (!_skinned)
        {
            Debug.LogError("[SkinnedColliderBaker] No SkinnedMeshRenderer on this GameObject.", this);
            enabled = false;
            return;
        }

        _collider = GetComponent<MeshCollider>();
        if (!_collider) _collider = gameObject.AddComponent<MeshCollider>();
        _collider.convex = false; // non-convex provides triangleIndex / textureCoord for paint raycasts

        _baked = new Mesh { name = "SkinnedColliderBaker_Baked" };
        Bake(); // valid collider on frame 0, before any consumer reads it
    }

    private void Update()
    {
        if (bakeInterval <= 0f) { Bake(); return; }
        _timer += Time.deltaTime;
        if (_timer < bakeInterval) return;
        _timer = 0f;
        Bake();
    }

    private void Bake()
    {
        if (!_skinned) return;
        _skinned.BakeMesh(_baked);

        // BakeMesh freezes the bone deformation — which already carries this transform's world scale —
        // into the mesh. The MeshCollider below then applies the same lossyScale a SECOND time, so a
        // scaled player (see PlayerScaler) would get a collider half/double the size of the visible
        // mesh. Divide the scale back out so the baked mesh is true scale-1 local geometry (the contract
        // this class already documents): the MeshCollider re-applies it exactly once (matching the
        // renderer), and MeshPainter / ConcealmentMeter — which raise the baked mesh to world via
        // localToWorldMatrix — stay correct at any player scale. No-op (and untouched) at scale 1; the
        // uniform divide is rotation-independent, which the player's uniform scale guarantees.
        GeometryUtil.RescaleToUnitScale(_baked, transform.lossyScale, _vbuf);

        _collider.sharedMesh = null;   // force a physics re-cook of the new geometry
        _collider.sharedMesh = _baked;
    }

    private void OnDestroy()
    {
        if (_baked) Destroy(_baked);
    }
}