using System.Collections.Generic;
using UnityEngine;

#if UNITY_EDITOR
using UnityEditor;
#endif

[ExecuteAlways]
[RequireComponent(typeof(BoxCollider))]
public class PlatformParenting : MonoBehaviour
{
    public enum TopFaceMode { ParentUp, WorldUpAuto }

    [Header("Fit Settings")]
    [Range(0.01f, 0.5f)] public float heightPercent = 0.05f;
    public float surfaceOffset = 0.002f;
    public bool isTrigger = false;

    [Tooltip("How to choose the platform's 'top' face.")]
    public TopFaceMode topFace = TopFaceMode.WorldUpAuto;

    [Tooltip("Align this child so its local Y points along the chosen top normal.")]
    public bool alignToTopFace = true;

    private BoxCollider _topBox;
    private Collider _parentCollider;
    private readonly Dictionary<Transform, Transform> _prevParents = new();

    void OnEnable() { Cache(); FitToParentCollider(); }
    void Reset() { Cache(); FitToParentCollider(); }
    //void OnValidate() { if (!isActiveAndEnabled) return; Cache(); FitToParentCollider(); }

    void Cache()
    {
        if (_topBox == null) _topBox = GetComponent<BoxCollider>();
        _parentCollider = null;
        if (transform.parent != null)
        {
            // Prefer exact colliders on the parent itself
            _parentCollider = transform.parent.GetComponent<BoxCollider>();
            if (_parentCollider == null) _parentCollider = transform.parent.GetComponent<MeshCollider>();
            if (_parentCollider == null) _parentCollider = transform.parent.GetComponent<Collider>();
        }
    }

    [ContextMenu("Fit To Parent Collider")]
    public void FitToParentCollider()
    {
        if (transform.parent == null) { Debug.LogWarning("[PlatformParenting] Must be a child of the platform."); return; }
        if (_topBox == null) _topBox = GetComponent<BoxCollider>();
        if (_parentCollider == null) { Debug.LogWarning("[PlatformParenting] No collider found on parent."); return; }

        // --- Use local bounds from BoxCollider or MeshCollider for oriented math ---
        if (_parentCollider is BoxCollider pb) { FitUsingLocalBounds(pb.transform, pb.size, pb.center); return; }
        if (_parentCollider is MeshCollider pm && pm.sharedMesh != null)
        {
            Bounds m = pm.sharedMesh.bounds; // local bounds of the mesh
            FitUsingLocalBounds(pm.transform, m.size, m.center);
            return;
        }

        // Fallback: world AABB (least precise)
        Bounds b = _parentCollider.bounds;
        float thinY = Mathf.Max(0.001f, b.size.y * Mathf.Clamp01(heightPercent));
        Vector3 worldCtr = new Vector3(b.center.x, b.max.y + surfaceOffset + thinY * 0.5f, b.center.z);

        if (alignToTopFace) transform.rotation = Quaternion.LookRotation(Vector3.forward, Vector3.up);
        transform.position = worldCtr;

        Vector3 lossy = Abs(transform.lossyScale);
        _topBox.size = new Vector3(b.size.x / lossy.x, thinY / lossy.y, b.size.z / lossy.z);
        _topBox.center = Vector3.zero;
        _topBox.isTrigger = isTrigger;
    }

    // Fits a thin box on the parent's true top face (relative to world-up)
    private void FitUsingLocalBounds(Transform src, Vector3 localSize, Vector3 localCenter)
    {
        // Parent local axes in world space
        Vector3 wr = src.right, wu = src.up, wf = src.forward;
        Vector3[] worldAxes = { wr, wu, wf };
        Vector3[] localAxes = { Vector3.right, Vector3.up, Vector3.forward };

        // Choose which local axis is most "up" in world space
        int topAxis = 1; // default Y
        int sign = 1;
        if (topFace == TopFaceMode.WorldUpAuto)
        {
            float best = -1f;
            for (int i = 0; i < 3; i++)
            {
                float d = Vector3.Dot(worldAxes[i], Vector3.up);
                float ad = Mathf.Abs(d);
                if (ad > best) { best = ad; topAxis = i; sign = (d >= 0f) ? 1 : -1; }
            }
        }
        else // ParentUp: use local Y, pick sign so it's closest to world up
        {
            float d = Vector3.Dot(wu, Vector3.up);
            topAxis = 1; sign = (d >= 0f) ? 1 : -1;
        }

        Vector3 localNormal = sign * localAxes[topAxis];
        Vector3 worldNormal = sign * worldAxes[topAxis];

        // World sizes (account for non-uniform scale)
        Vector3 srcLossy = Abs(src.lossyScale);
        Vector3 worldSize = new Vector3(localSize.x * srcLossy.x, localSize.y * srcLossy.y, localSize.z * srcLossy.z);
        float axisWorldSize = (topAxis == 0 ? worldSize.x : topAxis == 1 ? worldSize.y : worldSize.z);
        float thin = Mathf.Max(0.001f, axisWorldSize * Mathf.Clamp01(heightPercent));

        // Top face world center
        Vector3 topWorld = src.TransformPoint(localCenter + 0.5f * ComponentAlong(localSize, topAxis) * localNormal);
        Vector3 worldCenter = topWorld + worldNormal * (surfaceOffset + thin * 0.5f);
        transform.position = worldCenter;

        // Align this child so its local Y points along the top normal; keep forward projected on the plane
        if (alignToTopFace)
        {
            Vector3 planeForward = Vector3.ProjectOnPlane(src.forward, worldNormal);
            if (planeForward.sqrMagnitude < 1e-6f) planeForward = Vector3.ProjectOnPlane(src.right, worldNormal);
            transform.rotation = Quaternion.LookRotation(planeForward.normalized, worldNormal.normalized);
        }

        // Decide which of the remaining two parent axes becomes our local X vs Z by checking alignment to child.right
        int a = OtherIndex(topAxis, false);
        int b = OtherIndex(topAxis, true);
        float sizeA = ComponentAlong(worldSize, a);
        float sizeB = ComponentAlong(worldSize, b);
        Vector3 axisAWorld = worldAxes[a].normalized * Mathf.Sign(Vector3.Dot(worldAxes[a], transform.right));
        float dotA = Mathf.Abs(Vector3.Dot(axisAWorld.normalized, transform.right));

        float sizeXWorld = dotA >= 0.5f ? sizeA : sizeB;
        float sizeZWorld = dotA >= 0.5f ? sizeB : sizeA;

        Vector3 childLossy = Abs(transform.lossyScale);
        _topBox.size = new Vector3(
            sizeXWorld / childLossy.x,
            thin / childLossy.y,
            sizeZWorld / childLossy.z
        );
        _topBox.center = Vector3.zero;
        _topBox.isTrigger = isTrigger;
    }

    static float ComponentAlong(Vector3 v, int axis) => axis == 0 ? v.x : axis == 1 ? v.y : v.z;
    static int OtherIndex(int topAxis, bool second)
    {
        // returns the two indices other than topAxis; order stable
        if (topAxis == 0) return second ? 2 : 1;
        if (topAxis == 1) return second ? 2 : 0;
        return second ? 1 : 0;
    }
    static Vector3 Abs(Vector3 v) => new(Mathf.Abs(v.x), Mathf.Abs(v.y), Mathf.Abs(v.z));

    // ---------- Parenting behavior ----------
    private void ParentRider(Transform rider)
    {
        if (!_prevParents.ContainsKey(rider)) _prevParents[rider] = rider.parent;
        rider.parent = transform.parent != null ? transform.parent : transform;
    }
    private void UnparentRider(Transform rider)
    {
        if (_prevParents.TryGetValue(rider, out var orig)) rider.parent = orig; else rider.parent = null;
        _prevParents.Remove(rider);
    }

    private void OnCollisionEnter(Collision c) { if (!isTrigger && c.gameObject.CompareTag("Player")) ParentRider(c.transform); }
    private void OnCollisionExit(Collision c) { if (!isTrigger && c.gameObject.CompareTag("Player")) UnparentRider(c.transform); }
    private void OnTriggerEnter(Collider o) { if (isTrigger && o.CompareTag("Player")) ParentRider(o.transform); }
    private void OnTriggerExit(Collider o) { if (isTrigger && o.CompareTag("Player")) UnparentRider(o.transform); }

#if UNITY_EDITOR
    void OnDrawGizmosSelected()
    {
        if (_topBox == null) return;
        Gizmos.matrix = transform.localToWorldMatrix;
        Gizmos.DrawWireCube(_topBox.center, _topBox.size);
    }

    [CustomEditor(typeof(PlatformParenting))]
    class PlatformParentingEditor : Editor
    {
        public override void OnInspectorGUI()
        {
            DrawDefaultInspector();
            if (GUILayout.Button("Fit To Parent Collider"))
                ((PlatformParenting)target).FitToParentCollider();
        }
    }
#endif
}