using UnityEngine;

namespace HotUpdate
{
    /// <summary>
    /// 用地表 MeshCollider 的碰撞高度作为放置 Y。原点在底面中点的物件直接用该值。
    /// </summary>
    public static class GroundSit
    {
        const float RayStartY = 80f;
        const float RayLength = 160f;

        public static float Height(Vector3 xz, Transform searchRoot = null, float fallback = 0f)
        {
            Physics.SyncTransforms();
            var cols = Collect(searchRoot);
            var offsets = new[]
            {
                Vector3.zero,
                new Vector3(0.35f, 0f, 0.35f),
                new Vector3(-0.35f, 0f, 0.35f),
                new Vector3(0.35f, 0f, -0.35f),
            };
            foreach (var offset in offsets)
            {
                if (TryHit(cols, xz + offset, groundOnly: true, out var y))
                    return y;
            }
            foreach (var offset in offsets)
            {
                if (TryHit(cols, xz + offset, groundOnly: false, out var y))
                    return y;
            }
            return fallback;
        }

        static bool TryHit(MeshCollider[] cols, Vector3 xz, bool groundOnly, out float y)
        {
            var ray = new Ray(new Vector3(xz.x, RayStartY, xz.z), Vector3.down);
            var bestDist = float.MaxValue;
            y = 0f;
            var hitAny = false;
            foreach (var col in cols)
            {
                if (col == null || !col.enabled) continue;
                if (groundOnly && !IsGroundCollider(col)) continue;
                if (!col.Raycast(ray, out var hit, RayLength)) continue;
                if (hit.distance >= bestDist) continue;
                bestDist = hit.distance;
                y = hit.point.y;
                hitAny = true;
            }
            return hitAny;
        }

        static MeshCollider[] Collect(Transform searchRoot)
        {
            if (searchRoot != null)
                return searchRoot.GetComponentsInChildren<MeshCollider>();
            return Object.FindObjectsByType<MeshCollider>(FindObjectsSortMode.None);
        }

        static bool IsGroundCollider(MeshCollider col)
        {
            for (var t = col.transform; t != null; t = t.parent)
            {
                if (t.name.IndexOf("ground", System.StringComparison.OrdinalIgnoreCase) >= 0)
                    return true;
            }
            return false;
        }
    }
}