// Conservative native volume check; no scenery removal or alternate placement.
class ERR_ConvoyPlacement
{
 protected bool m_Obstructed;
 protected int m_Visited;
 protected string m_LastReason;
 protected float m_LastLowest;
 protected float m_LastHighest;
 protected IEntity m_FirstObstruction;
 protected float m_LastTrace = -1;
 float LastTraceFraction() { return m_LastTrace; }
 string Diagnostic()
 {
  string prefab = "none";
  vector position;
  if (m_FirstObstruction)
  {
   prefab = "no prefab";
   if (m_FirstObstruction.GetPrefabData()) prefab = m_FirstObstruction.GetPrefabData().GetPrefabName();
   position = m_FirstObstruction.GetOrigin();
  }
  return string.Format("%1; terrainY=%2..%3 span=%4; visited=%5; first=%6 at %7; trace=%8",
   m_LastReason, m_LastLowest, m_LastHighest, m_LastHighest - m_LastLowest, m_Visited, prefab, position, m_LastTrace);
 }
 protected bool Occupancy(IEntity entity)
 {
  m_Visited++;
  if (m_Visited > 128) { m_Obstructed = true; m_LastReason = "native query visit cap"; }
  else if (entity && entity.GetVObject())
  {
   m_Obstructed = true; m_LastReason = "native VObject volume overlap"; m_FirstObstruction = entity;
  }
  return !m_Obstructed;
 }
 static bool Terrain(float origin, float lowest, float highest)
 {
  return ERR_ForceRules.Finite(origin) && ERR_ForceRules.Finite(lowest) && ERR_ForceRules.Finite(highest)
   && lowest > 0.3 && highest >= lowest && highest - lowest <= 0.75 && origin >= lowest - 0.3 && origin <= highest + 0.3;
 }
 bool Clear(vector position, float heading)
 {
  m_LastReason = "invalid origin or heading"; m_LastLowest = 1e20; m_LastHighest = -1e20;
  m_FirstObstruction = null; m_Visited = 0; m_LastTrace = -1;
  if (!ERR_ForceRules.FiniteVector(position) || !ERR_ForceRules.Finite(heading)) return false;
  float radians = heading * Math.DEG2RAD;
  vector forward = Vector(Math.Sin(radians), 0, Math.Cos(radians));
  vector right = Vector(forward[2], 0, -forward[0]);
  float lowest = 1e20, highest = -1e20;
  vector low = position, high = position;
  for (int x = -1; x <= 1; x++)
  {
   for (int z = -1; z <= 1; z++)
   {
    vector sample = ERR_Actors.Ground(position + right * (x * 2.0) + forward * (z * 4.5));
    if (!ERR_ForceRules.FiniteVector(sample)) { m_LastReason = "nonfinite terrain sample"; return false; }
    if (ChimeraWorldUtils.TryGetWaterSurfaceSimple(GetGame().GetWorld(), sample))
    { m_LastReason = "water at footprint sample"; return false; }
    lowest = Math.Min(lowest, sample[1]); highest = Math.Max(highest, sample[1]);
    low[0] = Math.Min(low[0], sample[0]); low[2] = Math.Min(low[2], sample[2]);
    high[0] = Math.Max(high[0], sample[0]); high[2] = Math.Max(high[2], sample[2]);
   }
  }
  m_LastLowest = lowest; m_LastHighest = highest;
  if (!Terrain(position[1], lowest, highest))
  { m_LastReason = "terrain origin/height/span check"; return false; }
  low[1] = lowest + 0.05; high[1] = highest + 3.5;
  m_Obstructed = false; m_Visited = 0;
  GetGame().GetWorld().QueryEntitiesByAABB(low, high, Occupancy);
  // Entity bounding boxes can include distant branches or overhead wires.
  // Their overlap is diagnostic only; the filled native volume decides collision.
  vector center = (low + high) * 0.5;
  TraceBox volume = new TraceBox();
  volume.Start = center; volume.End = center + "0 0.01 0";
  volume.Mins = low - center; volume.Maxs = high - center;
  // Nine terrain/water samples already qualify the supporting ground below us.
  volume.Flags = TraceFlags.ENTS | TraceFlags.OCEAN;
  m_LastTrace = GetGame().GetWorld().TraceMove(volume, null);
  m_Obstructed = !ERR_ForceRules.Finite(m_LastTrace) || m_LastTrace < 1;
  m_FirstObstruction = null;
  if (m_Obstructed)
  {
   m_FirstObstruction = volume.TraceEnt;
   m_LastReason = "native filled volume collision";
   if (!ERR_ForceRules.Finite(m_LastTrace)) m_LastReason = "invalid native trace fraction";
  }
  else m_LastReason = "clear";
  return !m_Obstructed;
 }
}