using Unity.Collections;
using Unity.Mathematics;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Pure, deterministic build-placement helpers (unit-tested like <see cref="BaseGridMath"/> /
    /// <c>StorageMath</c>). Occupancy is DERIVED from the live structure set each placement (the structure
    /// ghosts are the source of truth — restart- and replay-order-safe), never cached on the immutable
    /// baked <see cref="BaseAnchor"/>. The server passes a Temp <see cref="NativeHashSet{T}"/> of occupied
    /// cells built by scanning live <see cref="PlacedStructure"/> ghosts.
    /// </summary>
    public static class BuildPlacementMath
    {
        /// <summary>True if <paramref name="cell"/> is occupied in the derived set.</summary>
        public static bool IsOccupied(in NativeHashSet<int2> occupied, int2 cell) => occupied.Contains(cell);

        /// <summary>Full server placement legality: the cell is in-plot (half-open, negative-safe) AND not occupied.</summary>
        public static bool CanPlace(in BaseAnchor anchor, in NativeHashSet<int2> occupied, int2 cell)
        {
            return BaseGridMath.IsCellInPlot(anchor, cell) && !occupied.Contains(cell);
        }
    }
}