namespace Server.Engines.Pathing.Cache;

/// <summary>
/// Per-chunk storage backing StepCache. Holds raw walkability masks and
/// destination Z values for each of 256 cells in a 16x16 chunk, plus build-time
/// metadata (multis version, multi-Z bitmap) and LRU bookkeeping.
/// </summary>
internal sealed class StepChunk
{
    public const int CellsPerChunk = 256; // 16 x 16

    /// <summary>Bit i of Mask[c] = "can step from cell c to neighbor (Direction)i". Raw — no diagonal corner-cut applied here.</summary>
    public readonly byte[] Mask = new byte[CellsPerChunk];

    public readonly sbyte[] SourceZ = new sbyte[CellsPerChunk];

    public readonly sbyte[] DestZN  = new sbyte[CellsPerChunk];
    public readonly sbyte[] DestZNE = new sbyte[CellsPerChunk];
    public readonly sbyte[] DestZE  = new sbyte[CellsPerChunk];
    public readonly sbyte[] DestZSE = new sbyte[CellsPerChunk];
    public readonly sbyte[] DestZS  = new sbyte[CellsPerChunk];
    public readonly sbyte[] DestZSW = new sbyte[CellsPerChunk];
    public readonly sbyte[] DestZW  = new sbyte[CellsPerChunk];
    public readonly sbyte[] DestZNW = new sbyte[CellsPerChunk];

    /// <summary>
    /// 32 bytes = 256 bits. Bit set = cell has &gt;1 walkable surface; route to slow path.
    /// TODO(PR2): lazy-init this. The vast majority of chunks are entirely single-Z, so
    /// allocating 32 bytes per chunk wastes ~256KB at full cap. Make nullable; allocate
    /// on first MarkCellMultiZ; IsCellMultiZ short-circuits to false when null.
    /// </summary>
    public readonly byte[] MultiZCells = new byte[32];

    /// <summary>Snapshot of Sector.MultisVersion at the time this chunk was built.</summary>
    public int BuiltMultisVersion;

    /// <summary>Updated on every cache hit/miss. Used by LRU fallback eviction.</summary>
    public long LastTouchedTicks;

    /// <summary>True if any cell in this chunk has more than one walkable surface (set during build).</summary>
    public bool HasAnyMultiZ;

    public bool IsCellMultiZ(int cellIndex) => (MultiZCells[cellIndex >> 3] & (1 << (cellIndex & 7))) != 0;

    public void MarkCellMultiZ(int cellIndex)
    {
        MultiZCells[cellIndex >> 3] |= (byte)(1 << (cellIndex & 7));
        HasAnyMultiZ = true;
    }
}