poe2-bot/src/Roboto.Memory/TerrainReader.cs

using Roboto.GameOffsets.States;
using Serilog;
using Terrain = Roboto.GameOffsets.States.Terrain;

namespace Roboto.Memory;

/// <summary>
/// Reads terrain walkability grid from AreaInstance, with caching and loading edge detection.
/// </summary>
public sealed class TerrainReader
{
    private readonly MemoryContext _ctx;
    private uint _cachedTerrainAreaHash;
    private WalkabilityGrid? _cachedTerrain;
    private bool _wasLoading;

    public TerrainReader(MemoryContext ctx)
    {
        _ctx = ctx;
    }

    /// <summary>
    /// Invalidates the terrain cache (called when LocalPlayer changes on zone change).
    /// </summary>
    public void InvalidateCache()
    {
        _cachedTerrain = null;
        _cachedTerrainAreaHash = 0;
    }

    /// <summary>
    /// Reads terrain data from AreaInstance into the snapshot.
    /// Handles both inline and pointer-based terrain layouts.
    /// </summary>
    public void ReadTerrain(GameStateSnapshot snap, nint areaInstance)
    {
        var mem = _ctx.Memory;
        var offsets = _ctx.Offsets;

        if (!offsets.TerrainInline)
        {
            // Pointer-based: AreaInstance → TerrainList → first terrain → dimensions
            var terrainListPtr = mem.ReadPointer(areaInstance + offsets.TerrainListOffset);
            if (terrainListPtr == 0) return;

            var terrainPtr = mem.ReadPointer(terrainListPtr);
            if (terrainPtr == 0) return;

            var dimsPtr = mem.ReadPointer(terrainPtr + offsets.TerrainDimensionsOffset);
            if (dimsPtr == 0) return;

            snap.TerrainCols = mem.Read<int>(dimsPtr);
            snap.TerrainRows = mem.Read<int>(dimsPtr + 4);
            if (snap.TerrainCols > 0 && snap.TerrainCols < 1000 &&
                snap.TerrainRows > 0 && snap.TerrainRows < 1000)
            {
                snap.TerrainWidth = snap.TerrainCols * offsets.SubTilesPerCell;
                snap.TerrainHeight = snap.TerrainRows * offsets.SubTilesPerCell;
            }
            else
            {
                snap.TerrainCols = 0;
                snap.TerrainRows = 0;
            }
            return;
        }

        // Inline mode: TerrainStruct is inline at AreaInstance + TerrainListOffset
        // Single Read<Terrain> (0x1B0 = 432 bytes) replaces 5 individual reads
        var terrainBase = areaInstance + offsets.TerrainListOffset;
        var t = mem.Read<Terrain>(terrainBase);

        var cols = (int)t.Dimensions.X;
        var rows = (int)t.Dimensions.Y;

        if (cols <= 0 || cols >= 1000 || rows <= 0 || rows >= 1000)
            return;

        snap.TerrainCols = cols;
        snap.TerrainRows = rows;
        snap.TerrainWidth = cols * offsets.SubTilesPerCell;
        snap.TerrainHeight = rows * offsets.SubTilesPerCell;

        // While loading, clear cached terrain and don't read (data is stale/invalid)
        if (snap.IsLoading)
        {
            _cachedTerrain = null;
            _cachedTerrainAreaHash = 0;
            return;
        }

        // Loading just finished — clear cache to force a fresh read
        if (_wasLoading)
        {
            _cachedTerrain = null;
            _cachedTerrainAreaHash = 0;
        }

        // Return cached grid if same area
        if (_cachedTerrain != null && _cachedTerrainAreaHash == snap.AreaHash)
        {
            snap.Terrain = _cachedTerrain;
            snap.TerrainWalkablePercent = CalcWalkablePercent(_cachedTerrain);
            return;
        }

        // Grid vector pointers already available from the Terrain struct read
        var gridBegin = t.WalkableGrid.First;
        var gridEnd = t.WalkableGrid.Last;
        if (gridBegin == 0 || gridEnd <= gridBegin)
            return;

        var gridDataSize = (int)(gridEnd - gridBegin);
        if (gridDataSize <= 0 || gridDataSize > 16 * 1024 * 1024)
            return;

        var bytesPerRow = t.BytesPerRow;
        if (bytesPerRow <= 0 || bytesPerRow > 0x10000)
            return;

        var gridWidth = cols * offsets.SubTilesPerCell;
        var gridHeight = rows * offsets.SubTilesPerCell;

        var rawData = mem.ReadBytes(gridBegin, gridDataSize);
        if (rawData is null)
            return;

        // Unpack 4-bit nibbles: each byte → 2 cells
        var data = new byte[gridWidth * gridHeight];
        for (var row = 0; row < gridHeight; row++)
        {
            var rowStart = row * bytesPerRow;
            for (var col = 0; col < gridWidth; col++)
            {
                var byteIndex = rowStart + col / 2;
                if (byteIndex >= rawData.Length) break;

                data[row * gridWidth + col] = (col % 2 == 0)
                    ? (byte)(rawData[byteIndex] & 0x0F)
                    : (byte)((rawData[byteIndex] >> 4) & 0x0F);
            }
        }

        var grid = new WalkabilityGrid(gridWidth, gridHeight, data);
        snap.Terrain = grid;
        snap.TerrainWalkablePercent = CalcWalkablePercent(grid);

        _cachedTerrain = grid;
        _cachedTerrainAreaHash = snap.AreaHash;

        Log.Information("Terrain grid read: {W}x{H} ({Cols}x{Rows} cells), {Pct}% walkable",
            gridWidth, gridHeight, cols, rows, snap.TerrainWalkablePercent);
    }

    /// <summary>
    /// Updates the loading edge detection state. Call after ReadTerrain.
    /// </summary>
    public void UpdateLoadingEdge(bool isLoading)
    {
        _wasLoading = isLoading;
    }

    public static int CalcWalkablePercent(WalkabilityGrid grid)
    {
        var walkable = 0;
        for (var i = 0; i < grid.Data.Length; i++)
            if (grid.Data[i] != 0) walkable++;
        return grid.Data.Length > 0 ? (int)(100L * walkable / grid.Data.Length) : 0;
    }
}