feat(core): add WorldView with 3x3 neighbor landblock computation

src/AcDream.Core/World/WorldView.cs

@@ -0,0 +1,55 @@
+// src/AcDream.Core/World/WorldView.cs
+using DatReaderWriter;
+
+namespace AcDream.Core.World;
+
+public sealed class WorldView
+{
+    public uint CenterLandblockId { get; }
+    public IReadOnlyList<LoadedLandblock> Landblocks { get; }
+    public IEnumerable<WorldEntity> AllEntities => Landblocks.SelectMany(lb => lb.Entities);
+
+    private WorldView(uint centerLandblockId, IReadOnlyList<LoadedLandblock> landblocks)
+    {
+        CenterLandblockId = centerLandblockId;
+        Landblocks = landblocks;
+    }
+
+    /// <summary>
+    /// Load the 3x3 grid of landblocks around <paramref name="centerLandblockId"/>.
+    /// Missing neighbors (edges of the world or absent from the cell dat) are silently skipped.
+    /// </summary>
+    public static WorldView Load(DatCollection dats, uint centerLandblockId)
+    {
+        var loaded = new List<LoadedLandblock>();
+        foreach (var id in NeighborLandblockIds(centerLandblockId))
+        {
+            var lb = LandblockLoader.Load(dats, id);
+            if (lb is not null)
+                loaded.Add(lb);
+        }
+        return new WorldView(centerLandblockId, loaded);
+    }
+
+    /// <summary>
+    /// Enumerate the 3x3 neighbor landblock ids around a center. Clamps at the world edges
+    /// (skipping neighbors that would underflow or overflow the 8-bit coordinate range).
+    /// </summary>
+    public static IEnumerable<uint> NeighborLandblockIds(uint centerLandblockId)
+    {
+        int cx = (int)((centerLandblockId >> 24) & 0xFFu);
+        int cy = (int)((centerLandblockId >> 16) & 0xFFu);
+
+        for (int dy = -1; dy <= 1; dy++)
+        {
+            for (int dx = -1; dx <= 1; dx++)
+            {
+                int nx = cx + dx;
+                int ny = cy + dy;
+                if (nx < 0 || nx > 0xFF || ny < 0 || ny > 0xFF)
+                    continue;
+                yield return (uint)((nx << 24) | (ny << 16) | 0xFFFFu);
+            }
+        }
+    }
+}

tests/AcDream.Core.Tests/World/WorldViewTests.cs

@@ -0,0 +1,46 @@
+// tests/AcDream.Core.Tests/World/WorldViewTests.cs
+using AcDream.Core.World;
+
+namespace AcDream.Core.Tests.World;
+
+public class WorldViewTests
+{
+    [Fact]
+    public void NeighborIds_Center_Returns9Ids()
+    {
+        var ids = WorldView.NeighborLandblockIds(0xA9B4FFFFu).ToList();
+
+        Assert.Equal(9, ids.Count);
+        Assert.Contains(0xA9B4FFFFu, ids);  // center
+        Assert.Contains(0xA8B3FFFFu, ids);  // NW
+        Assert.Contains(0xAAB5FFFFu, ids);  // SE
+    }
+
+    [Fact]
+    public void NeighborIds_LowerEdge_ClampsUnderflow()
+    {
+        // Landblock 0x0000FFFF — no west or south neighbors.
+        var ids = WorldView.NeighborLandblockIds(0x0000FFFFu).ToList();
+
+        // 4 neighbors should exist: center + E + N + NE
+        Assert.Equal(4, ids.Count);
+        Assert.Contains(0x0000FFFFu, ids);
+        Assert.Contains(0x0100FFFFu, ids);
+        Assert.Contains(0x0001FFFFu, ids);
+        Assert.Contains(0x0101FFFFu, ids);
+    }
+
+    [Fact]
+    public void NeighborIds_UpperEdge_ClampsOverflow()
+    {
+        // Landblock 0xFFFFFFFF — no east or north neighbors.
+        var ids = WorldView.NeighborLandblockIds(0xFFFFFFFFu).ToList();
+
+        // 4 neighbors: center + W + S + SW
+        Assert.Equal(4, ids.Count);
+        Assert.Contains(0xFFFFFFFFu, ids);
+        Assert.Contains(0xFEFFFFFFu, ids);
+        Assert.Contains(0xFFFEFFFFu, ids);
+        Assert.Contains(0xFEFEFFFFu, ids);
+    }
+}