Prevent players from spawning above the logical height of the map

src/main/java/io/github/haykam821/deathswap/game/map/DeathSwapMap.java

@@ -1,9 +1,13 @@
 package io.github.haykam821.deathswap.game.map;
 
+import net.minecraft.entity.EntityType;
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.world.ServerWorld;
 import net.minecraft.util.math.BlockBox;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.util.math.Direction;
 import net.minecraft.world.Heightmap;
+import net.minecraft.world.chunk.Chunk;
 import net.minecraft.world.dimension.DimensionType;
 
 public final class DeathSwapMap {
@@ -30,6 +34,31 @@ public BlockBox getBox() {
 	}
 
 	public int getSurfaceY(ServerWorld world, int x, int z) {
-		return this.chunkGenerator.getHeight(x, z, Heightmap.Type.WORLD_SURFACE, world, world.getChunkManager().getNoiseConfig());
+		int bottomY = world.getBottomY();
+		int maxY = Math.min(world.getTopY(), bottomY + world.getLogicalHeight()) - 1;
+
+		BlockPos.Mutable pos = new BlockPos.Mutable(x, maxY, z);
+		Chunk chunk = world.getChunk(pos);
+
+		int air = 0;
+
+		while (pos.getY() > bottomY) {
+			if (chunk.getBlockState(pos).isAir()) {
+				air += 1;
+			} else if (air > EntityType.PLAYER.getHeight()) {
+				air = 0;
+				break;
+			} else {
+				air = 0;
+			}
+
+			pos.move(Direction.DOWN);
+		}
+
+		if (pos.getY() == bottomY) {
+			pos.setY(chunk.sampleHeightmap(Heightmap.Type.WORLD_SURFACE, x, z));
+		}
+
+		return pos.getY() + 1;
 	}
 }