fix support for litematic v4

src/main/java/io/ib67/sfcraft/module/supervisor/web/SchematicUploader.java

@@ -10,7 +10,7 @@ import io.ib67.sfcraft.module.SignatureService;
 import io.ib67.sfcraft.module.supervisor.WebHandler;
 import io.ib67.sfcraft.util.Helper;
 import io.ib67.sfcraft.util.SFConsts;
-import io.ib67.sfcraft.util.litematic.LitematicConverterV3;
+import io.ib67.sfcraft.util.litematic.LitematicConverterFactory;
 import io.javalin.config.JavalinConfig;
 import io.javalin.http.Context;
 import io.javalin.http.UploadedFile;
@@ -145,7 +145,7 @@ public class SchematicUploader extends WebHandler {
             log.info("Saved " + fileName + " as a schematic.");
             sendSuccess(player, baseFileName);
         } else if (fileName.endsWith(".litematic")) {
-            try (var converter = new LitematicConverterV3(file.content(), new NbtAccounter(config.maxSchematicSize, 64))) {
+            try (var converter = LitematicConverterFactory.forFile(file.content(), new NbtAccounter(config.maxSchematicSize, 64))) {
                 converter.read((name, nbt) -> {
                     name = baseFileName + "-" + Helper.cleanFileName(name) + ".schematic";
                     try {

src/main/java/io/ib67/sfcraft/util/litematic/LitematicConverter.java

@@ -1,18 +1,15 @@
 package io.ib67.sfcraft.util.litematic;
 
+import com.google.common.collect.Lists;
 import io.ib67.sfcraft.util.TypedNbtList;
-import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import lombok.SneakyThrows;
 import net.minecraft.nbt.*;
 import net.minecraft.network.FriendlyByteBuf;
-import org.apache.commons.compress.utils.Lists;
 
 import java.io.InputStream;
 import java.util.ArrayList;
-import java.util.List;
 import java.util.function.BiConsumer;
-import java.util.stream.Collectors;
 
 /**
  * A cleaned up version of https://github.com/GoldenDelicios/Lite2Edit
@@ -21,31 +18,63 @@ import java.util.stream.Collectors;
 public class LitematicConverter implements AutoCloseable {
     protected final InputStream input;
     protected final NbtAccounter sizeTracker;
+    private final CompoundTag preParsedRoot;
 
     public LitematicConverter(InputStream input, NbtAccounter sizeTracker) {
         this.input = input;
         this.sizeTracker = sizeTracker;
+        this.preParsedRoot = null;
+    }
+
+    /**
+     * For converters whose root tag was already parsed and validated (see
+     * {@link LitematicConverterFactory}): {@link #read} uses this root instead of
+     * re-parsing the stream, and {@link #close} leaves the caller's input alone.
+     */
+    protected LitematicConverter(CompoundTag preParsedRoot, NbtAccounter sizeTracker) {
+        this.input = null;
+        this.sizeTracker = sizeTracker;
+        this.preParsedRoot = preParsedRoot;
     }
 
     @SneakyThrows
     public void read(
             BiConsumer<String, CompoundTag> schematicOutput
     ) {
-        var root = NbtIo.readCompressed(input, sizeTracker);
+        var root = preParsedRoot != null ? preParsedRoot : NbtIo.readCompressed(input, sizeTracker);
         var dataVersion = root.getInt("MinecraftDataVersion")
                 .orElseThrow(() -> new IllegalStateException("MinecraftDataVersion not found"));
+        // Template hooks: subclasses may adapt to the input format version
+        // (see LitematicConverterV4) without re-implementing the whole pipeline.
+        readInputVersion(root);
         var regionsNbt = root.getCompound("Regions")
                 .orElseThrow(() -> new IllegalStateException("Regions not found"));
-        var i = 0;
         for (String regionName : regionsNbt.keySet()) {
             var compound = regionsNbt.getCompound(regionName)
                     .orElseThrow(() -> new IllegalStateException("Region " + regionName + " not found"));
-            var j = i++;
-            var schematic = convertRegionToSchematic(dataVersion, compound);
+            var schematic = convertRegionToSchematic(readRegionDataVersion(compound, dataVersion), compound);
             schematicOutput.accept(regionName, schematic);
         }
     }
 
+    /**
+     * Template hook: the litematic input format version, read from the root tag.
+     * Subclasses may log, validate or reject unsupported versions here.
+     */
+    protected int readInputVersion(CompoundTag root) {
+        return root.getInt("Version").orElse(0);
+    }
+
+    /**
+     * Template hook: the data version to bake into each region's schematic output.
+     * The base implementation always uses the root {@code MinecraftDataVersion};
+     * newer litematic formats store a per-region {@code DataVersion} that takes
+     * precedence (litematica: {@code regionTag.getIntOrDefault("DataVersion", mainDataVersion)}).
+     */
+    protected int readRegionDataVersion(CompoundTag region, int fallback) {
+        return fallback;
+    }
+
     protected CompoundTag convertRegionToSchematic(int dataVersion, CompoundTag region) {
         var worldEditTag = new CompoundTag();
 
@@ -123,9 +152,12 @@ public class LitematicConverter implements AutoCloseable {
             if (_properties.isPresent()) {
                 var properties = _properties.get();
                 name.append("[");
+                // Sort keys so the produced palette string is deterministic
+                // (NbtCompound keySet order is unspecified in modern MC versions)
                 var props = new ArrayList<String>();
-                for (String key : properties.keySet()) {
-                    props.add(key + "=" + properties.getString(key));
+                for (String key : properties.keySet().stream().sorted().toList()) {
+                    props.add(key + "=" + properties.getString(key)
+                            .orElseThrow(() -> new IllegalStateException("Property " + key + " not found")));
                 }
                 name.append(String.join(",", props));
                 name.append("]");
@@ -172,12 +204,20 @@ public class LitematicConverter implements AutoCloseable {
             }
             buffer.writeVarInt(value);
         }
-        return buffer.array();
+        // Only return the bytes actually written: the backing array of an
+        // Unpooled.buffer() is a power-of-two slab that may be larger than the
+        // written data, and trailing garbage would be read back as extra blocks
+        // (as air) by WorldEdit's VarIntIterator.
+        var result = new byte[buffer.writerIndex()];
+        buffer.getBytes(0, result);
+        return result;
     }
 
     @Override
     public void close() throws Exception {
-        input.close();
+        if (input != null) {
+            input.close();
+        }
     }
 
     protected record SizeTuple(

src/main/java/io/ib67/sfcraft/util/litematic/LitematicConverterFactory.java

@@ -0,0 +1,52 @@
+package io.ib67.sfcraft.util.litematic;
+
+import lombok.SneakyThrows;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtAccounter;
+import net.minecraft.nbt.NbtIo;
+
+import java.io.InputStream;
+
+/**
+ * Selects the appropriate {@link LitematicConverter} for a litematic file based
+ * on its format version (root {@code Version} tag), so callers never hardcode a
+ * converter class.
+ *
+ * <p>Version → converter mapping (extend the dispatch as new formats appear):
+ * <ul>
+ *     <li><b>1</b> (legacy, ~MC 1.12): rejected — TileEntities use the
+ *     {@code {TileNBT, x, y, z}} wrapper format, which the flat-field conversion
+ *     in the converters does not support.</li>
+ *     <li><b>2–3</b> (flat TileEntities, single data version):
+ *     {@link LitematicConverterV3}.</li>
+ *     <li><b>4+</b> (per-region {@code DataVersion}, current litematica; the
+ *     sample {@code iron.litematic} is version 7): {@link LitematicConverterV4}.</li>
+ * </ul>
+ * A missing {@code Version} tag is treated as modern (>= 2).
+ *
+ * <p>The format version lives inside the gzip'd root tag, so the file is parsed
+ * once here; the parsed root is handed to the chosen converter (via its
+ * pre-parsed-root constructor) instead of being read a second time. The caller's
+ * stream is consumed and closed by this method.
+ */
+public final class LitematicConverterFactory {
+    private LitematicConverterFactory() {
+    }
+
+    @SneakyThrows
+    public static LitematicConverter forFile(InputStream input, NbtAccounter sizeTracker) {
+        var root = NbtIo.readCompressed(input, sizeTracker);
+        input.close();
+        int version = root.getInt("Version").orElse(0);
+        if (version == 1) {
+            throw new IllegalStateException(
+                    "Unsupported litematic input version 1: version 1 TileEntities use the legacy "
+                            + "{TileNBT, x, y, z} wrapper format, which the converters do not support");
+        }
+        if (version >= 2 && version < 4) {
+            return new LitematicConverterV3(root, sizeTracker);
+        }
+        // version 0 (missing tag) and 4+ (including the current v7 sample)
+        return new LitematicConverterV4(root, sizeTracker);
+    }
+}

src/main/java/io/ib67/sfcraft/util/litematic/LitematicConverterV3.java

@@ -17,6 +17,11 @@ public class LitematicConverterV3 extends LitematicConverter {
         super(input, sizeTracker);
     }
 
+    /** See {@link LitematicConverter#LitematicConverter(CompoundTag, NbtAccounter)}. */
+    protected LitematicConverterV3(CompoundTag preParsedRoot, NbtAccounter sizeTracker) {
+        super(preParsedRoot, sizeTracker);
+    }
+
     @Override
     protected CompoundTag convertRegionToSchematic(int dataVersion, CompoundTag region) {
         var schematicsTag = new CompoundTag();

src/main/java/io/ib67/sfcraft/util/litematic/LitematicConverterV4.java

@@ -0,0 +1,60 @@
+package io.ib67.sfcraft.util.litematic;
+
+import lombok.extern.log4j.Log4j2;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtAccounter;
+
+import java.io.InputStream;
+
+/**
+ * Version-aware litematic → Sponge v3 converter, targeting the current
+ * litematica schematic format (version 4+; the sample {@code iron.litematic}
+ * is version 7).
+ *
+ * <p>Output format is identical to {@link LitematicConverterV3}; this class only
+ * adds the input-side version handling via the template hooks in
+ * {@link LitematicConverter}:
+ * <ul>
+ *     <li>{@link #readInputVersion}: logs the detected format version and
+ *     rejects version 1, whose TileEntities use the legacy
+ *     {@code {TileNBT, x, y, z}} wrapper instead of flat fields.</li>
+ *     <li>{@link #readRegionDataVersion}: honors the per-region
+ *     {@code DataVersion} tag (written by litematica since format v4), falling
+ *     back to the root {@code MinecraftDataVersion}.</li>
+ * </ul>
+ */
+@Log4j2
+public class LitematicConverterV4 extends LitematicConverterV3 {
+    public LitematicConverterV4(InputStream input, NbtAccounter sizeTracker) {
+        super(input, sizeTracker);
+    }
+
+    /** See {@link LitematicConverter#LitematicConverter(CompoundTag, NbtAccounter)}. */
+    protected LitematicConverterV4(CompoundTag preParsedRoot, NbtAccounter sizeTracker) {
+        super(preParsedRoot, sizeTracker);
+    }
+
+    @Override
+    protected int readInputVersion(CompoundTag root) {
+        var version = super.readInputVersion(root);
+        if (version < 2) {
+            if (version == 0) {
+                log.warn("Litematic input has no 'Version' tag; assuming modern format (>= 2)");
+            } else {
+                throw new IllegalStateException(
+                        "Unsupported litematic input version " + version
+                                + ": version 1 TileEntities use the legacy {TileNBT, x, y, z} wrapper format, "
+                                + "which this converter does not support");
+            }
+        }
+        log.info("Detected litematic input format version {}", version);
+        return version;
+    }
+
+    @Override
+    protected int readRegionDataVersion(CompoundTag region, int fallback) {
+        // litematica format >= 4 stores a per-region DataVersion (see
+        // LitematicaSchematic.readRegions: getIntOrDefault("DataVersion", mainDataVersion))
+        return region.getInt("DataVersion").orElse(fallback);
+    }
+}

src/test/java/io/ib67/sfcraft/util/litematic/LitematicConverterFactoryTest.java

@@ -0,0 +1,124 @@
+package io.ib67.sfcraft.util.litematic;
+
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import net.minecraft.nbt.NbtAccounter;
+import net.minecraft.nbt.NbtIo;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.InputStream;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Exercises {@link LitematicConverterFactory}: the format version (root
+ * {@code Version} tag) must select the right converter class, reject the legacy
+ * v1 format, and resolve the sample {@code iron.litematic} (a v7 file) to
+ * {@link LitematicConverterV4}.
+ */
+class LitematicConverterFactoryTest {
+
+    private static final NbtAccounter ACCOUNTER = new NbtAccounter(10_240_000, 64);
+
+    @Test
+    void selectsV3ForVersion2And3() throws Exception {
+        for (int version : new int[]{2, 3}) {
+            try (var converter = forVersion(version)) {
+                assertEquals(LitematicConverterV3.class, converter.getClass(),
+                        "litematic version " + version + " must map to LitematicConverterV3");
+            }
+        }
+    }
+
+    @Test
+    void selectsV4ForVersion4And7() throws Exception {
+        for (int version : new int[]{4, 7}) {
+            try (var converter = forVersion(version)) {
+                assertInstanceOf(LitematicConverterV4.class, converter,
+                        "litematic version " + version + " must map to LitematicConverterV4");
+            }
+        }
+    }
+
+    @Test
+    void treatsMissingVersionAsModern() throws Exception {
+        var root = new CompoundTag();
+        root.putInt("MinecraftDataVersion", 4903);
+        root.put("Regions", new CompoundTag());
+        try (var converter = LitematicConverterFactory.forFile(toInputStream(root), ACCOUNTER)) {
+            assertInstanceOf(LitematicConverterV4.class, converter, "missing Version tag must map to V4");
+        }
+    }
+
+    @Test
+    void rejectsLegacyVersion1() throws Exception {
+        var root = new CompoundTag();
+        root.putInt("MinecraftDataVersion", 4903);
+        root.putInt("Version", 1);
+        root.put("Regions", new CompoundTag());
+        var ex = assertThrows(IllegalStateException.class,
+                () -> LitematicConverterFactory.forFile(toInputStream(root), ACCOUNTER));
+        assertTrue(ex.getMessage().contains("version 1"), "error must mention version 1: " + ex.getMessage());
+    }
+
+    /** The sample is litematic version 7 → V4, and the produced schematic must be valid Sponge v3. */
+    @Test
+    void sampleResolvesToV4AndConverts() throws Exception {
+        try (InputStream in = getClass().getResourceAsStream("/iron.litematic")) {
+            assertNotNull(in, "test resource /iron.litematic missing");
+            CompoundTag[] out = new CompoundTag[1];
+            try (var converter = LitematicConverterFactory.forFile(in, ACCOUNTER)) {
+                assertInstanceOf(LitematicConverterV4.class, converter, "sample is v7, must select V4");
+                converter.read((n, tag) -> out[0] = tag);
+            }
+            assertNotNull(out[0], "converter produced no output");
+            var schematic = out[0].getCompound("Schematic").orElseThrow();
+            assertEquals(3, schematic.getInt("Version").orElseThrow(), "output must be Sponge v3");
+            // sample region has no per-region DataVersion -> root MinecraftDataVersion (4903)
+            assertEquals(4903, schematic.getInt("DataVersion").orElseThrow(), "DataVersion falls back to root");
+        }
+    }
+
+    // --- helpers -----------------------------------------------------------
+
+    private static LitematicConverter forVersion(int version) throws Exception {
+        var root = new CompoundTag();
+        root.putInt("MinecraftDataVersion", 4903);
+        root.putInt("Version", version);
+        var regions = new CompoundTag();
+        regions.put("r", minimalRegion());
+        root.put("Regions", regions);
+        return LitematicConverterFactory.forFile(toInputStream(root), ACCOUNTER);
+    }
+
+    /** A minimal but structurally valid 1x1x1 region, all air. */
+    private static CompoundTag minimalRegion() {
+        var region = new CompoundTag();
+        var size = new CompoundTag();
+        size.putInt("x", 1);
+        size.putInt("y", 1);
+        size.putInt("z", 1);
+        region.put("Size", size);
+        var pos = new CompoundTag();
+        pos.putInt("x", 10);
+        pos.putInt("y", 20);
+        pos.putInt("z", 30);
+        region.put("Position", pos);
+        var palette = new ListTag();
+        var air = new CompoundTag();
+        air.putString("Name", "minecraft:air");
+        palette.add(air);
+        region.put("BlockStatePalette", palette);
+        region.putLongArray("BlockStates", new long[]{0});
+        region.put("TileEntities", new ListTag());
+        return region;
+    }
+
+    private static InputStream toInputStream(CompoundTag root) throws Exception {
+        var out = new ByteArrayOutputStream();
+        NbtIo.writeCompressed(root, out);
+        return new ByteArrayInputStream(out.toByteArray());
+    }
+}

src/test/java/io/ib67/sfcraft/util/litematic/LitematicConverterV4Test.java

@@ -0,0 +1,308 @@
+package io.ib67.sfcraft.util.litematic;
+
+import io.netty.buffer.Unpooled;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import net.minecraft.nbt.NbtAccounter;
+import net.minecraft.nbt.NbtIo;
+import net.minecraft.network.FriendlyByteBuf;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.InputStream;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Exercises {@link LitematicConverterV4} (the converter selected by
+ * {@link LitematicConverterFactory} for the sample, a v7 litematic) against
+ * {@code iron.litematic} and validates the output the same way WorldEdit's
+ * {@code SpongeSchematicV3Reader} would consume it. {@link #runConverter} goes
+ * through the factory, so this suite doubles as a regression test for the
+ * version-based selection path.
+ */
+class LitematicConverterV4Test {
+
+    private static final int EXPECTED_VOLUME = 3078;   // |19 * -9 * -18|
+    private static final int EXPECTED_TOTAL_BLOCKS = 409; // litematic Metadata.TotalBlocks
+
+    @Test
+    void convertsSampleWithoutError() throws Exception {
+        var result = runConverter();
+        assertNotNull(result.schematic(), "converter produced no output");
+        assertNotNull(result.name(), "converter produced no region name");
+        System.out.println("[test] region name       = " + result.name());
+        System.out.println("[test] schematic keys    = " + result.schematic().keySet());
+    }
+
+    @Test
+    void producesValidSpongeV3Structure() throws Exception {
+        var result = runConverter();
+        CompoundTag schematic = result.schematic();
+        CompoundTag schematicTag = requireCompound(schematic, "Schematic");
+
+        assertEquals(3, schematicTag.getInt("Version").orElseThrow(), "Version must be 3 (Sponge v3)");
+        assertEquals(19, (int) schematicTag.getShort("Width").orElseThrow(), "Width (|x|)");
+        assertEquals(9, (int) schematicTag.getShort("Height").orElseThrow(), "Height (|y|)");
+        assertEquals(18, (int) schematicTag.getShort("Length").orElseThrow(), "Length (|z|)");
+        assertEquals(3, schematicTag.getIntArray("Offset").orElseThrow().length, "Offset must be int[3]");
+
+        // Metadata.WorldEdit.Origin must be the minimum corner: (0, 0, 0) for this file
+        var metadata = requireCompound(schematicTag, "Metadata");
+        var worldEdit = requireCompound(metadata, "WorldEdit");
+        assertArrayEquals(new int[]{0, 0, 0}, worldEdit.getIntArray("Origin").orElseThrow(), "Origin should be min corner");
+
+        // Blocks container
+        var blocks = requireCompound(schematicTag, "Blocks");
+        assertTrue(blocks.contains("Palette"), "Blocks.Palette missing");
+        assertTrue(blocks.contains("Data"), "Blocks.Data missing");
+        assertTrue(blocks.contains("BlockEntities"), "Blocks.BlockEntities missing");
+    }
+
+    @Test
+    void paletteMatchesSource() throws Exception {
+        var result = runConverter();
+        var blocks = requireCompound(requireCompound(result.schematic(), "Schematic"), "Blocks");
+        var palette = requireCompound(blocks, "Palette");
+
+        // 22 palette entries in the source litematic
+        assertEquals(22, palette.size(), "palette entry count");
+
+        // Regression: property values must not be rendered as Optional[...] (getString returns Optional)
+        for (String key : palette.keySet()) {
+            assertFalse(key.contains("Optional["),
+                    "palette key must not contain Optional[...]: " + key);
+            assertFalse(key.contains("null"),
+                    "palette key must not contain 'null': " + key);
+        }
+
+        // air must be at id 0 (litematica always puts air first; WorldEdit needs a sane default)
+        assertEquals("minecraft:air", palette.keySet().stream()
+                .filter(k -> palette.getInt(k).orElseThrow() == 0)
+                .findFirst().orElseThrow(() -> new AssertionError("no palette entry with id 0")),
+                "id 0 must be minecraft:air");
+
+        System.out.println("[test] palette:");
+        var sorted = new TreeMap<Integer, String>();
+        palette.keySet().forEach(k -> sorted.put(palette.getInt(k).orElseThrow(), k));
+        sorted.forEach((id, name) -> System.out.printf("[test]   %2d -> %s%n", id, name));
+    }
+
+    @Test
+    void blockDataDecodesToValidPaletteIds() throws Exception {
+        var result = runConverter();
+        var blocks = requireCompound(requireCompound(result.schematic(), "Schematic"), "Blocks");
+        var palette = requireCompound(blocks, "Palette");
+        byte[] data = blocks.getByteArray("Data").orElseThrow();
+
+        var buf = new FriendlyByteBuf(Unpooled.wrappedBuffer(data));
+        List<Integer> ids = new ArrayList<>();
+        while (buf.isReadable()) {
+            ids.add(buf.readVarInt());
+        }
+
+        assertEquals(EXPECTED_VOLUME, ids.size(), "block count must equal |size| volume");
+
+        int paletteMax = palette.size();
+        long nonAir = 0;
+        for (int i = 0; i < ids.size(); i++) {
+            int id = ids.get(i);
+            assertTrue(id >= 0 && id < paletteMax,
+                    "block #" + i + " has palette id " + id + " but palette only has " + paletteMax + " entries");
+            if (id != 0) nonAir++;
+        }
+
+        // The source litematic metadata says 409 non-air blocks total
+        assertEquals(EXPECTED_TOTAL_BLOCKS, nonAir, "non-air block count");
+
+        // Sanity: the ground floor (y=0) at z=0 is a dirt_path strip in the source data
+        // WorldEdit index = (y * length + z) * width + x, so data index 0 = (0,0,0)
+        int first = ids.get(0);
+        String firstName = palette.keySet().stream()
+                .filter(k -> palette.getInt(k).orElseThrow() == first)
+                .findFirst().orElseThrow();
+        System.out.println("[test] block(0,0,0)      = id " + first + " " + firstName);
+        assertEquals("minecraft:dirt_path", firstName, "bottom-front-left block should be dirt_path (source ground)");
+    }
+
+    @Test
+    void worldEditRoundTripLayout() throws Exception {
+        // Re-implement WorldEdit's SpongeSchematicV3Reader decoding and check the
+        // produced layout matches the source litematic layout (min-corner ordered).
+        var result = runConverter();
+        CompoundTag schematicTag = requireCompound(result.schematic(), "Schematic");
+        int width = schematicTag.getShort("Width").orElseThrow();
+        int height = schematicTag.getShort("Height").orElseThrow();
+        int length = schematicTag.getShort("Length").orElseThrow();
+
+        var blocks = requireCompound(schematicTag, "Blocks");
+        var palette = requireCompound(blocks, "Palette");
+        byte[] data = blocks.getByteArray("Data").orElseThrow();
+
+        var buf = new FriendlyByteBuf(Unpooled.wrappedBuffer(data));
+        int[][] grid = new int[height][width * length];
+        int index = 0;
+        while (buf.isReadable()) {
+            int id = buf.readVarInt();
+            int y = index / (width * length);
+            int z = (index % (width * length)) / width;
+            int x = index % width;
+            grid[y][z * width + x] = id;
+            index++;
+        }
+
+        // Ground floor y=0 must be a solid path/grass layer (matches source analysis)
+        int groundNonAir = 0;
+        for (int i = 0; i < width * length; i++) {
+            if (grid[0][i] != 0) groundNonAir++;
+        }
+        System.out.println("[test] y=0 non-air      = " + groundNonAir + " of " + (width * length));
+        assertTrue(groundNonAir > 300, "ground floor should be mostly solid (source has 333 non-air at y=0)");
+
+        // Bed must sit at y=5 like the source (bed foot id=16, head id=17)
+        int bedAt = -1;
+        for (int y = 0; y < height; y++) {
+            for (int i = 0; i < width * length; i++) {
+                if (grid[y][i] == 16 || grid[y][i] == 17) bedAt = y;
+            }
+        }
+        System.out.println("[test] bed layer y     = " + bedAt);
+        assertEquals(5, bedAt, "bed must be on the same layer as in the source (y=5)");
+    }
+
+    // --- V4-specific behavior ------------------------------------------------
+
+    /** Missing 'Version' tag is tolerated (assumed modern format); must not throw. */
+    @Test
+    void toleratesMissingVersionTag() throws Exception {
+        var root = new CompoundTag();
+        root.putInt("MinecraftDataVersion", 4903);
+        root.put("Regions", new CompoundTag());
+        try (var converter = new LitematicConverterV4(toInputStream(root), new NbtAccounter(10_240_000, 64))) {
+            converter.read((n, t) -> fail("empty Regions must yield no regions"));
+        }
+    }
+
+    /** Format version 1 uses the legacy {TileNBT, x, y, z} TileEntities wrapper; reject it. */
+    @Test
+    void rejectsLegacyVersion1() throws Exception {
+        var root = new CompoundTag();
+        root.putInt("MinecraftDataVersion", 4903);
+        root.putInt("Version", 1);
+        root.put("Regions", new CompoundTag());
+        var ex = assertThrows(IllegalStateException.class, () -> {
+            try (var converter = new LitematicConverterV4(toInputStream(root), new NbtAccounter(10_240_000, 64))) {
+                converter.read((n, t) -> {
+                });
+            }
+        });
+        assertTrue(ex.getMessage().contains("version 1"), "error must mention version 1: " + ex.getMessage());
+    }
+
+    /**
+     * Litematica format >= 4 writes a per-region DataVersion. V4 must honor it
+     * (falling back to the root MinecraftDataVersion), while V3 always uses the
+     * root value. Run the same bytes through both to prove the difference.
+     */
+    @Test
+    void honorsPerRegionDataVersion() throws Exception {
+        var root = new CompoundTag();
+        root.putInt("MinecraftDataVersion", 4903);
+        root.putInt("Version", 7);
+        var regions = new CompoundTag();
+        regions.put("r", minimalRegion(4902));
+        root.put("Regions", regions);
+        byte[] bytes = toByteArray(root);
+
+        CompoundTag[] v4Out = new CompoundTag[1];
+        try (var converter = new LitematicConverterV4(new ByteArrayInputStream(bytes), new NbtAccounter(10_240_000, 64))) {
+            converter.read((n, t) -> v4Out[0] = t);
+        }
+        assertEquals(4902, requireCompound(v4Out[0], "Schematic").getInt("DataVersion").orElseThrow(),
+                "V4 must prefer the per-region DataVersion");
+
+        CompoundTag[] v3Out = new CompoundTag[1];
+        try (var converter = new LitematicConverterV3(new ByteArrayInputStream(bytes), new NbtAccounter(10_240_000, 64))) {
+            converter.read((n, t) -> v3Out[0] = t);
+        }
+        assertEquals(4903, requireCompound(v3Out[0], "Schematic").getInt("DataVersion").orElseThrow(),
+                "V3 falls back to the root MinecraftDataVersion");
+    }
+
+    // --- helpers -----------------------------------------------------------
+
+    private record ConversionResult(String name, CompoundTag schematic) {
+    }
+
+    private ConversionResult runConverter() throws Exception {
+        try (InputStream in = getClass().getResourceAsStream("/iron.litematic")) {
+            assertNotNull(in, "test resource /iron.litematic missing");
+            CompoundTag[] out = new CompoundTag[1];
+            String[] name = new String[1];
+            try (var converter = LitematicConverterFactory.forFile(in, new NbtAccounter(10_240_000, 64))) {
+                converter.read((n, tag) -> {
+                    name[0] = n;
+                    out[0] = tag;
+                });
+            }
+            return new ConversionResult(name[0], out[0]);
+        }
+    }
+
+    /** A minimal but structurally valid 1x1x1 region, all air, with the given per-region DataVersion. */
+    private static CompoundTag minimalRegion(int dataVersion) {
+        var region = new CompoundTag();
+        var size = new CompoundTag();
+        size.putInt("x", 1);
+        size.putInt("y", 1);
+        size.putInt("z", 1);
+        region.put("Size", size);
+        var pos = new CompoundTag();
+        pos.putInt("x", 10);
+        pos.putInt("y", 20);
+        pos.putInt("z", 30);
+        region.put("Position", pos);
+        var palette = new ListTag();
+        var air = new CompoundTag();
+        air.putString("Name", "minecraft:air");
+        palette.add(air);
+        region.put("BlockStatePalette", palette);
+        region.putLongArray("BlockStates", new long[]{0});
+        region.put("TileEntities", new ListTag());
+        region.putInt("DataVersion", dataVersion);
+        return region;
+    }
+
+    private static InputStream toInputStream(CompoundTag root) throws Exception {
+        return new ByteArrayInputStream(toByteArray(root));
+    }
+
+    private static byte[] toByteArray(CompoundTag root) throws Exception {
+        var out = new ByteArrayOutputStream();
+        NbtIo.writeCompressed(root, out);
+        return out.toByteArray();
+    }
+
+    private static CompoundTag requireCompound(CompoundTag parent, String key) {
+        return parent.getCompound(key).orElseThrow(() -> new AssertionError("missing compound: " + key));
+    }
+
+    /** compile-time sanity: NbtIo.writeCompressed should accept the produced tag (used by SchematicUploader) */
+    @Test
+    void outputCanBeSerialized() throws Exception {
+        var result = runConverter();
+        var tmp = java.nio.file.Files.createTempFile("schematic", ".schematic");
+        try {
+            NbtIo.writeCompressed(result.schematic(), tmp);
+            assertTrue(java.nio.file.Files.size(tmp) > 0);
+            System.out.println("[test] wrote " + java.nio.file.Files.size(tmp) + " bytes to " + tmp);
+        } finally {
+            java.nio.file.Files.deleteIfExists(tmp);
+        }
+    }
+}