structure.kt

fun StructureTemplate.readLitematicaOrException(
    lookup: RegistryEntryLookup<Block>,
    nbt: NbtCompound,
): Throwable? {
    val version = nbt.getInt("MinecraftDataVersion")

    val metadata = nbt.getCompound("Metadata")
    val author = metadata.getString("Author")

    val size = metadata.getVector("EnclosingSize")

    val newPalette = NbtList()
    val newBlocks = NbtList()

    val regions = nbt.getCompound("Regions")
    regions.keys.map { regions.getCompound(it) }
        .forEach {
            val regionSize = it.getVector("Size")

            val xSizeAbs = abs(regionSize.x)
            val zSizeAbs = abs(regionSize.z)

            // The litematic's block state palette is the same as nbt
            newPalette.addAll(it.getList("BlockStatePalette", 10))

            val palette = it.getLongArray("BlockStates")
            val bits = max(2.0, ceil(log2(palette.size.toDouble()))).floorToInt()

            // Convert the long array to byte array
            val buffer = ByteBuffer.allocate(palette.size * Long.SIZE_BYTES)
            palette.forEach { states -> buffer.putLong(states) }

            var blockIndex = 0
            VarIntIterator(buffer.array(), bitsPerEntry = bits)
                .forEach { blockId ->
                    val blockpos = positionFromIndex(xSizeAbs, zSizeAbs, blockIndex++)

                    newBlocks.add(NbtCompound().apply {
                        putIntList("pos", blockpos.x, blockpos.y, blockpos.z)
                        putInt("state", blockId)
                    })
                }
        }

    // Construct a structure compatible nbt compound
    nbt.putInt("DataVersion", version)
    nbt.putIntList("size", size.x, size.y, size.z)
    nbt.put("palette", newPalette)
    nbt.put("blocks", newBlocks)
    nbt.putString("author", author)

    // Fix the data for future versions
    DataFixTypes.STRUCTURE.update(mc.dataFixer, nbt, version)

    // Use the StructureTemplate NBT read utils in order to construct the template
    return readNbtOrException(lookup, nbt)
}