@NotNull
  private static XmlFileHeader calcXmlFileHeader(final PsiFile file) {

    // if (file.getFileType() == XmlFileType.INSTANCE) {
    //  VirtualFile virtualFile = file.getVirtualFile();
    //  if (virtualFile instanceof VirtualFileWithId) {
    //    ObjectStubTree tree = StubTreeLoader.getInstance().readFromVFile(file.getProject(),
    // virtualFile);
    //    if (tree != null) {
    //      return ((FileStub)tree.getRoot()).getHeader();
    //    }
    //  }
    // }
    if (file instanceof XmlFile && file.getNode().isParsed()) {
      final XmlDocument document = ((XmlFile) file).getDocument();
      if (document != null) {
        String publicId = null;
        String systemId = null;
        final XmlProlog prolog = document.getProlog();
        if (prolog != null) {
          final XmlDoctype doctype = prolog.getDoctype();
          if (doctype != null) {
            publicId = doctype.getPublicId();
            systemId = doctype.getSystemId();
            if (systemId == null) {
              systemId = doctype.getDtdUri();
            }
          }
        }

        final XmlTag tag = document.getRootTag();
        if (tag != null) {
          String localName = tag.getLocalName();
          if (StringUtil.isNotEmpty(localName)) {
            if (tag.getPrevSibling() instanceof PsiErrorElement) {
              return XmlFileHeader.EMPTY;
            }

            String psiNs = tag.getNamespace();
            return new XmlFileHeader(
                localName,
                psiNs == XmlUtil.EMPTY_URI || Comparing.equal(psiNs, systemId) ? null : psiNs,
                publicId,
                systemId);
          }
        }
      }
      return XmlFileHeader.EMPTY;
    }

    if (!file.isValid()) return XmlFileHeader.EMPTY;
    return NanoXmlUtil.parseHeader(file);
  }
  private static XmlFileHeader computeHeaderByPsi(XmlFile file) {
    final XmlDocument document = file.getDocument();
    if (document == null) {
      return XmlFileHeader.EMPTY;
    }

    String publicId = null;
    String systemId = null;
    final XmlProlog prolog = document.getProlog();
    if (prolog != null) {
      final XmlDoctype doctype = prolog.getDoctype();
      if (doctype != null) {
        publicId = doctype.getPublicId();
        systemId = doctype.getSystemId();
        if (systemId == null) {
          systemId = doctype.getDtdUri();
        }
      }
    }

    final XmlTag tag = document.getRootTag();
    if (tag == null) {
      return XmlFileHeader.EMPTY;
    }

    String localName = tag.getLocalName();
    if (StringUtil.isNotEmpty(localName)) {
      if (tag.getPrevSibling() instanceof PsiErrorElement) {
        return XmlFileHeader.EMPTY;
      }

      String psiNs = tag.getNamespace();
      return new XmlFileHeader(
          localName,
          psiNs == XmlUtil.EMPTY_URI || Comparing.equal(psiNs, systemId) ? null : psiNs,
          publicId,
          systemId);
    }
    return XmlFileHeader.EMPTY;
  }
  private XmlNSDescriptor getDefaultNSDescriptorInner(
      final String namespace, final boolean strict) {
    final XmlFile containingFile = XmlUtil.getContainingFile(this);
    if (containingFile == null) return null;
    final XmlProlog prolog = getProlog();
    final XmlDoctype doctype = prolog != null ? prolog.getDoctype() : null;
    boolean dtdUriFromDocTypeIsNamespace = false;

    if (XmlUtil.HTML_URI.equals(namespace)) {
      XmlNSDescriptor nsDescriptor =
          doctype != null ? getNsDescriptorFormDocType(doctype, containingFile, true) : null;
      if (doctype != null) {
        LOG.debug(
            "Descriptor from doctype "
                + doctype
                + " is "
                + (nsDescriptor != null ? nsDescriptor.getClass().getCanonicalName() : "NULL"));
      }

      if (nsDescriptor == null) {
        String htmlns =
            ExternalResourceManagerEx.getInstanceEx().getDefaultHtmlDoctype(getProject());
        if (htmlns.isEmpty()) {
          htmlns = Html5SchemaProvider.getHtml5SchemaLocation();
        }
        nsDescriptor = getDefaultNSDescriptor(htmlns, false);
      }
      return new HtmlNSDescriptorImpl(nsDescriptor);
    } else if (XmlUtil.XHTML_URI.equals(namespace)) {
      String xhtmlNamespace = XmlUtil.getDefaultXhtmlNamespace(getProject());
      if (xhtmlNamespace == null || xhtmlNamespace.isEmpty()) {
        xhtmlNamespace = Html5SchemaProvider.getXhtml5SchemaLocation();
      }
      return getDefaultNSDescriptor(xhtmlNamespace, false);
    } else if (namespace != null && namespace != XmlUtil.EMPTY_URI) {
      if (doctype == null || !namespace.equals(XmlUtil.getDtdUri(doctype))) {
        boolean documentIsSchemaThatDefinesNs =
            namespace.equals(XmlUtil.getTargetSchemaNsFromTag(getRootTag()));

        final XmlFile xmlFile =
            documentIsSchemaThatDefinesNs
                ? containingFile
                : XmlUtil.findNamespace(containingFile, namespace);
        if (xmlFile != null) {
          final XmlDocument document = xmlFile.getDocument();
          if (document != null) {
            return (XmlNSDescriptor) document.getMetaData();
          }
        }
      } else {
        dtdUriFromDocTypeIsNamespace = true;
      }
    }

    if (strict && !dtdUriFromDocTypeIsNamespace) return null;

    if (doctype != null) {
      XmlNSDescriptor descr = getNsDescriptorFormDocType(doctype, containingFile, false);

      if (descr != null) {
        return XmlExtension.getExtension(containingFile)
            .getDescriptorFromDoctype(containingFile, descr);
      }
    }

    if (strict) return null;
    if (namespace == XmlUtil.EMPTY_URI) {
      final XmlFile xmlFile = XmlUtil.findNamespace(containingFile, namespace);
      if (xmlFile != null) {
        return (XmlNSDescriptor) xmlFile.getDocument().getMetaData();
      }
    }
    try {
      final PsiFile fileFromText =
          PsiFileFactory.getInstance(getProject())
              .createFileFromText(
                  containingFile.getName() + ".dtd",
                  DTDLanguage.INSTANCE,
                  XmlUtil.generateDocumentDTD(this, false),
                  false,
                  false);
      if (fileFromText instanceof XmlFile) {
        fileFromText.putUserData(AUTO_GENERATED, Boolean.TRUE);
        return (XmlNSDescriptor) ((XmlFile) fileFromText).getDocument().getMetaData();
      }
    } catch (ProcessCanceledException ex) {
      throw ex;
    } catch (RuntimeException ignored) {
    } // e.g. dtd isn't mapped to xml type

    return null;
  }
  @NotNull
  @Override
  public Runnable processFile(final PsiFile file) {
    VirtualFile vFile = file.getVirtualFile();
    if (vFile instanceof VirtualFileWindow) vFile = ((VirtualFileWindow) vFile).getDelegate();
    final Project project = file.getProject();
    if (vFile == null
        || !ProjectRootManager.getInstance(project).getFileIndex().isInSourceContent(vFile)) {
      return EmptyRunnable.INSTANCE;
    }
    final List<Pair<String, Boolean>> names = new ArrayList<Pair<String, Boolean>>();
    final Set<String> demandedForNested = new HashSet<>();
    collectNamesToImport(names, demandedForNested, (XmlFile) file);
    Collections.sort(names, (o1, o2) -> StringUtil.compare(o1.first, o2.first, true));
    final CodeStyleSettings settings = CodeStyleSettingsManager.getSettings(project);
    final List<Pair<String, Boolean>> sortedNames =
        ImportHelper.sortItemsAccordingToSettings(names, settings);
    final HashSet<String> onDemand = new HashSet<String>();
    ImportHelper.collectOnDemandImports(sortedNames, onDemand, settings);
    onDemand.addAll(demandedForNested);
    final Set<String> imported = new HashSet<String>();
    final List<String> imports = new ArrayList<String>();
    for (Pair<String, Boolean> pair : sortedNames) {
      final String qName = pair.first;
      final String packageName = StringUtil.getPackageName(qName);
      if (imported.contains(packageName) || imported.contains(qName)) {
        continue;
      }
      if (onDemand.contains(packageName)) {
        imported.add(packageName);
        imports.add("<?import " + packageName + ".*?>");
      } else {
        imported.add(qName);
        imports.add("<?import " + qName + "?>");
      }
    }
    final PsiFileFactory factory = PsiFileFactory.getInstance(file.getProject());

    final XmlFile dummyFile =
        (XmlFile)
            factory.createFileFromText(
                "_Dummy_.fxml", StdFileTypes.XML, StringUtil.join(imports, "\n"));
    final XmlDocument document = dummyFile.getDocument();
    final XmlProlog newImportList = document != null ? document.getProlog() : null;
    if (newImportList == null) return EmptyRunnable.getInstance();
    return () -> {
      final XmlDocument xmlDocument = ((XmlFile) file).getDocument();
      final XmlProlog prolog = xmlDocument != null ? xmlDocument.getProlog() : null;
      if (prolog != null) {
        final Collection<XmlProcessingInstruction> instructions =
            PsiTreeUtil.findChildrenOfType(prolog, XmlProcessingInstruction.class);
        for (final XmlProcessingInstruction instruction : instructions) {
          final ASTNode node = instruction.getNode();
          final ASTNode nameNode = node.findChildByType(XmlTokenType.XML_NAME);
          if (nameNode != null && nameNode.getText().equals("import")) {
            instruction.delete();
          }
        }
        prolog.add(newImportList);
      } else {
        document.addBefore(newImportList, document.getRootTag());
      }
    };
  }