package dev.metaschema.core.metapath.item.node;
   
   import java.net.URI;
   import java.util.Collection;
   import java.util.List;
   import java.util.stream.Stream;
   
   import dev.metaschema.core.metapath.StaticContext;
  import dev.metaschema.core.metapath.format.IPathFormatter;
  import dev.metaschema.core.metapath.format.IPathSegment;
  import dev.metaschema.core.metapath.item.IItem;
  import dev.metaschema.core.metapath.item.IItemVisitor;
  import dev.metaschema.core.metapath.type.IItemType;
  import dev.metaschema.core.model.IResourceLocation;
  import dev.metaschema.core.qname.IEnhancedQName;
  import dev.metaschema.core.util.ObjectUtils;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import edu.umd.cs.findbugs.annotations.Nullable;
  
  /**
   * Represents a Metapath model node.
   */
  public interface INodeItem extends IItem, IPathSegment, INodeItemVisitable {
    /**
     * The type of node.
     */
    enum NodeType {
      /** A Metaschema module node. */
      MODULE,
      /** A document node representing the root of a data instance. */
      DOCUMENT,
      /** An assembly node containing fields and other assemblies. */
      ASSEMBLY,
      /** A field node containing flags and a value. */
      FIELD,
      /** A flag node containing a simple value. */
      FLAG;
    }
  
    /**
     * Get the node type for the node item.
     *
     * @return the node type
     */
    @NonNull
    NodeType getNodeType();
  
    /**
     * Get the static type information of the node item.
     *
     * @return the item type
     */
    @NonNull
    static IItemType type() {
      return IItemType.node();
    }
  
    /**
     * Retrieve the relative position of this node relative to sibling nodes.
     * <p>
     * A singleton item in a sequence will have a position value of {@code 1}.
     * <p>
     * The value {@code 1} is used as the starting value to align with the XPath
     * specification.
     *
     * @return a positive integer value designating this instance's position within
     *         a collection
     */
    default int getPosition() {
      // only model node items have positions other than 1
      return 1;
    }
  
    /**
     * Generate a path for this node in the directed node graph, using the provided
     * path formatter.
     */
    @Override
    String format(IPathFormatter formatter);
  
    /**
     * Gets the value of the provided node item.
     * <p>
     * If the provided node item is a document, this method get the first child node
     * item's value, since a document doesn't have a value.
     *
     * @param <CLASS>
     *          the type of the bound object to return
     * @param item
     *          the node item to get the value of
     * @return a bound object
     * @throws NullPointerException
     *           if the node item has no associated value
     */
    @SuppressWarnings("unchecked")
    @NonNull
    static <CLASS> CLASS toValue(@NonNull INodeItem item) {
      INodeItem valuedItem;
     if (item instanceof IDocumentNodeItem) {
       // get first child item, since the document has no value
       valuedItem = item.modelItems().findFirst().get();
     } else {
       valuedItem = item;
     }
     return ObjectUtils.requireNonNull((CLASS) valuedItem.getValue());
   }
 
   /**
    * Retrieve the parent node item if it exists.
    *
    * @return the parent node item, or {@code null} if this node item has no known
    *         parent
    */
   INodeItem getParentNodeItem();
 
   /**
    * Retrieve the parent content node item if it exists. A content node is a
    * non-document node.
    *
    * @return the parent content node item, or {@code null} if this node item has
    *         no known parent content node item
    */
   IModelNodeItem<?, ?> getParentContentNodeItem();
 
   /**
    * Get the kind of node item this is.
    *
    * @return the node item's kind
    */
   @NonNull
   NodeItemKind getNodeItemKind();
 
   /**
    * Retrieve the base URI of this node.
    * <p>
    * The base URI of a node will be in order of preference:
    * <ol>
    * <li>the base URI defined on the node
    * <li>the base URI defined on the nearest ancestor node
    * <li>the base URI defined on the document node
    * <li>{@code null} if the document node is unknown
    * </ol>
    *
    * @return the base URI or {@code null} if it is unknown
    */
   URI getBaseUri();
 
   /**
    * Get the path for this node item as a Metapath.
    *
    * @return the Metapath
    */
   @NonNull
   default String getMetapath() {
     return toPath(IPathFormatter.METAPATH_PATH_FORMATER);
   }
 
   @Override
   default Stream<? extends INodeItem> getPathStream() {
     INodeItem parent = getParentNodeItem();
     return ObjectUtils.notNull(
         parent == null ? Stream.of(this) : Stream.concat(getParentNodeItem().getPathStream(), Stream.of(this)));
   }
 
   /**
    * Get a stream of all ancestors of this node item. The stream is ordered from
    * closest to farthest ancestor.
    *
    * @return a stream of ancestor node items
    */
   @NonNull
   default Stream<? extends INodeItem> ancestor() {
     return ancestorsOf(this);
   }
 
   /**
    * Get a stream of this and all ancestors of this node item. The stream is
    * ordered from self, then closest to farthest ancestor.
    *
    * @return a stream of this node followed by all ancestor node items
    */
   @NonNull
   default Stream<? extends INodeItem> ancestorOrSelf() {
     return ObjectUtils.notNull(Stream.concat(ancestor(), Stream.of(this)));
   }
 
   /**
    * Get a stream of the ancestors of the provided {@code item}. The stream is
    * ordered from the farthest ancestor to the closest.
    *
    * @param item
    *          the target item to get ancestors for
    *
    * @return a stream of all ancestor node items
    */
   @NonNull
   static Stream<? extends INodeItem> ancestorsOf(@NonNull INodeItem item) {
     INodeItem parent = item.getParentNodeItem();
     return ObjectUtils.notNull(parent == null ? Stream.empty() : Stream.concat(ancestorsOf(parent), Stream.of(parent)));
   }
 
   /**
    * Get a stream of all descendant model items of this node item. The stream is
    * ordered from closest to farthest descendants in a depth-first order.
    *
    * @return a stream of descendant node items
    */
   @NonNull
   default Stream<? extends IModelNodeItem<?, ?>> descendant() {
     return decendantsOf(this);
   }
 
   /**
    * Get a stream of all descendant model items of the provided {@code item}. The
    * stream is ordered from closest to farthest descendants in a depth-first
    * order.
    *
    * @param item
    *          the target item to get descendants for
    *
    * @return a stream of descendant node items
    */
   @NonNull
   static Stream<? extends IModelNodeItem<?, ?>> decendantsOf(@NonNull INodeItem item) {
     Stream<? extends IModelNodeItem<?, ?>> children = item.modelItems();
 
     return ObjectUtils.notNull(children.flatMap(child -> {
       assert child != null;
       return Stream.concat(Stream.of(child), decendantsOf(child));
     }));
   }
 
   /**
    * Get a stream of this node, followed by all descendant model items of this
    * node item. The stream is ordered from closest to farthest descendants in a
    * depth-first order.
    *
    * @return a stream of this node and descendant node items
    */
   @NonNull
   default Stream<? extends INodeItem> descendantOrSelf() {
     return ObjectUtils.notNull(Stream.concat(Stream.of(this), descendant()));
   }
 
   /**
    * Get the children of this node's parent that occur after this node in a
    * depth-first order.
    *
    * @return a stream of nodes
    */
   @NonNull
   default Stream<? extends IModelNodeItem<?, ?>> followingSibling() {
     return ObjectUtils.notNull(Stream.empty());
   }
 
   /**
    * Get the children of this node's parent, and their descendants, that occur
    * before this node in a depth-first order.
    *
    * @return a stream of nodes
    */
   @NonNull
   default Stream<? extends IModelNodeItem<?, ?>> precedingSibling() {
     return ObjectUtils.notNull(Stream.empty());
   }
 
   /**
    * Get the children of this node's parent, and their descendants, that occur
    * before this node in a depth-first order.
    *
    * @return a stream of nodes
    */
   default Stream<? extends IModelNodeItem<?, ?>> following() {
     return ObjectUtils.notNull(Stream.empty());
   }
 
   /**
    * Get the children of this node's parent, and their descendants, that occur
    * after this node in a depth-first order.
    *
    * @return a stream of nodes
    */
   default Stream<? extends IModelNodeItem<?, ?>> preceding() {
     return ObjectUtils.notNull(Stream.empty());
   }
 
   /**
    * Get the flags and value data associated this node. The resulting collection
    * is expected to be ordered, with the results in document order.
    * <p>
    * The resulting collection may be modified, but such modification is not thread
    * safe
    *
    * @return a collection of flags
    */
   @NonNull
   Collection<? extends IFlagNodeItem> getFlags();
 
   /**
    * Lookup a flag and value data on this node by it's effective qualified name.
    *
    * @param name
    *          the effective qualified name of the flag
    * @return the flag with the matching effective name or {@code null} if no match
    *         was found
    */
   @Nullable
   IFlagNodeItem getFlagByName(@NonNull IEnhancedQName name);
 
   /**
    * Get the flags and value data associated with this node as a stream.
    *
    * @return the stream of flags or an empty stream if none exist
    */
   @SuppressWarnings("null")
   @NonNull
   default Stream<? extends IFlagNodeItem> flags() {
     return getFlags().stream();
   }
 
   /**
    * Get the model items (i.e., fields, assemblies) and value data associated this
    * node. A given model instance can be multi-valued, so the value of each
    * instance will be a list. The resulting collection is expected to be ordered,
    * with the results in document order.
    * <p>
    * The resulting collection may be modified, but such modification is not thread
    * safe
    *
    * @return a collection of list(s), with each list containing the items for a
    *         given model instance
    */
   @NonNull
   Collection<? extends List<? extends IModelNodeItem<?, ?>>> getModelItems();
 
   /**
    * Get the collection of model items associated with the instance having the
    * provided {@code name}.
    * <p>
    * The resulting collection may be modified, but such modification is not thread
    * safe
    *
    * @param name
    *          the instance name to get model items for
    * @return the sequence of items associated with the named model instance, or an
    *         empty list if an instance with that name is not present
    */
   @NonNull
   List<? extends IModelNodeItem<?, ?>> getModelItemsByName(@NonNull IEnhancedQName name);
 
   /**
    * Get the model items (i.e., fields, assemblies) and value data associated this
    * node as a stream.
    *
    * @return the stream of model items or an empty stream if none exist
    */
   @SuppressWarnings("null")
   @NonNull
   default Stream<? extends IModelNodeItem<?, ?>> modelItems() {
     return getModelItems().stream().flatMap(Collection::stream);
   }
 
   /**
    * Get the resource location information for the node, if known.
    *
    * @return the resource location information, or {@code null} if not known
    */
   @Nullable
   IResourceLocation getLocation();
 
   /**
    * Get the string value of the node.
    *
    * @return the string value of the node or an empty string if it has no value.
    */
   @NonNull
   String stringValue();
 
   /**
    * Get the static context to use to query this node item.
    *
    * @return the static context
    */
   @NonNull
   StaticContext getStaticContext();
 
   @Override
   default void accept(IItemVisitor visitor) {
     visitor.visit(this);
   }
 }