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package graphql.util;
import graphql.PublicApi;
import java.util.List;
import java.util.Map;
import java.util.Set;
 * Traversal context.
 * It is used as providing context for traversing, but also for returning an accumulate value. ({@link #setAccumulate(Object)}
 * There is always a "fake" root context with null node, null parent, null position. See {@link #isRootContext()}
 * @param <T> type of tree node
public interface TraverserContext<T> {
    enum Phase {
        LEAVE,
        ENTER,
        BACKREF
     * Returns current node being visited.
     * Special cases:
     * It is null for the root context and it is the changed node after {@link #changeNode(Object)} is called.
     * Throws Exception if the node is deleted.
     * @return current node traverser is visiting.
     * @throws graphql.AssertException if the current node is deleted
    T thisNode();
     * Returns the original, unchanged, not deleted Node.
     * @return the original node
    T originalThisNode();
     * Change the current node to the provided node. Only applicable in enter.
     * Useful when the tree should be changed while traversing.
     * Also: changing a node makes only a difference when it has different children than the current one.
     * @param newNode the new Node
    void changeNode(T newNode);
     * Deletes the current node.
    void deleteNode();
     * @return true if the current node is deleted (by calling {@link #deleteNode()}
    boolean isDeleted();
     * @return true if the current node is changed (by calling {@link #changeNode(Object)}
    boolean isChanged();
     * Returns parent context.
     * Effectively organizes Context objects in a linked list so
     * by following {@link #getParentContext() } links one could obtain
     * the current path as well as the variables {@link #getVar(java.lang.Class) }
     * stored in every parent context.
     * @return context associated with the node parent
    TraverserContext<T> getParentContext();
     * The list of parent nodes starting from the current parent.
     * @return list of parent nodes
    List<T> getParentNodes();
     * The parent node.
     * @return The parent node.
    T getParentNode();
     * The exact location of this node inside the tree as a list of {@link Breadcrumb}
     * @return list of breadcrumbs. the first element is the location inside the parent.
    List<Breadcrumb<T>> getBreadcrumbs();
     * The location of the current node regarding to the parent node.
     * @return the position or null if this node is a root node
    NodeLocation getLocation();
     * Informs that the current node has been already "visited"
     * @return {@code true} if a node had been already visited
    boolean isVisited();
     * Obtains all visited nodes and values received by the {@link TraverserVisitor#enter(graphql.util.TraverserContext) }
     * method
     * @return a map containing all nodes visited and values passed when visiting nodes for the first time
    Set<T> visitedNodes();
     * Obtains a context local variable
     * @param <S> type of the variable
     * @param key key to lookup the variable value
     * @return a variable value or {@code null}
    <S> S getVar(Class<? super S> key);
     * Searches for a context variable starting from the parent
     * up the hierarchy of contexts until the first variable is found.
     * @param <S> type of the variable
     * @param key key to lookup the variable value
     * @return a variable value or {@code null}
    <S> S getVarFromParents(Class<? super S> key);
     * Stores a variable in the context
     * @param <S>   type of a variable
     * @param key   key to create bindings for the variable
     * @param value value of variable
     * @return this context to allow operations chaining
    <S> TraverserContext<T> setVar(Class<? super S> key, S value);
     * Sets the new accumulate value.
     * Can be retrieved by {@link #getNewAccumulate()}
     * @param accumulate to set
    void setAccumulate(Object accumulate);
     * The new accumulate value, previously set by {@link #setAccumulate(Object)}
     * or {@link #getCurrentAccumulate()} if {@link #setAccumulate(Object)} not invoked.
     * @param <U> and me
     * @return the new accumulate value
    <U> U getNewAccumulate();
     * The current accumulate value used as "input" for the current step.
     * @param <U> and me
     * @return the current accumulate value
    <U> U getCurrentAccumulate();
     * Used to share something across all TraverserContext.
     * @param <U> and me
     * @return contextData
    <U> U getSharedContextData();
     * Returns true for the root context, which doesn't have a node or a position.
     * @return true for the root context, otherwise false
    boolean isRootContext();
     * In case of leave returns the children contexts, which have already been visited.
     * @return the children contexts. If the childs are a simple list the key is null.
    Map<String, List<TraverserContext<T>>> getChildrenContexts();
     * @return the phase in which the node visits currently happens (Enter,Leave or BackRef)
    Phase getPhase();
     * @return true if the traversing happens in parallel (multi threaded) or not.
    boolean isParallel();
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