/*
 * Copyright (c) 2006, 2021, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package com.sun.source.util;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;

import com.sun.source.tree.*;

/**
 * A path of tree nodes, typically used to represent the sequence of ancestor
 * nodes of a tree node up to the top-level {@code CompilationUnitTree} node.
 *
 * @author Jonathan Gibbons
 * @since 1.6
 */
public class TreePath implements Iterable<Tree> {
    /**
     * Returns a tree path for a tree node within a compilation unit,
     * or {@code null} if the node is not found.
     * @param unit the compilation unit to search
     * @param target the node to locate
     * @return the tree path
     */
    public static TreePath getPath(CompilationUnitTree unit, Tree target) {
        return getPath(new TreePath(unit), target);
    }

    /**
     * Returns a tree path for a tree node within a subtree identified by a TreePath object.
     * Returns {@code null} if the node is not found.
     * @param path the path in which to search
     * @param target the node to locate
     * @return the tree path of the target node
     */
    public static TreePath getPath(TreePath path, Tree target) {
        Objects.requireNonNull(path);
        Objects.requireNonNull(target);

        class PathFinder extends TreePathScanner<TreePath,Tree> {
            private TreePath result;


            @Override
            public TreePath scan(TreePath path, Tree target) {
                super.scan(path, target);
                return result;
            }

            @Override
            public TreePath scan(Tree tree, Tree target) {
                if (result == null) {
                    if (tree == target) {
                        result = new TreePath(getCurrentPath(), target);
                    } else {
                        super.scan(tree, target);
                    }
                }
                return result;
            }

            @Override
            public TreePath scan(Iterable<? extends Tree> nodes, Tree target) {
                if (nodes != null && result == null) {
                    for (Tree node : nodes) {
                        scan(node, target);
                        if (result != null) {
                            break;
                        }
                    }
                }
                return result;
            }
        }

        return path.getLeaf() == target ? path
                : new PathFinder().scan(path, target);
    }

    /**
     * Creates a TreePath for a root node.
     * @param node the root node
     */
    public TreePath(CompilationUnitTree node) {
        this(null, node);
    }

    /**
     * Creates a TreePath for a child node.
     * @param path the parent path
     * @param tree the child node
     */
    public TreePath(TreePath path, Tree tree) {
        if (tree.getKind() == Tree.Kind.COMPILATION_UNIT) {
            compilationUnit = (CompilationUnitTree) tree;
            parent = null;
        }
        else {
            compilationUnit = path.compilationUnit;
            parent = path;
        }
        leaf = tree;
    }
    /**
     * Returns the compilation unit associated with this path.
     * @return the compilation unit
     */
    public CompilationUnitTree getCompilationUnit() {
        return compilationUnit;
    }

    /**
     * Returns the leaf node for this path.
     * @return the leaf node
     */
    public Tree getLeaf() {
        return leaf;
    }

    /**
     * Returns the path for the enclosing node, or {@code null} if there is no enclosing node.
     * @return the path for the enclosing node
     */
    public TreePath getParentPath() {
        return parent;
    }

    /**
     * Iterates from leaves to root.
     */
    @Override
    public Iterator<Tree> iterator() {
        return new Iterator<>() {
            @Override
            public boolean hasNext() {
                return next != null;
            }

            @Override
            public Tree next() {
                if (next == null) {
                    throw new NoSuchElementException();
                }
                Tree t = next.leaf;
                next = next.parent;
                return t;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }

            private TreePath next = TreePath.this;
        };
    }

    private CompilationUnitTree compilationUnit;
    private Tree leaf;
    private TreePath parent;
}
