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1<?php
2
3/**
4 * @author: Doug Wilbourne (dougwilbourne@gmail.com)
5 */
6declare(strict_types=1);
7
8namespace pvc\struct\treesearch;
9
10use pvc\interfaces\struct\treesearch\NodeVisitableInterface;
11use pvc\interfaces\struct\treesearch\VisitStatus;
12
13/**
14 * Class SearchStrategyDepthFirstPostorder
15 * @template NodeType of NodeVisitableInterface
16 * @extends SearchDepthFirst<NodeType>
17 */
18class SearchDepthFirstPostorder extends SearchDepthFirst
19{
20    public function rewind(): void
21    {
22        parent::rewind();
23        /**
24         * The rewind method of the parent sets the current node to be the start node. This is correct for
25         * breadth first and depth first preorder searches.  But for depth-first-postorder searches, we want to recurse
26         * to the bottom of the tree so that the first node returned is at the bottom of the tree.
27         */
28        $this->next();
29    }
30
31    /**
32     * getMovementDirection
33     * @return Direction
34     *
35     * returns MOVE_DOWN if we should keep iterating by recursing down through child nodes,
36     * returns STOP if we should stop iterating
37     * returns MOVE_UP if we should continue iterating by returning up to the parent
38     *
39     * in post order mode, we go from never visited to partially visited and keep moving down if we can move down.
40     * if we cannot, we go to fully visited and stop
41     *
42     * in post order mode we go from partially visited to fully visited if all the children have been visited
43     * otherwise we move down.
44     *
45     * if a node is fully visited we always keep going up.
46     *
47     */
48    protected function getMovementDirection(): Direction
49    {
50        assert(!is_null($this->current()));
51
52        switch ($this->current()->getVisitStatus()) {
53
54            case VisitStatus::NEVER_VISITED:
55                if ($this->allChildrenFullyVisited() || $this->atMaxLevels()) {
56                    $this->current()->setVisitStatus(VisitStatus::FULLY_VISITED);
57                    $direction = Direction::DONT_MOVE;
58                }
59                else {
60                    $this->current()->setVisitStatus(VisitStatus::PARTIALLY_VISITED);
61                    $direction = Direction::MOVE_DOWN;
62                }
63                break;
64
65            case VisitStatus::PARTIALLY_VISITED:
66                if ($this->allChildrenFullyVisited() || $this->atMaxLevels()) {
67                    $this->current()->setVisitStatus(VisitStatus::FULLY_VISITED);
68                    $direction = Direction::DONT_MOVE;
69                } else {
70                    $direction = Direction::MOVE_DOWN;
71                }
72                break;
73
74            case VisitStatus::FULLY_VISITED:
75                $direction = Direction::MOVE_UP;
76                break;
77        }
78
79        return $direction;
80    }
81}