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