<?php

/**

 * Created by PhpStorm.

 * User: Mch

 * Date: 8/11/18

 * Time: 00:25

 */

class Node {

    public $value;

    public $next;

    public function __construct($data) {

        $this->value = $data;

        $this->next = null;

    }

}

class LinkedList implements Iterator, Countable {

    private $head;

    private $cur;

    public function __construct() {

        $this->head = $this->cur = null;

    }

    public function isEmpty() {

        return is_null($this->head);

    }

    public function count() {

        $p = $this->head;

        $count = 0;

        while ($p !== null) {

            $p = $p->next;

            $count++;

        }

        return $count;

    }

    public function current() {

        if ($this->isEmpty()) {

            return null;

        }

        return $this->cur->value;

    }

    public function next() {

        if (is_null($this->cur)) {

            return null;

        }

        $this->cur = $this->cur->next;

    }

    public function rewind() {

        $this->cur = $this->head;

    }

    public function valid() {

        return !is_null($this->cur);

    }

    public function key() {

        $p = $this->head;

        $key = 0;

        while ($p !== $this->cur) {

            $p = $p->next;

            $key++;

        }

        return $key;

    }

    public function push($value) {

        if ($this->isEmpty()) {

            $this->head = new Node($value);

            $this->cur = $this->head;

        } else {

            $this->cur = $this->head;

            while ($this->cur->next !== null) {

                $this->cur = $this->cur->next;

            }

            $this->cur->next = new Node($value);

        }

        return $this;

    }

    public function forEach(callable $callback, mixed $userdata = null) {

        $this->rewind();

        while($this->valid()) {

            call_user_func($callback, $this->current(), $this->key(), $userdata);

            $this->next();

        }

    }

    public function reverse() {

        if ($this->isEmpty())

            return;

        if ($this->count() < 2)

            return;

        $prev = null;

        $cur = $this->head;

        while ($cur) {

            // save next

            $next = $cur->next;

            // move cur to head

            $this->head = $cur;

            $cur->next = $prev;

            // iterate

            $prev = $cur;

            $cur = $next;

        }

    }

}

$list = new LinkedList();

for ($i = 65; $i < 91; $i++) {

    $list->push(chr($i));

}

$list->forEach(function($value, $index) {

    printf("[%d] => %s<br />", $index, $value);

});

echo '-------------------<br />';

$list->reverse();

$list->forEach(function($value, $index) {

    printf("[%d] => %s<br />", $index, $value);

});