I see an implementation here via a recursive function, but..

I've tried dozens of times to compose this function, but I can't get my head around the logic by which it should work, although at first glance it shouldn't be so difficult. I seem to understand the points where the exit from the recursive function should occur, but it doesn't give me anything.

I would like to understand the algorithm how it should work, in any language, perhaps at least in words, because so far I have not been able to "text" even mentally formulate what the solution should look like.

I want to implement a function to generate the resulting array in the format I need.I have prepared the data, input and output, so that it is clearer to you what I want to achieve.

INPUT

$input = ['h1', 'p', 'h2', 'p', 'p', 'h3', 'p', 'h2', 'p', 'h3', 'p', 'h1', 'p', 'h2', 'p', 'h3', 'p'];

OUTPUT

$output = [    ['title' => 'h1','descriptions' => ['p'],'childrens' => [            ['title' => 'h2','descriptions' => ['p', 'p'],'childrens' => [                    ['title' => 'h3','descriptions' => ['p'],                    ],                ]            ],            ['title' => 'h2','descriptions' => ['p'],'childrens' => [                    ['title' => 'h3','descriptions' => ['p']                    ]                ]            ]        ]    ],    ['title' => 'h1','descriptions' => ['p'],'childrens' => [            ['title' => 'h2','descriptions' => ['p'],'childrens' => [                    ['title' => 'h3','descriptions' => ['p']                    ]                ]            ]        ]    ]];

my (not working) implementation:

function parseDOM(array $inputArray): array {    $output = [];    $position = 0;    $domElementsQuantity = count($inputArray);    $parentTagLvl = 0;    function getCurrentTagLvl(string $node): bool|int    {        return match ($node) {'h1' => 1,'h2' => 2,'h3' => 3,'h4' => 4,'h5' => 5,'h6' => 6,            default => false,        };    }    function recursiveCreateTree(array $inputArray, int &$offsetIndex, $parentTagLvl) {        $tree = [];        $arrayItemsQuantity = count($inputArray);        while ($offsetIndex <= $arrayItemsQuantity) {            $currentNode = $inputArray[$offsetIndex];            $currentTagLvl = getCurrentTagLvl($currentNode);            if ($currentTagLvl !== false && $currentTagLvl < $parentTagLvl) {                return $tree;            }            if ($currentTagLvl === false) {                $tree['descriptions'][] = $currentNode;            } else {                $tree['title'] = $currentNode;                $tree['childrens'] = recursiveCreateTree($inputArray, $offsetIndex, $currentTagLvl);            }            $offsetIndex++;        }        return $tree;    }    while ($position <= $domElementsQuantity) {        $currentNode = $inputArray[$position];        $currentTagLvl = getCurrentTagLvl($currentNode);        if ($currentTagLvl === false) {        }        else {            if ($currentTagLvl > $parentTagLvl) {            }            else {                $parentTagLvl = $currentTagLvl - 1;            }        }    }    return $output;}

To display the results:

echo '<pre>';print_r(parseDOM($input));