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));