Lupine: Detect endless loops

lupine.php

<?php
class Node
{
    /**
     * @var list<Node>
     */
    public array $prev = [];

    /**
     * @var list<Node>
     */
    public array $next = [];

    public string $name;

    public function __construct(string $name)
    {
        $this->name = $name;
    }

    public function __toString(): string
    {
        return sprintf(
            '%s->{%s}',
            $this->name,
            implode(',', array_map(static fn (Node $node) => $node->name, $this->next))
        );
    }

    public function findInAncestors(Node $node): ?Node
    {
        foreach ($this->prev as $prev) {
            if ($prev === $node) {
                return $this;
            }
            $ancestor = $prev->findInAncestors($node);
            if ($ancestor !== null) {
                return $ancestor;
            }
        }
        return null;
    }
}

class Collection
{
    /**
     * @var array<string, Node>
     */
    public array $items = [];

    public function add(string $currentName, string $nextName): void
    {
        if (!isset($this->items[$currentName])) {
            $this->items[$currentName] = new Node($currentName);
        }
        $current = $this->items[$currentName];
        if (!isset($this->items[$nextName])) {
            $this->items[$nextName] = new Node($nextName);
        }
        $next = $this->items[$nextName];
        if (!in_array($next, $current->next,true)) {
            $current->next[] = $next;
        }
        if ($current->findInAncestors($next)) {
            throw new \RuntimeException(
                sprintf('Recursion when adding %s to %s', $next, $current)
            );
        }
        if (!in_array($current, $next->prev, true)) {
            $next->prev[] = $current;
        }
    }


    public function getEntryNodes(): array
    {
        return array_filter($this->items, static fn (Node $item) => $item->prev === []);
    }

    public function getLeafNodes(): array
    {
        return array_filter($this->items, static fn (Node $item) => $item->next === []);
    }
}

// will later show error `Recursion when adding B->{C,222} to E->{B}`
$text =<<< 'EOT'
A->B, B->C, C->111, B->222, 111->D, D->E, D->333, E->B
EOT;

$collection = new Collection();
$items = explode(',', $text);
$items = array_map('trim', $items);

try {
    foreach ($items as $item) {
        list($currentName, $nextName) = explode('->', $item, 2);
        $collection->add($currentName, $nextName);
    }
} catch (\Exception $e) {
    echo $e->getMessage() . PHP_EOL;
}