initial COmmit: Add KB Antora Importer plugin files

kb-antora-importer/includes/Antora/AntoraNavParser.php

@@ -0,0 +1,67 @@
+<?php
+declare(strict_types=1);
+
+namespace KbAntoraImporter\Antora;
+
+final class AntoraNavParser
+{
+    public function parse(string $nav): array
+    {
+        $root = [];
+        $stack = [];
+
+        foreach (preg_split('/\R/', $nav) ?: [] as $line) {
+            if (! preg_match('/^(\*+)\s+(.+)$/', trim($line), $matches)) {
+                continue;
+            }
+
+            $level = strlen($matches[1]);
+            $raw = trim($matches[2]);
+            $item = [
+                'title' => $raw,
+                'target' => '',
+                'children' => [],
+            ];
+
+            if (preg_match('/xref:([^\[]+)\[([^\]]*)\]/', $raw, $xref)) {
+                $item['target'] = trim($xref[1]);
+                $item['title'] = trim($xref[2]) ?: basename($item['target']);
+            }
+
+            while (count($stack) >= $level) {
+                array_pop($stack);
+            }
+
+            if (empty($stack)) {
+                $root[] = $item;
+                $stack[$level - 1] = &$root[array_key_last($root)];
+            } else {
+                $parent = &$stack[array_key_last($stack)];
+                $parent['children'][] = $item;
+                $stack[$level - 1] = &$parent['children'][array_key_last($parent['children'])];
+            }
+
+            unset($parent);
+        }
+
+        return $root;
+    }
+
+    public function flatten(array $tree): array
+    {
+        $items = [];
+        $walk = static function (array $nodes, int $level = 1) use (&$walk, &$items): void {
+            foreach ($nodes as $node) {
+                $items[] = [
+                    'title' => (string) ($node['title'] ?? ''),
+                    'target' => (string) ($node['target'] ?? ''),
+                    'level' => $level,
+                ];
+                $walk((array) ($node['children'] ?? []), $level + 1);
+            }
+        };
+        $walk($tree);
+
+        return $items;
+    }
+}