<?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;
    }
}