<?php
declare(strict_types=1);

/**
 * Automatically generates a Table of Contents and injects breadcrumbs for Markdown files.
 */

function generateToc(string $filePath, string $name): void
{
    if (!is_file($filePath)) {
        echo "$name not found.\n";
        return;
    }

    $content = file_get_contents($filePath);
    $lines = explode("\n", $content);

    $inToc = false;
    $headers = [];
    $bodyLines = [];

    foreach ($lines as $line) {
        if (trim($line) === '## Table of Contents') {
            $inToc = true;
            continue;
        }

        // We assume the TOC ends at the next header or double newline
        if ($inToc && (str_starts_with($line, '## ') || (str_contains($content, 'This document outlines') && str_starts_with($line, 'This document outlines')))) {
            $inToc = false;
        }

        if (!$inToc) {
            if (preg_match('/^(##+) (.*)/', $line, $matches)) {
                $level = strlen($matches[1]) - 1; // ## is level 1 in TOC
                if ($level > 0) {
                    $anchor = strtolower(trim($matches[2]));
                    $anchor = str_replace('~~', '', $anchor);
                    $anchor = preg_replace('/[^a-z0-9]+/', '-', $anchor);
                    $anchor = trim($anchor, '-');
                    $headers[] = [
                        'level' => $level,
                        'title' => trim($matches[2]),
                        'anchor' => $anchor
                    ];
                }

                // Add "Back to Top" breadcrumb before level 2 headers, except for the first one or if already present
                if ($level === 1 && !empty($bodyLines)) {
                    $lastLine = end($bodyLines);
                    if ($lastLine !== '' && !str_contains($lastLine, '[↑ Back to Top]')) {
                        $bodyLines[] = '';
                        $bodyLines[] = '[↑ Back to Top](#table-of-contents)';
                    }
                }
            }
            $bodyLines[] = $line;
        }
    }

    // Generate TOC text
    $tocText = "## Table of Contents\n";
    foreach ($headers as $header) {
        if ($header['title'] === 'Table of Contents') continue;
        $indent = str_repeat('  ', $header['level'] - 1);
        $tocText .= "{$indent}- [{$header['title']}](#{$header['anchor']})\n";
    }

    // Reconstruct file
    $finalLines = [];
    $tocInserted = false;
    foreach ($bodyLines as $line) {
        if (!$tocInserted && (str_starts_with($line, '## ') || (str_contains($content, 'This document outlines') && str_starts_with($line, 'This document outlines')))) {
            $finalLines[] = $tocText;
            $tocInserted = true;
        }
        $finalLines[] = $line;
    }

    file_put_contents($filePath, implode("\n", $finalLines));
    echo "$name TOC and breadcrumbs regenerated successfully.\n";
}

$root = __DIR__ . '/../..';
generateToc($root . '/SPECS.md', 'SPECS.md');
generateToc($root . '/MILESTONES.md', 'MILESTONES.md');