tcms/app/Markdown.php

<?php
declare(strict_types=1);

namespace NeonBlog;

final class Markdown
{
    public static function toHtml(string $markdown): string
    {
        $markdown = str_replace(["\r\n", "\r"], "\n", trim($markdown));
        if ($markdown === '') {
            return '';
        }

        $lines = explode("\n", $markdown);
        $html = [];
        $count = count($lines);
        $i = 0;

        while ($i < $count) {
            $line = rtrim($lines[$i]);
            if (trim($line) === '') {
                $i++;
                continue;
            }

            if (preg_match('/^```([A-Za-z0-9_-]*)\s*$/', $line, $matches)) {
                $language = $matches[1] !== '' ? ' class="language-' . self::e($matches[1]) . '"' : '';
                $code = [];
                $i++;
                while ($i < $count && !preg_match('/^```\s*$/', rtrim($lines[$i]))) {
                    $code[] = $lines[$i];
                    $i++;
                }
                $html[] = '<pre><code' . $language . '>' . self::e(implode("\n", $code)) . '</code></pre>';
                $i++;
                continue;
            }

            if (preg_match('/^(#{1,6})\s+(.+)$/', $line, $matches)) {
                $level = strlen($matches[1]);
                $html[] = '<h' . $level . '>' . self::inline($matches[2]) . '</h' . $level . '>';
                $i++;
                continue;
            }

            if (preg_match('/^(-{3,}|\*{3,}|_{3,})$/', trim($line))) {
                $html[] = '<hr>';
                $i++;
                continue;
            }

            if (preg_match('/^\s*>\s?(.*)$/', $line)) {
                $quote = [];
                while ($i < $count && preg_match('/^\s*>\s?(.*)$/', rtrim($lines[$i]), $matches)) {
                    $quote[] = $matches[1];
                    $i++;
                }
                $html[] = '<blockquote>' . self::toHtml(implode("\n", $quote)) . '</blockquote>';
                continue;
            }

            if (preg_match('/^\s*[-*+]\s+(.+)$/', $line)) {
                $items = [];
                while ($i < $count && preg_match('/^\s*[-*+]\s+(.+)$/', rtrim($lines[$i]), $matches)) {
                    $items[] = '<li>' . self::inline($matches[1]) . '</li>';
                    $i++;
                }
                $html[] = '<ul>' . implode('', $items) . '</ul>';
                continue;
            }

            if (preg_match('/^\s*\d+\.\s+(.+)$/', $line)) {
                $items = [];
                while ($i < $count && preg_match('/^\s*\d+\.\s+(.+)$/', rtrim($lines[$i]), $matches)) {
                    $items[] = '<li>' . self::inline($matches[1]) . '</li>';
                    $i++;
                }
                $html[] = '<ol>' . implode('', $items) . '</ol>';
                continue;
            }

            $paragraph = [$line];
            $i++;
            while ($i < $count && trim($lines[$i]) !== '' && !self::startsBlock(rtrim($lines[$i]))) {
                $paragraph[] = trim($lines[$i]);
                $i++;
            }
            $html[] = '<p>' . self::inline(implode(' ', $paragraph)) . '</p>';
        }

        return implode("\n", $html);
    }

    public static function excerpt(string $markdown, int $words = 28): string
    {
        $text = trim(preg_replace('/\s+/', ' ', strip_tags(self::toHtml($markdown))) ?? '');
        if ($text === '') {
            return '';
        }

        $parts = preg_split('/\s+/', $text) ?: [];
        if (count($parts) <= $words) {
            return $text;
        }

        return implode(' ', array_slice($parts, 0, $words)) . '...';
    }

    private static function startsBlock(string $line): bool
    {
        return (bool) preg_match('/^(#{1,6}\s+|```|^\s*[-*+]\s+|^\s*\d+\.\s+|^\s*>\s?|(-{3,}|\*{3,}|_{3,})$)/', $line);
    }

    private static function inline(string $text): string
    {
        $placeholders = [];
        $text = preg_replace_callback('/`([^`]+)`/', static function (array $matches) use (&$placeholders): string {
            $key = "\x1A" . count($placeholders) . "\x1A";
            $placeholders[$key] = '<code>' . self::e($matches[1]) . '</code>';
            return $key;
        }, $text) ?? $text;

        $text = self::e($text);
        $text = preg_replace_callback('/!\[([^\]]*)\]\(([^)\s]+)(?:\s+"([^"]+)")?\)/', static function (array $matches): string {
            $title = isset($matches[3]) ? ' title="' . self::e($matches[3]) . '"' : '';
            return '<img src="' . self::e($matches[2]) . '" alt="' . self::e($matches[1]) . '"' . $title . '>';
        }, $text) ?? $text;
        $text = preg_replace_callback('/\[([^\]]+)\]\(([^)\s]+)(?:\s+"([^"]+)")?\)/', static function (array $matches): string {
            $title = isset($matches[3]) ? ' title="' . self::e($matches[3]) . '"' : '';
            return '<a href="' . self::e($matches[2]) . '"' . $title . '>' . $matches[1] . '</a>';
        }, $text) ?? $text;
        $text = preg_replace('/\*\*([^*]+)\*\*/', '<strong>$1</strong>', $text) ?? $text;
        $text = preg_replace('/\*([^*]+)\*/', '<em>$1</em>', $text) ?? $text;

        return strtr($text, $placeholders);
    }

    private static function e(string $value): string
    {
        return htmlspecialchars($value, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
    }
}