HTML converter for note bodies.
*
* Supports headings, bold/italic, links, and (nested) ordered and unordered
* lists. Not a full Markdown spec — just enough for the note UX.
*/
final class Markdown
{
/**
* Convert a Markdown-flavoured string to safe HTML.
*
* The final output is run through {@see wp_kses_post()}, so even a
* regex that accidentally lets a stray tag through is contained at
* the boundary.
*/
public static function toHtml(string $text): string
{
$text = str_replace(["\r\n", "\r"], "\n", $text);
$text = trim($text);
$inlinePatterns = [
'/\#{6}\s?(.*)/' => '$1
',
'/\#{5}\s?(.*)/' => '$1
',
'/\#{4}\s?(.*)/' => '$1
',
'/\#{3}\s?(.*)/' => '$1
',
'/\#{2}\s?(.*)/' => '$1
',
'/\#{1}\s?(.*)/' => '$1
',
'/\*\*(.*?)\*\*|__(.*?)__/' => '$1$2',
'/\*(.*?)\*|_(.*?)_/' => '$1$2',
'/<(https?:\/\/[^\s<]+)>/' => '$1',
'/\[(.*?)\]\((.*?)\)/' => '$1',
'/(^|[\s>])(https?:\/\/[^\s<]+)(?=\s|$)/' => '$1$2',
];
$html = preg_replace(array_keys($inlinePatterns), array_values($inlinePatterns), $text);
$lines = explode("\n", $html);
$output = '';
$listStack = [];
$currentIndent = 0;
foreach ($lines as $line) {
preg_match('/^(\s*)/', $line, $leading);
$indent = strlen($leading[0]);
$line = ltrim($line);
if (preg_match('/^\d+\.\s+(.*)$/', $line, $matches)) {
[$output, $listStack, $currentIndent] = self::handleListItem(
'ol',
$matches[1],
$indent,
$output,
$listStack,
$currentIndent,
);
continue;
}
if (preg_match('/^-\s+(.*)$/', $line, $matches)) {
[$output, $listStack, $currentIndent] = self::handleListItem(
'ul',
$matches[1],
$indent,
$output,
$listStack,
$currentIndent,
);
continue;
}
while (! empty($listStack)) {
$list = array_pop($listStack);
$output .= $list['type'] === 'ul' ? "\n" : "\n";
}
$currentIndent = 0;
$output .= $line . "\n";
}
while (! empty($listStack)) {
$list = array_pop($listStack);
$output .= $list['type'] === 'ul' ? "\n" : "\n";
}
// Collapse runs of 3+ blank lines down to a single paragraph break
// so wpautop produces clean separators rather than ragged gaps.
$output = preg_replace('/\n{3,}/', "\n\n", $output);
return wp_kses_post(wpautop(trim($output)));
}
/**
* Convert plugin-generated HTML back to Markdown.
*
* Best-effort — used to round-trip note bodies during edits.
*/
public static function toMarkdown(string $html): string
{
$markdown = $html;
// Paragraph and break tags become explicit newlines before the
// generic tag-strip step runs, otherwise paragraph separators get
// swallowed and the source becomes one long run-on line.
$markdown = preg_replace('/]*>/i', '', $markdown);
$markdown = preg_replace('/<\/p\s*>/i', "\n\n", $markdown);
$markdown = preg_replace('//i', "\n", $markdown);
$markdown = preg_replace('/]*>(.*?)<\/h6>/', "\n###### $1\n", $markdown);
$markdown = preg_replace('/]*>(.*?)<\/h5>/', "\n##### $1\n", $markdown);
$markdown = preg_replace('/]*>(.*?)<\/h4>/', "\n#### $1\n", $markdown);
$markdown = preg_replace('/]*>(.*?)<\/h3>/', "\n### $1\n", $markdown);
$markdown = preg_replace('/]*>(.*?)<\/h2>/', "\n## $1\n", $markdown);
$markdown = preg_replace('/]*>(.*?)<\/h1>/', "\n# $1\n", $markdown);
$markdown = preg_replace('/(.*?)<\/strong>/', '**$1**', $markdown);
$markdown = preg_replace('/(.*?)<\/em>/', '_$1_', $markdown);
$markdown = preg_replace('/\1<\/a>/', '<$1>', $markdown);
$markdown = preg_replace('/(.*?)<\/a>/', '[$2]($1)', $markdown);
$lines = explode("\n", $markdown);
$inList = false;
$listType = '';
$listCount = 0;
$result = [];
foreach ($lines as $line) {
if (trim($line) === '' && ! $inList) {
$result[] = '';
continue;
}
if (strpos($line, '') !== false) {
$inList = true;
$listType = 'ul';
continue;
}
if (strpos($line, '') !== false) {
$inList = true;
$listType = 'ol';
$listCount = 0;
continue;
}
if (strpos($line, '
') !== false || strpos($line, '') !== false) {
$inList = false;
$listType = '';
$result[] = '';
continue;
}
if (preg_match('/(.*?)<\/li>/', $line, $matches)) {
$content = $matches[1];
if ($listType === 'ul') {
$result[] = '- ' . $content;
} elseif ($listType === 'ol') {
$listCount++;
$result[] = $listCount . '. ' . $content;
}
continue;
}
if (trim($line) !== '') {
$result[] = trim($line);
}
}
$markdown = implode("\n", $result);
$markdown = wp_strip_all_tags($markdown);
$markdown = preg_replace('/\n{3,}/', "\n\n", $markdown);
$markdown = preg_replace('/^(#{1,3}\s.*?)$/m', "\n$1\n", $markdown);
return trim($markdown);
}
/**
* Shared open/close logic for ordered and unordered list items.
*
* @param 'ol'|'ul' $type
* @param list $listStack
* @return array{0: string, 1: list, 2: int}
*/
private static function handleListItem(
string $type,
string $content,
int $indent,
string $output,
array $listStack,
int $currentIndent
): array {
$openTag = $type === 'ol' ? "\n" : "\n";
if (empty($listStack) || $indent > $currentIndent) {
$output .= $openTag;
$listStack[] = ['type' => $type, 'indent' => $indent];
} elseif ($indent < $currentIndent) {
while (! empty($listStack) && end($listStack)['indent'] > $indent) {
$list = array_pop($listStack);
$output .= $list['type'] === 'ul' ? "
\n" : "
\n";
}
}
$output .= '' . $content . "\n";
return [$output, $listStack, $indent];
}
}