MD_STD/MDFormatter.php

<?PHP
/**
 * Applies plain text formatting.
 *
 * @author Joshua Ramon Enslin <joshua@museum-digital.de>
 */
declare(strict_types = 1);

/**
 * Applies plain text formatting.
 */
final class MDFormatter {

    /** @var boolean */
    public static bool $use_underlined_hl = true;

    /**
     * Applies markdown formatting for main headline.
     *
     * @param string $input Headline text.
     *
     * @return string
     */
    public static function formatMarkdownHeadline1(string $input):string {

        if (self::$use_underlined_hl === false) {
            return '# ' . $input . PHP_EOL . PHP_EOL;
        }

        $hlLength = mb_strlen($input);

        $output = $input . PHP_EOL;
        for ($i = 0; $i < $hlLength; $i++) {
            $output .= '=';
        }
        $output .= PHP_EOL . PHP_EOL;

        return $output;

    }

    /**
     * Applies markdown formatting for secondary headline.
     *
     * @param string $input Headline text.
     *
     * @return string
     */
    public static function formatMarkdownHeadline2(string $input):string {

        if (self::$use_underlined_hl === false) {
            return '## ' . $input . PHP_EOL . PHP_EOL;
        }

        $hlLength = mb_strlen($input);

        $output = $input . PHP_EOL;
        for ($i = 0; $i < $hlLength; $i++) {
            $output .= '-';
        }
        $output .= PHP_EOL . PHP_EOL;

        return $output;

    }

    /**
     * Applies markdown formatting for tertiary headline.
     *
     * @param string $input Headline text.
     *
     * @return string
     */
    public static function formatMarkdownHeadline3(string $input):string {

        return '### ' . $input . PHP_EOL;

    }

    /**
     * Returns a horizontal rule in markdown.
     *
     * @return string
     */
    public static function formatMarkdownHorizontalRule():string {

        return '___' . PHP_EOL;

    }

    /**
     * Applies markdown formatting for a named link.
     *
     * @param string $link_name Link text.
     * @param string $link_url  Target URL.
     *
     * @return string
     */
    public static function formatMarkdownNamedLink(string $link_name, string $link_url):string {

        return "[{$link_name}]({$link_url})";

    }

    /**
     * Applies markdown formatting for a block quote.
     *
     * @param string $content Content of the block quote.
     *
     * @return string
     */
    public static function formatMarkdownBlockQuote(string $content):string {

        $output = '';
        $lines = \explode(PHP_EOL, $content);

        foreach ($lines as $line) {
            $output .= '> ' . $line . PHP_EOL;
        }

        return $output;

    }

    /**
     * Applies markdown formatting for a code block.
     *
     * @param string $content  Content of the code block.
     * @param string $language Progamming language for syntax highlighting. Optional.
     *
     * @return string
     */
    public static function formatMarkdownCodeBlock(string $content, string $language = ''):string {

        $output = '```' . $language . '
' . $content . '
```' . PHP_EOL;

        return $output;

    }

    /**
     * Applies markdown formatting for an unordered list item.
     *
     * @param string $content Content of the list item.
     *
     * @return string
     */
    public static function formatMarkdownUnorderedListItem(string $content):string {

        if (\strpos($content, PHP_EOL) === false) {
            return '- ' . $content . PHP_EOL;
        }

        $lines = \explode(PHP_EOL, $content);
        $output = '- ' . $lines[0] . PHP_EOL;

        foreach ($lines as $i => $line) {
            if ($i === 0) continue;
            $output .= '  ' . $line . PHP_EOL;
        }

        return $output;

    }
}