class Gitignore

class Gitignore {
    
    /**
     * Returns a regexp which is the equivalent of the gitignore pattern.
     *
     * Format specification: https://git-scm.com/docs/gitignore#_pattern_format
     */
    public static function toRegex(string $gitignoreFileContent) : string {
        return self::buildRegex($gitignoreFileContent, false);
    }
    public static function toRegexMatchingNegatedPatterns(string $gitignoreFileContent) : string {
        return self::buildRegex($gitignoreFileContent, true);
    }
    private static function buildRegex(string $gitignoreFileContent, bool $inverted) : string {
        $gitignoreFileContent = preg_replace('~(?<!\\\\)#[^\\n\\r]*~', '', $gitignoreFileContent);
        $gitignoreLines = preg_split('~\\r\\n?|\\n~', $gitignoreFileContent);
        $res = self::lineToRegex('');
        foreach ($gitignoreLines as $line) {
            $line = preg_replace('~(?<!\\\\)[ \\t]+$~', '', $line);
            if (str_starts_with($line, '!')) {
                $line = substr($line, 1);
                $isNegative = true;
            }
            else {
                $isNegative = false;
            }
            if ('' !== $line) {
                if ($isNegative xor $inverted) {
                    $res = '(?!' . self::lineToRegex($line) . '$)' . $res;
                }
                else {
                    $res = '(?:' . $res . '|' . self::lineToRegex($line) . ')';
                }
            }
        }
        return '~^(?:' . $res . ')~s';
    }
    private static function lineToRegex(string $gitignoreLine) : string {
        if ('' === $gitignoreLine) {
            return '$f';
            // always false
        }
        $slashPos = strpos($gitignoreLine, '/');
        if (false !== $slashPos && \strlen($gitignoreLine) - 1 !== $slashPos) {
            if (0 === $slashPos) {
                $gitignoreLine = substr($gitignoreLine, 1);
            }
            $isAbsolute = true;
        }
        else {
            $isAbsolute = false;
        }
        $regex = preg_quote(str_replace('\\', '', $gitignoreLine), '~');
        $regex = preg_replace_callback('~\\\\\\[((?:\\\\!)?)([^\\[\\]]*)\\\\\\]~', fn(array $matches): string => '[' . ('' !== $matches[1] ? '^' : '') . str_replace('\\-', '-', $matches[2]) . ']', $regex);
        $regex = preg_replace('~(?:(?:\\\\\\*){2,}(/?))+~', '(?:(?:(?!//).(?<!//))+$1)?', $regex);
        $regex = preg_replace('~\\\\\\*~', '[^/]*', $regex);
        $regex = preg_replace('~\\\\\\?~', '[^/]', $regex);
        return ($isAbsolute ? '' : '(?:[^/]+/)*') . $regex . (!str_ends_with($gitignoreLine, '/') ? '(?:$|/)' : '');
    }

}