materialFileName function

Implementation

String materialFileName({
  String? disposition,
  String? title,
  String? contentType,
  List<int> leadingBytes = const [],
}) {
  String? serverName;
  if (disposition case final disposition?) {
    try {
      final parameters = HeaderValue.parse(disposition).parameters;
      serverName = parameters['filename'];
      final encoded = parameters['filename*'];
      if (encoded case final encoded?) {
        final parts = encoded.split("'");
        if (parts.length == 3 && parts.first.toLowerCase() == 'utf-8') {
          serverName = Uri.decodeComponent(parts[2]);
        }
      }
    } on FormatException {
      // Retain filename when filename* is malformed; otherwise use the title.
    } on ArgumentError {
      // RFC 5987 filename encoding may itself be malformed.
    }
  }
  if (serverName case final attachmentName?) {
    serverName = p.posix
        .basename(p.windows.basename(attachmentName))
        .replaceAll(RegExp(r'''^['"]|['"]$'''), '');
  }
  final materialTitle = title?.trim();
  var name =
      (materialTitle != null && materialTitle.isNotEmpty
              ? materialTitle
              : serverName ?? 'material')
          .replaceAll(RegExp(r'[<>:"/\\|?*\x00-\x1f]'), '_')
          .replaceAll(RegExp(r'[. ]+$'), '')
          .trim();
  if (name.isEmpty || name == '.') name = 'material';
  // Dots in prose titles are not necessarily filename extensions.
  final extensionPattern = RegExp(r'^\.[a-zA-Z0-9]{1,10}$');
  final serverExtension = p.extension(serverName ?? '');
  final titleExtension = p.extension(name);
  final extension = extensionPattern.hasMatch(serverExtension)
      ? serverExtension
      : extensionPattern.hasMatch(titleExtension)
      ? titleExtension
      : switch (contentType?.split(';').first.trim().toLowerCase()) {
          'application/pdf' => '.pdf',
          'application/zip' || 'application/x-zip-compressed' => '.zip',
          'application/vnd.rar' ||
          'application/x-rar' ||
          'application/x-rar-compressed' => '.rar',
          'application/x-7z-compressed' => '.7z',
          'application/gzip' || 'application/x-gzip' => '.gz',
          'application/msword' => '.doc',
          'application/vnd.openxmlformats-officedocument.wordprocessingml.document' =>
            '.docx',
          'application/vnd.ms-powerpoint' => '.ppt',
          'application/vnd.openxmlformats-officedocument.presentationml.presentation' =>
            '.pptx',
          'application/vnd.ms-excel' => '.xls',
          'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet' =>
            '.xlsx',
          'text/plain' => '.txt',
          'image/jpeg' => '.jpg',
          'image/png' => '.png',
          _ => switch (leadingBytes) {
            [0x52, 0x61, 0x72, 0x21, 0x1a, 0x07, 0x00, ...] ||
            [0x52, 0x61, 0x72, 0x21, 0x1a, 0x07, 0x01, 0x00, ...] => '.rar',
            [0x37, 0x7a, 0xbc, 0xaf, 0x27, 0x1c, ...] => '.7z',
            [0x50, 0x4b, 0x03, 0x04, ...] ||
            [0x50, 0x4b, 0x05, 0x06, ...] ||
            [0x50, 0x4b, 0x07, 0x08, ...] => '.zip',
            [0x1f, 0x8b, 0x08, ...] => '.gz',
            [0x25, 0x50, 0x44, 0x46, 0x2d, ...] => '.pdf',
            _ => '',
          },
        };
  if (extension.isNotEmpty &&
      !name.toLowerCase().endsWith(extension.toLowerCase())) {
    name += extension;
  }
  const maxBytes = 240;
  if (utf8.encode(name).length > maxBytes) {
    final hasExtension =
        extension.isNotEmpty &&
        name.toLowerCase().endsWith(extension.toLowerCase());
    final suffix = hasExtension
        ? name.substring(name.length - extension.length)
        : '';
    final base = hasExtension
        ? name.substring(0, name.length - extension.length)
        : name;
    final byteBudget = maxBytes - utf8.encode(suffix).length;
    final truncated = StringBuffer();
    var usedBytes = 0;
    for (final rune in base.runes) {
      final character = String.fromCharCode(rune);
      final characterBytes = utf8.encode(character).length;
      if (usedBytes + characterBytes > byteBudget) break;
      truncated.write(character);
      usedBytes += characterBytes;
    }
    name = '$truncated$suffix';
  }
  if (RegExp(
    r'^(CON|PRN|AUX|NUL|COM[1-9]|LPT[1-9])$',
    caseSensitive: false,
  ).hasMatch(p.basenameWithoutExtension(name))) {
    name = '_$name';
  }
  return name;
}