getMaterial method

Implementation

Future<MaterialDto> getMaterial(
  MaterialRefDto material,
) async {
  await _selectCourse(material.course);

  // Step 1: Get launch.php to extract the course ID (cid)
  final launchResponse = await _iSchoolPlusDio.get('path/launch.php');

  // Extract cid from the JavaScript
  // e.g.: parent.s_catalog.location.replace('/learn/path/manifest.php?cid=...')
  final cidMatch = RegExp(r"cid=([^']+)").firstMatch(launchResponse.data);
  if (cidMatch == null) {
    throw Exception('Could not extract course ID from launch page.');
  }
  final cid = cidMatch.group(1)!;

  // Step 2: Get resource token from the course material tree endpoint
  // It contains a form with a token needed to fetch downloadable resources
  final materialTreeResponse = await _iSchoolPlusDio.get(
    'path/pathtree.php',
    queryParameters: {'cid': cid},
  );

  // Extract the read_key token from the HTML form
  final materialTreeDocument = parse(materialTreeResponse.data);
  final readKeyInput = materialTreeDocument.querySelector(
    '#fetchResourceForm>input[name="read_key"][value]',
  );
  if (readKeyInput == null) {
    throw Exception('Could not find read_key in material tree page.');
  }
  final fetchResourceToken = readKeyInput.attributes['value']!;

  // Step 3: Submit resource form and get resource URI
  final dioWithoutRedirects = _iSchoolPlusDio.clone()
    ..interceptors.removeWhere(
      (interceptor) => interceptor is RedirectInterceptor,
    );

  final resourceResponse = await dioWithoutRedirects.post(
    'path/SCORM_fetchResource.php',
    data: {
      'href': '@${material.href!}',
      'course_id': cid,
      'read_key': fetchResourceToken,
    },
    options: Options(contentType: Headers.formUrlEncodedContentType),
  );

  // Case 1: Response is a redirect
  // Replace preview URL with download URL
  if (resourceResponse.statusCode == HttpStatus.found) {
    final location =
        resourceResponse.headers[HttpHeaders.locationHeader]?.first;
    if (location == null) {
      throw Exception('Redirect location header is missing.');
    }

    final previewUri = Uri.tryParse(location);
    if (previewUri == null) {
      throw Exception('Invalid redirect URI: $location');
    }

    return (
      downloadUrl: previewUri.replace(path: "download.php"),
      referer: null,
      streamable: false,
    );
  }

  // Response is HTML with embedded download script, e.g.,
  // <script>location.replace("viewPDF.php?id=KheOh_TuNgPJOQTEmRW1zg,,");</script>

  // URI can be enclosed in either single or double quotes
  final quoteRegExp = RegExp(r'''(['"])([^'"]+)\1''');
  final quoteMatch = quoteRegExp.firstMatch(resourceResponse.data);
  if (quoteMatch == null || quoteMatch.groupCount < 2) {
    throw Exception('Could not extract download URI from response.');
  }

  // URI can be relative, so resolve against base URL
  final baseUrl = '${_iSchoolPlusDio.options.baseUrl}path/';
  final downloadUri = Uri.parse(baseUrl).resolve(quoteMatch.group(2)!);

  // Case 2: Material is a course recording
  if (downloadUri.host.contains("istream.ntut.edu.tw")) {
    // iStream videos can be streamed directly or downloaded
    // Testing confirmed no referer required
    return (
      downloadUrl: downloadUri,
      referer: null,
      streamable: true,
    );
  }

  // Case 3: Material is a PDF
  if (downloadUri.path.contains('viewPDF.php')) {
    // Fetch and find the value of DEFAULT_URL in JavaScript
    final viewPdfResponse = await _iSchoolPlusDio.getUri(downloadUri);

    final defaultUrlRegExp = RegExp(r'DEFAULT_URL[ =]+\"(.+)\"');
    final defaultUrlMatch = defaultUrlRegExp.firstMatch(viewPdfResponse.data);
    if (defaultUrlMatch == null || defaultUrlMatch.groupCount < 1) {
      throw Exception('Could not find DEFAULT_URL in PDF viewer page.');
    }
    final defaultUrl = defaultUrlMatch.group(1)!;

    return (
      downloadUrl: Uri.parse(baseUrl).resolve(defaultUrl),
      referer: downloadUri.toString(),
      streamable: false,
    );
  }

  // Case 4: Material is a standard downloadable file
  return (
    downloadUrl: downloadUri,
    referer: null,
    streamable: false,
  );
}