/// A backend-independent emergency notice, loaded from a foreign server URL.
///
/// Deliberately decoupled from MarianumConnect: if that backend is unreachable
/// (the disaster case this exists for), a plain text file on any other host can
/// still surface a message. The file is a small YAML-ish frontmatter followed
/// by a free Markdown body, so it stays hand-writable in an emergency — no JSON
/// escaping of the (multi-line) content.
///
/// See [parse] for the exact format.
class EmergencyNotice {
  /// Whether the notice can be dismissed. `false` renders it full-screen and
  /// blocks back/barrier taps.
  final bool dismissible;

  /// Optional heading shown above the body.
  final String? title;

  /// Markdown body (the message itself).
  final String body;

  const EmergencyNotice({
    required this.dismissible,
    required this.title,
    required this.body,
  });

  /// Parses the raw file into a displayable notice, or returns `null` when
  /// there is nothing to show. Never throws — any malformed input yields `null`
  /// so a broken file can never break the app.
  ///
  /// Format:
  /// ```
  /// ---
  /// active: true
  /// # dismissible: false   <- comment lines (# ...) are ignored
  /// dismissible: true
  /// title: Störung
  /// ---
  /// # Markdown heading
  /// Free **markdown** body.
  /// ```
  ///
  /// Rules:
  /// - The frontmatter is everything between the first `---` line and the next
  ///   `---` line. Both delimiters are required.
  /// - Frontmatter entries are `key: value`; a line whose trimmed form starts
  ///   with `#` is a comment. Unknown keys are ignored.
  /// - `active` (default `false`) must be explicitly true, else `null`.
  /// - `dismissible` defaults to `true`.
  /// - `title` is optional. The rest after the closing `---` is the Markdown
  ///   body; an empty body yields `null`.
  static EmergencyNotice? parse(String raw) {
    final lines = raw
        .replaceAll('\r\n', '\n')
        .replaceAll('\r', '\n')
        .split('\n');

    // Locate the opening `---` (skipping any leading blank lines).
    var i = 0;
    while (i < lines.length && lines[i].trim().isEmpty) {
      i++;
    }
    if (i >= lines.length || lines[i].trim() != '---') return null;
    final openIndex = i;

    // Locate the closing `---`.
    var closeIndex = -1;
    for (var j = openIndex + 1; j < lines.length; j++) {
      if (lines[j].trim() == '---') {
        closeIndex = j;
        break;
      }
    }
    if (closeIndex == -1) return null;

    final meta = <String, String>{};
    for (var j = openIndex + 1; j < closeIndex; j++) {
      final line = lines[j].trim();
      if (line.isEmpty || line.startsWith('#')) continue;
      final sep = line.indexOf(':');
      if (sep <= 0) continue;
      final key = line.substring(0, sep).trim().toLowerCase();
      final value = line.substring(sep + 1).trim();
      meta[key] = value;
    }

    if (_parseBool(meta['active']) != true) return null;

    final body = lines.sublist(closeIndex + 1).join('\n').trim();
    if (body.isEmpty) return null;

    final title = meta['title'];
    return EmergencyNotice(
      dismissible: _parseBool(meta['dismissible']) ?? true,
      title: (title == null || title.isEmpty) ? null : title,
      body: body,
    );
  }

  static bool? _parseBool(String? value) {
    switch (value?.trim().toLowerCase()) {
      case 'true':
      case 'yes':
      case '1':
      case 'on':
        return true;
      case 'false':
      case 'no':
      case '0':
      case 'off':
        return false;
      default:
        return null;
    }
  }
}