import 'dart:async';
import 'dart:convert';
import 'dart:typed_data';

class SSEParseUtil {
  static Stream<Message> parse(Stream<Uint8List> stream) {
    return stream.transform(SSETransformer());
  }
}

class Message {
  final String id;
  final String event;
  final String data;
  final int? retry;

  Message(
      {required this.id,
      required this.event,
      required this.data,
      required this.retry});

  @override
  String toString() {
    return 'Message{id: $id, event: $event, data: $data, retry: $retry}';
  }
}

class SSETransformer extends StreamTransformerBase<Uint8List, Message> {
  @override
  Stream<Message> bind(Stream<Uint8List> stream) {
    return Stream.eventTransformed(
      stream.map((uint8List) => List<int>.from(uint8List)),
      (sink) => SSESink(sink),
    );
  }
}

class SSESink implements EventSink<List<int>> {
  static final _eventSeparator = utf8.encode("\n\n");
  static const _fieldSeparator = "\n";
  static const _dataPrefix = "data:";
  static const _dataPrefixR = "data: ";
  static const _idPrefix = "id:";
  static const _idPrefixR = "id: ";
  static const _eventPrefix = "event:";
  static const _eventPrefixR = "event: ";
  static const _retryPrefix = "retry:";
  static const _retryPrefixR = "retry: ";
  static const _commentPrefix = ":";
  static const _commentPrefixR = ": ";

  final EventSink<Message> _eventSink;

  final List<int> _buffer = [];

  SSESink(this._eventSink);

  @override
  void add(List<int> event) {
    _buffer.addAll(event);

    while (true) {
      final endIndex = _indexOf(_buffer, _eventSeparator);
      if (endIndex == -1) {
        break;
      }

      final completedEvent = _buffer.sublist(0, endIndex);
      _buffer.removeRange(0, endIndex + _eventSeparator.length);
      parseEvent(completedEvent);
    }
  }

  @override
  void addError(Object error, [StackTrace? stackTrace]) {
    _eventSink.addError(error, stackTrace);
  }

  @override
  void close() {
    _eventSink.close();
  }

  int _indexOf(List<int> origin, List<int> target) {
    for (var i = 0; i < origin.length - target.length; i++) {
      var found = true;
      for (var j = 0; j < target.length; j++) {
        if (origin[i + j] != target[j]) {
          found = false;
          break;
        }
      }
      if (found) {
        return i;
      }
    }
    return -1;
  }

  void parseEvent(List<int> completedEvent) {
    final eventString = utf8.decode(completedEvent);
    final fields = eventString.split(_fieldSeparator);
    String? id;
    String? event;
    String data = "";
    int? retry;

    for (final field in fields) {
      final trimmedField = field.trim();
      if (trimmedField.isEmpty) {
        continue;
      }

      if (trimmedField.startsWith(_commentPrefix) ||
          trimmedField.startsWith(_commentPrefixR)) {
        continue;
      }

      if (trimmedField.startsWith(_retryPrefixR)) {
        retry = int.tryParse(trimmedField.substring(_retryPrefixR.length));
      } else if (trimmedField.startsWith(_dataPrefixR)) {
        data += trimmedField.substring(_dataPrefixR.length);
      } else if (trimmedField.startsWith(_eventPrefixR)) {
        event = trimmedField.substring(_eventPrefixR.length);
      } else if (trimmedField.startsWith(_idPrefixR)) {
        id = trimmedField.substring(_idPrefixR.length);
      } else if (trimmedField.startsWith(_idPrefix)) {
        id = trimmedField.substring(_idPrefix.length);
      } else if (trimmedField.startsWith(_eventPrefix)) {
        event = trimmedField.substring(_eventPrefix.length);
      } else if (trimmedField.startsWith(_dataPrefix)) {
        data += trimmedField.substring(_dataPrefix.length);
      } else if (trimmedField.startsWith(_retryPrefix)) {
        retry = int.tryParse(trimmedField.substring(_retryPrefix.length));
      }
    }

    _eventSink.add(
        Message(id: id ?? "", event: event ?? "", data: data, retry: retry));
  }
}