import 'dart:math';
import 'dart:typed_data';
import 'package:dio/dio.dart';

//Raised when data is not ready.
class NotReadyException implements Exception {}

//Raised when errro happened during the downloading.
class DownloadErrorException implements Exception {
  String _message;

  String get message => _message;

  DownloadErrorException(this._message);
}

typedef DownloadCallback = void Function(double progress, DownloadErrorException? error);

class VidUsDataHttpReader {
  late Uint8List _underlyingData = Uint8List(0);
  late int _bufferSize = 0;
  late int _index;
  late bool _error;
  late String _errorMsg;
  late String _url;
  late int _minChunkSize;
  late Dio _dio;
  late double _downloadProgress = 0;

  DownloadCallback? downloadCallback;

  VidUsDataHttpReader(String url, {this.downloadCallback, int minChunkSize = 65536, int connectTimeout = 30000, int receiveTimeout = 30000}) {
    _minChunkSize = minChunkSize;
    _url = url;
    _error = false;
    _errorMsg = '';
    _index = 0;
    _dio = Dio();
    _dio.options.connectTimeout = connectTimeout;
    _dio.options.receiveTimeout = receiveTimeout;
    _startDownload();
  }

  ///Return the internal underlying data.
  Uint8List toBytes() {
    return _underlyingData;
  }

  ///Start the download in async way.
  void _startDownload() async {
    try {
      //get file info
      var fileSize = await _getFileSize();
      if (!_error) {
        _underlyingData = Uint8List(fileSize);
        if (fileSize < _minChunkSize) {
          await _downloadChunk(0, fileSize - 1);
          if (!_error && downloadCallback != null) {
            _downloadProgress = _bufferSize / fileSize;
            downloadCallback!(_downloadProgress, null);
          }else{
            throw DownloadErrorException(_errorMsg);
          }
        } else {
          var chunkSize = max(_minChunkSize, fileSize~/100) ;
          var last = fileSize % chunkSize;
          var chunkCount = fileSize ~/ chunkSize;
          for (var i = 0; i < chunkCount; i++) {
            var start = i * chunkSize;
            var end = start + chunkSize - 1;
            await _downloadChunk(start, end);
            if (_error) {
              throw DownloadErrorException(_errorMsg);
            }
            if (downloadCallback != null) {
              _downloadProgress = _bufferSize / fileSize;
              downloadCallback!(_downloadProgress, null);
            }
          }
          if (!_error && last > 0) {
            var start = chunkCount * chunkSize;
            var end = start + last - 1;
            await _downloadChunk(start, end);
            if (!_error && downloadCallback != null) {
              _downloadProgress = _bufferSize / fileSize;
              downloadCallback!(_downloadProgress, null);
            }else{
              throw DownloadErrorException(_errorMsg);
            }
          }
        }
      }
    } on DownloadErrorException catch (e) {
      if (!_error && downloadCallback != null) {
        downloadCallback!(_downloadProgress, e);
      }
    } on Exception catch (e) {
      _error = true;
      _errorMsg = e.toString();
      if (!_error && downloadCallback != null) {
        downloadCallback!(_downloadProgress, DownloadErrorException(_errorMsg));
      }
    }
  }

  Future<int> _getFileSize() async {
    var response = await _dio.head(_url);
    if (response.statusCode != 200) {
      _error = true;
      _errorMsg = 'Get file info error.';
      return 0;
    } else {
      var contentLength = response.headers.value(Headers.contentLengthHeader);
      if (contentLength == null) {
        _error = true;
        _errorMsg = 'No Content-Length from headers.';
        return 0;
      } else {
        var fileSize = int.parse(contentLength);
        return fileSize;
      }
    }
  }

  Future _downloadChunk(int chunkStart, int chunkEnd) async {
    var response = await _dio.get<List<int>>(_url, options: Options(responseType: ResponseType.bytes, headers: {"range": "bytes=$chunkStart-$chunkEnd"}));
    if (response.statusCode == 206) {
      var downloadedData = response.data;
      if (downloadedData == null) {
        _error = true;
        _errorMsg = 'Download chunk error.';
      } else {
        //Update the buffer.
        _underlyingData.setAll(_bufferSize, downloadedData);
        _bufferSize += downloadedData.length;
      }
    } else {
      _error = true;
      _errorMsg = 'Target url does not support download with chunks.';
    }
  }

  //Close the reader and its http connection.
  void close() {
    _dio.close(force: true);
  }

  ///Read int value from binary data(little endian),
  int readInt([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_bufferSize - _index) < 4) {
        throw NotReadyException();
      }
      var intData = _underlyingData.buffer.asByteData(_index, 4);
      _index += 4;
      return intData.getInt32(0, Endian.little);
    } else {
      if ((_bufferSize - index) < 4) {
        throw NotReadyException();
      }
      var intData = _underlyingData.buffer.asByteData(index, 4);
      _index = index + 4;
      return intData.getInt32(0, Endian.little);
    }
  }

  ///Read string from the binary data, the string format is utf-16, which is unicode in C#
  String readString([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    int dataLength;
    if (index == -1) {
      dataLength = readInt();
      if ((_bufferSize - _index) < dataLength) {
        throw NotReadyException();
      }
    } else {
      dataLength = readInt(index);
      if ((_bufferSize - index) < dataLength) {
        throw NotReadyException();
      }
    }
    var stringData = _underlyingData.buffer.asUint8List(_index, dataLength);
    _index += dataLength;
    var unicodeStringData = Uint8List.fromList(stringData.toList()).buffer.asUint16List();
    return String.fromCharCodes(unicodeStringData);
  }

  ///Read int16 value from binary data(little endian)
  int readInt16([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_bufferSize - _index) < 2) {
        throw NotReadyException();
      }
      var intData = _underlyingData.buffer.asByteData(_index, 2);
      _index += 2;
      return intData.getInt16(0, Endian.little);
    } else {
      if ((_bufferSize - index) < 2) {
        throw NotReadyException();
      }
      var intData = _underlyingData.buffer.asByteData(index, 2);
      _index = index + 2;
      return intData.getInt16(0, Endian.little);
    }
  }

  ///Read int64 value from binary data(little endian)
  ///this method is not support in web platform use readInt64V2 instead.
  int readInt64([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_bufferSize - _index) < 8) {
        throw NotReadyException();
      }
      var intData = _underlyingData.buffer.asByteData(_index, 8);
      _index += 8;
      return intData.getInt64(0, Endian.little);
    } else {
      if ((_bufferSize - index) < 8) {
        throw NotReadyException();
      }
      var intData = _underlyingData.buffer.asByteData(index, 8);
      _index = index + 8;
      return intData.getInt64(0, Endian.little);
    }
  }

  ///Read int64 value from binary data(little endian)
  ///this method use two int32 to support read int64 on web platform
  int readInt64V2([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_bufferSize - _index) < 8) {
        throw NotReadyException();
      }
      int low = readInt();
      int high = readInt();
      int value = high >> 32;
      value |= low;
      return value;
    } else {
      if ((_bufferSize - index) < 8) {
        throw NotReadyException();
      }
      int low = readInt(index);
      //Read the next int.
      int high = readInt();
      int value = high >> 32;
      value |= low;
      return value;
    }
  }

  ///Read float value from binary data(little endian)
  double readFloat([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_bufferSize - _index) < 4) {
        throw NotReadyException();
      }
      var floatData = _underlyingData.buffer.asByteData(_index, 4);
      _index += 4;
      return floatData.getFloat32(0, Endian.little);
    } else {
      if ((_bufferSize - index) < 4) {
        throw NotReadyException();
      }
      var floatData = _underlyingData.buffer.asByteData(index, 4);
      _index = index + 4;
      return floatData.getFloat32(0, Endian.little);
    }
  }

  ///Read double value from binary data(little endian)
  double readDouble([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_bufferSize - _index) < 8) {
        throw NotReadyException();
      }
      var floatData = _underlyingData.buffer.asByteData(_index, 8);
      _index += 8;
      return floatData.getFloat64(0, Endian.little);
    } else {
      if ((_bufferSize - index) < 8) {
        throw NotReadyException();
      }
      var floatData = _underlyingData.buffer.asByteData(index, 8);
      _index = index + 8;
      return floatData.getFloat64(0, Endian.little);
    }
  }

  ///Read bool value from binary data
  bool readBool([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_bufferSize - _index) < 1) {
        throw NotReadyException();
      }
      var boolData = _underlyingData.buffer.asByteData(_index, 1);
      _index++;
      return boolData.getInt8(0) == 1;
    } else {
      if ((_bufferSize - index) < 1) {
        throw NotReadyException();
      }
      var boolData = _underlyingData.buffer.asByteData(index, 1);
      _index = index + 1;
      return boolData.getInt8(0) == 1;
    }
  }

  ///Read byte value from binary data
  int readByte([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_bufferSize - _index) < 1) {
        throw NotReadyException();
      }
      var byteData = _underlyingData.buffer.asByteData(_index, 1);
      _index++;
      return byteData.getInt8(0);
    } else {
      if ((_bufferSize - index) < 1) {
        throw NotReadyException();
      }
      var byteData = _underlyingData.buffer.asByteData(index, 1);
      _index = index + 1;
      return byteData.getInt8(0);
    }
  }

  ///Read bytes from the binary data.
  Uint8List readBytes([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    var dataLength = readInt(index);
    if ((_bufferSize - _index) < dataLength) {
      throw NotReadyException();
    }
    var bytes = _underlyingData.buffer.asUint8List(_index, dataLength);
    _index += dataLength;
    return bytes;
  }
}