Magic Code for Cotec Binary

main.dart

import "dart:convert";
import "dart:typed_data";

void main(){
  final List<int> mg = CotecBinMagic(0, 18, 3, true).asBinary;
  print("len: ${mg.length}");
  print("mgc: ${mg.map<String>((int e) => e.toRadixString(16)).join(" ")}");
  print("chr: «${utf8.decode(mg.skip(4).toList())}»");
  print("ch2: «${utf8.decode(mg)}»");
}

class CotecBinMagic {
  final int major;
  final int middle;
  final int extensions;
  final bool forCompressed;
  CotecBinMagic(this.major, this.middle, this.extensions, this.forCompressed);
  List<int> get asBinary => <int>[0xef, 0xfe, 0x8c, 0xfd].followedBy(utf8.encode(String.fromCharCodes(<int>[0x1f310].followedBy(toVariationSelector(this.major, true)).followedBy(<int>[0x00ad]).followedBy(toVariationSelector(this.middle, true)).followedBy(<int>[0x05be, 0x8a0f, 0x6c10, 0x2043, 0x0e1a, 0x0e35, 0x0e23, 0x1680]).followedBy(this.forCompressed ? <int>[0x200a] : <int>[]).followedBy(toVariationSelector(this.extensions, false)).followedBy(<int>[0x2001])))).toList();
}

Uint8List int32toBytes(int value) =>
    Uint8List(4)..buffer.asByteData().setInt32(0, value, Endian.big);
List<int> asint4(int value) => int32toBytes(value).map<List<int>>((int el) => <int>[(el & 240) >>> 4, el & 15]).expand((List<int> e) => e).toList();
List<int> toVariationSelector(int value, bool fe0nOnly) {
  if(fe0nOnly){
    return asint4(value).map<int>((int e) => e + 0xfe00).joiner(0x200d).toList();
  }else{
    return int32toBytes(value).map<int>((int e) => e < 16 ? e + 0xfe00 : e + 0xe0100).joiner(0x200d).toList();
  }
}
extension Jointing on Iterable<int> {
  Iterable<int> joiner(int joinerChar) => this.length < 2 ? this : this.take(this.length - 1).map<List<int>>((int e) => <int>[e, joinerChar]).expand((List<int> e) => e).followedBy(<int>[this.last]);
}