baudot_code.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const App());
}

class App extends StatelessWidget {
  const App({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: PaperTape(
            codes: encode(example).toList(),
          ),
        ),
      ),
    );
  }
}

class PaperTape extends StatelessWidget {
  const PaperTape({super.key, required this.codes});
  final List<int> codes;

  @override
  Widget build(BuildContext context) {
    return Container(
      width: 144,
      color: Colors.yellow.shade100,
      child: DefaultTextStyle(
        style: TextStyle(
          color: Colors.grey.shade600,
          fontFamily: 'Courier',
          fontFamilyFallback: const ['Courier New', 'monospace'],
          fontSize: 24,
        ),
        child: ListView.builder(
          padding: const EdgeInsets.all(24),
          itemBuilder: (context, index) => Code(code: codes[index]),
          itemCount: codes.length,
          itemExtent: 24,
        ),
      ),
    );
  }
}

class Code extends StatelessWidget {
  const Code({super.key, required this.code});
  final int code;

  @override
  Widget build(BuildContext context) {
    var data = '';
    for (var i = 0; i < 5; i++) {
      if (i == 2) data += '·';
      data += (code & (1 << i)) == 0 ? ' ' : '•';
    }
    return Center(child: Text(data));
  }
}

/// Converts [s] into a sequence of baudot-murray codes.
Iterable<int> encode(String s) sync* {
  const ltr = '\vE\nA SIU\rDRJNFCKTZLWHYPQOBG\vMXV\v';
  const fig = '\v3\n- "87\r\v4\b,!(5+)2\$6019?&\v./;\v';
  var isLtr = true;
  s = s.replaceAll('\v', '').replaceAll('\n', '\r\n').replaceAll("'", '"').toUpperCase();
  for (var i = 0; i < s.length; i++) {
    final j = (isLtr ? ltr : fig).indexOf(s[i]);
    if (j != -1) {
      yield j;
    } else {
      final k = (isLtr ? fig : ltr).indexOf(s[i]);
      if (k != -1) {
        yield (isLtr = !isLtr) ? 27 : 31; // (un)shift
        yield k;
      } else {
        yield 0; // invalid
      }
    }
  }
}

const example = '''
void main() {
  runApp(const App());
}

class App extends StatelessWidget {
  const App({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: PaperTape(
            codes: encode(example).toList(),
          ),
        ),
      ),
    );
  }
}

class PaperTape extends StatelessWidget {
  const PaperTape({super.key, required this.codes});
  final List<int> codes;

  @override
  Widget build(BuildContext context) {
    return Container(
      width: 144,
      color: Colors.yellow.shade100,
      child: DefaultTextStyle(
        style: TextStyle(
          color: Colors.grey.shade600,
          fontFamily: 'Courier',
          fontFamilyFallback: const ['Courier New', 'monospace'],
          fontSize: 24,
        ),
        child: ListView.builder(
          padding: const EdgeInsets.all(24),
          itemBuilder: (context, index) => Code(code: codes[index]),
          itemCount: codes.length,
          itemExtent: 24,
        ),
      ),
    );
  }
}

class Code extends StatelessWidget {
  const Code({super.key, required this.code});
  final int code;

  @override
  Widget build(BuildContext context) {
    var data = '';
    for (var i = 0; i < 5; i++) {
      if (i == 2) data += '·';
      data += (code & (1 << i)) == 0 ? ' ' : '•';
    }
    return Center(child: Text(data));
  }
}

/// Converts [s] into a sequence of baudot-murray codes.
Iterable<int> encode(String s) sync* {
  const ltr = '\vE\nA SIU\rDRJNFCKTZLWHYPQOBG\vMXV\v';
  const fig = '\v3\n- "87\r\v4\b,!(5+)2\$6019?&\v./;\v';
  var isLtr = true;
  s = s.replaceAll('\v', '').replaceAll('\n', '\r\n').replaceAll("'", '"').toUpperCase();
  for (var i = 0; i < s.length; i++) {
    final j = (isLtr ? ltr : fig).indexOf(s[i]);
    if (j != -1) {
      yield j;
    } else {
      final k = (isLtr ? fig : ltr).indexOf(s[i]);
      if (k != -1) {
        yield (isLtr = !isLtr) ? 27 : 31; // (un)shift
        yield k;
      } else {
        yield 0; // invalid
      }
    }
  }
}
''';