_README.md

Interactive CLI in Dart

Example how to build a interactive CLI application in Dart

main.dart

/// Copyright 2020, Pascal Welsch
/// 
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
/// 
/// http://www.apache.org/licenses/LICENSE-2.0
/// 
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.

import 'dart:io' as io;

Future<void> main() async {
  try {
    io.stdin.echoMode = false;
    io.stdin.lineMode = false;
  } catch (_) {
    print("Running in non-interactive mode, exiting");
    return;
  }

  print("How would you rate writing CLIs with Dart? (Press <space> to select)");
  final answer = await selectAnswer(["bad", "good", "amazing 🎉"]);
  print("selected $answer");
  io.exit(0);
}

const ESC = '\u001B[';
const eraseLine = ESC + '2K';
const cursorUp = ESC + '1A';
const cursorHide = ESC + '?25l';
const cursorShow = ESC + '?25h';
const arrowUp = ESC + 'A';
const arrowDown = ESC + 'B';
const space = " ";

Future<String> selectAnswer(List<String> options) async {
  var selection = 0;

  String _displayed = "";

  /// replaces all visible text in terminal with new one
  void render(String text) {
    final lines = _displayed.runes.where((c) => c == 10 /*\n*/).length;
    io.stdout.write(eraseLine);
    for (var i = 0; i < lines; i++) {
      io.stdout.write(eraseLine);
      io.stdout.write(cursorUp);
    }

    io.stdout.writeCharCode(13);
    io.stdout.write(text);
    _displayed = text;
  }

  /// print the options + selection to terminal
  void showOptions() {
    final sb = StringBuffer();
    for (var i = 0; i < options.length; i++) {
      final icon = () {
        if (selection == i) return "●";
        return "○";
      }();
      sb.write(" $icon ${options[i]}\n");
    }
    render(sb.toString());
  }

  void select() {
    render("");
    io.stdout.write(cursorShow);
  }

  // hide cursor
  io.stdout.write(cursorHide);
  // show cursor on forced exit
  io.ProcessSignal.sigint.watch().listen((event) {
    io.stdout.write(cursorShow);
    io.exit(1);
  });

  showOptions();

  await for (final input in io.stdin) {
    final String command = String.fromCharCodes(input);
    switch (command) {
      case arrowUp:
        selection = (options.length + selection - 1) % options.length;
        showOptions();
        continue;
      case arrowDown:
        selection = (selection + 1) % options.length;
        showOptions();
        continue;
      case space:
        select();
        return options[selection];
    }
  }

  throw "nothing selected";
}