deal.dart

import 'dart:math';
import 'dart:io';

import 'package:console/console.dart';

void main() {
  Console.init();
  double a = _askInputAndClearConsole('A, please tell me your value: ');
  double b = _askInputAndClearConsole('B, please tell me your cost: ');
  if (a < b) {
    print('No deal.');
  } else {
    double p = b + (a - b) * Random().nextDouble();
    print('Deal at price $p');
  }
}

class _PrivacyConsole {
  int _lineCount = 0;

  void printLine(String line) {
    print(line);
    _lineCount += 1;
  }

  String readLine() {
    String result = stdin.readLineSync();
    _lineCount += 1;
    return result;
  }

  void clear() {
    for (int i = 0; i < _lineCount; i += 1) {
      Console.moveCursorUp();
      Console.eraseLine();
    }
    _lineCount = 0;
  }
}

double _askInputAndClearConsole(String hint) {
  double result = -1;
  final _PrivacyConsole console = _PrivacyConsole();
  try {
    while (result == -1) {
      console.printLine(hint);
      String line = console.readLine();
      result = double.tryParse(line);
      if (result == null || result < 0 || result > 1) {
        console.printLine('$line is not a valid input. Please input a fractional number between 0.00 and 1.00.');
        result = -1;
      }
    }
    console.printLine('The number you input is: $result.');
    console.printLine('Enter y to confirm and clear the console.');
    console.printLine('Enter anything else to stop and clear the console.');
    String confirmation = console.readLine();
    if (confirmation != 'y') {
      throw Exception('Aborted by user input: $confirmation');
    }
    return result;
  } catch (e) {
    throw e;
  } finally {
    // make sure that nothing is leaked in all cases.
    console.clear();
  }
}