// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

// @dart = 2.9

/// @assertion bool single
/// @description Checks that [single] returns [true] if there is one element in
/// the iterable and [false] otherwise.
/// Throws a StateError if this is empty or has more than one element.
/// @author iarkh@unipro.ru

import "../../../Utils/expect.dart";
import "dart:collection";

class NaturalIterator implements Iterator<int> {
  int limit;
  int _current = 0;

  NaturalIterator(this.limit);

  bool moveNext() {
    if (_current < limit) {
      _current++;
      return true;
    } else {
      return false;
    }
  }

  int get current => _current;
}

class MyIterable extends Object with IterableMixin {
  int _limit;

  MyIterable(this._limit);

  Iterator<int> get iterator {
    return new NaturalIterator(_limit);
  }
}

main() {
  try {
    new MyIterable(0).single;
  } on StateError {
  }
  try {
    new MyIterable(10).single;
  } on StateError {
  }
  try {
    new MyIterable(150).single;
  } on StateError {
  }
  Expect.equals(1, new MyIterable(1).single);
}