using System;

using System.Threading;

​

public class IndexedItem

{

    private static int _nextItemIndex = 0;

​

    public int Value { get; set; }

    public int Index { get; private set; }

​

    public IndexedItem(int value)

    {

        Value = value;

        Index = GetNextIndex();

    }

​

    /// <summary>

    ///  Constructor for unit test cases.

    /// </summary>

    public IndexedItem()

    {

        _nextItemIndex = 0; // Initialize for unit tests

    }

    /// <summary>

    /// Gets the next available index for an IndexedItem.

    /// </summary>

    /// <returns>The next available index.</returns>

    /// <exception cref="InvalidOperationException">Thrown if the index is approaching int.MaxValue.</exception>

    public static int GetNextIndex()

    {

        int nextIndex = Interlocked.Increment(ref _nextItemIndex) -1;

​

        if (nextIndex == int.MaxValue - 1)

        {

            throw new InvalidOperationException("Cannot create more IndexedItem objects. Index is approaching Int32.MaxValue.");

        }

        return nextIndex;

    }

}

​

public class Program

{

    public static void Main(string[] args)

    {

        IndexedItem item1 = new IndexedItem(10);

        Console.WriteLine($"Item 1: Value = {item1.Value}, Index = {item1.Index}");

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        IndexedItem item2 = new IndexedItem(25);

        Console.WriteLine($"Item 2: Value = {item2.Value}, Index = {item2.Index}");

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        // Example of multithreading (optional - demonstrates thread safety)

        Thread thread1 = new Thread(() =>

        {

            IndexedItem item3 = new IndexedItem(5);

            Console.WriteLine($"Item 3 (Thread 1): Value = {item3.Value}, Index = {item3.Index}");

        });

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        Thread thread2 = new Thread(() =>

        {

            IndexedItem item4 = new IndexedItem(15);

            Console.WriteLine($"Item 4 (Thread 2): Value = {item4.Value}, Index = {item4.Index}");

        });

        thread1.Start();

        thread2.Start();

        thread1.Join();

        thread2.Join();

​

        IndexedItem item5 = new IndexedItem(30);

        Console.WriteLine($"Item 5: Value = {item5.Value}, Index = {item5.Index}");

    }

}

​