// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Generic;
using Microsoft.Build.Collections;
using Shouldly;
using Xunit;
 
#nullable disable
 
namespace Microsoft.Build.UnitTests.OM.Collections
{
    /// <summary>
    /// Tests for CopyOnReadEnumerable
    /// </summary>
    public class CopyOnReadEnumerable_Tests
    {
        [Fact]
        public void EnumeratesBackingCollection()
        {
            List<int> values = new List<int>(new int[] { 1, 2, 3 });
 
            CopyOnReadEnumerable<int, string> enumerable = new CopyOnReadEnumerable<int, string>(values, values, i => i.ToString());
 
            using (IEnumerator<int> enumerator = values.GetEnumerator())
            {
                foreach (string s in enumerable)
                {
                    enumerator.MoveNext();
                    enumerator.Current.ToString().ShouldBe(s);
                }
                enumerator.MoveNext().ShouldBeFalse();
            }
        }
 
        [Fact]
        public void CopiesBackingCollection()
        {
            List<string> values = new List<string>(new string[] { "a", "b", "c" });
 
            CopyOnReadEnumerable<string, string> enumerable = new CopyOnReadEnumerable<string, string>(values, values, s => s);
 
            int expectedCount = values.Count;
            var enumerator = enumerable.GetEnumerator();
 
            // The list has been copied and adding to it has no effect on the enumerable.
            values.Add("d");
 
            int actualCount = 0;
            while (enumerator.MoveNext())
            {
                actualCount++;
            }
            actualCount.ShouldBe(expectedCount);
        }
    }
}