// Licensed to the .NET Foundation under one or more agreements.

// The .NET Foundation licenses this file to you under the MIT license.

// See the LICENSE file in the project root for more information.

using System;

using System.Collections;

using System.Collections.Generic;

namespace System.Linq.Tests

{

public static class Shuffler

{

public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source, int seed)

{

return new ShuffledEnumerable<T>(source, seed);

}

public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source)

{

return new ShuffledEnumerable<T>(source);

}

private class ShuffledEnumerable<T> : IEnumerable<T>

{

private IEnumerable<T> _source;

private int? _seed;

public ShuffledEnumerable(IEnumerable<T> source)

{

_source = source;

}

public ShuffledEnumerable(IEnumerable<T> source, int seed)

: this(source)

{

_seed = seed;

}

public IEnumerator<T> GetEnumerator()

{

Random rnd = _seed.HasValue ? new Random(_seed.GetValueOrDefault()) : new Random();

T[] array = _source.ToArray();

int count = array.Length;

for (int i = array.Length - 1; i > 0; --i)

{

int j = rnd.Next(0, i + 1);

if (i != j)

{

T swapped = array[i];

array[i] = array[j];

array[j] = swapped;

}

}

return ((IEnumerable<T>)array).GetEnumerator();

}

IEnumerator IEnumerable.GetEnumerator()

{

return GetEnumerator();

}

}

}

}