// 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.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.Collections;
using Roslyn.Utilities;
using Xunit;
 
namespace Microsoft.CodeAnalysis.UnitTests;
 
[SuppressMessage("Usage", "VSTHRD104:Offer async methods", Justification = "This class tests specific behavior of tasks.")]
public sealed class SpecializedTasksTests
{
    private sealed record StateType;
    private sealed record IntermediateType;
    private sealed record ResultType;
 
    [Fact]
    public void WhenAll_Null()
    {
#pragma warning disable CA2012 // Use ValueTasks correctly (the instance is never created)
        Assert.Throws<ArgumentNullException>(() => SpecializedTasks.WhenAll<int>((IEnumerable<ValueTask<int>>)null!));
#pragma warning restore CA2012 // Use ValueTasks correctly
    }
 
    [Fact]
    public void WhenAll_Empty()
    {
        var whenAll = SpecializedTasks.WhenAll(SpecializedCollections.EmptyEnumerable<ValueTask<int>>());
        Debug.Assert(whenAll.IsCompleted);
        Assert.True(whenAll.IsCompletedSuccessfully);
        Assert.Same(Array.Empty<int>(), whenAll.Result);
    }
 
    [Fact]
    public void WhenAll_AllCompletedSuccessfully()
    {
        var whenAll = SpecializedTasks.WhenAll([new ValueTask<int>(0), new ValueTask<int>(1)]);
        Debug.Assert(whenAll.IsCompleted);
        Assert.True(whenAll.IsCompletedSuccessfully);
        Assert.Equal((int[])[0, 1], whenAll.Result);
    }
 
    [Fact]
    public async Task WhenAll_CompletedButCanceled()
    {
        var whenAll = SpecializedTasks.WhenAll([new ValueTask<int>(Task.FromCanceled<int>(new CancellationToken(true)))]);
        Assert.True(whenAll.IsCompleted);
        Assert.False(whenAll.IsCompletedSuccessfully);
        await Assert.ThrowsAsync<TaskCanceledException>(async () => await whenAll);
    }
 
    [Fact]
    public void WhenAll_NotYetCompleted()
    {
        var completionSource = new TaskCompletionSource<int>();
        var whenAll = SpecializedTasks.WhenAll([new ValueTask<int>(completionSource.Task)]);
        Assert.False(whenAll.IsCompleted);
        completionSource.SetResult(0);
        Assert.True(whenAll.IsCompleted);
        Debug.Assert(whenAll.IsCompleted);
        Assert.Equal((int[])[0], whenAll.Result);
    }
}