// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using Xunit;

namespace Microsoft.AspNetCore.Cryptography
{
    public class WeakReferenceHelpersTests
    {
        [Fact]
        public void GetSharedInstance_ExistingWeakRefHasBeenGCed_CreatesNew()
        {
            // Arrange
            WeakReference<MyDisposable> wrOriginal = new WeakReference<MyDisposable>(null);
            WeakReference<MyDisposable> wr = wrOriginal;
            MyDisposable newInstance = new MyDisposable();

            // Act
            var retVal = WeakReferenceHelpers.GetSharedInstance(ref wr, () => newInstance);

            // Assert
            MyDisposable target;
            Assert.NotNull(wr);
            Assert.NotSame(wrOriginal, wr);
            Assert.True(wr.TryGetTarget(out target));
            Assert.Same(newInstance, target);
            Assert.Same(newInstance, retVal);
            Assert.False(newInstance.HasBeenDisposed);
        }

        [Fact]
        public void GetSharedInstance_ExistingWeakRefIsNull_CreatesNew()
        {
            // Arrange
            WeakReference<MyDisposable> wr = null;
            MyDisposable newInstance = new MyDisposable();

            // Act
            var retVal = WeakReferenceHelpers.GetSharedInstance(ref wr, () => newInstance);

            // Assert
            MyDisposable target;
            Assert.NotNull(wr);
            Assert.True(wr.TryGetTarget(out target));
            Assert.Same(newInstance, target);
            Assert.Same(newInstance, retVal);
            Assert.False(newInstance.HasBeenDisposed);
        }

        [Fact]
        public void GetSharedInstance_ExistingWeakRefIsNull_AnotherThreadCreatesInstanceWhileOurFactoryRuns_ReturnsExistingInstanceAndDisposesNewInstance()
        {
            // Arrange
            WeakReference<MyDisposable> wr = null;
            MyDisposable instanceThatWillBeCreatedFirst = new MyDisposable();
            MyDisposable instanceThatWillBeCreatedSecond = new MyDisposable();

            // Act
            var retVal = WeakReferenceHelpers.GetSharedInstance(ref wr, () =>
            {
                // mimic another thread creating the instance while our factory is being invoked
                WeakReferenceHelpers.GetSharedInstance(ref wr, () => instanceThatWillBeCreatedFirst);
                return instanceThatWillBeCreatedSecond;
            });

            // Assert
            MyDisposable target;
            Assert.NotNull(wr);
            Assert.True(wr.TryGetTarget(out target));
            Assert.Same(instanceThatWillBeCreatedFirst, target);
            Assert.Same(instanceThatWillBeCreatedFirst, retVal);
            Assert.False(instanceThatWillBeCreatedFirst.HasBeenDisposed);
            Assert.True(instanceThatWillBeCreatedSecond.HasBeenDisposed);
        }

        private sealed class MyDisposable : IDisposable
        {
            public bool HasBeenDisposed { get; private set; }

            public void Dispose()
            {
                HasBeenDisposed = true;
            }
        }
    }
}