// 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 System.Collections.Generic;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.TagHelpers.Cache;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;
using Microsoft.AspNetCore.Routing;
using Microsoft.AspNetCore.Testing;
using Microsoft.Extensions.Caching.Distributed;
using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Internal;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using Microsoft.Extensions.WebEncoders.Testing;
using Moq;
using Xunit;

namespace Microsoft.AspNetCore.Mvc.TagHelpers
{
    public class DistributedCacheTagHelperTest
    {

        [Fact]
        public async Task ProcessAsync_DoesNotCache_IfDisabled()
        {
            // Arrange
            var childContent = "original-child-content";
            var storage = new Mock<IDistributedCacheTagHelperStorage>();
            var value = Encoding.UTF8.GetBytes("ok");
            storage.Setup(c => c.SetAsync(
                /*key*/ It.IsAny<string>(),
                /*value*/ value,
                /*options*/ It.IsAny<DistributedCacheEntryOptions>()));
            storage.Setup(c => c.GetAsync(It.IsAny<string>()))
                .Returns(Task.FromResult(value));
            var tagHelperContext = GetTagHelperContext();
            var service = new DistributedCacheTagHelperService(
                storage.Object,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance);
            var tagHelperOutput = GetTagHelperOutput(
                attributes: new TagHelperAttributeList(),
                childContent: childContent);
            var cacheTagHelper = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                Enabled = false
            };

            // Act
            await cacheTagHelper.ProcessAsync(tagHelperContext, tagHelperOutput);

            // Assert
            Assert.Equal(childContent, tagHelperOutput.Content.GetContent());
            storage.Verify(c => c.SetAsync(
                /*key*/ It.IsAny<string>(),
                /*content*/ value,
                /*options*/ It.IsAny<DistributedCacheEntryOptions>()),
                Times.Never);
        }

        [Fact]
        public async Task ProcessAsync_ReturnsCachedValue_IfEnabled()
        {
            // Arrange
            var childContent = "original-child-content";
            var storage = new Mock<IDistributedCacheTagHelperStorage>();
            var value = Encoding.UTF8.GetBytes(childContent);
            storage.Setup(c => c.SetAsync(
                /*key*/ It.IsAny<string>(),
                /*value*/ value,
                /*options*/ It.IsAny<DistributedCacheEntryOptions>()));
            storage.Setup(c => c.GetAsync(It.IsAny<string>()))
                .Returns(Task.FromResult<byte[]>(null));
            var service = new DistributedCacheTagHelperService(
                storage.Object,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance);
            var tagHelperContext = GetTagHelperContext();
            var tagHelperOutput = GetTagHelperOutput(
                attributes: new TagHelperAttributeList(),
                childContent: childContent);
            var cacheTagHelper = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                Enabled = true,
                Name = "some-name"
            };

            // Act
            await cacheTagHelper.ProcessAsync(tagHelperContext, tagHelperOutput);

            // Assert
            Assert.Empty(tagHelperOutput.PreContent.GetContent());
            Assert.Empty(tagHelperOutput.PostContent.GetContent());
            Assert.True(tagHelperOutput.IsContentModified);
            Assert.Equal(childContent, tagHelperOutput.Content.GetContent());

            storage.Verify(c => c.GetAsync(
                /*key*/ It.IsAny<string>()
                ),
                Times.Once);

            storage.Verify(c => c.SetAsync(
                /*key*/ It.IsAny<string>(),
                /*value*/ It.IsAny<byte[]>(),
                /*options*/ It.IsAny<DistributedCacheEntryOptions>()),
                Times.Once);

        }

        [Fact]
        public async Task ProcessAsync_ReturnsCachedValue_IfVaryByParamIsUnchanged()
        {
            // Arrange - 1
            var childContent = "original-child-content";
            var storage = GetStorage();
            var formatter = GetFormatter();
            var tagHelperContext1 = GetTagHelperContext();
            var tagHelperOutput1 = GetTagHelperOutput(
                attributes: new TagHelperAttributeList(),
                childContent: childContent);
            var service = new DistributedCacheTagHelperService(
                storage,
                formatter,
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance);
            var cacheTagHelper1 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                Enabled = true,
                VaryByQuery = "key1,key2",
                ViewContext = GetViewContext(),
            };
            cacheTagHelper1.ViewContext.HttpContext.Request.QueryString = new QueryString(
                "?key1=value1&key2=value2");

            // Act - 1
            await cacheTagHelper1.ProcessAsync(tagHelperContext1, tagHelperOutput1);

            // Assert - 1
            Assert.Empty(tagHelperOutput1.PreContent.GetContent());
            Assert.Empty(tagHelperOutput1.PostContent.GetContent());
            Assert.True(tagHelperOutput1.IsContentModified);
            Assert.Equal(childContent, tagHelperOutput1.Content.GetContent());

            // Arrange - 2
            var tagHelperContext2 = GetTagHelperContext();
            var tagHelperOutput2 = GetTagHelperOutput(
                attributes: new TagHelperAttributeList(),
                childContent: "different-content");
            var cacheTagHelper2 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                Enabled = true,
                VaryByQuery = "key1,key2",
                ViewContext = GetViewContext(),
            };
            cacheTagHelper2.ViewContext.HttpContext.Request.QueryString = new QueryString(
                "?key1=value1&key2=value2");

            // Act - 2
            await cacheTagHelper2.ProcessAsync(tagHelperContext2, tagHelperOutput2);

            // Assert - 2
            Assert.Empty(tagHelperOutput2.PreContent.GetContent());
            Assert.Empty(tagHelperOutput2.PostContent.GetContent());
            Assert.True(tagHelperOutput2.IsContentModified);
            Assert.Equal(childContent, tagHelperOutput2.Content.GetContent());
        }

        [Fact]
        public async Task ProcessAsync_RecalculatesValueIfCacheKeyChanges()
        {
            // Arrange - 1
            var childContent1 = "original-child-content";
            var storage = GetStorage();
            var service = new DistributedCacheTagHelperService(
                storage,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance);
            var tagHelperContext1 = GetTagHelperContext();
            var tagHelperOutput1 = GetTagHelperOutput(childContent: childContent1);
            tagHelperOutput1.PreContent.Append("<cache>");
            tagHelperOutput1.PostContent.SetContent("</cache>");
            var cacheTagHelper1 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                VaryByCookie = "cookie1,cookie2",
                ViewContext = GetViewContext(),
            };
            cacheTagHelper1.ViewContext.HttpContext.Request.Headers["Cookie"] = "cookie1=value1;cookie2=value2";

            // Act - 1
            await cacheTagHelper1.ProcessAsync(tagHelperContext1, tagHelperOutput1);

            // Assert - 1
            Assert.Empty(tagHelperOutput1.PreContent.GetContent());
            Assert.Empty(tagHelperOutput1.PostContent.GetContent());
            Assert.True(tagHelperOutput1.IsContentModified);
            Assert.Equal(childContent1, tagHelperOutput1.Content.GetContent());

            // Arrange - 2
            var childContent2 = "different-content";
            var tagHelperContext2 = GetTagHelperContext();
            var tagHelperOutput2 = GetTagHelperOutput(childContent: childContent2);
            tagHelperOutput2.PreContent.SetContent("<cache>");
            tagHelperOutput2.PostContent.SetContent("</cache>");
            var cacheTagHelper2 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                VaryByCookie = "cookie1,cookie2",
                ViewContext = GetViewContext(),
            };
            cacheTagHelper2.ViewContext.HttpContext.Request.Headers["Cookie"] = "cookie1=value1;cookie2=not-value2";

            // Act - 2
            await cacheTagHelper2.ProcessAsync(tagHelperContext2, tagHelperOutput2);

            // Assert - 2
            Assert.Empty(tagHelperOutput2.PreContent.GetContent());
            Assert.Empty(tagHelperOutput2.PostContent.GetContent());
            Assert.True(tagHelperOutput2.IsContentModified);
            Assert.Equal(childContent2, tagHelperOutput2.Content.GetContent());
        }

        [Fact]
        public void UpdateCacheEntryOptions_SetsAbsoluteExpiration_IfExpiresOnIsSet()
        {
            // Arrange
            var expiresOn = DateTimeOffset.UtcNow.AddMinutes(4);
            var storage = GetStorage();
            var service = new DistributedCacheTagHelperService(
                storage,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var cacheTagHelper = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ExpiresOn = expiresOn
            };

            // Act
            var cacheEntryOptions = cacheTagHelper.GetDistributedCacheEntryOptions();

            // Assert
            Assert.Equal(expiresOn, cacheEntryOptions.AbsoluteExpiration);
        }

        [Fact]
        public void UpdateCacheEntryOptions_DefaultsTo30SecondsSliding_IfNoEvictionCriteriaIsProvided()
        {
            // Arrange
            var slidingExpiresIn = TimeSpan.FromSeconds(30);
            var storage = GetStorage();
            var service = new DistributedCacheTagHelperService(
                storage,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var cacheTagHelper = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder());

            // Act
            var cacheEntryOptions = cacheTagHelper.GetDistributedCacheEntryOptions();

            // Assert
            Assert.Equal(slidingExpiresIn, cacheEntryOptions.SlidingExpiration);
        }

        [Fact]
        public void UpdateCacheEntryOptions_SetsAbsoluteExpiration_IfExpiresAfterIsSet()
        {
            // Arrange
            var expiresAfter = TimeSpan.FromSeconds(42);
            var storage = GetStorage();
            var service = new DistributedCacheTagHelperService(
                storage,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var cacheTagHelper = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ExpiresAfter = expiresAfter
            };

            // Act
            var cacheEntryOptions = cacheTagHelper.GetDistributedCacheEntryOptions();

            // Assert
            Assert.Equal(expiresAfter, cacheEntryOptions.AbsoluteExpirationRelativeToNow);
        }

        [Fact]
        public void UpdateCacheEntryOptions_SetsSlidingExpiration_IfExpiresSlidingIsSet()
        {
            // Arrange
            var expiresSliding = TimeSpan.FromSeconds(37);
            var storage = GetStorage();
            var service = new DistributedCacheTagHelperService(
                storage,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var cacheTagHelper = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ExpiresSliding = expiresSliding
            };

            // Act
            var cacheEntryOptions = cacheTagHelper.GetDistributedCacheEntryOptions();

            // Assert
            Assert.Equal(expiresSliding, cacheEntryOptions.SlidingExpiration);
        }

        [Fact]
        public async Task ProcessAsync_UsesExpiresAfter_ToExpireCacheEntry()
        {
            // Arrange - 1
            var currentTime = new DateTimeOffset(2010, 1, 1, 0, 0, 0, TimeSpan.Zero);
            var childContent1 = "original-child-content";
            var clock = new Mock<ISystemClock>();
            clock.SetupGet(p => p.UtcNow)
                .Returns(() => currentTime);
            var storage = GetStorage(Options.Create(new MemoryDistributedCacheOptions { Clock = clock.Object }));
            var service = new DistributedCacheTagHelperService(
                storage,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var tagHelperContext1 = GetTagHelperContext();
            var tagHelperOutput1 = GetTagHelperOutput(childContent: childContent1);
            tagHelperOutput1.PreContent.SetContent("<cache>");
            tagHelperOutput1.PostContent.SetContent("</cache>");
            var cacheTagHelper1 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                ExpiresAfter = TimeSpan.FromMinutes(10)
            };

            // Act - 1
            await cacheTagHelper1.ProcessAsync(tagHelperContext1, tagHelperOutput1);

            // Assert - 1
            Assert.Empty(tagHelperOutput1.PreContent.GetContent());
            Assert.Empty(tagHelperOutput1.PostContent.GetContent());
            Assert.True(tagHelperOutput1.IsContentModified);
            Assert.Equal(childContent1, tagHelperOutput1.Content.GetContent());

            // Arrange - 2
            var childContent2 = "different-content";
            var tagHelperContext2 = GetTagHelperContext();
            var tagHelperOutput2 = GetTagHelperOutput(childContent: childContent2);
            tagHelperOutput2.PreContent.SetContent("<cache>");
            tagHelperOutput2.PostContent.SetContent("</cache>");
            var cacheTagHelper2 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                ExpiresAfter = TimeSpan.FromMinutes(10)
            };
            currentTime = currentTime.AddMinutes(11);

            // Act - 2
            await cacheTagHelper2.ProcessAsync(tagHelperContext2, tagHelperOutput2);

            // Assert - 2
            Assert.Empty(tagHelperOutput2.PreContent.GetContent());
            Assert.Empty(tagHelperOutput2.PostContent.GetContent());
            Assert.True(tagHelperOutput2.IsContentModified);
            Assert.Equal(childContent2, tagHelperOutput2.Content.GetContent());
        }

        [Fact]
        public async Task ProcessAsync_UsesExpiresOn_ToExpireCacheEntry()
        {
            // Arrange - 1
            var currentTime = new DateTimeOffset(2010, 1, 1, 0, 0, 0, TimeSpan.Zero);
            var childContent1 = "original-child-content";
            var clock = new Mock<ISystemClock>();
            clock.SetupGet(p => p.UtcNow)
                .Returns(() => currentTime);
            var storage = GetStorage(Options.Create(new MemoryDistributedCacheOptions { Clock = clock.Object }));
            var service = new DistributedCacheTagHelperService(
                storage,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var tagHelperContext1 = GetTagHelperContext();
            var tagHelperOutput1 = GetTagHelperOutput(childContent: childContent1);
            tagHelperOutput1.PreContent.SetContent("<distributed-cache>");
            tagHelperOutput1.PostContent.SetContent("</distributed-cache>");
            var cacheTagHelper1 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                ExpiresOn = currentTime.AddMinutes(5)
            };

            // Act - 1
            await cacheTagHelper1.ProcessAsync(tagHelperContext1, tagHelperOutput1);

            // Assert - 1
            Assert.Empty(tagHelperOutput1.PreContent.GetContent());
            Assert.Empty(tagHelperOutput1.PostContent.GetContent());
            Assert.True(tagHelperOutput1.IsContentModified);
            Assert.Equal(childContent1, tagHelperOutput1.Content.GetContent());

            // Arrange - 2
            currentTime = currentTime.AddMinutes(5).AddSeconds(2);
            var childContent2 = "different-content";
            var tagHelperContext2 = GetTagHelperContext();
            var tagHelperOutput2 = GetTagHelperOutput(childContent: childContent2);
            tagHelperOutput2.PreContent.SetContent("<distributed-cache>");
            tagHelperOutput2.PostContent.SetContent("</distributed-cache>");
            var cacheTagHelper2 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                ExpiresOn = currentTime.AddMinutes(5)
            };

            // Act - 2
            await cacheTagHelper2.ProcessAsync(tagHelperContext2, tagHelperOutput2);

            // Assert - 2
            Assert.Empty(tagHelperOutput2.PreContent.GetContent());
            Assert.Empty(tagHelperOutput2.PostContent.GetContent());
            Assert.True(tagHelperOutput2.IsContentModified);
            Assert.Equal(childContent2, tagHelperOutput2.Content.GetContent());
        }

        [Fact]
        public async Task ProcessAsync_UsesExpiresSliding_ToExpireCacheEntryWithSlidingExpiration()
        {
            // Arrange - 1
            var currentTime = new DateTimeOffset(2010, 1, 1, 0, 0, 0, TimeSpan.Zero);
            var childContent1 = "original-child-content";
            var clock = new Mock<ISystemClock>();
            clock.SetupGet(p => p.UtcNow)
                .Returns(() => currentTime);
            var storage = GetStorage(Options.Create(new MemoryDistributedCacheOptions { Clock = clock.Object }));
            var service = new DistributedCacheTagHelperService(
                storage,
                Mock.Of<IDistributedCacheTagHelperFormatter>(),
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var tagHelperContext1 = GetTagHelperContext();
            var tagHelperOutput1 = GetTagHelperOutput(childContent: childContent1);
            tagHelperOutput1.PreContent.SetContent("<distributed-cache>");
            tagHelperOutput1.PostContent.SetContent("</distributed-cache>");
            var cacheTagHelper1 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                ExpiresSliding = TimeSpan.FromSeconds(30)
            };

            // Act - 1
            await cacheTagHelper1.ProcessAsync(tagHelperContext1, tagHelperOutput1);

            // Assert - 1
            Assert.Empty(tagHelperOutput1.PreContent.GetContent());
            Assert.Empty(tagHelperOutput1.PostContent.GetContent());
            Assert.True(tagHelperOutput1.IsContentModified);
            Assert.Equal(childContent1, tagHelperOutput1.Content.GetContent());

            // Arrange - 2
            currentTime = currentTime.AddSeconds(35);
            var childContent2 = "different-content";
            var tagHelperContext2 = GetTagHelperContext();
            var tagHelperOutput2 = GetTagHelperOutput(childContent: childContent2);
            tagHelperOutput2.PreContent.SetContent("<distributed-cache>");
            tagHelperOutput2.PostContent.SetContent("</distributed-cache>");
            var cacheTagHelper2 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                ExpiresSliding = TimeSpan.FromSeconds(30)
            };

            // Act - 2
            await cacheTagHelper2.ProcessAsync(tagHelperContext2, tagHelperOutput2);

            // Assert - 2
            Assert.Empty(tagHelperOutput2.PreContent.GetContent());
            Assert.Empty(tagHelperOutput2.PostContent.GetContent());
            Assert.True(tagHelperOutput2.IsContentModified);
            Assert.Equal(childContent2, tagHelperOutput2.Content.GetContent());
        }

        [Fact]
        public async Task ProcessAsync_ComputesValueOnce_WithConcurrentRequests()
        {
            // Arrange
            var childContent = "some-content";
            var event1 = new TaskCompletionSource<int>(TaskCreationOptions.RunContinuationsAsynchronously);
            var event2 = new TaskCompletionSource<int>(TaskCreationOptions.RunContinuationsAsynchronously);
            var event3 = new TaskCompletionSource<int>(TaskCreationOptions.RunContinuationsAsynchronously);
            var calls = 0;
            var formatter = GetFormatter();
            var storage = GetStorage();
            var service = new DistributedCacheTagHelperService(
                storage,
                formatter,
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var tagHelperContext1 = GetTagHelperContext();
            var tagHelperContext2 = GetTagHelperContext();

            var tagHelperOutput1 = new TagHelperOutput(
                "distributed-cache",
                new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    calls++;
                    event2.SetResult(0);

                    var tagHelperContent = new DefaultTagHelperContent();
                    tagHelperContent.SetHtmlContent(childContent);
                    return Task.FromResult<TagHelperContent>(tagHelperContent);
                });

            var tagHelperOutput2 = new TagHelperOutput(
                "distributed-cache",
                new TagHelperAttributeList(),
                getChildContentAsync: async (useCachedResult, encoder) =>
                {
                    calls++;
                    await event3.Task.TimeoutAfter(TimeSpan.FromSeconds(5));

                    var tagHelperContent = new DefaultTagHelperContent();
                    tagHelperContent.SetHtmlContent(childContent);
                    return tagHelperContent;
                });

            var cacheTagHelper1 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                Enabled = true
            };

            var cacheTagHelper2 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                Enabled = true
            };

            // Act

            var task1 = Task.Run(async () =>
            {
                await event1.Task.TimeoutAfter(TimeSpan.FromSeconds(5));
                await cacheTagHelper1.ProcessAsync(tagHelperContext1, tagHelperOutput1);
                event3.SetResult(0);
            });

            var task2 = Task.Run(async () =>
            {
                await event2.Task.TimeoutAfter(TimeSpan.FromSeconds(5));
                await cacheTagHelper2.ProcessAsync(tagHelperContext1, tagHelperOutput2);
            });

            event1.SetResult(0);
            await Task.WhenAll(task1, task2);

            // Assert
            Assert.Empty(tagHelperOutput1.PreContent.GetContent());
            Assert.Empty(tagHelperOutput1.PostContent.GetContent());
            Assert.True(tagHelperOutput1.IsContentModified);
            Assert.Equal(childContent, tagHelperOutput1.Content.GetContent());

            Assert.Empty(tagHelperOutput2.PreContent.GetContent());
            Assert.Empty(tagHelperOutput2.PostContent.GetContent());
            Assert.True(tagHelperOutput2.IsContentModified);
            Assert.Equal(childContent, tagHelperOutput2.Content.GetContent());

            Assert.Equal(1, calls);
        }

        [Fact]
        public async Task ProcessAsync_ExceptionInProcessing_DoesntBlockConcurrentRequests()
        {
            // Arrange
            var childContent = "some-content";
            var event1 = new TaskCompletionSource<int>(TaskCreationOptions.RunContinuationsAsynchronously);
            var event2 = new TaskCompletionSource<int>(TaskCreationOptions.RunContinuationsAsynchronously);
            var event3 = new TaskCompletionSource<int>(TaskCreationOptions.RunContinuationsAsynchronously);
            var calls = 0;
            var formatter = GetFormatter();
            var storage = GetStorage();
            var service = new DistributedCacheTagHelperService(
                storage,
                formatter,
                new HtmlTestEncoder(),
                NullLoggerFactory.Instance
                );
            var tagHelperContext1 = GetTagHelperContext();
            var tagHelperContext2 = GetTagHelperContext();

            var tagHelperOutput1 = new TagHelperOutput(
                "distributed-cache",
                new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    calls++;
                    event2.SetResult(0);

                    throw new Exception();
                });

            var tagHelperOutput2 = new TagHelperOutput(
                "distributed-cache",
                new TagHelperAttributeList(),
                getChildContentAsync: async (useCachedResult, encoder) =>
                {
                    calls++;
                    await event3.Task.TimeoutAfter(TimeSpan.FromSeconds(5));

                    var tagHelperContent = new DefaultTagHelperContent();
                    tagHelperContent.SetHtmlContent(childContent);
                    return tagHelperContent;
                });

            var cacheTagHelper1 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                Enabled = true
            };

            var cacheTagHelper2 = new DistributedCacheTagHelper(
                service,
                new HtmlTestEncoder())
            {
                ViewContext = GetViewContext(),
                Enabled = true
            };

            // Act

            var task1 = Task.Run(async () =>
            {
                await event1.Task.TimeoutAfter(TimeSpan.FromSeconds(5));
                await Assert.ThrowsAsync<Exception>(() => cacheTagHelper1.ProcessAsync(tagHelperContext1, tagHelperOutput1));
                event3.SetResult(0);
            });

            var task2 = Task.Run(async () =>
            {
                await event2.Task.TimeoutAfter(TimeSpan.FromSeconds(5));
                await cacheTagHelper2.ProcessAsync(tagHelperContext2, tagHelperOutput2);
            });

            event1.SetResult(0);
            await Task.WhenAll(task1, task2);

            // Assert
            Assert.Empty(tagHelperOutput1.PreContent.GetContent());
            Assert.Empty(tagHelperOutput1.PostContent.GetContent());
            Assert.False(tagHelperOutput1.IsContentModified);
            Assert.Empty(tagHelperOutput1.Content.GetContent());

            Assert.Empty(tagHelperOutput2.PreContent.GetContent());
            Assert.Empty(tagHelperOutput2.PostContent.GetContent());
            Assert.True(tagHelperOutput2.IsContentModified);
            Assert.Equal(childContent, tagHelperOutput2.Content.GetContent());

            Assert.Equal(2, calls);
        }

        [Fact]
        public async Task Deserialize_DoesntAlterValue_WhenSerialized()
        {
            // Arrange
            var content = "<b>some content</b>";
            var formatter = GetFormatter();
            var context = new DistributedCacheTagHelperFormattingContext
            {
                Html = new HtmlString(content)
            };
            var serialized = await formatter.SerializeAsync(context);

            // Act
            var deserialized = await formatter.DeserializeAsync(serialized);

            // Assert
            Assert.Equal(deserialized.ToString(), content);
        }

        private static ViewContext GetViewContext()
        {
            var actionContext = new ActionContext(new DefaultHttpContext(), new RouteData(), new ActionDescriptor());
            return new ViewContext(actionContext,
                Mock.Of<IView>(),
                new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()),
                Mock.Of<ITempDataDictionary>(),
                TextWriter.Null,
                new HtmlHelperOptions());
        }

        private static TagHelperContext GetTagHelperContext()
        {
            return new TagHelperContext(
                tagName: "test",
                allAttributes: new TagHelperAttributeList(),
                items: new Dictionary<object, object>(),
                uniqueId: "testid");
        }

        private static TagHelperOutput GetTagHelperOutput(
            string tagName = "distributed-cache",
            TagHelperAttributeList attributes = null,
            string childContent = "some child content")
        {
            attributes = attributes ?? new TagHelperAttributeList { { "attr", "value" } };

            return new TagHelperOutput(
                tagName,
                attributes,
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    var tagHelperContent = new DefaultTagHelperContent();
                    tagHelperContent.SetHtmlContent(childContent);
                    return Task.FromResult<TagHelperContent>(tagHelperContent);
                });
        }

        private static IDistributedCacheTagHelperStorage GetStorage(IOptions<MemoryDistributedCacheOptions> options = null)
        {
            return new DistributedCacheTagHelperStorage(new MemoryDistributedCache(options ?? Options.Create(new MemoryDistributedCacheOptions())));
        }

        private static IDistributedCacheTagHelperFormatter GetFormatter()
        {
            return new DistributedCacheTagHelperFormatter();
        }
    }
}
