// 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.Diagnostics.Tracing;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Internal;
using Xunit;

namespace Microsoft.AspNetCore.ConcurrencyLimiter.Tests
{
    public class ConcurrencyLimiterEventSourceTests
    {
        [Fact]
        public void MatchesNameAndGuid()
        {
            var eventSource = new ConcurrencyLimiterEventSource();

            Assert.Equal("Microsoft.AspNetCore.ConcurrencyLimiter", eventSource.Name);
            Assert.Equal(Guid.Parse("a605548a-6963-55cf-f000-99a6013deb01"), eventSource.Guid);
        }

        [Fact]
        public void RecordsRequestsRejected()
        {
            // Arrange
            var expectedId = 1;
            var eventListener = new TestEventListener(expectedId);
            var eventSource = GetConcurrencyLimiterEventSource();
            eventListener.EnableEvents(eventSource, EventLevel.Informational);

            // Act
            eventSource.RequestRejected();

            // Assert
            var eventData = eventListener.EventData;
            Assert.NotNull(eventData);
            Assert.Equal(expectedId, eventData.EventId);
            Assert.Equal(EventLevel.Warning, eventData.Level);
            Assert.Same(eventSource, eventData.EventSource);
            Assert.Null(eventData.Message);
            Assert.Empty(eventData.Payload);
        }

        [Fact]
        public async Task TracksQueueLength()
        {
            // Arrange
            using var eventListener = new TestCounterListener(new[] {
                "queue-length",
                "queue-duration",
                "requests-rejected",
            });

            using var eventSource = GetConcurrencyLimiterEventSource();

            using var timeoutTokenSource = new CancellationTokenSource(TimeSpan.FromSeconds(30));

            var lengthValues = eventListener.GetCounterValues("queue-length", timeoutTokenSource.Token).GetAsyncEnumerator();

            eventListener.EnableEvents(eventSource, EventLevel.Informational, EventKeywords.None,
                new Dictionary<string, string>
                {
                    {"EventCounterIntervalSec", "1" }
                });

            // Act
            eventSource.RequestRejected();

            Assert.True(await UntilValueMatches(lengthValues, 0));
            using (eventSource.QueueTimer())
            {
                Assert.True(await UntilValueMatches(lengthValues, 1));

                using (eventSource.QueueTimer())
                {
                    Assert.True(await UntilValueMatches(lengthValues, 2));
                }

                Assert.True(await UntilValueMatches(lengthValues, 1));
            }

            Assert.True(await UntilValueMatches(lengthValues, 0));
        }

        [Fact]
        public async Task TracksDurationSpentInQueue()
        {
            // Arrange
            using var eventListener = new TestCounterListener(new[] {
                "queue-length",
                "queue-duration",
                "requests-rejected",
            });

            using var eventSource = GetConcurrencyLimiterEventSource();

            using var timeoutTokenSource = new CancellationTokenSource(TimeSpan.FromSeconds(5));

            var durationValues = eventListener.GetCounterValues("queue-duration", timeoutTokenSource.Token).GetAsyncEnumerator();

            eventListener.EnableEvents(eventSource, EventLevel.Informational, EventKeywords.None,
                new Dictionary<string, string>
                {
                    {"EventCounterIntervalSec", "1" }
                });

            // Act
            Assert.True(await UntilValueMatches(durationValues, 0));

            using (eventSource.QueueTimer())
            {
                Assert.True(await UntilValueMatches(durationValues, 0));
            }

            // check that something (anything!) has been written
            while (await durationValues.MoveNextAsync())
            {
                if (durationValues.Current > 0)
                {
                    return;
                }
            }

            throw new TimeoutException();
        }

        private async Task<bool> UntilValueMatches(IAsyncEnumerator<double> enumerator, int value)
        {
            while (await enumerator.MoveNextAsync())
            {
                if (enumerator.Current == value)
                {
                    return true;
                }
            }

            return false;
        }

        private static ConcurrencyLimiterEventSource GetConcurrencyLimiterEventSource()
        {
            return new ConcurrencyLimiterEventSource(Guid.NewGuid().ToString());
        }
    }
}