using System;
using Shouldly;
using Xunit;
using ZB.MOM.WW.LmxOpcUa.Host.Metrics;

namespace ZB.MOM.WW.LmxOpcUa.Tests.Metrics
{
    /// <summary>
    /// Verifies operation timing aggregation, rolling buffers, and success tracking used by the bridge metrics subsystem.
    /// </summary>
    public class PerformanceMetricsTests
    {
        /// <summary>
        /// Confirms that a fresh metrics collector reports no statistics.
        /// </summary>
        [Fact]
        public void EmptyState_ReturnsZeroStatistics()
        {
            using var metrics = new PerformanceMetrics();
            var stats = metrics.GetStatistics();
            stats.ShouldBeEmpty();
        }

        /// <summary>
        /// Confirms that repeated operation recordings update total and successful execution counts.
        /// </summary>
        [Fact]
        public void RecordOperation_TracksCounts()
        {
            using var metrics = new PerformanceMetrics();
            metrics.RecordOperation("Read", TimeSpan.FromMilliseconds(10), true);
            metrics.RecordOperation("Read", TimeSpan.FromMilliseconds(20), false);

            var stats = metrics.GetStatistics();
            stats.ShouldContainKey("Read");
            stats["Read"].TotalCount.ShouldBe(2);
            stats["Read"].SuccessCount.ShouldBe(1);
            stats["Read"].SuccessRate.ShouldBe(0.5);
        }

        /// <summary>
        /// Confirms that min, max, and average timing values are calculated from recorded operations.
        /// </summary>
        [Fact]
        public void RecordOperation_TracksMinMaxAverage()
        {
            using var metrics = new PerformanceMetrics();
            metrics.RecordOperation("Write", TimeSpan.FromMilliseconds(10));
            metrics.RecordOperation("Write", TimeSpan.FromMilliseconds(30));
            metrics.RecordOperation("Write", TimeSpan.FromMilliseconds(20));

            var stats = metrics.GetStatistics()["Write"];
            stats.MinMilliseconds.ShouldBe(10);
            stats.MaxMilliseconds.ShouldBe(30);
            stats.AverageMilliseconds.ShouldBe(20);
        }

        /// <summary>
        /// Confirms that the 95th percentile is calculated from the recorded timing sample.
        /// </summary>
        [Fact]
        public void P95_CalculatedCorrectly()
        {
            using var metrics = new PerformanceMetrics();
            for (int i = 1; i <= 100; i++)
                metrics.RecordOperation("Op", TimeSpan.FromMilliseconds(i));

            var stats = metrics.GetStatistics()["Op"];
            stats.Percentile95Milliseconds.ShouldBe(95);
        }

        /// <summary>
        /// Confirms that the rolling buffer keeps the most recent operation durations for percentile calculations.
        /// </summary>
        [Fact]
        public void RollingBuffer_EvictsOldEntries()
        {
            var opMetrics = new OperationMetrics();
            for (int i = 0; i < 1100; i++)
                opMetrics.Record(TimeSpan.FromMilliseconds(i), true);

            var stats = opMetrics.GetStatistics();
            stats.TotalCount.ShouldBe(1100);
            // P95 should be from the last 1000 entries (100-1099)
            stats.Percentile95Milliseconds.ShouldBeGreaterThan(1000);
        }

        /// <summary>
        /// Confirms that a timing scope records an operation when disposed.
        /// </summary>
        [Fact]
        public void BeginOperation_TimingScopeRecordsOnDispose()
        {
            using var metrics = new PerformanceMetrics();

            using (var scope = metrics.BeginOperation("Test"))
            {
                // Simulate some work
                System.Threading.Thread.Sleep(5);
            }

            var stats = metrics.GetStatistics();
            stats.ShouldContainKey("Test");
            stats["Test"].TotalCount.ShouldBe(1);
            stats["Test"].SuccessCount.ShouldBe(1);
            stats["Test"].AverageMilliseconds.ShouldBeGreaterThan(0);
        }

        /// <summary>
        /// Confirms that a timing scope can mark an operation as failed before disposal.
        /// </summary>
        [Fact]
        public void BeginOperation_SetSuccessFalse()
        {
            using var metrics = new PerformanceMetrics();

            using (var scope = metrics.BeginOperation("Test"))
            {
                scope.SetSuccess(false);
            }

            var stats = metrics.GetStatistics()["Test"];
            stats.TotalCount.ShouldBe(1);
            stats.SuccessCount.ShouldBe(0);
        }

        /// <summary>
        /// Confirms that looking up an unknown operation returns no metrics bucket.
        /// </summary>
        [Fact]
        public void GetMetrics_UnknownOperation_ReturnsNull()
        {
            using var metrics = new PerformanceMetrics();
            metrics.GetMetrics("NonExistent").ShouldBeNull();
        }

        /// <summary>
        /// Confirms that operation names are tracked without case sensitivity.
        /// </summary>
        [Fact]
        public void OperationNames_AreCaseInsensitive()
        {
            using var metrics = new PerformanceMetrics();
            metrics.RecordOperation("Read", TimeSpan.FromMilliseconds(10));
            metrics.RecordOperation("read", TimeSpan.FromMilliseconds(20));

            var stats = metrics.GetStatistics();
            stats.Count.ShouldBe(1);
            stats["READ"].TotalCount.ShouldBe(2);
        }
    }
}