using System.Collections.Concurrent;
using System.Diagnostics;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.ScadaBridge.AuditLog.Site;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
using ZB.MOM.WW.ScadaBridge.Commons.Types;
using AuditEvent = ZB.MOM.WW.Audit.AuditEvent;

namespace ZB.MOM.WW.ScadaBridge.AuditLog.Tests.Site;

/// <summary>
/// Tests for <see cref="SiteAuditRetentionService"/> The hosted
/// service runs the site SQLite retention purge on a timer: first tick after
/// <see cref="SiteAuditRetentionOptions.InitialDelay"/>, then every
/// <see cref="SiteAuditRetentionOptions.ResolvedPurgeInterval"/>, passing a cutoff of
/// <c>UtcNow - ResolvedRetentionDays</c>. Per-tick failures are swallowed so a
/// transient SQLite error never tears the service down.
/// </summary>
public class SiteAuditRetentionServiceTests
{
    /// <summary>Verifies that stopping the service after it has been disposed does not throw.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task StopAsync_AfterDispose_DoesNotThrow()
    {
        // Regression: Dispose tears down the CTS StopAsync
        // cancels, and the host does not guarantee StopAsync is driven before the DI
        // container is disposed. Cancel() on a disposed CTS throws, and letting that
        // escape an IHostedService aborts the host's whole shutdown sequence.
        var queue = new RecordingSiteAuditQueue();
        var options = Options.Create(new SiteAuditRetentionOptions
        {
            RetentionDays = 7,
            PurgeIntervalOverride = TimeSpan.FromMilliseconds(50),
            InitialDelay = TimeSpan.Zero,
        });
        var svc = new SiteAuditRetentionService(queue, options, NullLogger<SiteAuditRetentionService>.Instance);

        await svc.StartAsync(CancellationToken.None);
        svc.Dispose();

        // The assertion is the absence of ObjectDisposedException.
        await svc.StopAsync(CancellationToken.None);
        svc.Dispose();
    }

    /// <summary>Verifies that a tick purges events older than the retention cutoff.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task Tick_Purges_With_RetentionCutoff()
    {
        var queue = new RecordingSiteAuditQueue();
        var options = Options.Create(new SiteAuditRetentionOptions
        {
            RetentionDays = 7,
            // Override bypasses the 1-min production clamp so the loop ticks in ms.
            PurgeIntervalOverride = TimeSpan.FromMilliseconds(50),
            InitialDelay = TimeSpan.Zero,
        });
        using var svc = new SiteAuditRetentionService(queue, options, NullLogger<SiteAuditRetentionService>.Instance);

        await svc.StartAsync(CancellationToken.None);
        await WaitUntilAsync(() => queue.PurgeCalls.Count >= 1, TimeSpan.FromSeconds(5));
        await svc.StopAsync(CancellationToken.None);

        var cutoff = queue.PurgeCalls.First();
        Assert.InRange(cutoff,
            DateTime.UtcNow.AddDays(-7).AddMinutes(-1),
            DateTime.UtcNow.AddDays(-7).AddMinutes(1));
    }

    /// <summary>Verifies that a failing tick is swallowed and later ticks still run.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task Tick_SwallowsExceptions_AndKeepsTicking()
    {
        var queue = new RecordingSiteAuditQueue { ThrowOnFirstCall = true };
        var options = Options.Create(new SiteAuditRetentionOptions
        {
            RetentionDays = 7,
            // Override bypasses the 1-min production clamp so the loop ticks in ms.
            PurgeIntervalOverride = TimeSpan.FromMilliseconds(50),
            InitialDelay = TimeSpan.Zero,
        });
        using var svc = new SiteAuditRetentionService(queue, options, NullLogger<SiteAuditRetentionService>.Instance);

        await svc.StartAsync(CancellationToken.None);
        // The first tick throws; a second tick must still arrive (service survives).
        await WaitUntilAsync(() => queue.PurgeCalls.Count >= 2, TimeSpan.FromSeconds(5));
        await svc.StopAsync(CancellationToken.None);

        Assert.True(queue.PurgeCalls.Count >= 2);
    }

    /// <summary>Verifies that stopping the service during an in-flight purge completes cleanly without surfacing a cancellation.</summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
    [Fact]
    public async Task StopAsync_MidPurge_CompletesCleanly_WithoutSurfacingCancellation()
    {
        // PurgeExpiredAsync blocks until cancelled, so shutdown lands mid-purge: SafePurgeAsync
        // rethrows the OCE by design (abort the purge promptly), but the loop task must still
        // complete CLEANLY — StopAsync hands _loop straight to the host, and a canceled task
        // there is shutdown-log noise (arch-review 04 round 2, R7).
        var queue = new RecordingSiteAuditQueue { BlockUntilCancelled = true };
        var options = Options.Create(new SiteAuditRetentionOptions
        {
            RetentionDays = 7,
            PurgeInterval = TimeSpan.FromHours(24),
            InitialDelay = TimeSpan.Zero,
        });
        using var svc = new SiteAuditRetentionService(queue, options, NullLogger<SiteAuditRetentionService>.Instance);

        await svc.StartAsync(CancellationToken.None);
        await WaitUntilAsync(() => queue.PurgeCalls.Count >= 1, TimeSpan.FromSeconds(5));

        // Must NOT throw TaskCanceledException back into the host's shutdown path.
        await svc.StopAsync(CancellationToken.None);
    }

    private static async Task WaitUntilAsync(Func<bool> condition, TimeSpan timeout)
    {
        var sw = Stopwatch.StartNew();
        while (!condition())
        {
            if (sw.Elapsed > timeout)
            {
                throw new TimeoutException("Condition was not met within the timeout.");
            }

            await Task.Delay(10);
        }
    }

    /// <summary>Stub queue that records purge cutoffs and can throw on the first tick.</summary>
    private sealed class RecordingSiteAuditQueue : ISiteAuditQueue
    {
        /// <summary>Not supported by this stub.</summary>
        /// <param name="executionIds">The execution ids to read.</param>
        /// <param name="sinceUtc">The lower time bound.</param>
        /// <param name="limit">The maximum number of rows.</param>
        /// <param name="ct">A token to cancel the operation.</param>
        /// <param name="afterEventId">The keyset cursor.</param>
        /// <returns>Never returns; always throws <see cref="NotSupportedException"/>.</returns>
        public Task<IReadOnlyList<AuditEvent>> ReadByExecutionIdsAsync(
            IReadOnlyCollection<Guid> executionIds, DateTime sinceUtc, int limit, CancellationToken ct = default, string? afterEventId = null)
            => throw new NotSupportedException("not exercised by the retention service");

        private readonly ConcurrentQueue<DateTime> _purgeCalls = new();
        private int _calls;

        /// <summary>Gets the cutoffs passed to each purge call, in call order.</summary>
        public IReadOnlyCollection<DateTime> PurgeCalls => _purgeCalls;
        /// <summary>Gets a value indicating whether the first purge call throws a simulated transient failure.</summary>
        public bool ThrowOnFirstCall { get; init; }

        /// <summary>When set, PurgeExpiredAsync records the call then blocks until the token
        /// cancels — simulating a shutdown that lands while a purge is in flight.</summary>
        public bool BlockUntilCancelled { get; init; }

        // Test stub: Records the cutoff and optionally throws or blocks, as configured.
        /// <inheritdoc />
        public async Task<int> PurgeExpiredAsync(DateTime olderThanUtc, CancellationToken ct = default)
        {
            var n = Interlocked.Increment(ref _calls);
            _purgeCalls.Enqueue(olderThanUtc);
            if (ThrowOnFirstCall && n == 1)
            {
                throw new InvalidOperationException("Simulated transient purge failure.");
            }

            if (BlockUntilCancelled)
            {
                await Task.Delay(Timeout.Infinite, ct).ConfigureAwait(false);
            }

            return 0;
        }

        /// <summary>Not supported by this stub.</summary>
        /// <param name="limit">The maximum number of rows.</param>
        /// <param name="ct">A token to cancel the operation.</param>
        /// <returns>Never returns; always throws <see cref="NotSupportedException"/>.</returns>
        public Task<IReadOnlyList<AuditEvent>> ReadPendingAsync(int limit, CancellationToken ct = default)
            => throw new NotSupportedException();
        /// <summary>Not supported by this stub.</summary>
        /// <param name="limit">The maximum number of rows.</param>
        /// <param name="ct">A token to cancel the operation.</param>
        /// <returns>Never returns; always throws <see cref="NotSupportedException"/>.</returns>
        public Task<IReadOnlyList<AuditEvent>> ReadPendingCachedTelemetryAsync(int limit, CancellationToken ct = default)
            => throw new NotSupportedException();
        // Test stub: Not supported by this stub.
        /// <inheritdoc />
        public Task MarkForwardedAsync(IReadOnlyList<Guid> eventIds, CancellationToken ct = default)
            => throw new NotSupportedException();
        /// <summary>Not supported by this stub.</summary>
        /// <param name="sinceUtc">The lower time bound.</param>
        /// <param name="batchSize">The maximum batch size.</param>
        /// <param name="afterId">The keyset cursor.</param>
        /// <param name="ct">A token to cancel the operation.</param>
        /// <returns>Never returns; always throws <see cref="NotSupportedException"/>.</returns>
        public Task<IReadOnlyList<AuditEvent>> ReadPendingSinceAsync(
            DateTime sinceUtc, int batchSize, string? afterId = null, CancellationToken ct = default)
            => throw new NotSupportedException();
        // Test stub: Not supported by this stub.
        /// <inheritdoc />
        public Task MarkReconciledAsync(IReadOnlyList<Guid> eventIds, CancellationToken ct = default)
            => throw new NotSupportedException();
        // Test stub: Not supported by this stub.
        /// <inheritdoc />
        public Task<int> MarkReconciledUpToAsync(DateTime sinceUtc, string? afterId, CancellationToken ct = default)
            => throw new NotSupportedException();
        // Test stub: Not supported by this stub.
        /// <inheritdoc />
        public Task<SiteAuditBacklogSnapshot> GetBacklogStatsAsync(CancellationToken ct = default)
            => throw new NotSupportedException();
    }
}