using System;
using System.Threading;
using System.Threading.Tasks;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Host.GalaxyRepository;
using ZB.MOM.WW.OtOpcUa.Tests.Helpers;

namespace ZB.MOM.WW.OtOpcUa.Tests.GalaxyRepository
{
    /// <summary>
    ///     Verifies the polling service that detects Galaxy deploy changes and triggers address-space rebuilds.
    /// </summary>
    public class ChangeDetectionServiceTests
    {
        /// <summary>
        ///     Confirms that the first poll always triggers an initial rebuild notification.
        /// </summary>
        [Fact]
        public async Task FirstPoll_AlwaysTriggers()
        {
            var repo = new FakeGalaxyRepository { LastDeployTime = new DateTime(2024, 1, 1) };
            var service = new ChangeDetectionService(repo, 1);
            var triggered = false;
            service.OnGalaxyChanged += () => triggered = true;

            service.Start();
            await Task.Delay(500);
            service.Stop();

            triggered.ShouldBe(true);
            service.Dispose();
        }

        /// <summary>
        ///     Confirms that repeated polls with the same deploy timestamp do not retrigger rebuilds.
        /// </summary>
        [Fact]
        public async Task SameTimestamp_DoesNotTriggerAgain()
        {
            var repo = new FakeGalaxyRepository { LastDeployTime = new DateTime(2024, 1, 1) };
            var service = new ChangeDetectionService(repo, 1);
            var triggerCount = 0;
            service.OnGalaxyChanged += () => Interlocked.Increment(ref triggerCount);

            service.Start();
            await Task.Delay(2500); // Should have polled at least twice
            service.Stop();

            triggerCount.ShouldBe(1); // Only the first poll
            service.Dispose();
        }

        /// <summary>
        ///     Confirms that a changed deploy timestamp triggers another rebuild notification.
        /// </summary>
        [Fact]
        public async Task ChangedTimestamp_TriggersAgain()
        {
            var repo = new FakeGalaxyRepository { LastDeployTime = new DateTime(2024, 1, 1) };
            var service = new ChangeDetectionService(repo, 1);
            var triggerCount = 0;
            service.OnGalaxyChanged += () => Interlocked.Increment(ref triggerCount);

            service.Start();
            await Task.Delay(500);

            // Change the deploy time
            repo.LastDeployTime = new DateTime(2024, 2, 1);
            await Task.Delay(1500);
            service.Stop();

            triggerCount.ShouldBeGreaterThanOrEqualTo(2);
            service.Dispose();
        }

        /// <summary>
        ///     Confirms that transient polling failures do not crash the service and allow later recovery.
        /// </summary>
        [Fact]
        public async Task FailedPoll_DoesNotCrash_RetriesNext()
        {
            var repo = new FakeGalaxyRepository { LastDeployTime = new DateTime(2024, 1, 1) };
            var service = new ChangeDetectionService(repo, 1);
            var triggerCount = 0;
            service.OnGalaxyChanged += () => Interlocked.Increment(ref triggerCount);

            service.Start();
            await Task.Delay(500);

            // Make it fail
            repo.ShouldThrow = true;
            await Task.Delay(1500);

            // Restore and it should recover
            repo.ShouldThrow = false;
            repo.LastDeployTime = new DateTime(2024, 3, 1);
            await Task.Delay(1500);
            service.Stop();

            // Should have triggered at least on first poll and on the changed timestamp
            triggerCount.ShouldBeGreaterThanOrEqualTo(1);
            service.Dispose();
        }

        /// <summary>
        ///     Confirms that stopping the service before it starts is a harmless no-op.
        /// </summary>
        [Fact]
        public void Stop_BeforeStart_DoesNotThrow()
        {
            var repo = new FakeGalaxyRepository();
            var service = new ChangeDetectionService(repo, 30);
            service.Stop(); // Should not throw
            service.Dispose();
        }
    }
}