LehrerApp/LehrerApp.Sync.Tests/SyncEngineTests.cs

using System.Net;
using System.Net.Http.Json;
using LehrerApp.Core.Models;
using LehrerApp.Data;
using LehrerApp.Sync.Crypto;
using LehrerApp.Sync.Models;
using Xunit;

namespace LehrerApp.Sync.Tests;

public sealed class SyncEngineTests
{
    private static LiteDbContext NewInMemoryContext() => new(new MemoryStream());
    private static readonly byte[] Key = SyncCrypto.GenerateKey();

    /// Regression: EventApplier.ApplyAsync fing früher nur LiteException ab. Jede andere Ausnahme
    /// (z.B. eine ungültige/korrupte Payload eines einzelnen Ereignisses) fiel unbehandelt aus
    /// SyncEngine.PullAsync heraus, BEVOR _queue.SetLastServerSeq() erreicht wurde — der nächste
    /// Sync-Versuch lud denselben Batch erneut und scheiterte am selben Ereignis erneut: ein
    /// dauerhaft blockierter Sync, bei dem selbst bereits im selben Batch erfolgreich angewendete
    /// Ereignisse (wie hier "goodStudent") nie durchkamen.
    [Fact]
    public async Task SyncNowAsync_KorruptesEreignisImPullBatch_BlockiertNachfolgendeEreignisseNicht()
    {
        using var temp = new TempEventQueue();
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);
        var resolver = new ConflictResolver(temp.Queue);
        var attachments = new AttachmentSyncer(db, new HttpClient(), Key);

        var goodStudent = new Student { FirstName = "Anna", LastName = "Beispiel" };
        var badEvent = new SyncEvent
        {
            DeviceId = "other-device", DeviceType = DeviceType.Desktop,
            EntityType = nameof(Student), EntityId = Guid.NewGuid().ToString(),
            Operation = "Save", Payload = "offensichtlich-keine-gueltige-verschluesselte-payload",
            SequenceNr = 1,
        };
        var goodEvent = new SyncEvent
        {
            DeviceId = "other-device", DeviceType = DeviceType.Desktop,
            EntityType = nameof(Student), EntityId = goodStudent.Id.ToString(),
            Operation = "Save", Payload = SyncCrypto.EncryptObject(goodStudent, Key),
            SequenceNr = 2,
        };

        var handler = new FakeHttpMessageHandler(req =>
        {
            if (req.RequestUri!.AbsolutePath == "/api/sync/pull")
                return new HttpResponseMessage(HttpStatusCode.OK)
                {
                    Content = JsonContent.Create(new PullResponse
                    { Events = [badEvent, goodEvent], ServerSequenceNr = 2 }),
                };
            return new HttpResponseMessage(HttpStatusCode.OK);
        });
        var http = new HttpClient(handler) { BaseAddress = new Uri("https://example.invalid") };
        var engine = new SyncEngine(temp.Queue, resolver, applier, attachments, http,
            new SyncConfig { DeviceId = "this-device" });

        var result = await engine.SyncNowAsync();

        Assert.True(result.Success);
        Assert.NotNull(db.Students.FindById(goodStudent.Id));
        // Nicht bei 0 stecken geblieben - der Batch gilt als vollständig verarbeitet, auch wenn ein
        // einzelnes Ereignis darin übersprungen werden musste.
        Assert.Equal(2, temp.Queue.GetLastServerSeq());
    }

    // ── PushAsync: Dedup, BasedOnServerSeq, AssignedServerSeqs (TODO 10.3.4) ────────────────

    [Fact]
    public async Task PushAsync_MehrereAusstehendeEreignisseDerselbenEntitaet_SendetNurDasJuengste()
    {
        using var temp = new TempEventQueue();
        var entityId = Guid.NewGuid().ToString();
        temp.Queue.Enqueue("this-device", DeviceType.Desktop, "Lesson", entityId, "Save", "alt");
        var newest = temp.Queue.Enqueue("this-device", DeviceType.Desktop, "Lesson", entityId, "Save", "neu");
        List<SyncEvent>? pushed = null;
        var handler = new FakeHttpMessageHandler(req =>
        {
            if (req.RequestUri!.AbsolutePath == "/api/sync/push")
            {
                pushed = req.Content!.ReadFromJsonAsync<List<SyncEvent>>().GetAwaiter().GetResult();
                return new HttpResponseMessage(HttpStatusCode.OK)
                { Content = JsonContent.Create(new PushResponse { ServerSequenceNr = 1 }) };
            }
            return new HttpResponseMessage(HttpStatusCode.OK)
            { Content = JsonContent.Create(new PullResponse()) };
        });
        var engine = MakeEngine(temp, handler);

        var result = await engine.SyncNowAsync();

        Assert.True(result.Success);
        var evt = Assert.Single(pushed!);
        Assert.Equal(newest.EventId, evt.EventId);
        Assert.Equal("neu", evt.Payload);
        Assert.Equal(0, temp.Queue.PendingCount());
    }

    [Fact]
    public async Task PushAsync_SetztBasedOnServerSeqAusLokalerVersionsverfolgung()
    {
        using var temp = new TempEventQueue();
        var entityId = Guid.NewGuid().ToString();
        temp.Queue.SetKnownServerSeq("Lesson", entityId, 5);
        temp.Queue.Enqueue("this-device", DeviceType.Desktop, "Lesson", entityId, "Save", "x");
        List<SyncEvent>? pushed = null;
        var handler = new FakeHttpMessageHandler(req =>
        {
            if (req.RequestUri!.AbsolutePath == "/api/sync/push")
            {
                pushed = req.Content!.ReadFromJsonAsync<List<SyncEvent>>().GetAwaiter().GetResult();
                return new HttpResponseMessage(HttpStatusCode.OK)
                { Content = JsonContent.Create(new PushResponse { ServerSequenceNr = 6 }) };
            }
            return new HttpResponseMessage(HttpStatusCode.OK)
            { Content = JsonContent.Create(new PullResponse()) };
        });
        var engine = MakeEngine(temp, handler);

        await engine.SyncNowAsync();

        Assert.Equal(5, Assert.Single(pushed!).BasedOnServerSeq);
    }

    [Fact]
    public async Task PushAsync_ErfolgreicherPush_AktualisiertLokaleVersionsverfolgung()
    {
        using var temp = new TempEventQueue();
        var entityId = Guid.NewGuid().ToString();
        var evt = temp.Queue.Enqueue("this-device", DeviceType.Desktop, "Lesson", entityId, "Save", "x");
        var handler = new FakeHttpMessageHandler(req =>
        {
            if (req.RequestUri!.AbsolutePath == "/api/sync/push")
                return new HttpResponseMessage(HttpStatusCode.OK)
                {
                    Content = JsonContent.Create(new PushResponse
                    { ServerSequenceNr = 7, AssignedServerSeqs = new() { [evt.EventId] = 7 } }),
                };
            return new HttpResponseMessage(HttpStatusCode.OK)
            { Content = JsonContent.Create(new PullResponse()) };
        });
        var engine = MakeEngine(temp, handler);

        await engine.SyncNowAsync();

        Assert.Equal(7, temp.Queue.GetKnownServerSeq("Lesson", entityId));
    }

    /// Regression: ein wegen neuerem Server-Stand abgelehnter Push blieb bisher unsichtbar - das
    /// Ereignis verschwand einfach nicht aus der Queue, ohne dass der Nutzer je erfuhr, dass es
    /// bereits neuere Daten gab (siehe TODO 10.3.4). RemoteWon-Fall: der Server-Stand gewinnt, wird
    /// sofort angewendet, und die lokale Änderung wird verworfen.
    [Fact]
    public async Task PushAsync_AbgelehnterPushRemoteWon_WendetServerStandAnUndVerwirftLokal()
    {
        using var temp = new TempEventQueue();
        using var db = NewInMemoryContext();
        var entityId = Guid.NewGuid();
        // Companion verliert immer gegen Desktop (siehe ConflictResolver.DetermineWinner).
        var local = temp.Queue.Enqueue("companion-device", DeviceType.Companion,
            nameof(Student), entityId.ToString(), "Save", "veraltete-lokale-payload");
        var remoteStudent = new Student { Id = entityId, FirstName = "Anna", LastName = "Beispiel" };
        var remoteEvent = new SyncEvent
        {
            DeviceId = "other-device", DeviceType = DeviceType.Desktop,
            EntityType = nameof(Student), EntityId = entityId.ToString(),
            Operation = "Save", Payload = SyncCrypto.EncryptObject(remoteStudent, Key),
            SequenceNr = 99,
        };
        var handler = new FakeHttpMessageHandler(req =>
        {
            if (req.RequestUri!.AbsolutePath == "/api/sync/push")
                return new HttpResponseMessage(HttpStatusCode.OK)
                {
                    Content = JsonContent.Create(new PushResponse
                    { ServerSequenceNr = 99, ConflictingEventIds = [local.EventId] }),
                };
            if (req.RequestUri!.AbsolutePath == $"/api/sync/entity/{nameof(Student)}/{entityId}")
                return new HttpResponseMessage(HttpStatusCode.OK) { Content = JsonContent.Create(remoteEvent) };
            return new HttpResponseMessage(HttpStatusCode.OK)
            { Content = JsonContent.Create(new PullResponse()) };
        });
        var applier = new EventApplier(db, Key, versions: temp.Queue);
        var engine = MakeEngine(temp, handler, applier);

        await engine.SyncNowAsync();

        var conflict = Assert.Single(temp.Queue.GetUnreviewed());
        Assert.Equal("RemoteWon", conflict.Resolution);
        Assert.NotNull(db.Students.FindById(entityId));
        Assert.Equal(0, temp.Queue.PendingCount());
        Assert.Equal(99, temp.Queue.GetKnownServerSeq(nameof(Student), entityId.ToString()));
    }

    /// Gegenstück: LocalWon-Fall - die lokale Änderung bleibt (unbestätigt) in der Queue, damit der
    /// nächste Sync-Versuch sie mit dem soeben aktualisierten BasedOnServerSeq erneut versucht.
    [Fact]
    public async Task PushAsync_AbgelehnterPushLocalWon_BleibtUnbestaetigtInDerQueue()
    {
        using var temp = new TempEventQueue();
        using var db = NewInMemoryContext();
        var entityId = Guid.NewGuid();
        // Desktop gewinnt immer gegen Companion (siehe ConflictResolver.DetermineWinner).
        var local = temp.Queue.Enqueue("this-device", DeviceType.Desktop,
            nameof(Student), entityId.ToString(), "Save", SyncCrypto.EncryptObject(
                new Student { Id = entityId, FirstName = "Lokal", LastName = "Beispiel" }, Key));
        var remoteEvent = new SyncEvent
        {
            DeviceId = "other-device", DeviceType = DeviceType.Companion,
            EntityType = nameof(Student), EntityId = entityId.ToString(),
            Operation = "Save", Payload = "irrelevant-verliert-ohnehin",
            SequenceNr = 42,
        };
        var handler = new FakeHttpMessageHandler(req =>
        {
            if (req.RequestUri!.AbsolutePath == "/api/sync/push")
                return new HttpResponseMessage(HttpStatusCode.OK)
                {
                    Content = JsonContent.Create(new PushResponse
                    { ServerSequenceNr = 42, ConflictingEventIds = [local.EventId] }),
                };
            if (req.RequestUri!.AbsolutePath == $"/api/sync/entity/{nameof(Student)}/{entityId}")
                return new HttpResponseMessage(HttpStatusCode.OK) { Content = JsonContent.Create(remoteEvent) };
            return new HttpResponseMessage(HttpStatusCode.OK)
            { Content = JsonContent.Create(new PullResponse()) };
        });
        var applier = new EventApplier(db, Key, versions: temp.Queue);
        var engine = MakeEngine(temp, handler, applier);

        await engine.SyncNowAsync();

        var conflict = Assert.Single(temp.Queue.GetUnreviewed());
        Assert.Equal("LocalWon", conflict.Resolution);
        Assert.Equal(1, temp.Queue.PendingCount());
        Assert.Equal(42, temp.Queue.GetKnownServerSeq(nameof(Student), entityId.ToString()));
    }

    private static SyncEngine MakeEngine(TempEventQueue temp, FakeHttpMessageHandler handler,
        EventApplier? applier = null)
    {
        var db = NewInMemoryContext();
        var http = new HttpClient(handler) { BaseAddress = new Uri("https://example.invalid") };
        return new SyncEngine(temp.Queue, new ConflictResolver(temp.Queue),
            applier ?? new EventApplier(db, Key), new AttachmentSyncer(db, http, Key), http,
            new SyncConfig { DeviceId = "this-device" });
    }

    private sealed class TempEventQueue : IDisposable
    {
        private readonly string _directory = Path.Combine(
            Path.GetTempPath(), $"lehrerapp-sync-tests-engine-{Guid.NewGuid():N}");
        public EventQueue Queue { get; }

        public TempEventQueue()
        {
            Directory.CreateDirectory(_directory);
            Queue = new EventQueue(Path.Combine(_directory, "queue.db"));
        }

        public void Dispose()
        {
            Queue.Dispose();
            if (Directory.Exists(_directory)) Directory.Delete(_directory, recursive: true);
        }
    }
}