using LehrerApp.Core.Models;
using LehrerApp.Data;
using LehrerApp.Sync.Crypto;
using LehrerApp.Sync.Models;
using Xunit;

namespace LehrerApp.Sync.Tests;

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

    [Fact]
    public async Task ApplyAsync_Save_SchreibtEntitaetDirektInDieCollection()
    {
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);
        var student = new Student { FirstName = "Anna", LastName = "Beispiel" };

        await applier.ApplyAsync(MakeEvent(nameof(Student), student.Id.ToString(), "Save", student));

        var saved = db.Students.FindById(student.Id);
        Assert.NotNull(saved);
        Assert.Equal("Anna", saved!.FirstName);
    }

    [Fact]
    public async Task ApplyAsync_Delete_EntferntDenDatensatz()
    {
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);
        var student = new Student { FirstName = "Anna", LastName = "Beispiel" };
        db.Students.Insert(student);

        await applier.ApplyAsync(MakeEvent(nameof(Student), student.Id.ToString(), "Delete", null));

        Assert.Null(db.Students.FindById(student.Id));
    }

    [Fact]
    public async Task ApplyAsync_UnbekannterEntityType_TutNichtsUndWirftNicht()
    {
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);

        var exception = await Record.ExceptionAsync(() =>
            applier.ApplyAsync(MakeEvent("UnbekannterTyp", Guid.NewGuid().ToString(), "Save", new { Foo = "Bar" })));

        Assert.Null(exception);
    }

    [Fact]
    public async Task ApplyAsync_GroupDelete_FuehrtDieselbeKaskadeAusWieDasRepository()
    {
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);
        var groupId = Guid.NewGuid();
        db.Groups.Insert(new LearningGroup { Id = groupId, Name = "8a", SchoolYear = "2025/26" });
        var gradeId = Guid.NewGuid();
        db.Grades.Insert(new Grade { Id = gradeId, GroupId = groupId, StudentId = Guid.NewGuid() });

        await applier.ApplyAsync(MakeEvent(nameof(LearningGroup), groupId.ToString(), "Delete", null));

        Assert.Null(db.Groups.FindById(groupId));
        Assert.Null(db.Grades.FindById(gradeId));
    }

    [Fact]
    public async Task ApplyAsync_VerletztHartenUniqueIndex_WirdUebersprungenOhneAusnahme()
    {
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);
        var studentId = Guid.NewGuid();
        var groupId = Guid.NewGuid();
        db.Memberships.Insert(new GroupMembership { StudentId = studentId, GroupId = groupId });
        // Zweite Mitgliedschaft für dasselbe Schüler/Gruppe-Paar verletzt den ux_student_group-Index.
        var duplicate = new GroupMembership { Id = Guid.NewGuid(), StudentId = studentId, GroupId = groupId };

        var exception = await Record.ExceptionAsync(() =>
            applier.ApplyAsync(MakeEvent(nameof(GroupMembership), duplicate.Id.ToString(), "Save", duplicate)));

        Assert.Null(exception);
        Assert.Single(db.Memberships.FindAll());
    }

    // ── Loop-Prevention: der wichtigste Test in dieser Datei ────────────────────
    // Ein angewendetes Ereignis darf NIE selbst wieder ein ausgehendes Ereignis auslösen,
    // sonst entsteht ein Sync-Ping-Pong zwischen den Geräten (siehe EventApplier-Kommentar).

    [Fact]
    public async Task ApplyAsync_Save_LoestNIEMALSDenOnChangeHookAus()
    {
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);
        var onChangeCallCount = 0;
        db.OnChange = (_, _, _, _) => onChangeCallCount++;
        var student = new Student { FirstName = "Anna", LastName = "Beispiel" };

        await applier.ApplyAsync(MakeEvent(nameof(Student), student.Id.ToString(), "Save", student));

        Assert.Equal(0, onChangeCallCount);
    }

    [Fact]
    public async Task ApplyAsync_Delete_LoestNIEMALSDenOnChangeHookAus()
    {
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);
        var student = new Student { FirstName = "Anna", LastName = "Beispiel" };
        db.Students.Insert(student);
        var onChangeCallCount = 0;
        db.OnChange = (_, _, _, _) => onChangeCallCount++;

        await applier.ApplyAsync(MakeEvent(nameof(Student), student.Id.ToString(), "Delete", null));

        Assert.Equal(0, onChangeCallCount);
    }

    [Fact]
    public async Task ApplyAsync_GroupDeleteKaskade_LoestNIEMALSDenOnChangeHookAus()
    {
        using var db = NewInMemoryContext();
        var applier = new EventApplier(db, Key);
        var groupId = Guid.NewGuid();
        db.Groups.Insert(new LearningGroup { Id = groupId, Name = "8a", SchoolYear = "2025/26" });
        db.Grades.Insert(new Grade { GroupId = groupId, StudentId = Guid.NewGuid() });
        db.Exams.Insert(new Exam { GroupId = groupId });
        var onChangeCallCount = 0;
        db.OnChange = (_, _, _, _) => onChangeCallCount++;

        await applier.ApplyAsync(MakeEvent(nameof(LearningGroup), groupId.ToString(), "Delete", null));

        Assert.Equal(0, onChangeCallCount);
    }

    // ── Fehlende Anhänge nachladen ───────────────────────────────────────────────

    [Fact]
    public async Task ApplyAsync_DocumentationMitFehlendemAnhang_LaedtIhnUeberHttpNach()
    {
        using var db = NewInMemoryContext();
        var storageId = Guid.NewGuid().ToString("N");
        var handler = new FakeHttpMessageHandler(req =>
        {
            Assert.Equal($"/api/sync/attachments/{storageId}", req.RequestUri!.AbsolutePath);
            var encrypted = SyncCrypto.Encrypt([9, 8, 7], Key);
            return new HttpResponseMessage(System.Net.HttpStatusCode.OK)
            { Content = new ByteArrayContent(encrypted) };
        });
        var http = new HttpClient(handler) { BaseAddress = new Uri("https://example.invalid") };
        var applier = new EventApplier(db, Key, http);
        var doc = new Documentation { StudentId = Guid.NewGuid(), Title = "Elternbrief" };
        doc.Attachments.Add(new DocumentAttachment { StorageId = storageId, FileName = "brief.pdf", SizeBytes = 3 });

        await applier.ApplyAsync(MakeEvent(nameof(Documentation), doc.Id.ToString(), "Save", doc));

        Assert.Single(handler.Requests);
        Assert.True(db.Attachments.Exists(storageId));
        using var read = db.Attachments.OpenRead(storageId);
        using var ms = new MemoryStream();
        await read.CopyToAsync(ms);
        Assert.Equal([9, 8, 7], ms.ToArray());
    }

    [Fact]
    public async Task ApplyAsync_DocumentationMitBereitsVorhandenemAnhang_LaedtNichtErneut()
    {
        using var db = NewInMemoryContext();
        var storageId = Guid.NewGuid().ToString("N");
        db.Attachments.Upload(storageId, "brief.pdf", new MemoryStream([1, 2, 3]));
        var handler = new FakeHttpMessageHandler(_ => new HttpResponseMessage(System.Net.HttpStatusCode.OK));
        var http = new HttpClient(handler) { BaseAddress = new Uri("https://example.invalid") };
        var applier = new EventApplier(db, Key, http);
        var doc = new Documentation { StudentId = Guid.NewGuid(), Title = "Elternbrief" };
        doc.Attachments.Add(new DocumentAttachment { StorageId = storageId, FileName = "brief.pdf", SizeBytes = 3 });

        await applier.ApplyAsync(MakeEvent(nameof(Documentation), doc.Id.ToString(), "Save", doc));

        Assert.Empty(handler.Requests);
    }

    private static SyncEvent MakeEvent(string entityType, string entityId, string operation, object? payload) => new()
    {
        DeviceId = "companion-1",
        DeviceType = DeviceType.Companion,
        EntityType = entityType,
        EntityId = entityId,
        Operation = operation,
        Payload = payload is null ? "" : SyncCrypto.EncryptObject(payload, Key),
        Timestamp = DateTime.UtcNow,
    };
}