using LehrerApp.Sync.Models;
using Xunit;

namespace LehrerApp.Sync.Tests;

public sealed class ConflictResolverTests
{
    // ── Kein Konflikt ─────────────────────────────────────────────────────────

    [Fact]
    public void TryResolve_KeinLokalesEreignisFuerDieselbeEntitaet_GibtNullZurueck()
    {
        using var temp = new TempEventQueue();
        var remote = MakeEvent("companion-1", DeviceType.Companion, "Student", "s1");

        var result = new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.Null(result);
    }

    [Fact]
    public void TryResolve_LokalesEreignisFuerAndereEntitaet_ZaehltNichtAlsKonflikt()
    {
        using var temp = new TempEventQueue();
        temp.Queue.Enqueue("desktop-1", DeviceType.Desktop, "Student", "s1", "Update", "{}");
        var remote = MakeEvent("companion-1", DeviceType.Companion, "Student", "s2"); // andere EntityId

        var result = new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.Null(result);
    }

    [Fact]
    public void TryResolve_LokalesEreignisVomSelbenGeraet_ZaehltNichtAlsKonflikt()
    {
        using var temp = new TempEventQueue();
        temp.Queue.Enqueue("companion-1", DeviceType.Companion, "Student", "s1", "Update", "{}");
        var remote = MakeEvent("companion-1", DeviceType.Companion, "Student", "s1"); // gleiche DeviceId

        var result = new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.Null(result);
    }

    // ── Desktop gewinnt immer gegen Companion ────────────────────────────────

    [Fact]
    public void TryResolve_LokalDesktopGegenRemoteCompanion_DesktopGewinnt()
    {
        using var temp = new TempEventQueue();
        var local = temp.Queue.Enqueue("desktop-1", DeviceType.Desktop, "Student", "s1", "Update", "{}");
        var remote = MakeEvent("companion-1", DeviceType.Companion, "Student", "s1");

        var result = new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.NotNull(result);
        Assert.Equal("LocalWon", result.Resolution);
        Assert.Equal(local.EventId, result.LocalEvent.EventId);
    }

    [Fact]
    public void TryResolve_LokalDesktopGegenRemoteCompanion_LokalesEreignisBleibtInDerQueue()
    {
        // Desktop gewinnt -> der lokale (gewinnende) Event wird NICHT bestätigt/entfernt,
        // da er ja noch zum Server gepusht werden muss.
        using var temp = new TempEventQueue();
        temp.Queue.Enqueue("desktop-1", DeviceType.Desktop, "Student", "s1", "Update", "{}");
        var remote = MakeEvent("companion-1", DeviceType.Companion, "Student", "s1");

        new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.Equal(1, temp.Queue.PendingCount());
    }

    [Fact]
    public void TryResolve_LokalCompanionGegenRemoteDesktop_DesktopGewinntTrotzAeltererZeit()
    {
        using var temp = new TempEventQueue();
        var local = temp.Queue.Enqueue("companion-1", DeviceType.Companion, "Student", "s1", "Update", "{}");
        // Remote (Desktop) ist zeitlich "älter", gewinnt aber trotzdem, weil Desktop immer gewinnt.
        var remote = MakeEvent("desktop-1", DeviceType.Desktop, "Student", "s1", timestamp: local.Timestamp.AddMinutes(-5));

        var result = new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.Equal("RemoteWon", result!.Resolution);
    }

    [Fact]
    public void TryResolve_RemoteGewinnt_LokalesEreignisWirdAusDerQueueEntfernt()
    {
        using var temp = new TempEventQueue();
        temp.Queue.Enqueue("companion-1", DeviceType.Companion, "Student", "s1", "Update", "{}");
        var remote = MakeEvent("desktop-1", DeviceType.Desktop, "Student", "s1");

        new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.Equal(0, temp.Queue.PendingCount());
    }

    // ── Gleichstand (beide gleicher Gerätetyp): späterer Timestamp gewinnt ──────

    [Fact]
    public void TryResolve_BeideCompanion_SpaetererTimestampGewinnt()
    {
        using var temp = new TempEventQueue();
        var local = temp.Queue.Enqueue("companion-1", DeviceType.Companion, "Student", "s1", "Update", "{}");
        var remote = MakeEvent("companion-2", DeviceType.Companion, "Student", "s1",
            timestamp: local.Timestamp.AddMinutes(5));

        var result = new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.Equal("RemoteWon", result!.Resolution);
    }

    [Fact]
    public void TryResolve_BeideDesktopGleicherTimestamp_LokalesEreignisGewinntBeiGleichstand()
    {
        using var temp = new TempEventQueue();
        temp.Queue.Enqueue("desktop-1", DeviceType.Desktop, "Student", "s1", "Update", "{}");
        // Den tatsächlich aus der Queue geladenen (und damit BSON-gerundeten) Zeitstempel
        // verwenden, sonst wäre ein "exakter" Gleichstand durch Rundung beim Rundtrip nicht
        // exakt reproduzierbar.
        var reloadedTimestamp = temp.Queue.GetPending()[0].Timestamp.ToUniversalTime();
        var remote = MakeEvent("desktop-2", DeviceType.Desktop, "Student", "s1", timestamp: reloadedTimestamp);

        var result = new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        // ">= " in der Ungleichung: bei exaktem Gleichstand gewinnt das lokale Ereignis.
        Assert.Equal("LocalWon", result!.Resolution);
    }

    [Fact]
    public void TryResolve_BeideCompanionAelteresLokalesEreignis_RemoteGewinntAlsNeuer()
    {
        using var temp = new TempEventQueue();
        var local = temp.Queue.Enqueue("companion-1", DeviceType.Companion, "Student", "s1", "Update", "{}");
        var remote = MakeEvent("companion-2", DeviceType.Companion, "Student", "s1",
            timestamp: local.Timestamp.AddSeconds(-1)); // remote ist älter -> lokal (neuer) gewinnt

        var result = new ConflictResolver(temp.Queue).TryResolve(remote, "desktop-1");

        Assert.Equal("LocalWon", result!.Resolution);
    }

    // ── Hilfsfunktionen ───────────────────────────────────────────────────────

    private static SyncEvent MakeEvent(string deviceId, DeviceType deviceType, string entityType,
        string entityId, DateTime? timestamp = null) => new()
    {
        DeviceId = deviceId,
        DeviceType = deviceType,
        EntityType = entityType,
        EntityId = entityId,
        Operation = "Update",
        Payload = "{}",
        Timestamp = timestamp ?? DateTime.UtcNow,
    };

    private sealed class TempEventQueue : IDisposable
    {
        private readonly string _directory = Path.Combine(
            Path.GetTempPath(), $"lehrerapp-sync-tests-{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);
        }
    }
}