LehrerApp/LehrerApp.Sync/SyncEngine.cs

using System.Net.Http.Json;
using LehrerApp.Core.Services;
using LehrerApp.Sync.Models;

namespace LehrerApp.Sync;

/// <summary>
/// Push/Pull Orchestrierung.
/// Automatisch alle N Minuten + manuell per SyncNowAsync().
/// </summary>
public class SyncEngine : IDisposable
{
    private readonly EventQueue _queue;
    private readonly ConflictResolver _resolver;
    private readonly EventApplier _applier;
    private readonly AttachmentSyncer _attachments;
    private readonly HttpClient _http;
    private readonly SyncConfig _config;
    private readonly AppLogger? _logger;
    private readonly Timer _timer;

    public SyncStatus Status { get; private set; } = new();
    public event Action<SyncStatus>? StatusChanged;

    public SyncEngine(EventQueue queue, ConflictResolver resolver, EventApplier applier,
        AttachmentSyncer attachments, HttpClient http, SyncConfig config, AppLogger? logger = null)
    {
        _queue       = queue;
        _resolver    = resolver;
        _applier     = applier;
        _attachments = attachments;
        _http        = http;
        _config      = config;
        _logger      = logger;
        _timer = new Timer(
            async _ => await SyncNowAsync(true), null,
            TimeSpan.FromMinutes(config.AutoSyncIntervalMinutes),
            TimeSpan.FromMinutes(config.AutoSyncIntervalMinutes));
        UpdateStatus();
    }

    public async Task<SyncResult> SyncNowAsync(bool isAutomatic = false)
    {
        if (Status.State == SyncState.Syncing)
            return new() { Skipped = true, Reason = "Sync bereits aktiv" };
        SetState(SyncState.Syncing);
        _logger?.Info($"Sync: Start ({(isAutomatic ? "automatisch" : "manuell")}), Gerät={_config.DeviceId}, " +
                      $"{_queue.PendingCount()} lokal ausstehend");
        try
        {
            var (pushed, pushConflicts) = await PushAsync();
            await _attachments.UploadPendingAsync(_queue);
            var (pulled, conflicts) = await PullAsync();
            _queue.SetLastSyncAt(DateTime.UtcNow);
            SetState(SyncState.Idle);
            _logger?.Info($"Sync: Fertig - {pushed} gepusht ({pushConflicts} Push-Konflikte), " +
                          $"{pulled} gepullt ({conflicts} Pull-Konflikte)");
            return new() { Success = true, EventsPushed = pushed, EventsPulled = pulled, Conflicts = conflicts };
        }
        catch (HttpRequestException ex)
        {
            // Sammelt sowohl echte Netzwerkfehler als auch nicht-erfolgreiche HTTP-Antworten
            // (EnsureSuccessStatusCode() in Push/PullAsync) unter demselben "Offline"-Status -
            // ohne Log wäre ein z.B. 401/500 vom Server nicht von "kein Internet" unterscheidbar.
            _logger?.Error("Sync fehlgeschlagen (HTTP)", ex);
            SetState(SyncState.Offline);
            return new() { Reason = "Server nicht erreichbar" };
        }
        catch (Exception ex)
        {
            _logger?.Error("Sync fehlgeschlagen", ex);
            SetState(SyncState.Error, ex.Message);
            return new() { Reason = ex.Message };
        }
    }

    private async Task<(int Pushed, int Conflicts)> PushAsync()
    {
        var pending = _queue.GetPending();
        if (pending.Count == 0) return (0, 0);
        _logger?.Info($"Sync: Push - {pending.Count} Ereignis(se) ausstehend: " +
                      string.Join(", ", pending.Select(e => $"{e.EntityType}/{e.Operation}")));
        var resp = await _http.PostAsJsonAsync("/api/sync/push", pending);
        resp.EnsureSuccessStatusCode();
        var result = await resp.Content.ReadFromJsonAsync<PushResponse>();
        if (result is null) { _logger?.Warn("Sync: Push - leere Server-Antwort."); return (0, 0); }
        _queue.Acknowledge(pending
            .Where(e => !result.ConflictingEventIds.Contains(e.EventId))
            .Select(e => e.EventId));
        _queue.SetLastServerSeq(result.ServerSequenceNr);
        _logger?.Info($"Sync: Push - vom Server bestätigt bis ServerSequenceNr={result.ServerSequenceNr}, " +
                      $"{result.ConflictingEventIds.Count} vom Server abgelehnt (Konflikt).");
        return (pending.Count - result.ConflictingEventIds.Count,
                result.ConflictingEventIds.Count);
    }

    private async Task<(int Pulled, int Conflicts)> PullAsync()
    {
        var since = _queue.GetLastServerSeq();
        _logger?.Info($"Sync: Pull - frage Server nach Ereignissen seit ServerSequenceNr={since}.");
        var resp = await _http.GetFromJsonAsync<PullResponse>(
            $"/api/sync/pull?since={since}&deviceId={_config.DeviceId}");
        if (resp is null || resp.Events.Count == 0)
        {
            _logger?.Info("Sync: Pull - keine neuen Ereignisse vom Server.");
            return (0, 0);
        }
        _logger?.Info($"Sync: Pull - {resp.Events.Count} Ereignis(se) vom Server erhalten: " +
                      string.Join(", ", resp.Events.Select(e => $"{e.EntityType}/{e.Operation}")));
        var conflicts = 0;
        foreach (var evt in resp.Events)
        {
            var c = _resolver.TryResolve(evt, _config.DeviceId);
            if (c is null) { await _applier.ApplyAsync(evt); continue; }
            _queue.AddConflict(c);
            conflicts++;
            _logger?.Info($"Sync: Pull - Konflikt bei {evt.EntityType}/{evt.EntityId}, " +
                          $"Auflösung={c.Resolution}");
            if (c.Resolution == "RemoteWon") await _applier.ApplyAsync(evt);
        }
        _queue.SetLastServerSeq(resp.ServerSequenceNr);
        return (resp.Events.Count, conflicts);
    }

    private void SetState(SyncState state, string? error = null)
    {
        Status = new SyncStatus
        {
            State         = state,
            LastSyncAt    = _queue.GetLastSyncAt(),
            PendingEvents = _queue.PendingCount(),
            ConflictCount = _queue.ConflictCount(),
            ErrorMessage  = error,
        };
        StatusChanged?.Invoke(Status);
    }
    private void UpdateStatus() => SetState(Status.State);
    public void Dispose() { _timer.Dispose(); _queue.Dispose(); }
}

public class SyncConfig
{
    public string ServerUrl { get; set; } = "";
    public string DeviceId { get; set; } = "";
    public DeviceType DeviceType { get; set; } = DeviceType.Desktop;
    public int AutoSyncIntervalMinutes { get; set; } = 5;
}

public class SyncResult
{
    public bool Success { get; set; }
    public bool Skipped { get; set; }
    public string? Reason { get; set; }
    public int EventsPushed { get; set; }
    public int EventsPulled { get; set; }
    public int Conflicts { get; set; }
}