LehrerApp/LehrerApp.Sync/SyncEngine.cs

using System.Net.Http.Json;
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 HttpClient _http;
    private readonly SyncConfig _config;
    private readonly Timer _timer;

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

    public SyncEngine(EventQueue queue, ConflictResolver resolver, EventApplier applier,
        HttpClient http, SyncConfig config)
    {
        _queue    = queue;
        _resolver = resolver;
        _applier  = applier;
        _http     = http;
        _config   = config;
        _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);
        try
        {
            var (pushed, _) = await PushAsync();
            var (pulled, conflicts) = await PullAsync();
            _queue.SetLastSyncAt(DateTime.UtcNow);
            SetState(SyncState.Idle);
            return new() { Success = true, EventsPushed = pushed, EventsPulled = pulled, Conflicts = conflicts };
        }
        catch (HttpRequestException) { SetState(SyncState.Offline); return new() { Reason = "Server nicht erreichbar" }; }
        catch (Exception 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);
        var resp = await _http.PostAsJsonAsync("/api/sync/push", pending);
        resp.EnsureSuccessStatusCode();
        var result = await resp.Content.ReadFromJsonAsync<PushResponse>();
        if (result is null) return (0, 0);
        _queue.Acknowledge(pending
            .Where(e => !result.ConflictingEventIds.Contains(e.EventId))
            .Select(e => e.EventId));
        _queue.SetLastServerSeq(result.ServerSequenceNr);
        return (pending.Count - result.ConflictingEventIds.Count,
                result.ConflictingEventIds.Count);
    }

    private async Task<(int Pulled, int Conflicts)> PullAsync()
    {
        var since = _queue.GetLastServerSeq();
        var resp = await _http.GetFromJsonAsync<PullResponse>(
            $"/api/sync/pull?since={since}&deviceId={_config.DeviceId}");
        if (resp is null || resp.Events.Count == 0) return (0, 0);
        var conflicts = 0;
        foreach (var evt in resp.Events)
        {
            var c = _resolver.TryResolve(evt, _config.DeviceId);
            if (c is null) { _applier.Apply(evt); continue; }
            _queue.AddConflict(c);
            conflicts++;
            if (c.Resolution == "RemoteWon") _applier.Apply(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; }
}