using LiteDB;
using LehrerApp.Sync.Models;

namespace LehrerApp.Sync;

/// <summary>
/// Lokale Event-Queue in LiteDB. Puffert Events bis sie
/// erfolgreich zum Server gepusht wurden.
/// </summary>
public class EventQueue : IDisposable
{
    private readonly LiteDatabase _db;
    private readonly ILiteCollection<SyncEvent> _queue;
    private readonly ILiteCollection<SyncMeta> _meta;
    private readonly ILiteCollection<ConflictEntry> _conflicts;
    private long _currentSeq;

    public EventQueue(string path)
    {
        _db       = new LiteDatabase(path);
        _queue    = _db.GetCollection<SyncEvent>("queue");
        _meta     = _db.GetCollection<SyncMeta>("meta");
        _conflicts = _db.GetCollection<ConflictEntry>("conflicts");
        _queue.EnsureIndex(x => x.SequenceNr);
        _currentSeq = _meta.FindById("seq")?.Value ?? 0;
    }

    public SyncEvent Enqueue(string deviceId, DeviceType deviceType,
        string entityType, string entityId, string operation, string payload)
    {
        var evt = new SyncEvent
        {
            DeviceId   = deviceId,
            DeviceType = deviceType,
            Timestamp  = DateTime.UtcNow,
            SequenceNr = ++_currentSeq,
            EntityType = entityType,
            EntityId   = entityId,
            Operation  = operation,
            Payload    = payload,
        };
        _queue.Insert(evt);
        _meta.Upsert(new SyncMeta { Id = "seq", Value = _currentSeq });
        return evt;
    }

    public List<SyncEvent> GetPending(int max = 200) =>
        _queue.Find(Query.All(nameof(SyncEvent.SequenceNr))).Take(max).ToList();
    public int PendingCount() => _queue.Count();
    public void Acknowledge(IEnumerable<Guid> ids) { foreach (var id in ids) _queue.Delete(id); }
    public long GetLastServerSeq() => _meta.FindById("serverSeq")?.Value ?? 0;
    public void SetLastServerSeq(long nr) => _meta.Upsert(new SyncMeta { Id = "serverSeq", Value = nr });
    public DateTime? GetLastSyncAt() => _meta.FindById("lastSync")?.Timestamp;
    public void SetLastSyncAt(DateTime dt) =>
        _meta.Upsert(new SyncMeta { Id = "lastSync", Value = 0, Timestamp = dt });
    public void AddConflict(ConflictEntry c) => _conflicts.Insert(c);
    public List<ConflictEntry> GetUnreviewed() => _conflicts.Find(c => !c.Reviewed).ToList();
    public int ConflictCount() => _conflicts.Count(c => !c.Reviewed);
    public void Dispose() => _db.Dispose();
}

public class ConflictEntry
{
    public Guid Id { get; init; } = Guid.NewGuid();
    public DateTime DetectedAt { get; init; } = DateTime.UtcNow;
    public SyncEvent LocalEvent { get; init; } = null!;
    public SyncEvent RemoteEvent { get; init; } = null!;
    public string Resolution { get; init; } = "";
    public bool Reviewed { get; set; }
}

internal class SyncMeta
{
    public string Id { get; set; } = "";
    public long Value { get; set; }
    public DateTime? Timestamp { get; set; }
}