using LehrerApp.Sync.Models;

namespace LehrerApp.Sync;

/// <summary>
/// Desktop gewinnt gegen Companion.
/// Bei Gleichstand: späterer Timestamp gewinnt.
/// </summary>
public class ConflictResolver(EventQueue queue)
{
    public ConflictEntry? TryResolve(SyncEvent remote, string localDeviceId)
    {
        var local = queue.GetPending()
            .FirstOrDefault(e => e.EntityType == remote.EntityType
                              && e.EntityId   == remote.EntityId
                              && e.DeviceId   != remote.DeviceId);
        if (local is null) return null;

        var winner = (local.DeviceType, remote.DeviceType) switch
        {
            (DeviceType.Desktop,   DeviceType.Companion) => local,
            (DeviceType.Companion, DeviceType.Desktop)   => remote,
            _ => local.Timestamp >= remote.Timestamp ? local : remote,
        };

        if (winner == remote) queue.Acknowledge([local.EventId]);

        return new ConflictEntry
        {
            LocalEvent  = local,
            RemoteEvent = remote,
            Resolution  = winner == local ? "LocalWon" : "RemoteWon",
        };
    }
}