public static IListenerRegistration Subscribe <TModel, TViewModel, TKey>(IQuery query,
GroupedObservableCollection <TKey, TViewModel> viewModels,
Func <TModel, TViewModel> getViewModel,
Action?afterSnapshotProcessed = null)
where TModel : BaseModel
where TViewModel : CardViewModel <TModel>
{
viewModels.Clear();
return(query.AddSnapshotListener((snapshot, ex) =>
{
if (snapshot is null)
{
viewModels.Clear();
}
else if (viewModels.Elements.Any())
{
foreach (var change in snapshot.DocumentChanges)
{
var doc = change.Document;
if (change.Type == DocumentChangeType.Added)
{
viewModels.Add(getViewModel(doc.ToObject <TModel>() !));
}
else
{
var vm = viewModels.Elements.SingleOrDefault(x => x.UID == doc.Id);
if (vm is null)
{
return;
}
if (change.Type == DocumentChangeType.Modified)
{
var oldKey = viewModels.GroupKeySelector(vm);
var oldPriority = viewModels.PrioritySelector(vm);
vm.Update(change.Document.ToObject <TModel>() !);
var newKey = viewModels.GroupKeySelector(vm) !;
if (!newKey.Equals(oldKey))
{
viewModels.MoveGroup(vm, oldKey);
}
else if (oldPriority != viewModels.PrioritySelector(vm))
{
viewModels.UpdatePriority(vm);
}
}
else
{
viewModels.Remove(vm);
}
}
}
}
else if (!snapshot.IsEmpty)
{
snapshot.Documents.ForEach(x => viewModels.Add(getViewModel(x.ToObject <TModel>() !)));
}
afterSnapshotProcessed?.Invoke();
}));
}
