public MergeResult Merge(IEnumerable<SubscriptionItem> previousItems, IEnumerable<FeedItem> currentItems)
{
var result = new MergeResult();
var previousAuxList = new KeyedCollection<string, SubscriptionItem>(x => x.Id, previousItems);
var currentAuxList = new KeyedCollection<string, FeedItem>(x => x.Id, currentItems);
var previousIds = previousAuxList.Select(x => x.Id).ToArray();
foreach (var id in previousIds)
{
if (!currentAuxList.Contains(id))
ChooseRemovedItem(id, previousAuxList, result);
else
ChooseMergeItem(id, previousAuxList, currentAuxList, result);
}
var newIds = currentAuxList.Select(x => x.Id).ToArray();
foreach (var id in newIds)
ChooseNewItem(id, currentAuxList, result);
return result;
}