public IList <Change <TObject, TKey> > Calculate(IKeyValueCollection <TObject, TKey> currentItems,
IKeyValueCollection <TObject, TKey> previousItems,
IChangeSet <TObject, TKey> sourceUpdates)
{
if (currentItems.SortReason == SortReason.ComparerChanged || currentItems.SortReason == SortReason.InitialLoad)
{
//clear collection and rebuild
var removed = previousItems.Select((item, index) => new Change <TObject, TKey>(ChangeReason.Remove, item.Key, item.Value, index));
var newitems = currentItems.Select((item, index) => new Change <TObject, TKey>(ChangeReason.Add, item.Key, item.Value, index));
return(new List <Change <TObject, TKey> >(removed.Union(newitems)));
}
var previousList = previousItems.ToList();
var keyComparer = new KeyComparer <TObject, TKey>();
var removes = previousItems.Except(currentItems, keyComparer).ToList();
var adds = currentItems.Except(previousItems, keyComparer).ToList();
var inbothKeys = new HashSet <TKey>(previousItems.Intersect(currentItems, keyComparer).Select(x => x.Key));
var result = new List <Change <TObject, TKey> >();
foreach (var remove in removes)
{
int index = previousList.IndexOf(remove);
previousList.RemoveAt(index);
result.Add(new Change <TObject, TKey>(ChangeReason.Remove, remove.Key, remove.Value, index));
}
foreach (var add in adds)
{
//find new insert position
int index = previousList.BinarySearch(add, currentItems.Comparer);
int insertIndex = ~index;
previousList.Insert(insertIndex, add);
result.Add(new Change <TObject, TKey>(ChangeReason.Add, add.Key, add.Value, insertIndex));
}
//Adds and removes have been accounted for
//so check whether anything in the remaining change set have been moved ot updated
var remainingItems = sourceUpdates
.EmptyIfNull()
.Where(u => inbothKeys.Contains(u.Key) &&
(u.Reason == ChangeReason.Update ||
u.Reason == ChangeReason.Moved ||
u.Reason == ChangeReason.Refresh))
.ToList();
foreach (var change in remainingItems)
{
if (change.Reason == ChangeReason.Update)
{
var current = new KeyValuePair <TKey, TObject>(change.Key, change.Current);
var previous = new KeyValuePair <TKey, TObject>(change.Key, change.Previous.Value);
//remove from the actual index
var removeIndex = previousList.IndexOf(previous);
previousList.RemoveAt(removeIndex);
//insert into the desired index
int desiredIndex = previousList.BinarySearch(current, currentItems.Comparer);
int insertIndex = ~desiredIndex;
previousList.Insert(insertIndex, current);
result.Add(new Change <TObject, TKey>(ChangeReason.Update, current.Key, current.Value,
previous.Value, insertIndex, removeIndex));
}
else if (change.Reason == ChangeReason.Moved)
{
//TODO: We have the index already, would be more efficient to calculate new position from the original index
var current = new KeyValuePair <TKey, TObject>(change.Key, change.Current);
var previousindex = previousList.IndexOf(current);
int desiredIndex = currentItems.IndexOf(current);
if (previousindex == desiredIndex)
{
continue;
}
if (desiredIndex < 0)
{
throw new SortException("Cannot determine current index");
}
previousList.RemoveAt(previousindex);
previousList.Insert(desiredIndex, current);
result.Add(new Change <TObject, TKey>(current.Key, current.Value, desiredIndex, previousindex));
}
else
{
//TODO: re-evaluate to check whether item should be moved
result.Add(change);
}
}
//Alternative to evaluate is to check order
var evaluates = remainingItems.Where(c => c.Reason == ChangeReason.Refresh)
.OrderByDescending(x => new KeyValuePair <TKey, TObject>(x.Key, x.Current), currentItems.Comparer)
.ToList();
//calculate moves. Very expensive operation
//TODO: Try and make this better
foreach (var u in evaluates)
{
var current = new KeyValuePair <TKey, TObject>(u.Key, u.Current);
var old = previousList.IndexOf(current);
if (old == -1)
{
continue;
}
int newposition = GetInsertPositionLinear(previousList, current, currentItems.Comparer);
if (old < newposition)
{
newposition--;
}
if (old == newposition)
{
continue;
}
previousList.RemoveAt(old);
previousList.Insert(newposition, current);
result.Add(new Change <TObject, TKey>(u.Key, u.Current, newposition, old));
}
return(result);
}