/// <summary>
/// Performs the grouping operation for specified items.
/// </summary>
/// <param name="items">The items.</param>
/// <param name="level">The level.</param>
/// <param name="parent">The parent.</param>
/// <returns></returns>
public virtual GroupCollection <T> Perform(IReadOnlyCollection <T> items, int level, Group <T> parent)
{
GroupDescriptorCollection groupDescriptors = this.index.CollectionView.GroupDescriptors;
if (level >= groupDescriptors.Count)
{
return(GroupCollection <T> .Empty);
}
IGroupFactory <T> groupFactory = this.index.CollectionView.GroupFactory;
GroupCollection <T> cache = GetCachedGroups(items, level);
if (!IsValid(level, groupDescriptors))
{
if (cache != null)
{
cache.Dispose();
}
return(this.index.CollectionView.GroupFactory.CreateCollection(GroupBuilder <T> .Empty));
}
IComparer <Group <T> > newComparer = Activator.CreateInstance(this.Comparer.GetType()) as IComparer <Group <T> >;
if (newComparer == null)
{
newComparer = this.Comparer;
}
if (newComparer is GroupComparer <T> )
{
((GroupComparer <T>)newComparer).Directions = this.GetComparerDirections(level);
}
AvlTree <Group <T> > groupList = new AvlTree <Group <T> >(newComparer);
AvlTree <Group <T> > list = new AvlTree <Group <T> >(new GroupComparer <T>(this.GetComparerDirections(level)));
foreach (T item in items)
{
object key = this.GroupPredicate(item, level);
Group <T> group, newGroup = new DataItemGroup <T>(key);
group = list.Find(newGroup); groupList.Find(newGroup);
if (group == null)
{
group = GroupBuilder <T> .GetCachedGroup(cache, newGroup);
if (group == null)
{
group = groupFactory.CreateGroup(key, parent);
DataItemGroup <T> dataGroup = group as DataItemGroup <T>;
dataGroup.GroupBuilder = this;
}
list.Add(group);// groupList.Add(group);
}
group.Items.Add(item);
}
for (int i = 0; i < list.Count; i++)
{
groupList.Add(list[i]);
}
if (cache != null)
{
cache.Dispose();
}
return(groupFactory.CreateCollection(groupList));
}