private IChangeSet <T> ProcessImpl(ChangeAwareList <T> target, IChangeSet <T> changes)
{
var refreshes = new List <T>(changes.Refreshes);
foreach (var change in changes)
{
switch (change.Reason)
{
case ListChangeReason.Add:
{
var current = change.Item.Current;
Insert(target, current);
break;
}
case ListChangeReason.AddRange:
{
var ordered = change.Range.OrderBy(t => t, _comparer).ToList();
if (target.Count == 0)
{
target.AddRange(ordered);
}
else
{
ordered.ForEach(item => Insert(target, item));
}
break;
}
case ListChangeReason.Remove:
{
var current = change.Item.Current;
Remove(target, current);
break;
}
case ListChangeReason.Refresh:
{
// add to refresh list so position can be calculated
refreshes.Add(change.Item.Current);
// add to current list so downstream operators can receive a refresh
// notification, so get the latest index and pass the index up the chain
var indexed = target.IndexOfOptional(change.Item.Current).ValueOrThrow(() => new SortException($"Cannot find index of {typeof(T).Name} -> {change.Item.Current}. Expected to be in the list"));
target.Refresh(indexed.Item, indexed.Index);
break;
}
case ListChangeReason.Replace:
{
var current = change.Item.Current;
// TODO: check whether an item should stay in the same position
// i.e. update and move
Remove(target, change.Item.Previous.Value);
Insert(target, current);
break;
}
case ListChangeReason.RemoveRange:
{
target.RemoveMany(change.Range);
break;
}
case ListChangeReason.Clear:
{
target.Clear();
break;
}
}
}
// Now deal with refreshes [can be expensive]
foreach (var item in refreshes)
{
var old = target.IndexOf(item);
if (old == -1)
{
continue;
}
int newPosition = GetInsertPositionLinear(target, item);
if (old < newPosition)
{
newPosition--;
}
if (old == newPosition)
{
continue;
}
target.Move(old, newPosition);
}
return(target.CaptureChanges());
}