/// <summary>
/// Trims an existing list to the specified length and returns the excess blocks as a new list.
/// </summary>
/// <param name="listHeadBlockIndex">The starting block of the list to trim.</param>
/// <param name="newListLength">The length in blocks that the list will be shortened to.</param>
/// <returns>The index of the head node of the removed blocks.</returns>
public int Trim(int listHeadBlockIndex, int newListLength)
{
int blocksRemaining = newListLength;
int nextEntry = BlockToEntryIndex(listHeadBlockIndex);
int listAIndex = -1;
int listBIndex = -1;
while (blocksRemaining > 0)
{
if (nextEntry == 0)
{
return(-1);
}
int currentEntryIndex = nextEntry;
ReadEntry(EntryIndexToBlock(currentEntryIndex), out int nextBlock, out int _, out int segmentLength);
nextEntry = BlockToEntryIndex(nextBlock);
if (segmentLength == blocksRemaining)
{
listAIndex = currentEntryIndex;
listBIndex = nextEntry;
}
else if (segmentLength > blocksRemaining)
{
Split(EntryIndexToBlock(currentEntryIndex), blocksRemaining);
listAIndex = currentEntryIndex;
listBIndex = currentEntryIndex + blocksRemaining;
}
blocksRemaining -= segmentLength;
}
if (listAIndex == -1 || listBIndex == -1)
{
return(-1);
}
AllocationTableEntry listANode = ReadEntry(listAIndex);
AllocationTableEntry listBNode = ReadEntry(listBIndex);
listANode.SetNext(0);
listBNode.MakeListStart();
WriteEntry(listAIndex, listANode);
WriteEntry(listBIndex, listBNode);
return(EntryIndexToBlock(listBIndex));
}
