//TODO: Figure out how to do readahead detection better - tracking the last seen sequence number
// is too slow
public bool Accept(byte data, ref int sequenceNumber, out TerminalLocation <T> terminal)
{
//If we're getting data from closer to the end of the stream instead
// of the next byte we're expecting, things that start before the new
// sequence number can be discarded (as they won't have read what they
// think they've read
if (sequenceNumber > _expectedSequenceNumber)
{
for (int i = 0; i < _activePaths.Count; ++i)
{
if (_activePaths[i].StartSequenceNumber < sequenceNumber)
{
_activePaths.RemoveAt(i--);
}
}
}
//The sequence number could also have lessened (an early terminal in
// a path has finally been deemed OK to return, the buffer position
// returns to the position after the matched token). If the buffer
// position advances into data where a match has already been read
// we need to remove those paths. For paths that start after the
// new sequence number, they can simply wait to be processed again
// until the sequence number catches up to the expected sequence
// number
else if (sequenceNumber < _expectedSequenceNumber)
{
if (!_waitForSequenceNumberCatchUp || sequenceNumber < _lastSeenSequenceNumber)
{
//Remove entries that have been impacted by a readahead
if (_lastReturnedTerminalEndSequenceNumber != sequenceNumber)
{
for (int i = 0; i < _activePaths.Count; ++i)
{
if (_activePaths[i].StartSequenceNumber < sequenceNumber)
{
_activePaths.RemoveAt(i--);
}
}
}
_waitForSequenceNumberCatchUp = true;
}
//We may be walking through an overlapped match
// here, check to see if we've made it to the
// end of an already completed path
_lastSeenSequenceNumber = sequenceNumber;
return(TryGetNext(false, ref sequenceNumber, out terminal));
}
_lastSeenSequenceNumber = sequenceNumber;
//If we've made it here (we didn't end up quitting early due to
// sequence numbers being too low), we can process matches.
// Bump up the next expected byte and make sure we don't think
// we're in waiting mode.
_expectedSequenceNumber = sequenceNumber + 1;
_waitForSequenceNumberCatchUp = false;
TrieNode <T> next;
//Process paths in progress
for (int i = 0; i < _activePaths.Count; ++i)
{
TriePath <T> path = _activePaths[i];
//If the current path can advance...
if (path.CurrentNode != null)
{
//If we matched another byte, advance the current node in
// the path and log the encountered terminal (if applicable)
if (path.CurrentNode.NextNodes.TryGetValue(data, out next))
{
path.CurrentNode = next;
if (next.IsTerminal)
{
path.EncounteredTerminals.AddRange(next.Terminals);
}
}
//If we didn't match and no terminals were found in the
// path, remove the path from tracking
else if (path.EncounteredTerminals.Count == 0)
{
_activePaths.RemoveAt(i--);
}
//If we didn't match, but did find terminals, indicate
// that the path can no longer advance
else
{
path.CurrentNode = null;
}
}
}
//Try to start a new path in the trie
if (_trie.NextNodes.TryGetValue(data, out next))
{
TriePath <T> path = new TriePath <T>(sequenceNumber)
{
CurrentNode = next
};
if (next.IsTerminal)
{
path.EncounteredTerminals.AddRange(next.Terminals);
}
_activePaths.Add(path);
}
return(TryGetNext(false, ref sequenceNumber, out terminal));
}
public bool TryGetNext(bool isFinal, ref int sequenceNumber, out TerminalLocation <T> terminalLocation)
{
//See if there's anything we can return yet using the following
// conditions
// 1) There must be at least one active path
// 2) The 0th path must have terminated
// 3) Any terminal being returned must be the leftmost available
// 4) The same terminal should never be returned more than once
if (_activePaths.Count > 0)
{
int endedAt = 0;
T best = null;
int bestPath = -1;
int minNonTerminatedPathStart = int.MaxValue;
int minTerminalStart = int.MaxValue;
for (int i = 0; i < _activePaths.Count; ++i)
{
TriePath <T> path = _activePaths[i];
if (path.CurrentNode != null && !isFinal)
{
if (path.StartSequenceNumber < minNonTerminatedPathStart)
{
minNonTerminatedPathStart = path.StartSequenceNumber;
if (best != null && minNonTerminatedPathStart < minTerminalStart)
{
best = null;
}
}
}
else
{
int ssn = path.StartSequenceNumber;
for (int j = 0; j < path.EncounteredTerminals.Count; ++j)
{
T terminal = path.EncounteredTerminals[j];
int start = terminal.Start + ssn;
if (start >= _lastReturnedTerminalEndSequenceNumber)
{
if (start < minNonTerminatedPathStart && (best == null || start < minTerminalStart || start == minTerminalStart && terminal.End > best.End))
{
bestPath = i;
best = terminal;
minTerminalStart = start;
endedAt = terminal.End + ssn;
}
}
else
{
path.EncounteredTerminals.RemoveAt(j--);
}
}
if (path.EncounteredTerminals.Count == 0)
{
_activePaths.RemoveAt(i--);
}
}
}
if (best != null)
{
terminalLocation = new TerminalLocation <T>(best, minTerminalStart);
_lastReturnedTerminalEndSequenceNumber = endedAt;
sequenceNumber = endedAt;
if (bestPath > -1 && bestPath < _activePaths.Count && _activePaths[bestPath].EncounteredTerminals.Contains(best))
{
_activePaths[bestPath].EncounteredTerminals.Remove(best);
if (_activePaths[bestPath].EncounteredTerminals.Count == 0)
{
_activePaths.RemoveAt(bestPath);
}
}
return(true);
}
}
terminalLocation = null;
return(false);
}