/// <summary>
/// Reads the first header encountered with a valid date-time stamp.
/// </summary>
/// <param name="firstValidStamp">The date-time that was encountered.</param>
/// <returns>the number of records before the first valid date-time stamp was encountered.</returns>
/// <remarks>
/// When no valid header is found the method will return -1 and <paramref name="firstValidStamp"/> will be set to default(DateTime).
/// </remarks>
public int ReadNextValidStamp(out DateTime firstValidStamp)
{
// TODO: if the stream is not at a multiple of 8, scoot it back
if (_isClosed || _stream.Position >= _stream.Length)
{
_isClosed = true;
firstValidStamp = default(DateTime);
return(-1);
}
int recordCount = 0;
var headerBuffer = new byte[DaqDataFileInfo.RecordSize];
while (DaqDataFileInfo.RecordSize == _stream.Read(headerBuffer, 0, DaqDataFileInfo.RecordSize))
{
if (DaqDataFileInfo.HeaderCodeByte == headerBuffer[LastRecordIndex])
{
if (DaqDataFileInfo.TryConvert7ByteDateTime(headerBuffer, 0, out firstValidStamp))
{
return(recordCount);
}
}
else
{
recordCount++;
}
}
firstValidStamp = default(DateTime);
return(-1);
}
/// <summary>
/// Moves to the next record in the DAQ file.
/// </summary>
/// <returns>true when the move was successful.</returns>
public bool MoveNext()
{
if (_isClosed || _stream.Position >= _stream.Length)
{
_isClosed = true;
return(false);
}
var recordData = new byte[DaqDataFileInfo.RecordSize];
while (true)
{
if (_stream.Position >= _stream.Length ||
DaqDataFileInfo.RecordSize != _stream.Read(recordData, 0, DaqDataFileInfo.RecordSize))
{
_current = new PackedReading();
_isClosed = true;
return(false);
}
if (DaqDataFileInfo.HeaderCodeByte == recordData[DaqDataFileInfo.RecordSize - 1])
{
// a header record
if (DaqDataFileInfo.TryConvert7ByteDateTime(recordData, 0, out _currentBaseTime))
{
_timeBaseFromReadAhead = false;
_chunkRecordCounter = 0;
}
else
{
// invalid time stamp
if (!_timeBaseFromReadAhead)
{
// if we havnt already read ahead for a good stamp we
// need to read ahead to get the next valid time stamp
var positionRestore = _stream.Position;
var dataRecordsRead = ReadNextValidStamp(out _currentBaseTime);
if (dataRecordsRead < 0)
{
return(false); // failed to find any more time stamp records, quit
}
// skipped over some data records
if (0 != dataRecordsRead)
{
// need to adjust the stamp we got for those records
_currentBaseTime = _currentBaseTime.Subtract(
new TimeSpan(0, 0, dataRecordsRead)
);
// also need to put the stream back how found it
_stream.Seek(positionRestore, SeekOrigin.Begin);
}
// this is the start of a new "virtual" chunk
_chunkRecordCounter = 0;
// virtual because invalid headers immediately following this will be ignored
_timeBaseFromReadAhead = true;
}
else
{
; // just skip it, pretend it doesen't exist because we already read ahead
}
}
}
else
{
// a data record
var values = PackedReadingValues.FromDeviceBytes(recordData, 0);
if (!values.IsValid)
{
_chunkRecordCounter++;
continue;
}
_current = new PackedReading(
_currentBaseTime.Add(new TimeSpan(0, 0, _chunkRecordCounter)),
values
);
_chunkRecordCounter++;
return(true);
}
}
}