/// <summary>
/// Force the specified direction
/// </summary>
private void SetDirection(EnumerationDirection direction)
{
Check.Require(IsReadingSequential, StorageResources.CannotChangeReadingDirectionWhenNonSequential);
bool hadData = this.HasItem;
_direction = direction;
_timeComparison = TimeComparer.GetComparer(direction);
if (!Backwards)
{
_getFirstItemToReadFromFileName = (f) => f.FirstItemTimestamp;
_getLastItemToReadFromFileName = (f) => f.LastItemTimestamp;
}
else
{
_getFirstItemToReadFromFileName = (f) => f.LastItemTimestamp;
_getLastItemToReadFromFileName = (f) => f.FirstItemTimestamp;
}
if (IsDataLoaded && _listReader.Direction != direction)
{
_listReader = _listReader.Reverse();
Check.Ensure(_listReader.Direction == Direction);
}
int moveCount = 0;
if (IsDataLoaded)
{
// in sequential mode and when data is loaded iterator points to the data file to load next, so need to move by 2
// (skipping currently loaded file)
moveCount = 2;
}
else
{
// data is not loaded; 2 cases: 1) seek found file with data beyond seek time and 2) seek time is contained in the file
if (!NextFileFound || IsNextFileToBeReadInFull)
{
// case 1
moveCount = 1;
}
// case 2: next file remains valid because will have to read some data from it in the opposite direction
}
_fileIterator.Backwards = Backwards;
for (int n = 0; n < moveCount; ++n)
{
MoveIteratorToNextFile();
}
if (!hadData)
{
_position.SetEmpty(direction);
}
}
/// <summary>
/// Given first logical (according to direction) item timestamp in file and logical time comparison (again, according
/// to direction) determine whether the file is to be read in full when restoring this position
/// </summary>
/// <param name="firstItemTimestampInFile">
/// First logical item timestamp in the file (of either first or last item when going forward and backwards respectively)
/// </param>
/// <param name="comparison">
/// Time comparison implementation
/// </param>
/// <returns>
/// <see langword="true"/> if first item in the file represented by <paramref name="firstItemTimestampInFile"/> will have to be read
/// <see langword="false"/> otherwise, i.e. when at least 1 item will have to be skipped
/// </returns>
public bool IsFileToBeReadInFull(DateTime firstItemTimestampInFile, Util.IDirectedTimeComparison comparison)
{
int cmp = comparison.Compare(firstItemTimestampInFile, Time);
return cmp > 0 || (cmp == 0 && NumberOfItemsWithTheTimestampRead == 0);
}
