async Task <InputChunk> MakeChunk(IChunk chunk, Scan scan, long from, long to)
{
while (true)
{
if (chunk == null)
{
return(null);
}
InputChunk res = await Decompress(chunk);
if (res != null)
{
return(res);
}
switch (scan)
{
case Scan.None:
return(null);
case Scan.Forward:
chunk = await _reader.ReadFirstAsync(chunk.BeginPosition + 1, to);
break;
case Scan.Backward:
chunk = await _reader.ReadLastAsync(from, chunk.BeginPosition);
break;
default:
Debug.Fail("Invalid scan");
break;
}
}
}
public async Task <bool> MoveNextAsync(CancellationToken cancel)
{
if (_done)
{
return(false);
}
if (_chunk == null)
{
_chunk = await _reader._reader.ReadAtPartitionAsync(_from, _to, u => new DateTime(u.Long0) > _after);
}
else
{
_chunk.Dispose();
_chunk = await _reader._reader.ReadFirstAsync(_next, _to);
}
if (_chunk == null)
{
_done = true;
return(false);
}
else
{
Current = new TimeSeriesChunk(_chunk, _reader.Decoder);
_next = _chunk.EndPosition;
return(true);
}
}
public void Reset()
{
_chunk?.Dispose();
_chunk = null;
_next = 0;
_done = false;
}
public TimeSeriesChunk(InputChunk chunk, ITimeSeriesDecoder <T> decoder)
{
BeginPosition = chunk.BeginPosition;
EndPosition = chunk.EndPosition;
_data = Decode();
IEnumerable <T> Decode()
{
decoder.DecodePrimary(chunk, new DateTime(chunk.UserData.Long0, DateTimeKind.Utc), out T val);
yield return(val);
while (decoder.DecodeSecondary(chunk, out val))
{
yield return(val);
}
}
}
static async Task <InputChunk> Decompress(IChunk chunk)
{
var content = new byte[chunk.ContentLength];
if (!await chunk.ReadContentAsync(content, 0))
{
return(null);
}
var res = new InputChunk(chunk.BeginPosition, chunk.EndPosition, chunk.UserData);
try {
Compression.DecompressTo(content, 0, content.Length, res);
} catch {
res.Dispose();
// This translation of decompression errors into missing chunks is the only reason
// why ReadAtPartitionAsync is implemented in BufferedReader rather than ChunkReader.
return(null);
}
return(res);
}