public long SeekTo(
long granulePos, int preRoll, GetPacketGranuleCountDelegate getPacketGranuleCount)
{
if (_reader == null)
{
throw new ObjectDisposedException(GetType().FullName);
}
int pageIndex = _reader.FindPage(granulePos);
int packetIndex;
if (granulePos == 0)
{
// for this, we can generically say the first packet on the first page having a non-zero granule
packetIndex = 0;
}
else
{
packetIndex = FindPacket(pageIndex, ref granulePos, getPacketGranuleCount);
packetIndex -= preRoll;
}
if (!NormalizePacketIndex(ref pageIndex, ref packetIndex))
{
throw new ArgumentOutOfRangeException(nameof(granulePos));
}
_lastPacket = null;
_pageIndex = pageIndex;
_packetIndex = packetIndex;
return(granulePos);
}
private int FindPacket(
int pageIndex, ref long granulePos, GetPacketGranuleCountDelegate getPacketGranuleCount)
{
// we will only look through the current page...
// if the granule isn't on the page, behavior is:
// - if before: return 0
// - if after: return packetCount - (isContinued ? 2 : 1)
// neither should happen because we're already looking at the correct page
if (!_reader.GetPage(
pageIndex, out long pageGranulePos, out bool isResync, out _, out bool isContinued,
out int packetCount, out int pageOverhead))
{
return(-1);
}
var gp = pageGranulePos;
var packetIndex = packetCount - (isContinued ? 2 : 1);
while (packetIndex > 0)
{
if (gp >= granulePos)
{
var packet = CreatePacket(
ref pageIndex, ref packetIndex, false, pageGranulePos, isResync, isContinued,
packetCount, pageOverhead);
if (packet == null)
{
break;
}
gp -= getPacketGranuleCount(packet, false);
}
if (gp < granulePos)
{
granulePos = gp;
return(packetIndex);
}
--packetIndex;
}
if (packetIndex == 0)
{
// we're likely in the right spot for the granulePos...
if (pageIndex > 0 &&
_reader.GetPage(pageIndex - 1, out var prevGranulePos, out _, out _, out _, out _, out _))
{
granulePos = prevGranulePos;
return(0);
}
}
return(-1);
}
