/// <summary>
/// Function to open a chunk for reading.
/// </summary>
/// <param name="chunkId">The ID of the chunk to open.</param>
/// <returns>A <see cref="GorgonBinaryReader" /> that will allow reading within the chunk.</returns>
/// <remarks>
/// <para>
/// Use this to read data from a chunk within the file. If the <paramref name="chunkId"/> is not found, then this method will throw an exception. To mitigate this, check for the existence of a chunk in
/// the <see cref="GorgonChunkFile{T}.Chunks"/> collection.
/// </para>
/// <para>
/// This method will provide minimal validation for the chunk in that it will only check the <paramref name="chunkId"/> to see if it matches what's in the file, beyond that, the user is responsible for
/// validating the data that lives within the chunk.
/// </para>
/// </remarks>
/// <exception cref="IOException">Thrown if the chunk was opened without calling <see cref="GorgonChunkFile{T}.Open"/> first.</exception>
/// <exception cref="GorgonException">Thrown when the <paramref name="chunkId" /> does not match the chunk in the file.</exception>
/// <exception cref="KeyNotFoundException">Thrown when the <paramref name="chunkId" /> was not found in the chunk table.</exception>
public override GorgonBinaryReader OpenChunk(ulong chunkId)
{
if (!IsOpen)
{
throw new IOException(Resources.GOR_ERR_CHUNK_FILE_NOT_OPEN);
}
ValidateChunkID(chunkId);
GorgonChunk chunk = Chunks[chunkId];
if (chunk.Equals(GorgonChunk.EmptyChunk))
{
throw new KeyNotFoundException(string.Format(Resources.GOR_ERR_CHUNK_NOT_FOUND, chunkId.FormatHex()));
}
if (_activeChunk.ID != 0)
{
if (_activeChunk.ID == chunkId)
{
return(_activeReader);
}
CloseChunk();
}
_activeChunk = chunk;
GorgonBinaryReader reader = null;
// Validate the chunk ID at the offset.
try
{
reader = new GorgonBinaryReader(Stream, true);
Stream.Position = ((long)_activeChunk.FileOffset + _headerEnd) - sizeof(long);
ulong fileChunkId = reader.ReadUInt64();
if (fileChunkId != _activeChunk.ID)
{
throw new GorgonException(GorgonResult.CannotRead,
string.Format(Resources.GOR_ERR_CHUNK_FILE_CHUNK_MISMATCH,
_activeChunk.FileOffset.FormatHex(),
_activeChunk.ID.FormatHex()));
}
}
finally
{
reader?.Dispose();
}
_activeReader = new GorgonBinaryReader(new GorgonStreamWrapper(Stream, 0, _activeChunk.Size), true);
return(_activeReader);
}
