/// <summary>
/// Returns a new log buffer which acts as a view onto the original buffer.
/// If the original buffer already contains the desired column, then the original buffer is returned.
/// If it does not, then an additional temporary buffer of equal length is created which
/// holds data for the given <paramref name="columns"/> and the returned buffer combines both the
/// <paramref name="that" /> as well as the temporary buffer into one view.
/// </summary>
/// <remarks>
/// This method exists for those cases, where, in order to fulfill a certain <see cref="ILogSource.GetEntries(System.Collections.Generic.IReadOnlyList{LogLineIndex}, ILogBuffer, int, LogSourceQueryOptions)"/>
/// request, one has to make certain to retrieve a particular column from the source. Nothing needs to be done
/// if the caller is also interested in said column, however if the caller is not, then it becomes a one liner
/// to create a combined buffer which acts as a proxy for the original for every column but the desired one,
/// which is copied into an additional buffer.
///
/// If it were permissible to query the source log file countless times, then this method wouldn't need to exist,
/// however since we don't want to do exactly that, we'll have to do this procedure to improve performance, now
/// that log files are streamed into memory on-demand.
/// </remarks>
/// <param name="that"></param>
/// <param name="columns"></param>
/// <returns></returns>
public static ILogBuffer CreateViewWithAdditionalColumns(this ILogBuffer that, IReadOnlyList <IColumnDescriptor> columns)
{
if (columns.Count == 0)
{
return(that);
}
var missingColumns = columns.Except(that.Columns).ToList();
if (missingColumns.Count == 0)
{
return(that);
}
var temporaryBuffer = new LogBufferArray(that.Count, missingColumns);
var combinedView = new CombinedLogBufferView(new[] { that, temporaryBuffer });
return(combinedView);
}
public CombinedLogEntryView(CombinedLogBufferView buffer, int index)
{
_buffer = buffer;
_index = index;
}
