function h = nc_change_history( ncf, his_text, postpend )
% nc_change_history - Add text to nc file history field
% h = nc_change_history( ncf, his_text, postpend )
% 
% Also adds date/time string to beginning of his_text
%
% Input:
%   ncf - name of target netCDF file
%   his_text - character string of text to be inserted
%   postpend (optional): 0 = prepend the text (default)
%                      : 1 = postpend the text
%
% Returned:
%   h - new character string with history
%

% csherwood@usgs.gov
% $Rev$
% $LastChangedDate$
% 
% This program intended for use in adjusting metadata terms in 
% netCDF files from the USGS CMGP Oceanographic time-series data 
% archive.
%
% Program written in Matlab (R2009a)
% Program ran on Windows XP PC.
%
% "Although this program has been used by the USGS, no warranty, 
% expressed or implied, is made by the USGS or the United States 
% Government as to the accuracy and functioning of the program 
% and related program material nor shall the fact of distribution 
% constitute any such warranty, and no responsibility is assumed 
% by the USGS in connection therewith."

if(nargin<3),postpend=0;,end

nc = netcdf(ncf, 'write');
if isempty(nc)
   disp([' ## Unable to open: ',ncf])
   return
end
nowstr = datestr(now);

% add info to the history
hist = nc.history(:);
if(postpend),
   cmnt = sprintf(': %s %s',nowstr,his_text);
   nc.history = ncchar([hist cmnt]);
else
   cmnt = sprintf('%s %s :',nowstr,his_text);
   nc.history = ncchar([cmnt hist]);
end
h = char(nc.history(:));
close(nc)
return