function oasis_get_xnat(ss, od, N, agargs)
% get_oasis(ss, od)
% get_oasis(ss, od, N)
% get_oasis(ss, od, N, agargs)
% Example:
%  ss = 'spreadsheet.csv'
%  od = '../output_directory/'
%  N = 30; % (gets all subjects if N left out or inf)
%  agargs = '-proc'; % optional ArcGet arguments, e.g. get processed only

arcget = 'ArcGet -host www.oasis-brains.org -u guest -p guest';
% NB: seems it must be in current dir to find java libs

if ~exist('od', 'var') || isempty(od)
    od = '../data/oasis/tmp'; % can include relative or full path
end
if ~exist('ss', 'var') || isempty(ss)
    ss = 'oasis_subset.csv';
end
if ~exist('N', 'var')
    N = inf;
end
if ~exist('agargs', 'var')
    agargs = '';
end

[H C] = oasis_read_csv(ss);

sessions = [];
for col = 1:length(H)
    if strcmpi(H{col}, 'MR Session')
        sessions = C{col};
        break;
    end
end
if isempty(sessions)
    error('oasis_get_xnat:spreadsheet', ...
        'failed to find session column in spreadsheet %s', ss)
end

N = min(N, numel(sessions));

for n = 1:N
    id2 = sessions{n};
    id1 = regexprep(id2, 'MR2$', 'MR1');
    if ~strcmpi(id1, id2) % must be reliability data, get both
        cmd = sprintf('%s %s -o %s -s %s -s %s', ...
            arcget, agargs, od, id1, id2);
    else % must be cross-sectional data, get just first
        cmd = sprintf('%s %s -o %s -s %s', arcget, agargs, od, id1);
    end
    display(cmd)
    [status stdout] = system(cmd);
    if status ~= 0
        warning('oasis_get_xnat:arcget', stdout)
    end
end