function [hdr] = ft_fetch_header(data)

% FT_FETCH_HEADER mimics the behavior of FT_READ_HEADER, but for a FieldTrip

% raw data structure instead of a file on disk.

%

% Use as

% hdr = ft_fetch_header(data)

%

% See also FT_READ_HEADER, FT_FETCH_DATA, FT_FETCH_EVENT

% Copyright (C) 2008, Esther Meeuwissen

%

% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org

% for the documentation and details.

%

% FieldTrip is free software: you can redistribute it and/or modify

% it under the terms of the GNU General Public License as published by

% the Free Software Foundation, either version 3 of the License, or

% (at your option) any later version.

%

% FieldTrip is distributed in the hope that it will be useful,

% but WITHOUT ANY WARRANTY; without even the implied warranty of

% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

% GNU General Public License for more details.

%

% You should have received a copy of the GNU General Public License

% along with FieldTrip. If not, see <http://www.gnu.org/licenses/>.

%

% $Id$

% check whether input is data

data = ft_checkdata(data, 'datatype', 'raw', 'hassampleinfo', 'yes');

trlnum = length(data.trial);

trllen = zeros(trlnum,1);

for trllop=1:trlnum

trllen(trllop) = size(data.trial{trllop},2);

end

if isfield(data, 'sampleinfo')

% construct the trial definition according to thew samples from the original data file

trl = data.sampleinfo;

trl(:,3) = 0;

else

% construct the trial definition as if it is a continuous piece of data

trl = [1 sum(trllen) 0];

end

% fill in some header details

hdr.Fs = data.fsample;

hdr.label = data.label(:);

hdr.nChans = numel(data.label);

% fill in the channel type

if isfield(data, 'chantype')

hdr.chantype = data.chantype(:);

elseif isfield(data, 'hdr') && isfield(data.hdr, 'chantype')

% keep them ordered according to the FieldTrip data structure, which might differ from the original header

[datindx, hdrindx] = match_str(data.label, data.hdr.label);

hdr.chantype = repmat({'unknown'}, hdr.nChans, 1);

hdr.chantype(datindx) = data.hdr.chantype(hdrindx);

else

% try to determine them on the basis of heuristics

hdr.chantype = ft_chantype(data);

end

% fill in the channel unit

if isfield(data, 'chanunit')

hdr.chanunit = data.chanunit(:);

elseif isfield(data, 'hdr') && isfield(data.hdr, 'chanunit')

% keep them ordered according to the FieldTrip data structure, which might differ from the original header

[datindx, hdrindx] = match_str(data.label, data.hdr.label);

hdr.chanunit = repmat({'unknown'}, hdr.nChans, 1);

hdr.chanunit(datindx) = data.hdr.chanunit(hdrindx);

else

% try to determine them on the basis of heuristics

hdr.chanunit = ft_chanunit(data);

end

% retain the original header details

if isfield(data, 'hdr') && isfield(data.hdr, 'orig')

hdr.orig = data.hdr.orig;

end

% determine hdr.nSamples, hdr.nSamplesPre, hdr.nTrials

% always pretend that it is continuous data

hdr.nSamples = max(trl(:,2));

hdr.nSamplesPre = 0;

hdr.nTrials = 1;

% retrieve the gradiometer and/or electrode and/or optode information

if isfield(data, 'grad')

hdr.grad = data.grad;

elseif isfield(data, 'hdr') && isfield(data.hdr, 'grad')

hdr.grad = data.hdr.grad;

end

if isfield(data, 'elec')

hdr.elec = data.elec;

elseif isfield(data, 'hdr') && isfield(data.hdr, 'elec')

hdr.elec = data.hdr.elec;

end

if isfield(data, 'opto')

hdr.opto = data.opto;

elseif isfield(data, 'hdr') && isfield(data.hdr, 'opto')

hdr.opto = data.hdr.opto;

end

% retrieve the synchronization information

if isfield(data, 'hdr') && isfield(data.hdr, 'FirstTimeStamp')

hdr.FirstTimeStamp = data.hdr.FirstTimeStamp;

end

if isfield(data, 'hdr') && isfield(data.hdr, 'TimeStampPerSample')

hdr.TimeStampPerSample = data.hdr.TimeStampPerSample;

end