function [header2]  = readcortex_header(filename)
% READCORTEX_HEADER reads a Cortex data file and returns the header (if
% present) written by the write_header() function in the timing file
%
% NOTE: Only checks the first trial for header information - does not check
% any other trials!
%
% [header] = READCORTEX_HEADER(filename)

% Matthew A. Smith
% Revised: 20050720

MAXNUMTRIALS = 1000;
fid = fopen(filename, 'r','ieee-le');
if (fid == -1)
    error(['Cannot open file: ',filename]);
end
time_arr  = zeros(1, MAXNUMTRIALS);	% array of time_code arrays
event_arr = zeros(1, MAXNUMTRIALS);	% array of event_code arrays
header2 = [];
hd=zeros(1,13);					% a single header (read every trial)
flength = fread(fid, 1, 'unsigned short');
if (isempty(flength)~=1)
    hd(1,1:8)= (fread(fid, 8, 'unsigned short'))'; 
    hd(1,9:10) = (fread(fid, 2, 'unsigned char'))'; 
    hd(1,11:13)= (fread(fid, 3, 'unsigned short'))';
    hd(1,5)=hd(1,5)/4;	% reduce the size of the time_code array 
    hd(1,6)=hd(1,6)/2;	% idem for event_code array
    if (sum(floor(hd) - hd) ~= 0)
        error('READCORTEX: Header data contains non-integers, endian needs to be changed');
    end
    % read the time codes and event_codes for this trial
    time_arr(1:(hd(1,5)),1)   = (fread (fid,(hd(1,5)) , 'unsigned long'));   
    event_arr(1:(hd(1,6)),1) = (fread (fid,(hd(1,6)), 'unsigned short'));
end

fclose(fid);

%%%%% decode the special write_header() info %%%%%
first_trial = event_arr(:,1);
i = find (first_trial < 256);
if (~isempty(i) && (first_trial(1) == 65535))
    % If the first code sent is 65535, that's a marker
    % to indicate there is write_header() data
    t = first_trial(1:min(i)-1);
    for I=1:length(t)
        t2(2*I) = floor(t(I)/256);
        t2(2*I-1) = mod(t(I),256);
    end
    % add a trailing 255 if necessary to help with parsing the header
    if (t2(length(t2)) ~= 255)
        t2(length(t2)+1) = 255;
    end
    % 255 is used to space out the data in the header
    j = find(t2 == 255);
    % if the header starts with 3 255's, cut it down to 2.
    if (sum(t2(1:3)) == 765)
        j(1) = [];
    end
    % Get the required header data
    header2.data_file = char(t2(j(2)+1:j(3)-1));
    header2.cnd_file = char(t2(j(3)+1:j(4)-1));
    header2.ext_file = char(t2(j(4)+1:j(5)-1));
    header2.item_file = char(t2(j(5)+1:j(6)-1));
    header2.css_file = char(t2(j(6)+1:j(7)-1));
    header2.xdim = char(t2(j(7)+1:j(8)-1));
    header2.ydim = char(t2(j(8)+1:j(9)-1));
    header2.fps = char(t2(j(9)+1:j(10)-1));
    header2.hpix = char(t2(j(10)+1:j(11)-1));
    header2.vpix = char(t2(j(11)+1:j(12)-1));
    header2.bpp = char(t2(j(12)+1:j(13)-1));
    % Get the extern header data (if it's present)
    num_externs = ceil((length(j) - 13 - 1)/2);
    if (num_externs > 0)
        header2.ext_name = cell(num_externs,1);
        header2.ext_val = cell(num_externs,1);
        for I=1:(num_externs*2)
            if (mod(I,2) == 1)
                namestart = j(13+I-1)+1;
                namestop = j(13+I)-1;
                header2.ext_name{floor(I/2)+1} = char(t2(namestart:namestop));
            end
            if (mod(I,2) == 0)
                valstart = j(13+I-1)+1;
                valstop = j(13+I)-1;
                header2.ext_val{I/2} = char(t2(valstart:valstop));
            end    
        end
    end
end