function [missing,added] = SIOActiveSensorTest(path,file,actmodlist)
%this function accepts a path, file and active module list as a cell array.
%It opens the log file specified by path & file, and checks to see what
%modules, if any, have been added or removed from the list.
%it then returns the missing and/or added modules as individual cell arrays

%create full path name
file_in = fullfile(path,file);
%open file for reading
in = fopen(file_in,'rt');

%size of actmodlist, the "old" or status quo data
szactold = size(actmodlist,1);

%this string indicates the start of the data set
activemodstart = 'Active Modules:';
amstsize = size(activemodstart,2);

%this is the end tag of the data we are after
endstring = 'Inoperative Modules:';
ensize = size(endstring,2);
%init
modstr = '';
onflag = 0;

%infinite loop
while 1
    %grab the whole row
    tline = fgetl(in);
    %break when the value returned by fgetl is empty
    if ~ischar(tline), break, end
    
    %if the line is an empty string, or shorter than the shortest tag we
    %are looking for, skip the line
    if (isempty(tline) | (amstsize > size(tline,2)))
        continue;
    end
    %check the flag to see if we are "on" and collecting strings, or off
    %and skipping them
    if (~onflag)
        %we're off
        if ((strcmp(tline(1:amstsize),activemodstart)))
            %we've seen the start tag now, let's become "on"
            onflag = 1;
            %skip to the next line, this line is just a tag
            continue;
        end
    else
        %must be that we are on
        if (strcmp(tline(1:ensize),endstring))
            %we've hit the end tag, let's do some processing
            
            %splits the module names on spaces and inserts them into a cell
            %array.  This is the "new" data.
            mods = strread(modstr,'%s','delimiter',' ');
            
            %size of the new data
            szactnew = size(mods,1);
            %init's an index of all zeros
            addind = zeros(szactnew,1);
            
            %iterate over the old data, checking to see if what has been
            %added to the new list since the last update.  Since ~strcmp
            %outputs a logical array with a 0 where the match occurs, we XOR
            %all of the arrays together to get a map at the end
            for i=1:szactold
                addind = xor(addind,~strcmp(actmodlist{i},mods));
            end
            %init's another index
            missind = zeros(szactold,1);
            %do the same thing as above, except this time we are looking
            %for data that has been removed since the last go around
            for j=1:szactnew
               missind = missind | strcmp(mods{j},actmodlist); 
            end
            added = mods(addind);
            missing = actmodlist(~missind);
            break;
        end
        %while we're on, let's concatenate all the data into one long space
        %separated line
        modstr = [modstr ' ' tline];
    end
end