function timeSecs=JavaTimeToGetSecs(javaTime, updateInterval)

% timeSecs=JavaTimeToGetSecs(javaTime, [updateInterval])
%
% Convert time as reported by "java.lang.System.currentTimeMillis()" to
% GetSecs units.  
%
% The Java timebase and JavaTimeToGetSecs are used internally by GetChar
% because Java calls underlying GetChar timestamp keyboard events in those
% units.
%
% updateInterval is the number of seconds before this function updates its
% internal timing cache measuring the difference between GetSecs and
% java.lang.System.currentTimeMillis().  If set to -1, the cache is only
% made the first time this function funs.  When ommitted, it defaults to 0,
% i.e., it recaches at every call.
%
%
% see also:

% HISTORY
%
% 6/7/06    awi Wrote it.
% 6/13/06   awi Do not cache difference between Java and GetSecs clocks;
%               their clocks run at different rates. 
% 6/14/06   awi Commented out Priority calls surrounding the loop which 
%               samples GetSecs and java.lang.System.currentTimeMillis()
%               for purpose of finding their difference.  Those calls would
%               make JavaTimeToGetSecs impractically slow for use by
%               GetSecs, JavaTimeToGetSecs' raison d'?tre.  This is not 
%               really so bad; if you want better timing, raise Priority 
%               before calling GetChar.  

persistent JAVA_CURRENTTIMEMILIS_GETSECS_CLOCKS_DIFF;

if nargin == 2
    updateIntervalSecs = updateInterval;
else
    updateIntervalSecs = 0;
end

updateLoops = 10;

if isempty(JAVA_CURRENTTIMEMILIS_GETSECS_CLOCKS_DIFF)
    doRecache = true;
elseif updateIntervalSecs < 0
    doRecache = false;
else
    doRecache = (GetSecs - JAVA_CURRENTTIMEMILIS_GETSECS_CLOCKS_DIFF.lastSampleTimeSecs)  >= updateIntervalSecs;
end

% Periodically re-estimate and cache the difference between the
% java.lang.System.currentTimeMillis() and GetSecs clocks.
if doRecache
    JAVA_CURRENTTIMEMILIS_GETSECS_CLOCKS_DIFF.lastSampleTimeSecs = GetSecs;
    timeASecs=zeros(1,updateLoops);
    timeBMillisecs=zeros(1,updateLoops);
    timeCSecs=zeros(1,updateLoops);
    for i = 1:updateLoops
        timeASecs(i)=GetSecs;
        timeBMilliSecs(i)=java.lang.System.currentTimeMillis();
        timeCSecs(i)=GetSecs;
    end
    timeBSecs= timeBMilliSecs/1000;
    passIntervals= timeCSecs-timeASecs;
    [shortPassTime, shortPassIndex]=min(passIntervals);
    getSecsAtJavaCall= (timeCSecs(shortPassIndex) - timeASecs(shortPassIndex)) / 2 + timeASecs(shortPassIndex);
    JAVA_CURRENTTIMEMILIS_GETSECS_CLOCKS_DIFF.diffSecs = timeBSecs(shortPassIndex) - getSecsAtJavaCall;
end

% Using estimated difference between clocks, calculate GetSecs time for given Java currentTimeMillis() value.  
timeSecs= javaTime / 1000.0 - JAVA_CURRENTTIMEMILIS_GETSECS_CLOCKS_DIFF.diffSecs;