Time elapsed between 2 unix datetimes

// This script gets the time that will elapse between the present time and a future date. Add the later date below.

integer tyear = 2018; // add the year
integer tmonth = 10; // add the month
integer tday = 30; // add the day
integer thour = 00; // add the hour
integer tmin = 45; //add the min
integer tsec = 00; // add the seconds
integer thenUnix;
list nowList;
integer nowUnix;



integer DAYS_PER_YEAR        = 365;           // Non leap year
integer SECONDS_PER_YEAR     = 31536000;      // Non leap year
integer SECONDS_PER_DAY      = 86400;
integer SECONDS_PER_HOUR     = 3600;
integer SECONDS_PER_MINUTE   = 60;

list MonthNameList = [  "JAN", "FEB", "MAR", "APR", "MAY", "JUN",
                        "JUL", "AUG", "SEP", "OCT", "NOV", "DEC" ];

// This leap year test works for all years from 1901 to 2099 (yes, including 2000)
// Which is more than enough for UnixTime computations, which only operate over the range [1970, 2038].  (Omei Qunhua)
integer LeapYear( integer year)
{
    return !(year & 3);
}

integer DaysPerMonth(integer year, integer month)
{
    // Compact Days-Per-Month algorithm. Omei Qunhua.
    if (month == 2)      return 28 + LeapYear(year);
    return 30 + ( (month + (month > 7) ) & 1);           // Odd months up to July, and even months after July, have 31 days
}

integer DaysPerYear(integer year)
{
    return 365 + LeapYear(year);
}

///////////////////////////////////////////////////////////////////////////////////////
// Convert Unix time (integer) to a Date and Time string
///////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////// Unix2DataTime() ///////////////////////////////////////

list Unix2DateTime(integer unixtime)
{
    integer days_since_1_1_1970     = unixtime / SECONDS_PER_DAY;
    integer day = days_since_1_1_1970 + 1;
    integer year  = 1970;
    integer days_per_year = DaysPerYear(year);

    while (day > days_per_year)
    {
        day -= days_per_year;
        ++year;
        days_per_year = DaysPerYear(year);
    }

    integer month = 1;
    integer days_per_month = DaysPerMonth(year, month);

    while (day > days_per_month)
    {
        day -= days_per_month;

        if (++month > 12)
        {
            ++year;
            month = 1;
        }

        days_per_month = DaysPerMonth(year, month);
    }

    integer seconds_since_midnight  = unixtime % SECONDS_PER_DAY;
    integer hour        = seconds_since_midnight / SECONDS_PER_HOUR;
    integer second      = seconds_since_midnight % SECONDS_PER_HOUR;
    integer minute      = second / SECONDS_PER_MINUTE;
    second              = second % SECONDS_PER_MINUTE;

    return [ year, month, day, hour, minute, second ];
}

///////////////////////////////// MonthName() ////////////////////////////

string MonthName(integer month)
{
    if (month >= 0 && month < 12)
        return llList2String(MonthNameList, month);
    else
        return "";
}

///////////////////////////////// DateString() ///////////////////////////

string DateString(list timelist)
{
    integer year       = llList2Integer(timelist,0);
    integer month      = llList2Integer(timelist,1);
    integer day        = llList2Integer(timelist,2);

    return (string)day + "-" + MonthName(month - 1) + "-" + (string)year;
}

///////////////////////////////// TimeString() ////////////////////////////

string TimeString(list timelist)
{
    string  hourstr     = llGetSubString ( (string) (100 + llList2Integer(timelist, 3) ), -2, -1);
    string  minutestr   = llGetSubString ( (string) (100 + llList2Integer(timelist, 4) ), -2, -1);
    string  secondstr   = llGetSubString ( (string) (100 + llList2Integer(timelist, 5) ), -2, -1);
    return  hourstr + ":" + minutestr + ":" + secondstr;
}

///////////////////////////////////////////////////////////////////////////////
// Convert a date and time to a Unix time integer
///////////////////////////////////////////////////////////////////////////////

////////////////////////// DateTime2Unix() ////////////////////////////////////

integer DateTime2Unix(integer year, integer month, integer day, integer hour, integer minute, integer second)
{
    integer time = 0;
    integer yr = 1970;
    integer mt = 1;
    integer days;

    while(yr < year)
    {
        days = DaysPerYear(yr++);
        time += days * SECONDS_PER_DAY;
    }

    while (mt < month)
    {
        days = DaysPerMonth(year, mt++);
        time += days * SECONDS_PER_DAY;
    }

    days = day - 1;
    time += days * SECONDS_PER_DAY;
    time += hour * SECONDS_PER_HOUR;
    time += minute * SECONDS_PER_MINUTE;
    time += second;

    return time;
}

// Convert Unix Time to SLT, identifying whether it is currently PST or PDT (i.e. Daylight Saving aware)
// Omei Qunhua December 2013

list weekdays = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];

string Unix2PST_PDT(integer insecs)
{
    string str = Convert(insecs - (3600 * 8) );   // PST is 8 hours behind GMT
    if (llGetSubString(str, -3, -1) == "PDT")     // if the result indicates Daylight Saving Time ...
        str = Convert(insecs - (3600 * 7) );      // ... Recompute at 1 hour later
    return str;
}

// This leap year test is correct for all years from 1901 to 2099 and hence is quite adequate for Unix Time computations


string Convert(integer insecs)
{
    integer w; integer month; integer daysinyear;
    integer mins = insecs / 60;
    integer secs = insecs % 60;
    integer hours = mins / 60;
    mins = mins % 60;
    integer days = hours / 24;
    hours = hours % 24;
    integer DayOfWeek = (days + 4) % 7;    // 0=Sun thru 6=Sat

    integer years = 1970 +  4 * (days / 1461);
    days = days % 1461;                  // number of days into a 4-year cycle

    @loop;
    daysinyear = 365 + LeapYear(years);
    if (days >= daysinyear)
    {
        days -= daysinyear;
        ++years;
        jump loop;
    }
    ++days;

    for (w = month = 0; days > w; )
    {
        days -= w;
        w = DaysPerMonth(years, ++month);
    }
    string str =  ((string) years + "-" + llGetSubString ("0" + (string) month, -2, -1) + "-" + llGetSubString ("0" + (string) days, -2, -1) + "-"+
    llGetSubString ("0" + (string) hours, -2, -1) + "-" + llGetSubString ("0" + (string) mins, -2, -1)+ "-" + llGetSubString ("0" + (string) secs, -2, -1) );

    integer LastSunday = days - DayOfWeek;
    string PST_PDT = " PST";                  // start by assuming Pacific Standard Time
    // Up to 2006, PDT is from the first Sunday in April to the last Sunday in October
    // After 2006, PDT is from the 2nd Sunday in March to the first Sunday in November
    if (years > 2006 && month == 3  && LastSunday >  7)     PST_PDT = " PDT";
    if (month > 3)                                          PST_PDT = " PDT";
    if (month > 10)                                         PST_PDT = " PST";
    if (years < 2007 && month == 10 && LastSunday > 24)     PST_PDT = " PST";
    return (str);
}

default
{
    touch_start(integer total_number)
    {
        llOwnerSay("Date: " +  (string)Unix2DateTime(llGetUnixTime())); // displays date as DD-MON-YYYY


        list nstring = llParseString2List(Unix2PST_PDT(llGetUnixTime()),["-"],[""]);
        integer nyear = (integer)llList2String(nstring,0);
        integer nmonth = (integer)llList2String(nstring,1);
        integer nday = (integer)llList2String(nstring,2);
        integer nhour = (integer)llList2String(nstring,3);
        integer nmin = (integer)llList2String(nstring,4);
        integer nsec = (integer)llList2String(nstring,5);


        nowUnix = DateTime2Unix(nyear,nmonth,nday,nhour,nmin,nsec);



        llOwnerSay((string)nyear + " " +(string)nmonth + " " +(string)nday + " " +(string)nhour + " " +(string)nmin + " " +(string)nsec);
        llOwnerSay("now unix is " + (string)nowUnix);

        thenUnix = DateTime2Unix(tyear,tmonth,tday,thour,tmin,tsec);
        integer elapsed = thenUnix - nowUnix;

        elapsed -=3660;

        integer ehours = elapsed/3660;
        elapsed = elapsed %=3600;
        integer emins = elapsed /60;
        elapsed = elapsed %= 60;
        integer esecs = elapsed;



        llOwnerSay("time elapsed is " + (string)ehours+ " hours "+ (string)emins + "mins " + (string)esecs + "secs");




    }
}