/* Special Thanks to John Walker, Original Developer of this Script : http://www.fourmilab.com/documents/calendar/
   Edited and Customized By Mani MalekMohammadi : mm.mani@gmail.com
*/

/*  You may notice that a variety of array variables logically local
    to functions are declared globally here.  In JavaScript, construction
    of an array variable from source code occurs as the code is
    interpreted.  Making these variables pseudo-globals permits us
    to avoid overhead constructing and disposing of them in each
    call on the function in which whey are used.  */

var J0000 = 1721424.5;                // Julian date of Gregorian epoch: 0000-01-01
var J1970 = 2440587.5;                // Julian date at Unix epoch: 1970-01-01
var JMJD  = 2400000.5;                // Epoch of Modified Julian Date system
var J1900 = 2415020.5;                // Epoch (day 1) of Excel 1900 date system (PC)
var J1904 = 2416480.5;                // Epoch (day 0) of Excel 1904 date system (Mac)

var NormLeap = new Array("Normal year", "Leap year");

/*  WEEKDAY_BEFORE  --  Return Julian date of given weekday (0 = Sunday)
                        in the seven days ending on jd.  */

var FinalPersianDate;

function weekday_before(weekday, jd)
{
    return jd - jwday(jd - weekday);
}

/*  SEARCH_WEEKDAY  --  Determine the Julian date for: 

            weekday      Day of week desired, 0 = Sunday
            jd           Julian date to begin search
            direction    1 = next weekday, -1 = last weekday
            offset       Offset from jd to begin search
*/

function search_weekday(weekday, jd, direction, offset)
{
    return weekday_before(weekday, jd + (direction * offset));
}

//  Utility weekday functions, just wrappers for search_weekday

function nearest_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, 1, 3);
}

function next_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, 1, 7);
}

function next_or_current_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, 1, 6);
}

function previous_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, -1, 1);
}

function previous_or_current_weekday(weekday, jd)
{
    return search_weekday(weekday, jd, 1, 0);
}

function TestSomething()
{
}

//  LEAP_GREGORIAN  --  Is a given year in the Gregorian calendar a leap year ?

function leap_gregorian(year)
{
    return ((year % 4) == 0) &&
            (!(((year % 100) == 0) && ((year % 400) != 0)));
}

//  GREGORIAN_TO_JD  --  Determine Julian day number from Gregorian calendar date

var GREGORIAN_EPOCH = 1721425.5;

function gregorian_to_jd(year, month, day)
{
    return (GREGORIAN_EPOCH - 1) +
           (365 * (year - 1)) +
           Math.floor((year - 1) / 4) +
           (-Math.floor((year - 1) / 100)) +
           Math.floor((year - 1) / 400) +
           Math.floor((((367 * month) - 362) / 12) +
           ((month <= 2) ? 0 :
                               (leap_gregorian(year) ? -1 : -2)
           ) +
           day);
}

//  JD_TO_GREGORIAN  --  Calculate Gregorian calendar date from Julian day

function jd_to_gregorian(jd) {
    var wjd, depoch, quadricent, dqc, cent, dcent, quad, dquad,
        yindex, dyindex, year, yearday, leapadj;

    wjd = Math.floor(jd - 0.5) + 0.5;
    depoch = wjd - GREGORIAN_EPOCH;
    quadricent = Math.floor(depoch / 146097);
    dqc = mod(depoch, 146097);
    cent = Math.floor(dqc / 36524);
    dcent = mod(dqc, 36524);
    quad = Math.floor(dcent / 1461);
    dquad = mod(dcent, 1461);
    yindex = Math.floor(dquad / 365);
    year = (quadricent * 400) + (cent * 100) + (quad * 4) + yindex;
    if (!((cent == 4) || (yindex == 4))) {
        year++;
    }
    yearday = wjd - gregorian_to_jd(year, 1, 1);
    leapadj = ((wjd < gregorian_to_jd(year, 3, 1)) ? 0
                                                  :
                  (leap_gregorian(year) ? 1 : 2)
              );
    month = Math.floor((((yearday + leapadj) * 12) + 373) / 367);
    day = (wjd - gregorian_to_jd(year, month, 1)) + 1;

    return new Array(year, month, day);
}

/*  PAD  --  Pad a string to a given length with a given fill character.  */


function pad(str, howlong, padwith) {
    var s = str.toString();

    while (s.length < howlong) {
        s = padwith + s;
    }
    return s;
}



//  JULIAN_TO_JD  --  Determine Julian day number from Julian calendar date

var JULIAN_EPOCH = 1721423.5;

function leap_julian(year)
{
    return (year % 4) == ((year > 0) ? 0 : 3);
}

function julian_to_jd(year, month, day)
{

    /* Adjust negative common era years to the zero-based notation we use.  */

    if (year < 1) {
        year++;
    }

    /* Algorithm as given in Meeus, Astronomical Algorithms, Chapter 7, page 61 */

    if (month <= 2) {
        year--;
        month += 12;
    }

    return ((Math.floor((365.25 * (year + 4716))) +
            Math.floor((30.6001 * (month + 1))) +
            day) - 1524.5);
}

//  JD_TO_JULIAN  --  Calculate Julian calendar date from Julian day

function jd_to_julian(td) {
    var z, a, alpha, b, c, d, e, year, month, day;

    td += 0.5;
    z = Math.floor(td);

    a = z;
    b = a + 1524;
    c = Math.floor((b - 122.1) / 365.25);
    d = Math.floor(365.25 * c);
    e = Math.floor((b - d) / 30.6001);

    month = Math.floor((e < 14) ? (e - 1) : (e - 13));
    year = Math.floor((month > 2) ? (c - 4716) : (c - 4715));
    day = b - d - Math.floor(30.6001 * e);

    /*  If year is less than 1, subtract one to convert from
        a zero based date system to the common era system in
        which the year -1 (1 B.C.E) is followed by year 1 (1 C.E.).  */

    if (year < 1) {
        year--;
    }

    return new Array(year, month, day);
}



//  LEAP_PERSIAN  --  Is a given year a leap year in the Persian calendar ?

function leap_persian(year)
{
    return ((((((year - ((year > 0) ? 474 : 473)) % 2820) + 474) + 38) * 682) % 2816) < 682;
}


//  PERSIAN_TO_JD  --  Determine Julian day from Persian date

var PERSIAN_EPOCH = 1948320.5;
var PERSIAN_WEEKDAYS = new Array("Yekshanbeh", "Doshanbeh",
                                 "Seshhanbeh", "Chaharshanbeh",
                                 "Panjshanbeh", "Jomeh", "Shanbeh");

function persian_to_jd(year, month, day)
{
    var epbase, epyear;

    epbase = year - ((year >= 0) ? 474 : 473);
    epyear = 474 + mod(epbase, 2820);

    return day +
            ((month <= 7) ?
                ((month - 1) * 31) :
                (((month - 1) * 30) + 6)
            ) +
            Math.floor(((epyear * 682) - 110) / 2816) +
            (epyear - 1) * 365 +
            Math.floor(epbase / 2820) * 1029983 +
            (PERSIAN_EPOCH - 1);
}

//  JD_TO_PERSIAN  --  Calculate Persian date from Julian day

function jd_to_persian(jd)
{
    var year, month, day, depoch, cycle, cyear, ycycle,
        aux1, aux2, yday;


    jd = Math.floor(jd) + 0.5;

    depoch = jd - persian_to_jd(475, 1, 1);
    cycle = Math.floor(depoch / 1029983);
    cyear = mod(depoch, 1029983);
    if (cyear == 1029982) {
        ycycle = 2820;
    } else {
        aux1 = Math.floor(cyear / 366);
        aux2 = mod(cyear, 366);
        ycycle = Math.floor(((2134 * aux1) + (2816 * aux2) + 2815) / 1028522) +
                    aux1 + 1;
    }
    year = ycycle + (2820 * cycle) + 474;
    if (year <= 0) {
        year--;
    }
    yday = (jd - persian_to_jd(year, 1, 1)) + 1;
    month = (yday <= 186) ? Math.ceil(yday / 31) : Math.ceil((yday - 6) / 30);
    day = (jd - persian_to_jd(year, month, 1)) + 1;
    return new Array(year, month, day);
}

/*  updateFromGregorian  --  Update all calendars from Gregorian.
                             "Why not Julian date?" you ask.  Because
                             starting from Gregorian guarantees we're
                             already snapped to an integral second, so
                             we don't get roundoff errors in other
                             calendars.  */

function updateFromGregorian()
{
    var j, year, mon, mday, hour, min, sec,
        weekday, julcal, hebcal, islcal, hmindex, utime, isoweek,
        may_countcal, mayhaabcal, maytzolkincal, bahcal, frrcal,
        indcal, isoday, xgregcal;
        
    var julYear, julMonth, julDay, julWeekday,
        persianYear, persianMonth, persianDay, persianWeekday;
    
    var today = new Date();
    //year = new Number(document.gregorian.year.value);
    year = today.getFullYear()
    //mon = document.gregorian.month.selectedIndex;
    mon = today.getMonth();
    //mday = new Number(document.gregorian.day.value);
    mday = today.getDate();
    hour = min = sec = 0;
    //hour = new Number(document.gregorian.hour.value);
    //min = new Number(document.gregorian.min.value);
    //sec = new Number(document.gregorian.sec.value);

    //  Update Julian day

    j = gregorian_to_jd(year, mon + 1, mday) +
           (Math.floor(sec + 60 * (min + 60 * hour) + 0.5) / 86400.0);
    julDay = j;
    
    //document.julianday.day.value = j;
    //document.modifiedjulianday.day.value = j - JMJD;

    //  Update day of week in Gregorian box

    weekday = jwday(j);
    //document.gregorian.wday.value = Weekdays[weekday];

    //  Update leap year status in Gregorian box

    //document.gregorian.leap.value = NormLeap[leap_gregorian(year) ? 1 : 0];

    //  Update Julian Calendar

    julcal = jd_to_julian(j);
    //document.juliancalendar.year.value = julcal[0];
    //document.juliancalendar.month.selectedIndex = julcal[1] - 1;
    //document.juliancalendar.day.value = julcal[2];
    //document.juliancalendar.leap.value = NormLeap[leap_julian(julcal[0]) ? 1 : 0];
     
    //  Update Persian Calendar

    perscal = jd_to_persian(j);
    //document.persian.year.value = perscal[0];
    persianYear = perscal[0];
    //document.persian.month.selectedIndex = perscal[1] - 1;
    persianMonth = perscal[1] - 1;
    //document.persian.day.value = perscal[2];
    persianDate = perscal[2];
    //document.persian.wday.value = PERSIAN_WEEKDAYS[weekday];
    persianWeekday = PERSIAN_WEEKDAYS[weekday];
    //document.persian.leap.value = NormLeap[leap_persian(perscal[0]) ? 1 : 0];
    persianMonth+=1;
    FinalPersianDate = persianYear + '/' + persianMonth + '/' + persianDate;
    return FinalPersianDate;
    //document.forms['form1'].elements['TextBox1'].value = persianYear + '/' + persianMonth + '/' + persianDate
}   

//  calcGregorian  --  Perform calculation starting with a Gregorian date

function calcGregorian()
{
    updateFromGregorian();
}

//  calcJulian  --  Perform calculation starting with a Julian date

/*
function calcJulian()
{
    var j, date, time;

    j = new Number(document.julianday.day.value);
    date = jd_to_gregorian(j);
    time = jhms(j);
    document.gregorian.year.value = date[0];
    document.gregorian.month.selectedIndex = date[1] - 1;
    document.gregorian.day.value = date[2];
    document.gregorian.hour.value = pad(time[0], 2, " ");
    document.gregorian.min.value = pad(time[1], 2, "0");
    document.gregorian.sec.value = pad(time[2], 2, "0");
    updateFromGregorian();
}


//  setJulian  --  Set Julian date and update all calendars

function setJulian(j)
{
    document.julianday.day.value = new Number(j);
    calcJulian();
}

//  calcModifiedJulian  --  Update from Modified Julian day

function calcModifiedJulian()
{
    setJulian((new Number(document.modifiedjulianday.day.value)) + JMJD);
}

//  calcJulianCalendar  --  Update from Julian calendar

function calcJulianCalendar()
{
    setJulian(julian_to_jd((new Number(document.juliancalendar.year.value)),
                           document.juliancalendar.month.selectedIndex + 1,
                           (new Number(document.juliancalendar.day.value))));
}

//  calcPersian  --  Update from Persian calendar

function calcPersian()
{
    setJulian(persian_to_jd((new Number(document.persian.year.value)),
                           document.persian.month.selectedIndex + 1,
                           (new Number(document.persian.day.value))));
                          
}
*/