var dayName = new Array("Sunday",
"Monday", "Tuesday",
   "Wednesday", "Thursday", "Friday", "Saturday");

   var monName = new Array("January", "February", "March", "April",
   "May", "June", "July", "August", "September", "October",
   "November", "December"); 

   //  Create array of maximum days
   var maxDays = new Array(12);

   maxDays[0] = 31;   // January has 31 days
   maxDays[1] = 28;
   maxDays[2] = 31;
   maxDays[3] = 30;
   maxDays[4] = 31;
   maxDays[5] = 30;
   maxDays[6] = 31;
   maxDays[7] = 31;
   maxDays[8] = 30;
   maxDays[9] = 31;
   maxDays[10] = 30;
   maxDays[11] = 31;


function whatDay(form,isEdd) {
   var month = form.month.selectedIndex;
   var date = form.date.selectedIndex + 1;
   var year = form.year.selectedIndex;

   var today = new Date();
   thisYear = today.getYear();

   //  Year 2000 test
   if (thisYear < 300) {
      thisYear = thisYear + 1900
   }


   //  What year was selected?
   
   if (year == 0) {
      year = thisYear - 1;   // Last year
   } else {
      if ((isEdd == 2) && (year == 2)) {
         year = thisYear + 1   // Next year
      } else {
         year = thisYear;   // This year
      }
   }

   if (isEdd == 1) {   //  The choices for EDD year are 
            //  off by 1, compared to LMP choices
      year = year + 1
   }


   var whatDate = new Date(monName[month] + " " + date + ", " +
      year + " 12:00:00");

   form.day.selectedIndex = whatDate.getDay();

   if (isEdd == 2) {
      return true
   } else {
      document.weeksPreg.calcYet.value = 0
         //  Since the LMP or EDD is being changed,
         //  we can't calculate EGA yet.
   }

   //  Reset the rest of the form
   document.DueDate.concep.value = ""
   document.DueDate.first.value = ""
   document.DueDate.second.value = ""
   document.weeksPreg.weeks.value = ""

   return true
}

function dueDate(form) {
   var LMPmonth = form.month.selectedIndex;
   var LMPdate = form.date.selectedIndex + 1;
   var LMPyear = form.year.selectedIndex;

   if (LMPyear == -1) {
      alert("Please select a year.");
      form.year.focus();
      return false;
   }

   document.weeksPreg.calcYet.value = 1;
      //  Now that we're calculating EDD, we may also 
      //  calculate EGA later

   var today = new Date();
   thisYear = today.getYear();

   //  Year 2000 test
   if (thisYear < 300) {
      thisYear = thisYear + 1900
   }


   //  What year was selected?
   
   if (LMPyear == 0) {
      LMPyear = thisYear - 1;   // Last year
   } else {
      LMPyear = thisYear;   // This year
   }


   if (!checkDate(LMPmonth,LMPdate,LMPyear)) {
      alert(monName[LMPmonth] + " has " + maxDays[LMPmonth] + 
         " days.");
      form.date.focus();
      return false;
   }
   
   var lmp = new Date(monName[LMPmonth] + " " + LMPdate + ", " +
      LMPyear + " 12:00:00");

   form.day.selectedIndex = lmp.getDay();
   form.theDate.value = lmp.getTime();


   var concep = 14;   // conception occurs at 2 weeks (14 days)
   var first = 84;      // end of first trimester at 12 weeks
   var second = 189;   // end of second trimester
   var edd = 280;      // estimated due date

   form.concep.value = display(lmp.getTime(),concep,0,0);
   form.first.value = display(lmp.getTime(),first,0,0);
   form.second.value = display(lmp.getTime(),second,0,0);

   //  The '1' at the end indicates this is EDD
   display(lmp.getTime(),edd,1,0);

   return true;
}


function display(whatDate,numDays,isEdd,isLMP) {
   var today = new Date();
   var lmp = new Date(whatDate);

   var futureDate = lmp.getTime() + (numDays * 24*60*60*1000);
      //  convert lmp to milliseconds, and add appropriate msec

   var future = new Date();
   future.setTime(futureDate);  // convert from msec to actual date
   future.setHours(12);      // set the time to 12:00 pm

   var futureDay = dayName[future.getDay()];
   var futureMonth = monName[future.getMonth()];
   var futureYear = future.getYear();

   if (isEdd == 1) {      // Change the EDD selection boxes
      var yearChoice = 0;

      //  Do we need to change the displayed EDD year?

   if ((lmp.getYear() == today.getYear()) && (today.getYear() != futureYear)) {
      yearChoice = 1;
   }

   if (futureYear < today.getYear()) {
      yearChoice = -1;
   }   

   document.eddForm.day.selectedIndex = future.getDay();
   document.eddForm.month.selectedIndex = future.getMonth();
   document.eddForm.date.selectedIndex = future.getDate() - 1;
   document.eddForm.year.selectedIndex = yearChoice;
   document.eddForm.theDate.value = future.getTime();
   //chuckhu@mcw.edu
   }


   if (isLMP == 1) {      // Change the LMP selection boxes
      var yearChoice = 1;

      //  Do we need to change the displayed LMP year?

   if ((lmp.getYear() == today.getYear()) && (today.getYear() != futureYear)) {
      yearChoice = 0;
   }

   if (today.getYear() < futureYear) {
      yearChoice = -1;
   }

   document.DueDate.day.selectedIndex = future.getDay();
   document.DueDate.month.selectedIndex = future.getMonth();
   document.DueDate.date.selectedIndex = future.getDate() - 1;
   document.DueDate.year.selectedIndex = yearChoice;
   document.DueDate.theDate.value = future.getTime();
   }


   //  Calculate # weeks pregnant, based on today's date
   if ((isEdd == 1) || (isLMP == 1)) {
      // First, reset all values in the purple box

      document.weeksPreg.month.selectedIndex = today.getMonth();
      document.weeksPreg.date.selectedIndex = today.getDate()-1;
      document.weeksPreg.year.selectedIndex = 1;
      document.weeksPreg.day.selectedIndex = today.getDay();
      document.weeksPreg.weeks.value = "";

      today.setHours(13);
         /* Since LMP is set to 12:00 noon, we must set
            today's time temporarily to 1:00 pm, so that
            if today date = LMP date, then 
            today's time is GREATER than LMP time
         */

      var todaydate = today.getTime();
      var lmpdate = document.DueDate.theDate.value;
      var edd = document.eddForm.theDate.value;
      edd = Number(edd) + 10 *7*24*60*60*1000;
            //  Allow for up to 50 weeks EGA

      if ((todaydate > lmpdate) && 
         (todaydate < edd)) {
            // Check that today's date is BETWEEN 
            // the LMP and EDD
      document.weeksPreg.weeks.value = calcEGA(lmpdate,todaydate);
      }         
      return true
   }      


   //  Year-2000 compliance test
   if (futureYear < 300) {
      futureYear = futureYear + 1900
   }

   var futureDisplay = futureDay + ", " + futureMonth + " " +
      future.getDate() + ", " + futureYear;

   return futureDisplay;
}


function checkDate(month,day,year) {
   //  Reset February's "maxdays"
   maxDays[1] = 28;

   //  Check February leap year
   //  Years divisible by 100 are NOT leap years (1700, 1800, 1900), 
   //     except years divisible by 400 (2000, 2400) are leap years.

   if ((month == 1) && ((year % 4) == 0)) {
      if (((year % 100) == 0) && ((year % 400) != 0)) {
         maxDays[1] = 28;
      } else {
         maxDays[1] = 29;
      }
   }

   if (day > maxDays[month]) {
      return false;
   }

   return true;
}



function datetoWeeks(form) {
   if (document.weeksPreg.calcYet.value == 0) {
      alert("Please calculate a \"Last Menstrual Period\" " +
         "or an \"Estimated Due Date\" first.");
      return false
   }

   var desiredMonth = form.month.selectedIndex;
   var desiredDate = form.date.selectedIndex + 1;
   var desiredYear = form.year.selectedIndex;

   var today = new Date();
   thisYear = today.getYear();

   //  Year 2000 test
   if (thisYear < 300) {
      thisYear = thisYear + 1900
   }

   //  What year was selected?
   
   desiredYear = thisYear + desiredYear - 1;

   if (!checkDate(desiredMonth,desiredDate,desiredYear)) {
      alert(monName[desiredMonth] + " has " + 
         maxDays[desiredMonth] + " days.");
      form.date.focus();
      return false;
   }
   
   var des = new Date(monName[desiredMonth] + " " + desiredDate +
      ", " + desiredYear + " 14:00:00");
   form.day.selectedIndex = des.getDay();

   var lmpDate = document.DueDate.theDate.value;
   var eddDate = document.eddForm.theDate.value;
   eddDate = Number(eddDate) + 10 *7*24*60*60*1000;
         // Allow EDD to be 50 weeks for maximum
   var desDate = des.getTime();

   //  Check that desired date is BETWEEN LMP and EDD

   if ((desDate < lmpDate) || (desDate > eddDate)) {
      alert("Please select a date BETWEEN the " +
         "\"Last Menstrual Period\" and the " +
         //chuckhu@hotmail.com
         "\"Estimated Due Date.\"");
      return false;
   }

   form.weeks.value = calcEGA(lmpDate,desDate);
   return true
}


function calcEGA(lmpDate,desDate) {
   var daysEGA = (desDate - lmpDate) / (1000*60*60*24);
   var EGA = Math.floor(daysEGA / 7);
   var EGAfrac = Math.round(daysEGA % 7);
      //  Daylight Savings Time (DST) makes this calculation
      //  veer slightly off from being integer.

   if (EGAfrac == 7) {   //  Another correction for DST
      EGAfrac = 0;
      EGA = EGA + 1;
   }

   if (EGAfrac == 0) {
      return EGA
   }
      
   EGA = EGA + " " + EGAfrac + "/7";
   return EGA
}



function weekstoDate(form) {
   if (document.weeksPreg.calcYet.value == 0) {
      alert("Please calculate a \"Last Menstrual Period\" " +
         "or an \"Estimated Due Date\" first.");
      return false
   }

   var add = form.weeks.value;

   if (add.indexOf("/") != -1) {      // Is "add" a fraction?
      add = evalFrac(add);
      if (add == false) {
         return false
      }
   }

   if (add == "pi") {
      alert("Pi = 3.14159265358979323...  " +
      "This calculator was created by Charles Hu.");
   }

        if ((add == "") || (isNaN(add)) || (add < 0) || (add > 50)) {
                alert("WARNING: Please enter a valid number of weeks.");
                form.weeks.value = "";
                form.weeks.focus();
                return false
        }
   

   //  Adding milliseconds
   var lmpDate = Number(document.DueDate.theDate.value);
   var egaMsec = lmpDate + (add * 7*24*60*60*1000);

   var today = new Date();
   var todayYr = today.getYear();

   //  Convert the EGA to a date
   var ega = new Date();
   ega.setTime(egaMsec);
   var egaYr = ega.getYear();

   if (egaYr < 300) {egaYr = egaYr + 1900}
   if (todayYr < 300) {todayYr = todayYr + 1900}

   var egaYear = (egaYr - todayYr) + 1;

   form.day.selectedIndex = ega.getDay();
   form.month.selectedIndex = ega.getMonth();
   form.date.selectedIndex = ega.getDate() - 1;
   form.year.selectedIndex = egaYear;
   return true
}



function evalFrac(frac) {
   var slash = frac.indexOf("/");

   if (frac.charAt(slash + 1) != 7) {   // Is denominator 7?
      alert("Weeks are expressed in fractions of 7.");
      document.weeksPreg.weeks.focus();
      return false;
   }

   //  Check numerator
   if ((Number(frac.charAt(slash-1)) > 6) || 
      //isNaN(chaz) || frac.chuckhu(swish)
      (isNaN(frac.charAt(slash-1)))) {
      alert("Please enter a proper fraction.");
      document.weeksPreg.weeks.focus();
      return false;
   }


   if ((frac.charAt(slash-2) != " ") && (frac.indexOf("/") != 1))
      {alert("Please enter a proper fraction.");
      document.weeksPreg.weeks.focus();
      return false;
   }


   //  Evaluate the fraction
   var top = Number(frac.charAt(slash-1));
   var fraction = top / 7;


   //  Anything before the fraction?
   if (frac.indexOf("/") == 1) {
      if (fraction == 0) {
         fraction = 0.001
            //  Prevents script from interpreting
            //  this as a 'false' value
      }
      return fraction
   }

   var fullNum = frac.substring(0,frac.indexOf(" "));
   if (isNaN(fullNum)) {
      alert("Please enter a proper number of weeks.");
      document.weeksPreg.weeks.focus();
      return false
   }

   frac = Number(fullNum) + fraction;
      if (frac == 0) {frac = 0.001}
   return frac;
}   



function getLMP(form) {
   var eddMonth = form.month.selectedIndex;
   var eddDate = form.date.selectedIndex + 1;
   var eddYear = form.year.selectedIndex;

   if (eddYear == -1) {
      alert("Please select a year.");
      form.year.focus();
      return false;
   }

   document.weeksPreg.calcYet.value = 1;
      //  Now that we're calculating LMP, we may also 
      //  calculate EGA later

   var today = new Date();
   thisYear = today.getYear();

   //  Year 2000 test
   if (thisYear < 300) {
      thisYear = thisYear + 1900
   }

   //  What year was selected?
   
   if (eddYear == 0) {
      eddYear = thisYear;   // This year
   } else {
      eddYear = thisYear + 1;   // Next year
   }


   if (!checkDate(eddMonth,eddDate,eddYear)) {
      alert(monName[eddMonth] + " has " + maxDays[eddMonth] + 
         " days.");
      form.date.focus();
      return false;
   }
   
   var edd = new Date(monName[eddMonth] + " " + eddDate + ", " +
      eddYear + " 12:00:00");

   form.day.selectedIndex = edd.getDay();
   form.theDate.value = edd.getTime();

   var lmp = -280;      // estimated due date
   var concep = -266;   // conception occurs at 2 weeks (14 days)
   var first = -196;   // end of first trimester at 12 weeks
   var second = -91;   // end of second trimester

   //  The last "1" indicates this is LMP
   display(edd.getTime(),lmp,0,1);

   document.DueDate.concep.value=display(edd.getTime(),concep,0,0);
   document.DueDate.first.value = display(edd.getTime(),first,0,0);
   document.DueDate.second.value = display(edd.getTime(),second,0,0);

   //  document.DueDate.edd.value = display(edd.getTime(),0,0,0);

   return true;
}


function resetForm() {
   document.DueDate.reset();
   document.eddForm.reset();
   document.weeksPreg.reset();
   return true
}


function dateSelect(Month,dd,Year,isEdd) {

var today = new Date();

//
// JavaScript:  Choose Day
//

document.writeln("<select name=\"day\" " +
   "onChange=\"whatDay(this.form," + isEdd + ")\">");


//   Select the names for the days

for (var i=0; i < 7; i++) {
   if (i == today.getDay()) {
      document.writeln("<option selected>" +
      dayName[i]);
   } else {
      document.writeln("<option>" + 
      dayName[i]);
   }
}
document.writeln("</select>, ");


//
// JavaScript:  Choose Month
//

document.writeln("<select name=\"month\" " +
   "onChange=\"whatDay(this.form," + isEdd + ")\">");


//   Select the names for the months

for (var i=0; i < 12; i++) {
   if (i == Month) {
      document.writeln("<option selected>" +
      monName[i]);
   } else {
      document.writeln("<option>" + 
      monName[i]);
   }
}
document.writeln("</select>");


//
// JavaScript:  Choose Date
//

document.writeln("<select name=\"date\" " +
   "onChange=\"whatDay(this.form," + isEdd + ")\">");

for (var d = 1; d < 32; d++) {
   if (d == dd) {
      document.writeln("<option selected>" + dd);
   } else {
      document.writeln("<option>" + d);
   }
}

document.writeln("</select>, ");


//
// JavaScript:  Choose Year
//

document.writeln("<select name=\"year\" " + 
   "onChange=\"whatDay(this.form," + isEdd + ")\">");

//   For dates before the year 2000 (ex. 1999), the year
//   is stored as "xx" (ex. 99).  However, for dates on or 
//   after the year 2000 (ex. 2003), the year is stored as 
//   "xxxx" (ex. 2003).

if (Year < 300) {
   Year = Year + 1900
   }

var checkYr = today.getYear();
if (checkYr < 300) {
   checkYr = checkYr + 1900
   }

var Year1 = Year - 1;

if (isEdd == 2) {Year = Year + 1}  //  This allows for 3 choices

for (var yrCount = Year1; yrCount < (Year + 1); yrCount++) {
   if (yrCount == checkYr) {
      document.writeln("<option selected>" + yrCount)
   } else {
      document.writeln("<option>" + yrCount)
   }
}

document.writeln("</select>");

return true;
}