// JavaScript routines for date differences

dayMsec=24*3600*1000;     // 1 day in milliseconds

// Convert an integer to a string with commas
// ---------------------------------------

function niceString(x)
{
var s=x.toString();
var n=s.length;
if (n<=3) return s;
var t="";
for (var i=0;i<n;i++)
 {
 t+=s.substring(i,i+1);
 if ((n-i-1)%3==0 && i!=n-1) t+=",";
 };
return t;
}

// The length in days of a given month of a given year
// ---------------------------------------------

// Here we use the JavaScript convention of month numbers starting at 0

function monthLength(month,year)
{
var firstOfMonth=new Date(year,month,1);
var firstOfNext;
if (month==11) firstOfNext=new Date(year+1,0,1);
else firstOfNext=new Date(year,month+1,1);
return Math.floor((firstOfNext-firstOfMonth)/dayMsec);
}

// Number of days since a date in the past
// -----------------------------------

function intDaysSince(year,month,day, year2,month2,day2)
{
var originalDate=new Date(year,month-1,day);    // JavaScript starts months at 0
var secondDate=year2<0 ? new Date() : new Date(year2,month2-1,day2);
var differenceMillisecs=secondDate-originalDate;
return Math.floor(differenceMillisecs/dayMsec);
}

// A text representation of the number of days since a date in the past
// -------------------------------------------------------------

function daysSince(year,month,day,year2,month2,day2)
{
return niceString(intDaysSince(year,month,day,year2,month2,day2))+"&nbsp;days";
}

// A text representation of the number of years, days and months since a date in the past
// ------------------------------------------------------------------------------

function yearsMonthsDaysSince(y,m,d, y2,m2,d2)
{
var diff=new Array(0,0,0);
m=m-1;    // JavaScript starts months at 0

// Get y1, m1, d1 as year, month day of current date

var secondDate=y2<0 ? new Date() : new Date(y2,m2-1,d2);
var y1=secondDate.getYear();
if (y1<1900) y1+=1900;
var m1=secondDate.getMonth();
var d1=Math.floor(secondDate.getDate());

// The difference in days

if (d1>=d) diff[2]=d1-d;
else
 {
 // Need to borrow days from the month
 if (m1==0) {y1--; m1=11;}
 else m1--;
 diff[2]=d1+monthLength(m1,y1)-d;
 };

// The difference in months

if (m1>=m) diff[1]=m1-m;
else
 {
 // Need to borrow months from the years
 diff[1]=m1+12-m;
 y1--;
 };

// The difference in years

diff[0]=y1-y;

// String text versions of the difference together, nicely punctuated

var s="";
if (diff[0]!=0) s=diff[0].toString()+(diff[0]==1?"&nbsp;year":"&nbsp;years");
if (diff[1]!=0)
 {
 if (s!="")
  {
  if (diff[2]==0) s+=" and "; else s+=", ";
  }; 
 s+=diff[1].toString()+(diff[1]==1?"&nbsp;month":"&nbsp;months");
 };
if (diff[2]!=0)
 {
 if (s!="") s+=" and ";
 s+=diff[2].toString()+(diff[2]==1?"&nbsp;day":"&nbsp;days");
 };
return s;
}

// A table of images representing the number of days since a date in the past
// --------------------------------------------------------------------------


function daysSinceTable(year,month,day, year2,month2,day2, imageDirURL,ncols)
{
var d=intDaysSince(year,month,day,year2,month2,day2);
var nrows=Math.ceil(d/(5*ncols));
var i=0;
var str='<table class="days" align="left" border="0" cellpadding="0" cellspacing="0"><tr><td colspan="';
str+=ncols.toString()+'" align="center"><b>'+daysSince(year,month,day,year2,month2,day2)+'</b></td></tr>';

for (var irow=0;irow<nrows;irow++)
 {
 str+='<tr>';
 for (var icol=0;icol<ncols;icol++)
  {
  str+='<td class="days">';
  if (d>0)
   {
   if (d<5) k=d; else k=5;
   var year=1+Math.floor(i/365);
   src=imageDirURL+"y"+year.toString()+k.toString()+".gif";
   str+='<image src="'+src+'" width="36" height="36" />';
   d-=k;
   i+=k;
   }
  else
   {
   str+='&nbsp;';
   };
  str+='</td>';
  };
 str+='</tr>';
 };
str+='</table>';
return str;
}