/* Calendar Utility (c) 2009 Mel Knoyle    calendar.js  (do not remove this notice) (updated 8/1/2009 12:32am)
    (This utility works with the Gregorian Calendar (Oct 1582 - 4000)
   
/*global ActiveXObject, form, window, document, alert */

function leapadj(yyyy) {		// leapyear test
    if (((yyyy % 4) === 0) && ((yyyy % 100) !== 0) || ((yyyy % 400) === 0)) {
        return 1;
    } else {
        return 0;
    }    
}
function daysInMonth(month, year) {
    var leap = leapadj(year);
    if (month === 1) {
        return (leap + 28);
    }
    if (month === 3 || month === 5 || month === 8 || month === 10) { 
        return (30);
    } else {
        return (31);
    } 
}
function monthTable(cal, mday, month, year, startdate, weekday, maxdays, full) { 
    var monthname = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']; 
    var nextday = 1;    				// days in the month start with 1
    var inmonth = 0;    				// days prior to first = false (0) 1st and after is true (1)
    var i = 0;					// counter
    cal += '                        <table class="calendar">\n';
    cal += '                            <tr class="header"><th colspan = "7">' + monthname[month] + '  ' + year + '<\/th><\/tr>';
    cal += '\n                            <tr class="hilite"><th>Su<\/th><th>Mo<\/th><th>Tu<\/th><th>We<\/th><th>Th<\/th><th>Fr<\/th><th>Sa<\/th><\/tr>';
    while (nextday <= maxdays) {
        for (i = 0; (i < 7); i++) { 
            if (i === 0) {
                cal += '\n                            <tr>';
            }    
            inmonth += (i === weekday);

            if ((full === 0) && (nextday === mday) && inmonth) { 
                cal += '<td class="today">';			// highlight the target day of the month
            } else {
                if ((year === 1752) && (month === 8) && ((nextday > 2) && (nextday < 14))) {
                     cal += '<td class="skip">';			// this day was skipped in Sep 1752
                } else {
                    if ((year === 1582) && (month === 9) && ((nextday > 4) && (nextday < 15))) {
                        cal += '<td class="skip">';			// this day was skipped in Sep 1582
                    } else {
                        if ((year === 4000) && (month === 1) && (nextday === 29)) {
                           cal += '<td class="skip">';			// this day may be skipped in Feb 4000
                            } else {
                                cal += '<td>';
                     }
                    }
                }
            }    

            if (((i < weekday) && (nextday === 1)) || (nextday > maxdays)) {
                cal += ' ';					// before the 1st or after the last day of the month
            } else {
                cal += ' ' + nextday + ' ';
                nextday += 1;
            }
            cal += '<\/td>';
            if (i === 6) {
                cal += '<\/tr>';
            }
        }
    }
    cal += '\n                        <\/table>\n';
    return cal;
}
function calendar(form) {
    var monthname = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']; 
    var cmd = "";			// user input command string
    var cal = "";                       		// contains calendar in html format
    var container = "";			// contains css class for calendar area
    var i = 0;				// counter
    var mm = 0;                         		// month number
    var m = 0;                          		// months between dates
    var days = 0;                       		// days between dates
    var yr = 0;                         		// years between dates
    var daysleft = 0;                  		// days remaining after calculating years and months between
    var d1 = 0;                        		// day of the month (first date)
    var m1 = 0;            			// month number (0 thru 11) first date
    var y1 = 0;             			// year (4 digits) first date
    var myDate = new Date();		// default date = system date
    var nextDate;                       		// second date identified in the command argument
    var ms = 86400000;                  		// milliseconds in one day
    var dnoun = "";                     		// day or days
    var str = document.form.arg.value;  	// user supplied argument (1 or 2 dates formatted mm/dd/yyyy)
    var dstring = str.replace(/^\s+/g, ""); 	// trim all leading spaces
    dstring = str.replace(/\s+/g, " ");	// replace multiple spaces between dates with single space
    dstring = str.replace(/\/|-/g, " ");	// replace forward slashes and dashes with spaces
    cmd = dstring.split(" ");           		// separate date string elements
    var mday = 0;                       		// the day of the month. 
    var month = 0;                      		// the month number (0 thru 11). 
    var year = 0;                       		// the year (4 digits).
    var startdate = 0;                 		// ms for day 1 of month
    var weekday = 0;                    		// month starts on weekday (0 thru 6) 
    var leap = 0;                       		// leap year is true (1) or false (0)
    var maxdays = 0;                    		// number of days in month
    var full = 0;                       		// full year calendar true (1) or false (0)
    for (i = 0; i < 6; i++) {
        cmd[i] = parseInt(cmd[i], 10);  	// convert input string values to numeric
    }
    if (cmd[2] && cmd[5]) {
        container = "double";		// css double class reserves space for 2 months
    } else {
        if (str.length === 4) {
            container = "quad";		// css quad class reserves space for 4 months
            full = 1;
        } else {
        container = "single";		// css single class reserves space for 1 month
        }
    }    
    if (cmd[0] && (str.length > 4)) {		// Validate the first date.
        if ((cmd[0] > 0) && (cmd[0] <= 12) && (cmd[1] <= 31) && (cmd[2] > 999)) {	// if year, month and day are valid
            myDate = new Date(cmd[2], (cmd[0] - 1), cmd[1]);	// myDate is new date object
        } else {
            alert(cmd[0] + "/" + cmd[1] + "/" + cmd[2] + " =  wrong format or invalid date.");
            return;
        }
    }
    if (cmd[3]) {			// Validate the second date, if given.
        if ((cmd[3] > 0) && (cmd[3] <= 12) && (cmd[4] <= 31) && (cmd[5] > 999)) {    // if year, month and day are valid
            nextDate = new Date(cmd[5], (cmd[3] - 1), cmd[4]);	// nextDate is new date object 
        } else {
            alert(cmd[3] + "/" + cmd[4] + "/" + cmd[5] + " =  wrong format or invalid date.");
            return;
        }
    } 
    if (nextDate) {
        days = Math.abs(Math.round((nextDate - myDate) / ms));
        if ((Math.round(myDate / ms) < -141437) && (Math.round(nextDate / ms) > -141428)) {
            days = days - 10;
        }
        if ((Math.round(myDate / ms) < -79377) && (Math.round(nextDate / ms) > -79367)) {
            days = days - 11;
        }
    }
 				// display calendar information in a new window
    var calpage = window.open('', 'calendar', 'width=900, height=640, top=28, left=0, resizable=1, scrollbars=1, menubar = 1, directories = 1');
    calpage.document.open('text/html', '_self');
				// create html for calendar display
    calpage.document.writeln('<!DOCTYPE HTML PUBLIC \"-\/\/W3C\/\/DTD HTML 4.01 Transitional\/\/EN\" \"http:\/\/www.w3.org\/TR\/html4\/loose.dtd\">');
    calpage.document.writeln('<html>');
    calpage.document.writeln('    <head>');
    calpage.document.writeln('        <title>Calendar</title>');
    calpage.document.writeln('        <meta http-equiv="Content-Type" content="text\/html; charset=us-ascii">');
    calpage.document.writeln('        <link rel="stylesheet" href="calendar.css" type="text\/css">');
    calpage.document.writeln('    <\/head>');
    calpage.document.writeln('    <body>');
    calpage.document.writeln('        <div id="wrapper">');
    calpage.document.writeln('            <div id="mainarea">');
    calpage.document.writeln('                <div class="upper transparent">');
    calpage.document.writeln('                    <h1>Calendar Utility<\/h1>');
    calpage.document.writeln('                <\/div><!-- End of upper transparent -->');
    calpage.document.writeln('                <div class="middle transparent">');
    calpage.document.writeln('                    <div class="' + container + '">'); 
    if (str.length === 4) {			// display full year calendar
        for (i = 0; i < 12; i++) {
            myDate = new Date(str, i, 1);		// convert str to date object
            mday = myDate.getDate();		// the day of the month	
            month = myDate.getMonth();		// the month number (0 thru 11). 
            year = myDate.getFullYear();		// the year (4 digits).
            startdate = new Date(year, month, 1);	// ms for day 1 of month
            weekday = startdate.getDay(); 		// month starts on weekday (0 thru 6) 
            leap = leapadj(year);			// leap year is true (1) or false (0)
            maxdays = daysInMonth(month, year);	// number of days in month
            cal = monthTable(cal, mday, month, year, startdate, weekday, maxdays, full);
        }
    } else {					// display calendar for 1st month entered
        mday = myDate.getDate();
        month = myDate.getMonth();
        year = myDate.getFullYear();
        startdate = new Date(year, month, 1);
        weekday = startdate.getDay(); 
        leap = leapadj(year);
        maxdays = daysInMonth(month, year);
        cal = monthTable(cal, mday, month, year, startdate, weekday, maxdays, full);
          if (nextDate) {				// prepare calendar for second month
            d1 = mday;                          			// save old day of the month
            mday = nextDate.getDate();		// Get the day of the month. 
            m1 = month;
            month = nextDate.getMonth();		// Get the month number (0 thru 11). 
            y1 = year;
            year = nextDate.getFullYear();		// Get the year (4 digits).
            startdate = new Date(year, month, 1);
            weekday = startdate.getDay(); 
            leap = leapadj(year);
            maxdays = daysInMonth(month, year);
            cal = monthTable(cal, mday, month, year, startdate, weekday, maxdays, full);
        }
    }
    calpage.document.write(cal);
    calpage.document.writeln("                    <\/div><!-- End of single double or quad -->");
    if (nextDate) {
        calpage.document.writeln("            <div class='summary'>");
        calpage.document.write("               There ");
        if (days === 1) {
            calpage.document.write("is ");
            dnoun = "day";
        } else {
            calpage.document.write("are ");
            dnoun = "days";
        }
        calpage.document.writeln(days + " " + dnoun + " between " + monthname[m1] + " " + d1 + ", " + y1 + " and " + monthname[cmd[3] - 1] + " " + cmd[4] + ", " + cmd[5] + ".");
        yr = cmd[5] - cmd[2];			// calculate years between  (2nd year - 1st year)
        if (cmd[0] > cmd[3]) {			// if 1st month > 2nd month, last year is less than 12 months
            yr = yr - 1;
            m = 12 - cmd[0] + cmd[3];			// calculate months between (12 - 1st month + 2nd month
        } else {
            m = cmd[3] - cmd[0];			// if 1st month < 2nd month  (month = 2nd month - 1st month
        }
					// adjust months and years
        if (cmd[4] < cmd[1]) {			// if 2nd monthdate < 1st monthdate, last month is less than a full month
            m = m - 1;
            if (cmd[3] === cmd[0]) {			// if 2nd month = 1st month, last year is less than 12 months
                yr = yr - 1;
                m = 11;
            }
        }
        daysleft = cmd[4] - cmd[1];			// calculate days between  (2nd monthdate - 1st monthdate)
        if (daysleft < 0) {
            mm = cmd[3] - 1;			// mm = 1 month prior to 2nd month  note cmd[3] contains (1 thru 12)
            if (mm === 0) {				// december of previous year
                mm = 12;				// mm = december
                leap = leapadj(cmd[5] - 1); 		// if prior year is a leap year, leap is true (1).  else leap is false (0)
            } else {
                leap = leapadj(cmd[5]);			// if 2nd year is a leap year.
            }
            maxdays = daysInMonth(mm - 1, year);	// mm - 1  (months 0 thru 11)
            daysleft = maxdays + daysleft;
        }
					// display years, months and days between dates
        if ((days > 1) && ((m > 0) || (yr > 0))) {
            calpage.document.write("                <br>" + days + " " + dnoun + " = ");
            if (yr) {
                if (yr === 1) {
                    calpage.document.write(yr + " year ");
                } else {
                    calpage.document.write(yr + " years ");
                }
            }
            if (m) {
                if (m === 1) {
                    calpage.document.write(m + " month ");
                } else {
                    calpage.document.write(m + " months ");
                }
            }
            if (daysleft) {
                if (daysleft === 1) {
                    calpage.document.write(" and " + daysleft + " day");
                } else {
                    calpage.document.write(" and " + daysleft + " days");
                }
            }
        }
        calpage.document.writeln("\n            <\/div>");
    }
    if (((str.length === 4) && (str === "1582")) || (cmd[2] === 1582) || ((cmd[5] && (cmd[5] === 1582)))) {
        calpage.document.writeln("            <div class='textbox'>");
        calpage.document.writeln("                <br><strong>Note: <\/strong>");
        calpage.document.writeln("                In October 1582, Pope Gregory ordered 10 days <span class='skip'>( 5 thru 14 )<\/span> be omitted to more closely align with the vernal equinox.");
        calpage.document.writeln("            <\/div>");
    }
    if (((str.length === 4) && (str === "1752")) || (cmd[2] === 1752) || ((cmd[5] && (cmd[5] === 1752)))) {
        calpage.document.writeln("            <div class='textbox'>");
        calpage.document.writeln("                <br><strong>Note:<\/strong>");
        calpage.document.writeln("                11 days <span class='skip'>( 3 thru 13 )<\/span> were omitted in September 1752 when the UK converted to the Gregorian calendar.");
        calpage.document.writeln("            <\/div>");
    }
    if ((cmd[2] >= 4000) || (cmd[5] >= 4000) || (str >= 4000)) {
        calpage.document.writeln("            <div class='textbox'>");
        calpage.document.writeln("                <br><strong>Note:<\/strong>");
        calpage.document.writeln("                 There will be a calendar error of approximately  one day by the year 4000.<br>Feb 29, 4000, may be skipped.");
        calpage.document.writeln("            <\/div>"); 
    }
    calpage.document.writeln("                <\/div><!-- End of middle transparent -->");
    calpage.document.writeln("                <div class='lower copyright transparent'>");
    calpage.document.writeln("                    <br>&copy; Calendar Utility 2009 Mel Knoyle");
    calpage.document.writeln("                <\/div><!-- End of lower copyright transparent");
    calpage.document.writeln("            <\/div><!-- End of mainarea -->");
    calpage.document.writeln("        <\/div><!-- End of wrapper -->");
    calpage.document.writeln("    <\/body>");
    calpage.document.writeln("<\/html>");
    calpage.document.close();
}