Levian calendar calculator. https://www.vikomprenas.com/levcal/

levcal.js

// Levian Calendar calculator
// Copyright (C) 2015 Vi Komprenas <[email protected]>
// This is free and unencumbered software released into the public domain. <http://unlicense.org/>
// Requires jQuery (tested on 1.11.3).
//    <div id="levcal">Loading!</div>

jQuery(function levcal(){
var $ = window.jQuery;

var widgetcontent = "";

widgetcontent += '<form>';
widgetcontent += '<input type="button" value="Clear input" id="levcal-reset"></input>';
widgetcontent += 'Gregorian calendar date (YYYY-MM-DD): <input type="text" autocomplete="off" id="levcal-gregorian"></input><br/>';
widgetcontent += '<input type="button" value="Help" id="levcal-help"></input>';
widgetcontent += '<a href="https://www.nationstates.net/nation=leveat/detail=factbook/id=484140">Levian calendar</a> date (Y/M/W.D or Y//X.D): <input type="text" autocomplete="off" id="levcal-levian"></input>';
widgetcontent += '<div id="levcal-message"></div>';
widgetcontent += '</form>';

function message(mesg) {
    $("#levcal-message").html(mesg + '<br/>');
}

function defaultmessage() {
    message("Levian calendar calculator. <a href=\"http://www.vikomprenas.com/levcal/\">Made by Vi Komprenas</a>.")
}

function daysInMonth(month, isLeapYear) {
    if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) {
        return 31;
    } else if (month == 4 || month == 6 || month == 9 || month == 11) {
        return 30;
    } else if (month == 2) { // feb
        return isLeapYear ? 29 : 28;
    } else { // emergency
        return -1;
    }
}

function isLeapYear(year) {
    var leap = (year % 4 == 0);
    if (year % 100 == 0) {
        leap = leap && (year % 400 == 0);
    }
    return leap;
}

// https://stackoverflow.com/questions/10073699/pad-a-number-with-leading-zeros-in-javascript
function pad(n, width, z) {
    z = z || '0';
    n = n + '';
    return n.length >= width ? n : new Array(width - n.length + 1).join(z) + n;
}

function updateLevian() {
    // First, verify the Gregorian date at least looks like a date
    var gregstr = $("#levcal-gregorian").val();
    if (gregstr == "") {
        defaultmessage(); // don't bother the user if the box is blank
        return;
    } else if (!/^[0-9]{4}-[0-9]{2}-[0-9]{2}$/.test(gregstr)) {
        message("Invalid Gregorian date.");
        return;
    } else {
        defaultmessage();
    }
    
    // Now split it apart and verify it in more detail
    var gregdate = gregstr.split("-");
    var gregyear = parseInt(gregdate[0]);
    var gregmonth = parseInt(gregdate[1]);
    var gregday = parseInt(gregdate[2]);
    
    if (gregyear == 0 || // we won't try to handle dates BCE yet
        gregmonth == 0 ||
        gregmonth > 12 ||
        gregday == 0) {
        message("Invalid Gregorian date.");
        return;
    }
    
    // Last verification step: make sure gregday is within bounds for gregmonth
    var daysingregmonth = daysInMonth(gregmonth, isLeapYear(gregyear));
    if (daysingregmonth == -1) {
        message("Error: couldn't compute number of days in that month.");
        return;
    }
    if (gregday > daysingregmonth) {
        message("Invalid Gregorian date.");
        return;
    }
    
    // Now actually compute the Levian date
    var levyear;
    var levmonth;
    var levweek;
    var levday;
    
    // First, compute number of days since 1800-01-01 (epoch)
    if (gregyear < 1800) {
        message("Support for dates prior to 1800 is not yet available.");
        return;
    }
    
    var daysSinceEpoch = 0;
    for (y = 1800; y < gregyear; y++) { // don't include the year of the input date yet
        daysSinceEpoch += (isLeapYear(y)) ? 366 : 365;
    }
    
    for (m = 1; m < gregmonth; m++) {
        daysSinceEpoch += daysInMonth(m, isLeapYear(gregyear));
    }
    
    daysSinceEpoch += gregday - 1; // -1 since there is no day 0 in any G. (or L.) month
    
    var daysLeft = daysSinceEpoch; // renaming to better illustrate its role in the next bit
    console.log(daysLeft);
    
    // Remove days to make a year
    levyear = Math.floor(daysLeft / 365);
    daysLeft -= 365 * levyear;
    levyear += 1;
    
    // Remove days to make a month
    levmonth = Math.floor(daysLeft / 30);
    daysLeft -= 30 * levmonth;
    levmonth += 1;
    
    // Work out what week of the month it is
    levweek = Math.floor(daysLeft / 5);
    daysLeft -= 5 * levweek;
    levweek += 1;
    
    // And the day.
    levday = daysLeft
    daysLeft -= levday;
    levday += 1;
    
    // Now make it into a string
    var levstr = levyear + '/' + levmonth + '/' + levweek + '.' + levday;
    if (levmonth == 13) {
        levstr = levyear + '//X.' + levday;
    }
    $("#levcal-levian").val(levstr);
}

function updateGregorian() {
    // First, verify the Levian date at least looks like a date
    var levstr = $("#levcal-levian").val();
    if (levstr == "") {
        defaultmessage(); // Don't bother the user if it's blank
        return;
    } else if (!/^[0-9]+\/([0-9]+\/[1-6]|\/X)\.[1-5]$/.test(levstr)) {
        message("Invalid Levian date.");
        return;
    } else {
        defaultmessage();
    }
    
    // Now split it apart and verify it in more detail
    var levdate = levstr.split('/');
    var levyear = parseInt(levdate[0]);
    var levmonth;
    var levweek;
    var levday = parseInt(levdate[2].split('.')[1]);
    var levfree = /^[0-9]+\/\/X\.[1-5]$/.test(levstr);
    if (levfree) {
        levmonth = 13;
        levweek = 1;
    } else {
        levmonth = parseInt(levdate[1]);
        levweek = parseInt(levdate[2].split('.')[0]);
        
        if (levmonth == 13) {
            // Not so fast.
            message("Invalid Levian date.");
            return;
        }
    }
    
    if (levmonth < 1 || levmonth > 13 ||
        levweek < 1 || levweek > 6 ||
        levday < 1 || levday > 5 ||
        levmonth == 13 && levweek != 1) {
        message("Invalid Levian date.");
        return;
    }
    
    // Now actually compute the Gregorian date
    
    // First, convert the Levian date to days since the epoch
    var daysSinceEpoch = levday - 1;
    daysSinceEpoch += (levweek - 1) * 5;
    daysSinceEpoch += (levmonth - 1) * 30;
    daysSinceEpoch += (levyear - 1) * 365;
    
    // Then, start adding those days into a Gregorian date.
    var gregyear = 1800;
    var gregmonth = 1;
    var gregday = 1;
    
    // I could divide, too, but this is neater to understand
    for (daysLeft=daysSinceEpoch; daysLeft > 0; daysLeft--) {
        gregday += 1;
        if (gregday > daysInMonth(gregmonth, isLeapYear(gregyear))) {
            gregday = 1;
            gregmonth += 1;
            if (gregmonth > 12) {
                gregmonth = 1;
                gregyear += 1;
            }
        }
    }
    
    // Lastly, stringify and display the result
    var gregstr = pad(gregyear, 4) + "-" + pad(gregmonth, 2) + "-" + pad(gregday, 2);
    $("#levcal-gregorian").val(gregstr);
}

function reset() {
    defaultmessage();
    $("#levcal-gregorian").val("");
    $("#levcal-levian").val("");
}

function help() {
    message("Enter a date in either box and press Enter for magic.");
}

function init() {
    $("#levcal").html(widgetcontent);
    $("#levcal").css("font-weight", "400");
    $("#levcal-message").css("font-weight", "600");
    $("#levcal-reset").css("float", "right");
    $("#levcal-reset").click(reset);
    $("#levcal-help").css("float", "right");
    $("#levcal-help").click(help);
    $("#levcal-gregorian").change(updateLevian);
    $("#levcal-levian").change(updateGregorian);
    defaultmessage();
}

init();

});