strftime.js

/* Copyright (c) 2012, Markus Ivan Peloquin <markus@cs.wisc.edu>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED 'AS IS' AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
 * IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

// TODO test the week logic more

/*
 * Usage:
 *
 * var d = new Date(0);
 * var format = '%F %T %Z';
 *
 * // module interface
 * Strftime.strftime(format, d);     // 1969-12-31 16:00:00 UTC-8
 * Strftime.strftime_utc(format, d); // 1970-01-01 00:00:00 UTC
 *
 * // OO interface
 * d.strftime(format);               // 1969-12-31 16:00:00 UTC-8
 * d.strftime_utc(format);           // 1970-01-01 00:00:00 UTC
 *
 * The language must be overriden by adding the strings to Strftime.langs.XX
 * and setting Strftime.lang = 'XX'. The locale must be overriden by adding
 * the strings to Strftime.locales.YY and setting Strftime.locale = 'YY'.
 */

Strftime = (function(){ // begin Strftime namespace
var Strftime = {
    langs: {},
    locales: {},
};

function pad2z(x)
{
    return (x<10 ? '0' : '') + x;
}
function pad2w(x)
{
    return (x<10 ? ' ' : '') + x;
}
function pad3z(x)
{
    return (x<100 ? (x<10 ? '00' : '0') : '') + x;
}
function weekday(lang, x, abbrev)
{
    return lang.weekdays[abbrev?1:0][x];
}
function month(lang, x, abbrev)
{
    return lang.months[abbrev?1:0][x];
}
function short_hour(x)
{
    return !x ? 12 : x>12 ? x-12 : x;
}
// recursion could be used, but...
function insert(fmt, chars)
{
    var chars0 = fmt.split('');
    chars0.reverse();
    chars.push.apply(chars, chars0);
}
// weeknum(real day-of-year, day-of-year of first day of week 1)
function weeknum(days, day0)
{
    days -= day0;
    return days<0 ? 52 : (days/7 |0) + 1;
}
// it's much easier to compute these all at once rather than piecemeal;
// people usually want both cweek and cwyear anyway
function make_week_stats(date)
{
    var start = new Date(date.getTime());
    start.setMonth(0);
    start.setDate(1);
    start.setHours(0);
    start.setMinutes(0);
    start.setSeconds(0);
    start.setMilliseconds(0);

    var days = (date.getTime() - start.getTime()) /
        (1000 * 60 * 60 * 24) |0;
    var start_weekday = start.getDay();

    // day0_sun =  -sw mod 7,  0<=day0_sun<7
    var day0_sun = (start_weekday<1 ? 0 : 7) - start_weekday;
    // day0_mon = 1-sw mod 7,  0<=day0_mon<7
    var day0_mon = (start_weekday<2 ? 1 : 8) - start_weekday;
    // day0_cw  = 1-sw mod 7, -2<=day0_cw <4
    var day0_cw  = (start_weekday<4 ? 1 : 8) - start_weekday;

    var cweek = weeknum(days, day0_cw);
    var cwyear = date.getFullYear() + (
        days<7   && cweek==52 ? -1 :
        days>300 && cweek==1  ?  1 : 0);

    return {
        days: days,
        week_sun: weeknum(days, day0_sun),
        week_mon: weeknum(days, day0_mon),
        cweek: cweek,
        cwyear: cwyear,
    };
}

function strftime(fmt, date)
{
    var chars = fmt.split('');
    chars.reverse();
    var lang = Strftime.langs[Strftime.lang];
    var locale = Strftime.locales[Strftime.locale];
    var res = '';
    var week_stats = null;

    var c;
    var code;

    // temporary variables
    var days;
    var h;
    var minutes;
    var sign;
    while ((c = chars.pop()) != null) {
        if (c != '%') {
            res += c;
            continue;
        }

        if ((c = chars.pop()) == null)
            throw new Error('Format cannot end with `%\'');
        code = c.charCodeAt(0);

        switch (c) {
        case 'g': case 'G':
        case 'j':
        case 'U': case 'V': case 'W':
            week_stats = week_stats || make_week_stats(date);
        }

        switch (c) {
        // weekday name
        case 'a': case 'A':
            // abbreviate if 'a'
            res += weekday(lang, date.getDay(), code==0x61);
            break;
        // month name
        case 'b': case 'B':
        case 'h':
            // abbreviate if not 'B'
            res += month(lang, date.getMonth(), code!=0x42);
            break;
        // locale
        case 'c': // datetime
        case 'X': // time
        case 'x': // date
            insert(locale[code==0x63 ? 'datetime' :
                code==0x78 ? 'date' : 'time'], chars);
            break;
        // century
        case 'C':
            res += pad2z(date.getFullYear() / 100 |0);
            break;
        // date
        case 'd':
        case 'e':
            // pad with zeros for 'd'
            res += (code==0x64 ? pad2z : pad2w)(date.getDate());
            break;
        // MM/DD/YY
        case 'D':
            insert('%m/%d/%y', chars);
            break;
        // YYYY-MM-DD
        case 'F':
            insert('%Y-%m-%d', chars);
            break;
        // ISO8601 year
        case 'g':
            res += pad2z(week_stats.cwyear % 100);
            break;
        // ISO8601 year
        case 'G':
            res += week_stats.cwyear;
            break;
        // hour
        case 'H': // zero-padded
        case 'k': // white-padded
            res += (code==0x48 ? pad2z : pad2w)(date.getHours());
            break;
        // short hour
        case 'I': // zero-padded
        case 'l': // white-padded
            res += (code==0x49 ? pad2z : pad2w)(short_hour(
                date.getHours()));
            break;
        // day-of-year
        case 'j':
            res += pad3z(week_stats.days);
            break;
        // month
        case 'm':
            res += pad2z(date.getMonth()+1);
            break;
        // minutes
        case 'M':
            res += pad2z(date.getMinutes());
            break;
        // newline
        case 'n':
            res += '\n';
            break;
        // am/pm
        case 'p':
        case 'P':
            res += lang.ampm[date.getHours()>11 ?
                (code==0x50 ? 3 : 1) : // pm : PM
                (code==0x50 ? 2 : 0)]; // am : AM
            break;
        // H:MM:SS AMPM
        // e.g. ' 9:00:00 PM'
        case 'r':
            insert('%I:%M:%S %p', chars);
            break;
        // HH:MM
        case 'R':
            insert('%H:%M', chars);
            break;
        // seconds
        case 'S':
            res += pad2z(date.getSeconds());
            break;
        // tab
        case 't':
            res += '\t';
            break;
        // HH:MM:SS
        case 'T':
            insert('%H:%M:%S', chars);
            break;
        // day of week, 1-7, monday=1
        case 'u':
            res += date.getDay()+1;
            break;
        // week num, start sun, 1 has first sun
        case 'U':
            res += pad2z(week_stats.week_sun);
            break;
        // week num, start mon, 1 has jan 4
        case 'V':
            res += pad2z(week_stats.cweek);
            break;
        // day of week, 0-6, monday=1
        case 'w':
            res += date.getDay();
            break;
        // week num, start mon, 1 has first mon
        case 'W':
            res += pad2z(week_stats.week_mon);
            break;
        // not technically correct, but...
        case 'E':
        case 'O':
            insert(locale.datetime, chars);
            break;
        // year w/o century
        case 'y':
            res += pad2z(date.getYear() % 100);
            break;
        // full year
        case 'Y':
            res += date.getFullYear();
            break;
        // utc offset -hhmm +hhmm
        case 'z':
            minutes = date._is_utc ? 0 : date.getTimezoneOffset();
            res += minutes<0 ? '+' : '-';
            minutes = Math.abs(minutes);
            res += pad2z(minutes / 60 |0) + pad2z(minutes % 60);
            break;
        // tz name (lazy implementation)
        case 'Z':
            minutes = date._is_utc ? 0 : date.getTimezoneOffset();
            sign = minutes<0 ? '+' : '-';
            minutes = Math.abs(minutes);
            if (minutes % 60)
                insert('%z', chars);
            else if (!minutes)
                res += 'UTC';
            else
                res += 'UTC' + sign + (minutes / 60 |0);
            break;
        case '%':
            res += '%';
            break;
        default:
            throw new Error('Unrecognized format %' + c);
        }
    }
    return res;
}

function utc(date)
{
    date = new Date(date.getTime() + date.getTimezoneOffset() * 60000);
    date._is_utc = true;
    return date;
}

function strftime_utc(fmt, date)
{
    return strftime(fmt, utc(date));
}

Strftime.strftime = strftime;
Strftime.strftime_utc = strftime_utc;
Date.prototype.strftime = function(fmt) { return strftime(fmt, this) };
Date.prototype.strftime_utc = function(fmt) { return strftime_utc(fmt, this) };

return Strftime;
})(); // end Strftime namespace

Strftime.langs.en = {
    weekdays: [
        'Sunday Monday Tuesday Wednesday Thursday Friday Saturday'.split(' '),
        'Sun Mon Tue Wed Thurs Fri Sat'.split(' ')
    ],
    months: [
        'January February March April May June July August September October November December'.split(' '),
        'Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec'.split(' ')
    ],
    ampm: ['AM', 'PM', 'am', 'pm']
};
Strftime.langs.de = {
    weekdays: [
        'Sonntag Montag Dienstag Mittwoch Donnerstag Freitag Samstag'.split(' '),
        'So Mo Di Mi Do Fr Sa'.split(' ')
    ],
    months: [
        'Januar Februar M\0xe4rz April Mai Juni Juli August September Oktober November Dezember'.split(' '),
        'Jan Feb Maart Apr Mei Juni Juli Aug Sept Okt Nov Dec'.split(' ')
    ],
    ampm: ['AM', 'PM', 'am', 'pm']
};

// the Unix 'C' locale
Strftime.locales.C = {
    datetime: '%Y-%m-%d %H:%M:%S',
    date: '%Y-%m-%d',
    time: '%H:%M:%S'
};
Strftime.locales.DE = Strftime.locales.C;
Strftime.locales.US = {
    datetime: '%m/%d/%y %H:%M:%S',
    date: '%m/%d/%y',
    time: '%H:%M:%S',
};
Strftime.locales.UK = {
    // ick
    datetime: '%d/%m/%y %H:%M:%S',
    date: '%d/%m/%y',
    time: '%H:%M:%S',
};

// setting the default language/locale
Strftime.lang = 'en';
Strftime.locale = 'C';