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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
const SUNDAY = 0;
const THURSDAY = 4;
const lazy = {};
XPCOMUtils.defineLazyPreferenceGetter(lazy, "startWeekday", "calendar.week.start", SUNDAY);
export function CalWeekInfoService() {
this.wrappedJSObject = this;
}
CalWeekInfoService.prototype = {
QueryInterface: ChromeUtils.generateQI(["calIWeekInfoService"]),
classID: Components.ID("{6877bbdd-f336-46f5-98ce-fe86d0285cc1}"),
// calIWeekInfoService:
getWeekTitle(aDateTime) {
/**
* This implementation is based on the ISO 8601 standard.
* ISO 8601 defines week one as the first week with at least 4
* days, and defines Monday as the first day of the week.
* Equivalently, the week one is the week with the first Thursday.
*
* This implementation uses the second definition, because it
* enables the user to set a different start-day of the week
* (Sunday instead of Monday is a common setting). If the first
* definition was used, all week-numbers could be off by one
* depending on the week start day. (For example, if weeks start
* on Sunday, a year that starts on Thursday has only 3 days
* [Thu-Sat] in that week, so it would be part of the last week of
* the previous year, but if weeks start on Monday, the year would
* have four days [Thu-Sun] in that week, so it would be counted
* as week 1.)
*/
// The week number is the number of days since the start of week 1,
// divided by 7 and rounded up. Week 1 is the week containing the first
// Thursday of the year.
// Thus, the week number of any day is the same as the number of days
// between the Thursday of that week and the Thursday of week 1, divided
// by 7 and rounded up. (This takes care of days at end/start of a year
// which may be part of first/last week in the other year.)
// The Thursday of a week is the Thursday that follows the first day
// of the week.
// The week number of a day is the same as the week number of the first
// day of the week. (This takes care of days near the start of the year,
// which may be part of the week counted in the previous year.) So we
// need the startWeekday.
// The number of days since the start of the week.
// Notice that the result of the subtraction might be negative.
// We correct for that by adding 7, and then using the remainder operator.
const sinceStartOfWeek = (aDateTime.weekday - lazy.startWeekday + 7) % 7;
// The number of days to Thursday is the difference between Thursday
// and the start-day of the week (again corrected for negative values).
const startToThursday = (THURSDAY - lazy.startWeekday + 7) % 7;
// The yearday number of the Thursday this week.
let thisWeeksThursday = aDateTime.yearday - sinceStartOfWeek + startToThursday;
if (thisWeeksThursday < 1) {
// For the first few days of the year, we still are in week 52 or 53.
const lastYearDate = aDateTime.clone();
lastYearDate.year -= 1;
thisWeeksThursday += lastYearDate.endOfYear.yearday;
} else if (thisWeeksThursday > aDateTime.endOfYear.yearday) {
// For the last few days of the year, we already are in week 1.
thisWeeksThursday -= aDateTime.endOfYear.yearday;
}
const weekNumber = Math.ceil(thisWeeksThursday / 7);
return weekNumber;
},
/**
* gets the first day of a week of a passed day under consideration
* of the preference setting "calendar.week.start"
*
* @param aDate a date time object
* @returns a dateTime-object denoting the first day of the week
*/
getStartOfWeek(aDate) {
const date = aDate.clone();
date.isDate = true;
const offset = lazy.startWeekday - aDate.weekday;
date.day += offset;
if (offset > 0) {
date.day -= 7;
}
return date;
},
/**
* gets the last day of a week of a passed day under consideration
* of the preference setting "calendar.week.start"
*
* @param aDate a date time object
* @returns a dateTime-object denoting the last day of the week
*/
getEndOfWeek(aDate) {
const date = this.getStartOfWeek(aDate);
date.day += 6;
return date;
},
};