shithub: mc

ref: f7228d204a9cbe40f7b6286ba8987ef65691bfbd
dir: /lib/date/date.myr/

use std
use "types.use"
use "zoneinfo.use"

pkg date =
	/* useful constructors */
	const utcnow	: (-> instant)
	const now	: (tz : byte[:] -> instant)
	const tozone	: (d : instant, zone : byte[:]	-> instant)
	const mkinstant	: (tm : std.time, zone : byte[:]	-> instant)

	const localoff	: (tm : std.time -> duration)
	const tzoff	: (tzname : byte[:], tm : std.time	-> duration)
	const isleap	: (d : instant	-> bool)

	/* date differences */
	const add	: (d : instant, dt : duration	-> instant)
	const sub	: (d : instant, dt : duration	-> instant)
	const addperiod	: (d : instant, dt : period	-> instant)
	const subperiod	: (d : instant, dt : period	-> instant)

	const duration	: (a : instant, b : instant	-> duration)
;;

const Days400y	= 365*400 + 4*25 - 3
const Days4y	= 365*4 + 1
const DayUsec	= (24*60*60*1_000_000)
const Mdays	= [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

const utcnow = {
	-> mkinstant(std.now(), "")
}

const now = {tz : byte[:]
	var tm

	tm = std.now()
	-> mkinstant(tm, tz)
}

const tozone = {d, tz
	-> mkinstant(d.actual, tz)
}

const mkinstant = {tm, tz 
	var j, y, m, d
	var t, e
	var inst
	var off

	inst.actual = tm
	/* time zones */
	std.assert(tz.len <= inst._tzbuf.len, "time zone name too long\n")
	off =_zoneinfo.findtzoff(tz, tm) 
	inst.tzoff = off
	std.slcp(inst._tzbuf[:tz.len], tz)
	inst.tzname = inst._tzbuf[:tz.len]
	tm += off castto(std.time)

	/* break up time */
	t = tm % DayUsec	/* time */
	e = tm / DayUsec	/* epoch day */

	if t < 0
		t += DayUsec
		e -= 1
	;;

	/* microseconds, seconds, minutes, hours */
	inst.us  = (t % 1_000_000) castto(int)
	t /= 1_000_000
	inst.s = (t % 60) castto(int)
	t /= 60
	inst.m = (t % 60) castto(int)
	t /= 60
	inst.h = t castto(int)

	/* weekday */
	inst.wday = ((e + 4) % 7) castto(int)	/* the world started on Thursday */

	/*
	split up year, month, day.

	Implemented according to "Algorithm 199, conversions between calendar 
	date and Julian day number", Robert G. Tantzen, Air Force Missile Development
	Center, Holloman AFB, New Mex.

	Lots of magic. Yer a wizard, 'arry.
	*/
	j = (tm + 2440588 * DayUsec) / DayUsec 
	j -= 1721119

	y = (4 * j - 1) / Days400y
	j = 4 * j - 1 - Days400y * y
	d = j / 4

	j = (4 * d + 3) / Days4y
	d = 4 * d + 3 - Days4y * j
	d = (d + 4) / 4 ;

	m = (5 * d - 3) / 153
	d = 5 * d - 3 - 153 * m
	d = (d + 5) / 5

	y = 100 * y + j
	if m < 10
		m += 3
	else
		m -= 9 
		y++
	;;

	/* there's no year 0 */
	if y <= 0
		y--
	;;
	/* and if j negative, the day and month are also negative */
	if m < 0
		m += 12
	;;
	if d < 0
		d += Mdays[m - 1] 
	;;

	inst.year = y castto(int)
	inst.mon = m castto(int)
	inst.day = d castto(int)
	-> inst
}

const localoff = {tm
	-> _zoneinfo.findtzoff("local", tm)
}

const tzoff = {tz, tm
	-> _zoneinfo.findtzoff(tz, tm)
}

const isleap = {d
	-> d.year % 4 == 0 && (d.year % 100 != 0 || d.year % 400 == 0)
}

const add  = {d, dt
	-> mkinstant(d.actual + (dt castto(std.time)), d.tzname)
}

const sub  = {d, dt
	-> mkinstant(d.actual - (dt castto(std.time)), d.tzname)
}

const addperiod = {inst, p
	match p
	| `Year	y:	inst.year += y
	| `Month m:	inst.mon += m
	| `Day	d:	inst.day += d
	| `Hour	h:	inst.h += h
	| `Minute m:	inst.m += m
	| `Second s:	inst.s += s
	;;
	-> mkinstant(recalc(inst), inst.tzname)
}

const subperiod = {inst, p
	match p
	| `Year	y:	inst.year -= y
	| `Month m:	inst.mon -= m
	| `Day	d:	inst.day -= d
	| `Hour	h:	inst.h -= h
	| `Minute m:	inst.m -= m
	| `Second s:	inst.s -= s
	;;
	-> mkinstant(recalc(inst), inst.tzname)
}

const duration = {a, b
	-> (b.actual - a.actual) castto(duration)
}

const recalc = {inst
	var c, ya, j, tm
	var year, mon, day
	var h, m, s, us

	year = inst.year castto(std.time)
	mon = inst.mon castto(std.time)
	day = inst.day castto(std.time)
	h = inst.h castto(std.time)
	m = inst.m castto(std.time)
	s = inst.s castto(std.time)
	us = inst.us castto(std.time)

	if m > 2
		mon -= 3
	else
		mon += 9
		year -= 1
	;;
	c = year / 100
	ya = year - 100 * c
	j = (c*Days400y/4 + Days4y*ya/4 + (153*mon+2)/5 + day)
	j -= 719469
	tm = j * DayUsec
	tm += (3600*h + 60*m + s)*1_000_000 + us
	-> tm
}