""" ntptime2

ntptime rewritten to improve the APIs and the communication with (pools of) NTP server.
At 2023-05-06: https://github.com/micropython/micropython-lib/blob/master/micropython/net/ntptime/ntptime.py

Note: time.time() is platform dependant. See time_to_posix().
	Some micros use the epoch of 2000-01-01 00:00:00 UTC
	There's currently no timezone support in MicroPython; the RTC is set in UTC time.

Stable API	: settime()
New API		: fetch_ntp_time(), ntp_to_time(), posix_to_time(), rfc2822_datetime(), time_to_posix()
Broken API	: time() is no more exposed, renamed to _time()

The correct method to set the RTC and get the current time() is:
- call once ntptime2.settime()
- use time.time()

Platforms: python, micropython
Author: massimo.sala.71@gmail.com
"""

#-----------------------------------------------------------------
# set this parameters before calling fetch_ntp_time() / settime()

host = "pool.ntp.org"
timeout = 2
#-----------------------------------------------------------------

from compatibility import *
from time import gmtime
import socket
from select import select

gc_collect(__name__)

MONTHS				= const(b"Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec")
WEEK_DAYS			= const(b"Mon Tue Wed Thu Fri Sat Sun")
RFC2822_UTC_FORMAT	= const(b"%s, %02d %s %d %02d:%02d:%02d GMT")

NTP_TO_POSIX_DELTA	= const(2208988800)
NTP_TO_Y2K_DELTA	= const(3155673600)

Y2K_TO_POSIX_DELTA	= const(946684800)		# yes, it isn't NTP_TO_Y2K_DELTA - NTP_TO_POSIX_DELTA

# NTP protocol
_pkt_size			= const(48)
_V3_CLIENT_query	= const(b"\x1b\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00")
_V3_SERVER			= const(0x1c)
_V4_SERVER			= const(0x24)
_LI_NOT_SYNC		= const(3)

_LOCALTIME_BASE_YEAR = gmtime(0)[0]


def fetch_ntp_time() :
# Output: seconds from 1900-01-01
# Note: DO NOT use in tight loops: you flood the servers, they will ban your requests.
	try :
		addrs = socket.getaddrinfo(host, 123)
	except Exception as ex :
		printf("fetch_ntp_time: getaddrinfo error", host, ex)
		return

	for _host in addrs :
		_host = _host[-1]

		client = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
		try :
			client.sendto(_V3_CLIENT_query, _host)

			resp = None
			rx, _, err = select([client], [], [client], timeout)
			if err :
				raise RuntimeError("socket.select: error")
			if rx :
				resp = client.recv(_pkt_size)
			if not resp :
				raise RuntimeError("timed out")

			if len(resp) == _pkt_size :
				LI = resp[0] >> 6
				mode = resp[0] & 0x3f
				stratum = resp[1]
				if mode in [_V3_SERVER, _V4_SERVER] and LI != _LI_NOT_SYNC and stratum >= 1 and stratum <= 15 :
					i = int.from_bytes(resp[40 : 44], "big")
					if i :			# RFC: 0 is invalid
						return	i
			raise RuntimeError("invalid reply")

		except Exception as ex :
			# keep going with the next server
			printf("fetch_ntp_time", _host, ex)
		finally :
			client.close()


def ntp_to_time(ntp) :
# Convert NTP time to local time.time()
	if _LOCALTIME_BASE_YEAR == 1970 :
		return	ntp - NTP_TO_POSIX_DELTA
	elif _LOCALTIME_BASE_YEAR == 2000 :
		return	ntp - NTP_TO_Y2K_DELTA
	raise OSError("Unsupported python epoch: base year is %d" % _LOCALTIME_BASE_YEAR)


def posix_to_time(tim) :
# Convert POSIX time to local time.time()
	if _LOCALTIME_BASE_YEAR == 1970 :
		return	tim
	elif _LOCALTIME_BASE_YEAR == 2000 :
		return	tim - Y2K_TO_POSIX_DELTA
	raise OSError("Unsupported python epoch: base year is %d" % _LOCALTIME_BASE_YEAR)


def time_to_posix(tim) :
# Convert local time.time() to POSIX time
	if _LOCALTIME_BASE_YEAR == 1970 :
		return	tim
	elif _LOCALTIME_BASE_YEAR == 2000 :
		return	tim + Y2K_TO_POSIX_DELTA
	raise OSError("Unsupported python epoch: base year is %d" % _LOCALTIME_BASE_YEAR)


def _time() :
# Output: local time.time() retrieved from Internet.
# Notes: internal function, used by settime(); see fetch_ntp_time() notes.
	ntp = fetch_ntp_time()
	if not ntp :
		raise RuntimeError("Cannot acquire NTP time from %s" % host)
	return	ntp_to_time(ntp)


def settime(tim = None) :
# Set the board RTC.
# Input: local time.time(); without an argument it calls _time(), see its notes.
	if tim is None :
		tim = _time()
	tm = gmtime(tim)

	if not MICRO :
		printf("Unsupported platform, no RTC")
		return

	from machine import RTC
	RTC().datetime((tm[0], tm[1], tm[2], tm[6] + 1, tm[3], tm[4], tm[5], 0))


def rfc2822_datetime(tim) :
# Input: local time.time()
# Output: used in HTTP headers, so its in bytes
	year, month, mday, hour, minute, second, wday = gmtime(tim)[: 7]
	wday *= 4
	month = (month - 1) * 4
	return	RFC2822_UTC_FORMAT % (WEEK_DAYS[wday : wday + 3], mday, MONTHS[month : month + 3], year, hour, minute, second)


#ISO8601_UTC_FORMAT	= const("%Y-%m-%dT%H:%M:%SZ")
#	return	ISO8601_UTC_FORMAT % (year, month, mday, hour, minute, second)