radiosonde_auto_rx/auto_rx/autorx/sonde_specific.py

#!/usr/bin/env python
#
#   radiosonde_auto_rx - Radiosonde-Type Specific Functions
#
#   Copyright (C) 2019  Mark Jessop <vk5qi@rfhead.net>
#   Released under GNU GPL v3 or later
#
import datetime
import hashlib
from dateutil.parser import parse



def fix_datetime(datetime_str, local_dt_str = None):
	'''
	Given a HH:MM:SS string from a telemetry sentence, produce a complete timestamp, using the current system time as a guide for the date.
	'''

	if local_dt_str is None:
		_now = datetime.datetime.utcnow()
	else:
		_now = parse(local_dt_str)

	# Are we in the rollover window?
	if _now.hour == 23 or _now.hour == 0:
		_outside_window = False
	else:
		_outside_window = True
	

	# Parsing just a HH:MM:SS will return a datetime object with the year, month and day replaced by values in the 'default'
	# argument. 
	_imet_dt = parse(datetime_str, default=_now)

	if _outside_window:
		# We are outside the day-rollover window, and can safely use the current zulu date.
		return _imet_dt
	else:
		# We are within the window, and need to adjust the day backwards or forwards based on the sonde time.
		if _imet_dt.hour == 23 and _now.hour == 0:
			# Assume system clock running slightly fast, and subtract a day from the telemetry date.
			_imet_dt = _imet_dt - datetime.timedelta(days=1)

		elif _imet_dt.hour == 00 and _now.hour == 23:
			# System clock running slow. Add a day.
			_imet_dt = _imet_dt + datetime.timedelta(days=1)

		return _imet_dt


#
#	iMet Radiosonde Functions
#

def imet_unique_id(telemetry, custom=""):
	'''
	Generate a 'unique' imet radiosonde ID based on the power-on time, frequency, and an optional location code.
	This requires the following fields be present in the telemetry dict:
		datetime_dt (datetime)  (will need to be generated above)
		frame (int) - Frame number
		freq (str) - Frequency, as "%.3f MHz"
	'''

	_imet_dt = telemetry['datetime_dt']

	# Determine power on time: Current time -  number of frames (one frame per second)
	_power_on_time = _imet_dt - datetime.timedelta(seconds=telemetry['frame'])

	# Now we generate a string to hash based on the power-on time, the frequency, and the custom field.
	_temp_str = _power_on_time.strftime("%Y-%m-%dT%H:%M:%SZ") + telemetry['freq'] + custom

	# Calculate a SHA256 hash of the 
	_hash = hashlib.sha256(_temp_str.encode('ascii')).hexdigest().upper()

	return "IMET-" + _hash[-8:]




if __name__ == "__main__":

	# Testing scripts for the above.

	test_data = [
		{'datetime':'23:59:58', 'frame': 50, 'freq': '402.000 MHz', 'local_dt': "2019-03-01T23:59:58Z"},
		{'datetime':'23:59:58', 'frame': 50, 'freq': '402.000 MHz', 'local_dt': "2019-03-01T23:59:57Z"},
		{'datetime':'23:59:58', 'frame': 50, 'freq': '402.000 MHz', 'local_dt': "2019-03-02T00:00:03Z"},
		{'datetime':'00:00:00', 'frame': 52, 'freq': '402.000 MHz', 'local_dt': "2019-03-01T23:59:57Z"},
		{'datetime':'00:00:00', 'frame': 52, 'freq': '402.000 MHz', 'local_dt': "2019-03-02T00:00:03Z"},
		{'datetime':'00:00:01', 'frame': 53, 'freq': '402.000 MHz', 'local_dt': "2019-03-01T23:59:57Z"},
		{'datetime':'00:00:01', 'frame': 53, 'freq': '402.000 MHz', 'local_dt': "2019-03-02T00:00:03Z"},
		{'datetime':'11:59:58', 'frame': 42, 'freq': '402.000 MHz', 'local_dt': "2019-03-01T12:00:03Z"},
		{'datetime':'12:00:02', 'frame': 46, 'freq': '402.000 MHz', 'local_dt': "2019-03-01T12:00:03Z"},
		]

	for _test in test_data:

		_test['datetime_dt'] = imet_fix_datetime(_test['datetime'], local_dt_str = _test['local_dt'])
		print("Input Time: %s, Local Time: %s, Output Time: %s" % (_test['datetime'], _test['local_dt'], _test['datetime_dt'].strftime("%Y-%m-%dT%H:%M:%SZ")))
		_test['id'] = imet_unique_id(_test)
		print("Generated ID: %s" % _test['id'])
		print(" ")