#!/usr/bin/env python3
#
# This script is used both to register what the atmospheric
# pressure was at the start of the last run and to periodically
# update the pressure difference that has occured since then.
#
# This is run from two places:
#
# 1. The run_prestart (run_prestart.local) script with the
#    "PRESTART" argument
#
# 2. A cronjob from the hdops account on gluon47 with no
#    arguments
#
#
# For case 1. all PVs listed below are updated
#
# For case 2. only the hb, p_diff, and t_diff variables
#             are updated
#
#
# The HD:coda:atm_pressure:p_diff value is used to alarm
# which provides notification to the shoft worker when
# it goes out of range (currently >0.1). The alarm only
# makes sense when a run is in progress. Thus, the 
# the value of HD:coda:daq:status is checked to be non-zero.
# If it is not, then a value of 0 is written to p_diff
# to avoid alarming.
#
# n.b. HD:coda:daq:status is set to 0 at run end, 1 at
# prestart, and 2 at go. The value is set in the CODA
# state transition scripts found in $DAQ_HOME/scripts.
#
#
# HD:coda:atm_pressure:hb
# HD:coda:atm_pressure:p0
# HD:coda:atm_pressure:p_diff
# HD:coda:atm_pressure:t0
# HD:coda:atm_pressure:t_diff
#
#
# The pressure does not need to be checked more than once
# every few minutes. However, the heartbeat should occur
# every 2 seconds. The choice is whether to have this
# script run continuously or to be run periodically via
# cronjob. It is considered more robust to have cron run
# this script periodically. Thus, this will set the PVs
# appropriately upon startup, but then continue to update 
# the heartbeat for 2 minutes before exiting. This will
# all detection if the heartbeat is failing which indicates
# an issue with this script, while still allowing cron to
# run the script.
#
# Note: This means the time this script lives for while
# updating the heartbeat should match the period in the 
# crontab!
#

import sys
import time
from epics import *

# Total time to live for this script. Script will continue
# to update heartbeat until this amount of time has passed
# and then exit. This should match cronjob period (see
# above).
max_time_to_live = 119.0  # seconds
tstart = time.time()

# Timeout for epics operations
timeout = 2.0

# TODO: The calls to caget() below are protected via timeout,
# TODO: but nothing checks for if this actually happens.
# TODO: (does caget return None in this case?)

# Set p0 and t0
if 'PRESTART' in sys.argv[1:]:
	# Set pressure and time
	print('atm_pressure_monitor: setting p0 and t0')
	caput('HD:coda:atm_pressure:p0', caget('RESET:i:GasPanelBarPress1', timeout=timeout), timeout=timeout )
	caput('HD:coda:atm_pressure:t0', time.time(), timeout=timeout )
	print('atm_pressure_monitor: done')

# Set p_diff and t_diff
print('atm_pressure_monitor: setting p_diff and t_diff')
p_diff = caget('RESET:i:GasPanelBarPress1', timeout=timeout) - caget('HD:coda:atm_pressure:p0', timeout=timeout )
t_diff = time.time() - caget('HD:coda:atm_pressure:t0', timeout=timeout )
coda_status = caget('HD:coda:daq:status', timeout=timeout)
if int(coda_status) == 0: p_diff=0.0
caput('HD:coda:atm_pressure:p_diff', abs(p_diff), timeout=timeout)
caput('HD:coda:atm_pressure:t_diff',     t_diff , timeout=timeout)
print('atm_pressure_monitor: done')

# Sleep for two seconds at a time, updating heartbeat,
# until we have lived for max_time_to_live
while (time.time()-tstart) < max_time_to_live:
	# update heartbeat
	print('atm_pressure_monitor: heartbeat ...')
	caput('HD:coda:atm_pressure:hb', caget('HD:coda:atm_pressure:hb')+1)
	# sleep for 2 seconds
	time.sleep(2.0)

# n.b. This script seems to seg. fault on exit. This is an issue
# with pyepics.