#!/usr/bin/env python

import sys
import os
import time
import atexit
import subprocess as sub
from signal import SIGTERM 

# Seconds to sleep between I2C queries
sleep_between_i2c_query = 2

# Grace time between "on-battery" state and "shutdown"
# Actual grace time after the on-battery event is:
# sleep_between_i2c_query * grace_loop = seconds 
grace_loops = 20

class Daemon:
	"""
	A generic daemon class.
	
	Usage: subclass the Daemon class and override the run() method
	"""
	def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/var/log/picoisd.log'):
		self.stdin = stdin
		self.stdout = stdout
		self.stderr = stderr
		self.pidfile = pidfile
	
	def daemonize(self):
		"""
		do the UNIX double-fork magic, see Stevens' "Advanced 
		Programming in the UNIX Environment" for details (ISBN 0201563177)
		http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
		"""
		try: 
			pid = os.fork() 
			if pid > 0:
				# exit first parent
				sys.exit(0) 
		except OSError, e: 
			sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
			sys.exit(1)
	
		# decouple from parent environment
		os.chdir("/") 
		os.setsid() 
		os.umask(0) 
	
		# do second fork
		try: 
			pid = os.fork() 
			if pid > 0:
				# exit from second parent
				sys.exit(0) 
		except OSError, e: 
			sys.stderr.write("fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
			sys.exit(1) 
	
		# redirect standard file descriptors
		sys.stdout.flush()
		sys.stderr.flush()
		si = file(self.stdin, 'r')
		so = file(self.stdout, 'a+')
		se = file(self.stderr, 'a+', 0)
		os.dup2(si.fileno(), sys.stdin.fileno())
		os.dup2(so.fileno(), sys.stdout.fileno())
		os.dup2(se.fileno(), sys.stderr.fileno())
	
		# write pidfile
		atexit.register(self.delpid)
		pid = str(os.getpid())
		file(self.pidfile,'w+').write("%s\n" % pid)
	
	def delpid(self):
		os.remove(self.pidfile)

	def start(self):
		"""
		Start the daemon
		"""
		# Check for a pidfile to see if the daemon already runs
		try:
			pf = file(self.pidfile,'r')
			pid = int(pf.read().strip())
			pf.close()
		except IOError:
			pid = None
	
		if pid:
			message = "pidfile %s already exist. Daemon already running?\n"
			sys.stderr.write(message % self.pidfile)
			sys.exit(1)
		
		# Start the daemon
		self.daemonize()
		self.run()

	def stop(self):
		"""
		Stop the daemon
		"""
		# Get the pid from the pidfile
		try:
			pf = file(self.pidfile,'r')
			pid = int(pf.read().strip())
			pf.close()
		except IOError:
			pid = None
	
		if not pid:
			message = "pidfile %s does not exist. Daemon not running?\n"
			sys.stderr.write(message % self.pidfile)
			return # not an error in a restart

		# Try killing the daemon process	
		try:
			while 1:
				os.kill(pid, SIGTERM)
				time.sleep(0.1)
		except OSError, err:
			err = str(err)
			if err.find("No such process") > 0:
				if os.path.exists(self.pidfile):
					os.remove(self.pidfile)
			else:
				print str(err)
				sys.exit(1)

	def restart(self):
		"""
		Restart the daemon
		"""
		self.stop()
		self.start()

	def run(self):
		"""
		You should override this method when you subclass Daemon. It will be called after the process has been
		daemonized by start() or restart().
		"""

class MyDaemon(Daemon):
	def run(self):
		on_battery_counter = 1
		while True:
			p = sub.Popen(['i2cget', '-y', '1', '0x69', '0x00'], stdout=sub.PIPE, stderr=sub.PIPE)
			out, err = p.communicate()
			ret = p.returncode

			out = out.strip()
			err = err.strip()

			if ret != 0 or err:
				sys.stderr.write(str("Returncode: " + ret + "\n"))
				sys.stderr.write(str("ERRout: " + err + "\n"))
				sys.stderr.write(str("STDout: " + out + "\n"))
				daemon.stop()
				
			if out == "0x01":
				if on_battery_counter > 1:
					sys.stderr.write("\n")
					on_battery_counter = 1

			elif out == "0x02":
				msgtime = time.strftime("%a, %d %b %Y %H:%M:%S", time.localtime())
				msg = "%(date)s: On battery %(loop)s/%(loops)s\n" % {"date": msgtime , "loop": on_battery_counter, "loops": grace_loops}
				sys.stderr.write(msg)
				if on_battery_counter >= grace_loops:
					sys.stderr.write('/sbin/shutdown -h now \n')
					os.system('/sbin/shutdown -h now')
				else:
					on_battery_counter += 1
			else:
				sys.stderr.write("Unknown output: " + out + "\n")
				daemon.stop()
			
			time.sleep(sleep_between_i2c_query)
 	

if __name__ == "__main__":
	daemon = MyDaemon('/var/run/picoisd.pid')
	if len(sys.argv) == 2:
		if 'start' == sys.argv[1]:
			daemon.start()
		elif 'stop' == sys.argv[1]:
			daemon.stop()
		elif 'restart' == sys.argv[1]:
			daemon.restart()
		else:
			print "Unknown command"
			sys.exit(2)
		sys.exit(0)
	else:
		print "usage: %s start|stop|restart" % sys.argv[0]
		sys.exit(2)