"""
Original Source:
https://web.archive.org/web/20131017130434/http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/
https://web.archive.org/web/20131017130434/http://www.jejik.com/files/examples/daemon3x.py
See daemon3x.py in the uplink source tree.

More Information:
https://franklingu.github.io/programming/2016/03/01/creating-daemon-process-python-example-explanation/
https://dpbl.wordpress.com/2017/02/12/a-tutorial-on-python-daemon/
"""

import sys
import os
import time
import atexit
import signal


# TODO.md: Check why pid files are not being deleted when sending the TERM signal
class Daemon:

	def __init__(self, pid_file):
		self.pid_file = pid_file

	def daemonize(self):
		try:
			pid = os.fork()
			if pid > 0:
				sys.exit(0)
		except OSError as err:
			sys.stderr.write('fork #1 failed: {0}\n'.format(err))
			sys.exit(1)

		os.chdir('/')
		os.setsid()
		os.umask(0)

		try:
			pid = os.fork()
			if pid > 0:
				sys.exit(0)
		except OSError as err:
			sys.stderr.write('fork #2 failed: {0}\n'.format(err))
			sys.exit(1)

		sys.stdout.flush()
		sys.stderr.flush()
		si = open(os.devnull, 'r')
		so = open(os.devnull, 'a+')
		se = open(os.devnull, 'a+')

		os.dup2(si.fileno(), sys.stdin.fileno())
		os.dup2(so.fileno(), sys.stdout.fileno())
		os.dup2(se.fileno(), sys.stderr.fileno())

		atexit.register(self.del_pid)

		pid = str(os.getpid())
		with open(self.pid_file, 'w+') as f:
			f.write(pid + '\n')

	def del_pid(self):
		os.remove(self.pid_file)

	def start(self):
		try:
			with open(self.pid_file, 'r') as pf:
				pid = int(pf.read().strip())
		except IOError:
			pid = None

		if pid:
			message = "pid_file {0} already exist. Daemon already running?\n"
			sys.stderr.write(message.format(self.pid_file))
			sys.exit(1)

		self.daemonize()
		self.run()

	def stop(self):
		try:
			with open(self.pid_file, 'r') as pf:
				pid = int(pf.read().strip())
		except IOError:
			pid = None

		if not pid:
			message = "pid_file {0} does not exist. Daemon not running?\n"
			sys.stderr.write(message.format(self.pid_file))
			return

		try:
			while 1:
				os.kill(pid, signal.SIGTERM)
				time.sleep(0.1)
		except OSError as err:
			e = str(err.args)
			if e.find("No such process") > 0:
				if os.path.exists(self.pid_file):
					os.remove(self.pid_file)
			else:
				print(str(err.args))
				sys.exit(1)

	def restart(self):
		self.stop()
		self.start()

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