import os
import sys


def spawnDaemon(fun):
	# do the UNIX double-fork magic, see Stevens' "Advanced
	# Programming in the UNIX Environment" for details (ISBN 0201563177)
	try:
		pid = os.fork()
		if pid > 0:
			# parent process, return and keep running
			return
	except OSError as e:
		print("fork #1 failed: {0} ({1})".format(e.errno,e.strerror),file=sys.stderr)
		sys.exit(1)

	os.setsid()

	# do second fork
	try:
		pid = os.fork()
		if pid > 0:
			# exit from second parent
			print("[{0}] server running".format(pid))
			sys.exit(0)
	except OSError as e:
		print("fork #2 failed: {0} ({1})".format(e.errno,e.strerror),file=sys.stderr)
		sys.exit(1)

	fun()

	# all done
	os._exit(os.EX_OK)


class Progress:
	def __init__(self,n,i0=0):
		self._n=n
		self._i0=i0
		self._i=i0
		self._last=""

	def p(self,i):
		i0=self._i0
		n=self._n

		assert i0<=i<n or n<i<=i0, (i0,i,n)
		percentage=Progress._p(i,n,i0)
		res="{0}%".format(percentage)
		if res!=self._last:
			print(res,end="\r")
			self._last=res

	def done(self):
		print("100%")

	@staticmethod
	def _p(i,n,i0):
		_1=1 if n>=i0 else -1
		return 100*(i+_1-i0)//(n-i0)