#!/usr/bin/env python3

import os
import shutil
import sys

class DnsFixer:
	
	DEBUG=True
	
	def __init__(self):
		
		self.dns_file="/var/lib/dnsmasq/config/extra-dns"
		self.backup_dir="/var/backups/"
		self.old_dns=["172.27.111.5","172.27.111.6"]
		self.new_dns=["10.239.3.7","10.239.3.8"]
		
		if self.check_dns_file():
			self.pprint("Old DNSs detected")
			self.create_backup()
			new_lines=self.prepare_new_content()
			self.write_new_file(new_lines)
			self.restart_dnsmasq()
			self.pprint("Done")
		else:
			self.pprint("Nothing to do. Exiting ...")
			
		
	#def init
	
	def pprint(self,data):
		
		if DnsFixer.DEBUG:
			print("[DnsFixer] %s"%str(data))
			
	#def pprint
	
	def read_dns_file(self):
		
		f=open(self.dns_file)
		dns_lines=f.readlines()
		f.close()
		
		return dns_lines
		
	#def read_dns_file
	
	def check_dns_file(self):
		
		self.pprint("Checking '%s' ..."%self.dns_file)
		if not os.path.exists(self.dns_file):
			return False
			
		self.dns_lines=self.read_dns_file()
		
		for line in self.dns_lines:
			for dns in self.old_dns:
				if dns in line:
					return True
					
		return False
		
	#def check_dns_file
	
	def prepare_new_content(self):
		
		new_lines=[]
		for line in self.dns_lines:
			line=line.replace(self.old_dns[0],self.new_dns[0])
			line=line.replace(self.old_dns[1],self.new_dns[1])
			new_lines.append(line)
			
		return new_lines
		
	#def prepare_new_content
	
	def create_backup(self):
		
		self.pprint("Creating backup file...")
		if not os.path.exists(self.backup_dir):
			os.makedirs(self.backup_dir)
		shutil.copy(self.dns_file,self.backup_dir+"extra-dns.old")
		self.pprint("\t"+self.backup_dir+"extra-dns.old")
		
	#def create_backup
	
	def write_new_file(self,new_lines):
		
		file_name=self.dns_file
				
		self.pprint("Writing new config file...")
		self.pprint("\t%s"%file_name)
		f=open(file_name,"w")
		
		for line in new_lines:
			f.write(line)
		f.close()
		
		
	#def write_new_file
	
	def restart_dnsmasq(self):
		
		self.pprint("Restarting dnsmasq...")
		os.system("systemctl restart dnsmasq || true")
		
	#def restart_dnsmasq
	
#class DnsFixer


if __name__=="__main__":
	
	df=DnsFixer()