import shutil
import os
import re

try:
	shutil.move("./xhtml/nav.xhtml", ".")

	with open('nav.xhtml', 'r') as f : #read the file and modify nav.xhtml link
		filedata = f.read()
	filedata = filedata.replace(r'href="', r'href="xhtml/')

	with open('nav.xhtml', 'w') as f : #reopen the file and write the replaced contents
		f.write(filedata)

except shutil.Error: #my exercise :)
	print("The nav.xhtml was already moved. First phase was skipped.")


with open('package.opf', 'r') as f : #modify package.opf links
	filedata = f.read()
filedata = filedata.replace(r"xhtml/nav.xhtml", r"nav.xhtml")

with open('package.opf', 'w') as f :
	f.write(filedata)