from os import path,rename
def init():
	if not path.exists(config['path']): raise Exception(f"Backend directory doesn't exist: {config['path']}")
	for n in ['users','invite_tokens','access_tokens']:
		p=path.join(config['path'],n+'.csv')
		globals()[n]=p
		if not path.exists(p): open(p,'w').write('\n')
		if path.isdir(p): raise Exception(f"Backend file is a directory: {p}")
		try: open(p).close()
		except PermissionError: raise Exception(f"Backend file can't be read: {p}")
		try: open(p,'a').close()
		except PermissionError: raise Exception(f"Backend file can't be written: {p}")

def _load(name,pos,file,obj):
	for line in linegen(file):
		split=line.split(',')
		if split[pos]==name: return obj(*split)
	raise Exception(f'No such {obj.__name__} with identifier {name}')
def _load_multi(name,pos,file,obj):
	out=[]
	for line in linegen(file):
		split=line.split(',')
		if split[pos]==name: out.append(obj(*split))
	return out
def _save(thing,pos,file,comp):
	gen=linegen(file)
	for line in gen:
		split=line.split(',')
		if split[pos]==comp: update(file,{gen.send(True):thing.serialise}); break
	else: update(file,{-1:thing.serialise})
def _delete(thing,pos,file,comp):
	gen=linegen(file)
	for line in gen:
		split=line.split(',')
		if split[pos]==comp: remove(file,[gen.send(True)]); break

def load_user(username):
	return _load(username,0,users,models.User)
def save_user(user):
	return _save(user,0,users,user.username)
def delete_user(user):
	return _delete(user,0,users,user.username)

def load_token(tokeid):
	return _load(tokeid,0,access_tokens,models.AccessToken)
def load_tokens(user):
	return _load_multi(user.username,1,access_tokens,models.AccessToken)
def save_token(token):
	return _save(token,0,access_tokens,token.value)
def delete_token(token):
	return _delete(token,0,access_tokens,token.value)

def load_invite(tokeid):
	return _load(tokeid,0,invite_tokens,models.InviteToken)
def load_invites(user):
	return _load_multi(user.username,1,invite_tokens,models.InviteToken)
def save_invite(token):
	return _save(token,0,invite_tokens,token.value)
def delete_invite(token):
	return _delete(token,0,invite_tokens,token.value)

def linegen(path):
	i=0
	file=open(path)
	line=file.readline().rstrip('\n') # Maybe sometimes there won't be one.
	while line:
		i+=1
		response=yield line
		if response is not None: yield i
		line=file.readline()
	file.close()

def update(path,lines):
	def _action(file,i,line):
		if i in lines: file.write(lines[i]+'\n')
		else: file.write(line)
	def _post(file):
		if -1 in lines: file.write(lines[-1]+'\n')
	writefile(path,_action,_post)

def remove(path,lines):
	def _action(file,i,line):
		if i not in lines: file.write(line)
	writefile(path,_action)

def writefile(path,action,post=None):
	i=0
	file=open(path)
	write=open(f'{path}.tmp','w')
	line=file.readline()
	while line:
		i+=1
		action(write,i,line)
		line=file.readline().rstrip('\n')
	if post is not None: post(write)
	file.close()
	write.close()
	rename(f'{path}.tmp',path)