#!/usr/bin/env python
# -*- coding: utf-8 -*-

# Automated Certificate Manager using ACME
# Copyright (c) Markus Hauschild & David Klaftenegger, 2016.
# available under the ISC license, see LICENSE


import acertmgr_ssl
import acertmgr_web
import datetime
import dateutil.relativedelta
import grp
import os
import pwd
import re
import shutil
import subprocess
import tempfile
import yaml


ACME_DIR="/etc/acme/"
ACME_CONF=ACME_DIR + "acme.conf"
ACME_CONFD=ACME_DIR + "domains.d/"


class FileNotFoundError(OSError):
	pass


class InvalidCertificateError(Exception):
	pass

# @brief check whether existing target file is still valid or source crt has been updated
# @param target string containing the path to the target file
# @param crt_file string containing the path to the certificate file
# @return True if target file is at least as new as the certificate, False otherwise
def target_isCurrent(target, crt_file):
	if not os.path.isfile(target):
		return False
	target_date = os.path.getmtime(target)
	crt_date = os.path.getmtime(crt_file)
	return target_date >= crt_date

# @brief check whether existing certificate is still valid or expiring soon
# @param crt_file string containing the path to the certificate file
# @param ttl_days the minimum amount of days for which the certificate must be valid
# @return True if certificate is still valid for at least ttl_days, False otherwise
def cert_isValid(crt_file, ttl_days):
	if not os.path.isfile(crt_file):
		return False
	else:
		(valid_from, valid_to) = acertmgr_ssl.cert_valid_times(crt_file)

		now = datetime.datetime.now()
		if valid_from > now:
			raise InvalidCertificateError("Certificate seems to be from the future")

		expiry_limit = now + dateutil.relativedelta.relativedelta(days=+ttl_days)
		if valid_to < expiry_limit:
			return False

		return True


# @brief fetch new certificate from letsencrypt
# @param domain string containing the domain name
# @param settings the domain's configuration options
def cert_get(domains, settings):
	domain = domains.split(' ')[0]
	print("Getting certificate for %s." % domain)

	key_file = ACME_DIR + "server.key"
	if not os.path.isfile(key_file):
		raise FileNotFoundError("The server key file (%s) is missing!" % key_file)

	acc_file = ACME_DIR + "account.key"
	if not os.path.isfile(acc_file):
		raise FileNotFoundError("The account key file (%s) is missing!" % acc_file)

	_, csr_file = tempfile.mkstemp(".csr", "%s." % domain)
	_, crt_file = tempfile.mkstemp(".crt", "%s." % domain)

	challenge_dir = settings.get("webdir", "/var/www/acme-challenge/")
	if not os.path.isdir(challenge_dir):
		raise FileNotFoundError("Challenge directory (%s) does not exist!" % challenge_dir)

	if settings['mode'] == 'standalone':
		port = settings.get('port', 80)

		current_dir = os.getcwd()
		os.chdir(challenge_dir)
		server = acertmgr_web.ACMEHTTPServer(port)
		server.start()
	try:
		key_fd = open(key_file, "r")
		key = key_fd.read()
		key_fd.close()
		cr = acertmgr_ssl.cert_request(domains.split(), key)
		crt = acertmgr_ssl.get_crt_from_csr(acc_file, cr, domains.split(), challenge_dir, settings['authority'])
		with open(crt_file, "w") as crt_fd:
			crt_fd.write(crt)

		#  if resulting certificate is valid: store in final location
		if cert_isValid(crt_file, 60):
			crt_final = ACME_DIR + "%s.crt" % domain
			shutil.copy2(crt_file, crt_final)

	finally:
		if settings['mode'] == 'standalone':
			server.stop()
			os.chdir(current_dir)
		os.remove(csr_file)
		os.remove(crt_file)


# @brief put new certificate in place
# @param domain string containing the domain name
# @param settings the domain's configuration options
# @return the action to be executed after the certificate update
def cert_put(domain, settings):
	# TODO error handling
	ca_file = settings.get("cafile", "")
	crt_user = settings['user']
	crt_group = settings['group']
	crt_perm = settings['perm']
	crt_path = settings['path']
	crt_format = settings['format'].split(",")
	crt_action = settings['action']

	key_file = ACME_DIR + "server.key"
	crt_final = ACME_DIR + "%s.crt" % domain.split(' ')[0]

	with open(crt_path, "w+") as crt_fd:
		for fmt in crt_format:
			if fmt == "crt":
				src_fd = open(crt_final, "r")
				crt_fd.write(src_fd.read())
				src_fd.close()
			if fmt == "key":
				src_fd = open(key_file, "r")
				crt_fd.write(src_fd.read())
				src_fd.close()
			if fmt == "ca":
				if not os.path.isfile(ca_file):
					raise FileNotFoundError("The server key file (%s) is missing!" % ca_file)
				src_fd = open(ca_file, "r")
				crt_fd.write(src_fd.read())
				src_fd.close()
			else:
				# TODO error handling
				pass

	# set owner and permissions
	uid = pwd.getpwnam(crt_user).pw_uid
	gid = grp.getgrnam(crt_group).gr_gid
	try:
		os.chown(crt_path, uid, gid)
	except OSError:
		print('Warning: Could not set certificate file ownership!')
	try:
		os.chmod(crt_path, int(crt_perm, 8))
	except OSError:
		print('Warning: Could not set certificate file permissions!')

	return crt_action


# @brief augment configuration with defaults
# @param domainconfig the domain configuration
# @param defaults the default configuration
# @return the augmented configuration
def complete_config(domainconfig, defaults):
	if defaults:
		for name, value in defaults.items():
			if name not in domainconfig:
				domainconfig[name] = value
	if 'action' not in domainconfig:
		domainconfig['action'] = None
	return domainconfig


if __name__ == "__main__":
	# load global configuration
	if os.path.isfile(ACME_CONF):
		with open(ACME_CONF) as config_fd:
			config = yaml.load(config_fd)
	if not config:
		config = {}
	if 'defaults' not in config:
		config['defaults'] = {}

	config['domains'] = []
	# load domain configuration
	for config_file in os.listdir(ACME_CONFD):
		if config_file.endswith(".conf"):
			with open(ACME_CONFD + config_file) as config_fd:
				for entry in yaml.load(config_fd).items():
					config['domains'].append(entry)

	# post-update actions (run only once)
	actions = set()

	# check certificate validity and obtain/renew certificates if needed
	for domains, domaincfgs in config['domains']:
		# skip domains without any output files
		if domaincfgs is None:
			continue
		crt_file = ACME_DIR + "%s.crt" % domains.split(' ')[0]
		ttl_days = int(config.get('ttl_days', 15))
		if not cert_isValid(crt_file, ttl_days):
			cert_get(domains, config)
		for domaincfg in domaincfgs:
			cfg = complete_config(domaincfg, config['defaults'])
			if not target_isCurrent(cfg['path'], crt_file):
				actions.add(cert_put(domains, cfg))

		# run post-update actions
		for action in actions:
			if action is not None:
				subprocess.call(action.split())