#!/usr/bin/env python3

import os
import json
import sys
import signal
import logging
import time
import hashlib
import threading

import list_domains
from docker import Client

cert_path = '/data/haproxy'
cert_file = cert_path + '/cert.pem'
pid_file = '/haproxy.pid'
max_age = 24 * 60 * 60
delay = 10


def hash_cert_file():
    """Creates the sha256 hash of the certificate file for HAProxy. If the file
    does not exist, an empty string is returned.
    """
    if not os.path.isfile(cert_file):
        return ''
    file_obj = open(cert_file, 'rb')
    hash_generator = hashlib.sha256()
    buf = file_obj.read(65536)
    while len(buf) > 0:
        hash_generator.update(buf)
        buf = file_obj.read(65536)
    return hash_generator.digest()


def setup_logging():
    """Sets up logging with a nice format"""
    logging.basicConfig(format='%(asctime)s [%(levelname)s]: %(message)s', level=logging.INFO)


def get_pid():
    """This function reads the process id from the given file and returns as int."""
    with open(pid_file, 'r') as file:
        return int(file.read())


def kill_haproxy():
    """Stops the currently running instance of HAProxy by issuing a kill signal to its pid."""
    logging.info('killing HAProxy')
    try:
        os.kill(get_pid(), signal.SIGKILL)
    except OSError:
        pass


def start_haproxy_ssl():
    """Start HAProxy with SSL activated. Returns True, if HAProxy is running, False otherwise."""
    kill_haproxy()
    logging.info('starting HAProxy with SSL')
    os.system('/usr/sbin/haproxy -f /haproxy_ssl.conf -p ' + pid_file)
    return is_haproxy_running()


def start_haproxy():
    """Start HAProxy without SSL activated. Returns True, if HAProxy is running, False otherwise."""
    kill_haproxy()
    logging.info('starting HAProxy without SSL')
    os.system('/usr/sbin/haproxy -f /haproxy.conf -p ' + pid_file)
    return is_haproxy_running()


def is_haproxy_running():
    """Check if HAProxy is running by sending a signal to its pid."""
    try:
        os.kill(get_pid(), 0)
        return True
    except OSError:
        return False


def ssl_possible():
    """Check if a certificate is available."""
    if not os.path.isfile(cert_file):
        return False
    else:
        return True


def read_file(filename):
        file=open(filename, 'r')
        read_data = file.read()
        file.close()
        return read_data


def write_file(filename, content):
        file=open(filename, 'w')
        file.write(content)
        file.close()


def create_haproxy_cert():
    """Combines the freshly created fullchain.pem and privkey.pem into /data/haproxy/cert.pem"""
    logging.info('updating %s', cert_file)

    # make sure the path exists...
    if not os.path.exists(cert_path):
        logging.info('creating cert_path path: %s', cert_path)
        os.mkdir(cert_path)

    # find the youngest directory
    youngest_modify_time = 0
    youngest_directory = ''
    for root, directories, files in os.walk('/data/config/live'):
        for directory in directories:
            modify_time = os.stat('/data/config/live/' + directory).st_mtime
            if modify_time > youngest_modify_time:
                youngest_modify_time = modify_time
                youngest_directory = directory
    youngest_directory = '/data/config/live/' + youngest_directory

    logging.info('using %s as base dir', youngest_directory)

    # read fullchain.pem and privkey.pem
    if not os.path.exists(youngest_directory + '/fullchain.pem') or not os.path.exists(youngest_directory + '/privkey.pem'):
        logging.info('either fullchain.pem or privkey.pem is missing.')
        return

    fullchain = read_file(youngest_directory + '/fullchain.pem')
    privkey = read_file(youngest_directory + '/privkey.pem')
    return fullchain + privkey


def create_cert_data_standalone(domains):
    if len(domains) == 0:
        logging.info('no domains for SSL found.')
        return

    domains = " -d ".join(domains)

    # we should use tls-sni-01 if ssl is already running!
    os.system(
        '/letsencrypt/letsencrypt-auto --config letsencrypt.conf certonly --http-01-port 54321 -d ' + domains)


def cert_watcher():
    ssl_active = ssl_possible() and is_haproxy_running()
    cert_file_hash = hash_cert_file()
    while True:
        time.sleep(delay)

        if not ssl_active:
            if ssl_possible():
                # we should be able to start with SSL, but ...
                kill_haproxy()
                start_haproxy_ssl()
                if is_haproxy_running():
                    # running with SSL succeeded
                    cert_file_hash = hash_cert_file()
                    logging.info('NON SSL -> SSL')
                    ssl_active = True
                else:
                    # something went wrong (maybe broken certificate) but without SSL we can run it
                    start_haproxy()
                    logging.info('NON SSL -> NON SSL')
            else:
                # currently not running with SSL but also no cert, so we do not attempt to start with SSL
                pass
        else:
            if cert_file_hash != hash_cert_file():
                # we are running with SSL and the certificate has changed so we need to restart haproxy
                logging.info('cert has changed')
                kill_haproxy()
                start_haproxy_ssl()
                if is_haproxy_running():
                    # restart with SSL succeeded, update hash
                    logging.info('SSL -> SSL')
                else:
                    # restart with SSL failed, so we start without SSL again
                    start_haproxy()
                    logging.info('SSL -> NON SSL')
                    ssl_active = False
                cert_file_hash = hash_cert_file()


if __name__ == '__main__':
    setup_logging()

    logging.info('starting ssl endpoint')

    client = Client(base_url='unix://var/run/docker.sock', version='1.15')

    # try to start in SSL mode, no problem if that fails
    logging.info('try in SSL mode')
    if not start_haproxy_ssl():
        logging.info('SSL mode failed')

    if not is_haproxy_running():
        # tried to start haproxy and this failed, so we need to create a certificate and try again:
        #  - start non ssl haproxy to be able to get a valid cert
        logging.info('try in NON SSL mode')
        start_haproxy()
        #  - get all domains
        resolved_domains = list_domains.get_resolving_domains_from_containers(client)
        #  - create cert
        create_cert_data_standalone(resolved_domains)
        create_haproxy_cert()
        start_haproxy_ssl()

    # now we should have it up and running or something weird happened.
    if not is_haproxy_running():
        logging.error('could not start after generating cert. See output above.')
        sys.exit(1)

    t = threading.Thread(target=cert_watcher)
    t.start()

    cert_cache = {}
    for line in client.events():
        line_str = line.decode("utf-8")
        event = json.loads(line_str)

        if event['Action'] in ['create']:
            # check if there is any domain name configured
            container_id = event['id']
            if len(list_domains.handle_container(client, container_id)) > 0:
                resolved_domains = list_domains.get_resolving_domains_from_containers(client)
                resolved_domains = sorted(resolved_domains)
                if resolved_domains in cert_cache:
                    cached_data = cert_cache[resolved_domains]
                    if time.time() - cached_data['time'] <= max_age:
                        logging.info('get cached cert: %s s old', time.time() - cached_data['time'])
                        write_file(cert_file, cached_data['data'])
                        logging.info('file written')
                        continue
                # no previous data or to old
                logging.info('create new cert')
                create_cert_data_standalone(resolved_domains)
                cert_data = create_haproxy_cert()
                cert_cache[resolved_domains] = {
                    'time': time.time(),
                    'data': cert_data
                }
                write_file(cert_file, cert_data)
                logging.info('file written')