#!/usr/bin/python3.4

from docker import Client
from docker.errors import APIError
from string import Template
import json
import signal
import os
import logging

target_path="/tmp/nginx/"
pid_file="/var/run/nginx.pid"
non_location_template = """# proxy for container '$containername'
server {
    listen $listen;
    server_name $name;
    location / {
        proxy_set_header X-Real-IP  $$remote_addr;
        proxy_set_header X-Forwarded-For $$remote_addr;
        proxy_set_header Host $$host;
        proxy_pass http://$ip:$port/;
    }
}
"""

location_template="""# proxy for container '$containername'
server {
    listen $listen;
    server_name $name;
    location / {
        return 301 $$scheme://$name/$location;
    }
    location /$location {
        proxy_set_header X-Real-IP  $$remote_addr;
        proxy_set_header X-Forwarded-For $$remote_addr;
        proxy_set_header Host $$host;
        proxy_pass http://$ip:$port/;
    }
}
"""

def print_json(data):
    """Prints the given value in JSON to stdout. Use this for debugging only"""
    print(json.dumps(data, sort_keys=True, indent=4))

def analyse_env_vars(inspect_data):
    """Extracts the environment variables from the given result of an 'inspect
        container' call."""
    env_data = {}
    for env_var in inspect_data['Config']['Env']:
        t = env_var.split("=")
        env_data[t[0]] = t[1]
    return env_data

def analyse_proxy_data(data):
    """Extracts the data for the proxy configuration (envrionment variable
        'PROXY_DATA' and converts it to a dictionary."""
    proxy_data = {}
    for proxy_var in data['PROXY_DATA'].split(','):
        t = proxy_var.split(":",1)
        proxy_data[t[0]] = t[1]
    return proxy_data

def extract_ip(inspect_data):
    """extracts the container's ip from the given inspect data"""
    return inspect_data['NetworkSettings']['IPAddress']

def extract_name(inspect_data):
    """extracts the container's name from the given inspect data"""
    return inspect_data['Name']

def get_if_available(dict, key, defValue):
    if key in dict:
        return dict[key]
    else:
        return defValue

def handle_container(id):
    """This function take a container's id and collects all data required
        to create a proper proxy configuration. The configuration is then
        written to the directory of temporary nginx files"""
    inspect_data = client.inspect_container(id)
    env_vars = analyse_env_vars(inspect_data)
    if 'PROXY_DATA' in env_vars:
        proxy_data = analyse_proxy_data(env_vars)
        substitutes = {
            'containername': extract_name(inspect_data),
            'ip': extract_ip(inspect_data),
            'location': get_if_available(proxy_data, 'location', ''),
            'name': get_if_available(proxy_data, 'server_name', ''),
            'port': get_if_available(proxy_data, 'port', 80),
            'listen': get_if_available(proxy_data, 'ip', '*') + ':80'
        }
        logging.info('writing to %sproxy_%s', target_path, id)
        with open(target_path + '/proxy_'+id, 'w') as file:
            if substitutes['location'] == '':
                del substitutes['location']
                file.write(Template(non_location_template).substitute(substitutes))
            else:
                file.write(Template(location_template).substitute(substitutes))

def reload_nginx_configuration():
    logging.info('HUPing nginx')
    os.kill(pid, signal.SIGHUP)

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

def setup_logging():
    logging.basicConfig(format='%(asctime)s [%(levelname)s]: %(message)s', level=logging.INFO)

if __name__ == '__main__':
    setup_logging()

    # prepare required stuff
    pid = get_pid()
    logging.info('nginx pid: %s', str(pid))
    if not os.path.exists(target_path):
        logging.info('creating target path: %s', target_path)
        os.mkdir(target_path)

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

    # handle all running containers existing at startup of this container
    container_ids = client.containers(quiet=True)
    for container_id in container_ids:
        handle_container(container_id['Id'])
    reload_nginx_configuration()

    # hook to the events
    for line in client.events():
        line_str = line.decode("utf-8")
        event = json.loads(line_str)

        container_id = event['id']
        try:
            inspect_data = client.inspect_container(container_id)
            ip = extract_ip(inspect_data)
        except APIError:
            ip = ''

        if ip == '':
            logging.info('removing %sproxy_%s', target_path, container_id)
            if os.path.exists(target_path + 'proxy_' + container_id):
                os.remove(target_path + 'proxy_' + container_id)
        else:
            handle_container(container_id)

        reload_nginx_configuration()