#!/usr/bin/env python3
# Copyright (c) 2014, Ralf Jung <post@ralfj.de>
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
# 
# 1. Redistributions of source code must retain the above copyright notice, this
#    list of conditions and the following disclaimer. 
# 2. Redistributions in binary form must reproduce the above copyright notice,
#    this list of conditions and the following disclaimer in the documentation
#    and/or other materials provided with the distribution.
# 
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#==============================================================================

import urllib.request, socket, sys, argparse, os, configparser, itertools, subprocess, re

def readConfig(fname, defSection = 'DEFAULT'):
    config = configparser.ConfigParser()
    with open(fname) as file:
        stream = itertools.chain(("["+defSection+"]\n",), file)
        config.read_file(stream)
    return config

def getConfigDir():
    try:
        from xdg import BaseDirectory
        return os.path.join(BaseDirectory.xdg_config_home, "dyn-nsupdate")
    except ImportError:
        return os.path.expanduser("~/.config/dyn-nsupdate")

def urlopen(url):
    return urllib.request.urlopen(url).read().decode('utf-8').strip()

def getMyIP(family, config, methods = {}, verbose = False):
    '''Returns our current IP address (<family> can be "IPv4" or "IPv6"), detected as given by the configuration.
       Additional detection methods can be supplied via <methods>.'''
    method = config[family]['method']
    if method == 'none':
        return None
    elif method == 'web':
        server = config[family].get('server', config['DEFAULT']['server'])
        ip = urlopen('https://'+server+'/checkip')
        if verbose:
            print("Server",server,"says my",family,"is",ip)
        return ip
    elif method in methods:
        return methods[method]()
    else:
        raise Exception("Unsupported "+family+" detection method: "+method)

def getMyIPv4(config, verbose = False):
    '''Returns our current IPv4 address, detected as given by the configuration'''
    return getMyIP("IPv4", config, verbose=verbose)

def getMyIPv6(config, verbose = False):
    '''Returns our current IPv6 address, detected as given by the configuration'''
    def local():
        out = subprocess.check_output(["ip", "addr"])
        for line in out.decode('utf-8').split('\n'):
            m = re.search('inet6 ([a-fA-F0-9:]+)/64 ([a-zA-Z0-9 ]*)', line)
            if m is not None:
                ip = m.group(1)
                flags = m.group(2).split()
                if not 'temporary' in flags and not 'deprecated' in flags:
                    if verbose:
                        print("Local IPv6 detected to be",ip)
                    return ip
        raise Exception("Unable to detect correct local IPv6 address")
    return getMyIP("IPv6", config, methods={'local': local}, verbose=verbose)

def getCurIP(domain, family):
    '''Return the current IP of the given <domain>. <family> can be socket.AF_INET or socket.AF_INET6.'''
    try:
        addr = socket.getaddrinfo(domain, None, family=family)
        return addr[0][4][0]
    except socket.gaierror: # domain not found
        return ""

def getCurIPv4(domain):
    '''Returns the current IPv4 address of the given domain'''
    return getCurIP(domain, socket.AF_INET)

def getCurIPv6(domain):
    '''Returns the current IPv6 address of the given domain'''
    return getCurIP(domain, socket.AF_INET6)

def updateDomain(server, domain, ipv4, ipv6, password, verbose):
    '''Update the given domain, using the server, password. ipv4 or ipv6 can be None to not update that record, or strings with the respective addresses.
       Updates ae only performed if necessary.
       Returns True on success, False on failure.'''
    assert ipv4 is not None or ipv6 is not None
    
    # check what the domain is currently mapped to
    curIPv4 = getCurIPv4(domain)
    curIPv6 = getCurIPv6(domain)
    if verbose:
        print("Current status of domain {} is: IPv4 address '{}', IPv6 address '{}'".format(domain, curIPv4, curIPv6))
    
    # check if there's something to do
    needUpdate = (ipv4 is not None and curIPv4 != ipv4) or (ipv6 is not None and curIPv6 != ipv6)
    if not needUpdate:
        if verbose:
            print("Everything already up-to-date, nothing to do")
        return True

    # we need to update the IP
    url = 'https://'+server+'/update?password='+urllib.parse.quote(password)+'&domain='+urllib.parse.quote(domain)
    expected = "good"
    if ipv4 is not None:
        url += '&ip='+urllib.parse.quote(ipv4)
        expected += " "+ipv4
    if ipv6 is not None:
        url += '&ipv6='+urllib.parse.quote(ipv6)
        expected += " "+ipv6
    result = urlopen(url)
    
    # did everything go as planned?
    if result == expected:
        if verbose:
            print("Successfully updated domain",domain,"on",server)
        # all went all right
        return True
    else:
        # Something went wrong
        print("Unexpected answer from server",server,"while updating",domain)
        print(result)
        return False

if __name__ == "__main__":
    # allow overwriting some values on the command-line
    parser = argparse.ArgumentParser(description='Update a domain managed by a dyn-nsupdate server')
    parser.add_argument("-c", "--config",
                        dest="config", default=os.path.join(getConfigDir(), "dyn-ns-client.conf"),
                        help="The configuration file")
    parser.add_argument("-v", "--verbose",
                        action="store_true", dest="verbose",
                        help="Be more verbose")
    args = parser.parse_args()
    
    # read config
    if not os.path.isfile(args.config):
        raise Exception("The config file does not exist: "+args.config)
    config = readConfig(args.config)

    # get our own addresses
    myIPv4 = getMyIPv4(config, args.verbose)
    myIPv6 = getMyIPv6(config, args.verbose)

    # update all the domains
    exitcode = 0
    domains = map(str.strip, config['DEFAULT']['domains'].split(','))
    if not domains:
        raise Exception("No domain given to update!")
    for domain in domains:
        if not updateDomain(config['DEFAULT']['server'], domain, myIPv4, myIPv6, config['DEFAULT']['password'], verbose=args.verbose):
            exitcode = 1
    sys.exit(exitcode)