#!/usr/bin/python
# -*- coding: utf-8 -*-
#
# Copyright 2015 clowwindy
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

# SOCKS5 UDP Request
# +----+------+------+----------+----------+----------+
# |RSV | FRAG | ATYP | DST.ADDR | DST.PORT |   DATA   |
# +----+------+------+----------+----------+----------+
# | 2  |  1   |  1   | Variable |    2     | Variable |
# +----+------+------+----------+----------+----------+

# SOCKS5 UDP Response
# +----+------+------+----------+----------+----------+
# |RSV | FRAG | ATYP | DST.ADDR | DST.PORT |   DATA   |
# +----+------+------+----------+----------+----------+
# | 2  |  1   |  1   | Variable |    2     | Variable |
# +----+------+------+----------+----------+----------+

# shadowsocks UDP Request (before encrypted)
# +------+----------+----------+----------+
# | ATYP | DST.ADDR | DST.PORT |   DATA   |
# +------+----------+----------+----------+
# |  1   | Variable |    2     | Variable |
# +------+----------+----------+----------+

# shadowsocks UDP Response (before encrypted)
# +------+----------+----------+----------+
# | ATYP | DST.ADDR | DST.PORT |   DATA   |
# +------+----------+----------+----------+
# |  1   | Variable |    2     | Variable |
# +------+----------+----------+----------+

# shadowsocks UDP Request and Response (after encrypted)
# +-------+--------------+
# |   IV  |    PAYLOAD   |
# +-------+--------------+
# | Fixed |   Variable   |
# +-------+--------------+

# HOW TO NAME THINGS
# ------------------
# `dest`    means destination server, which is from DST fields in the SOCKS5
#           request
# `local`   means local server of shadowsocks
# `remote`  means remote server of shadowsocks
# `client`  means UDP clients that connects to other servers
# `server`  means the UDP server that handles user requests

from __future__ import absolute_import, division, print_function, \
    with_statement

import sys
import socket
import logging
import struct
import errno
import random

from shadowsocks import encrypt, eventloop, lru_cache, common, shell
from shadowsocks.common import parse_header, pack_addr, onetimeauth_verify, \
    onetimeauth_gen, ONETIMEAUTH_BYTES, ADDRTYPE_AUTH


BUF_SIZE = 65536


def client_key(source_addr, server_af):
    # notice this is server af, not dest af
    return '%s:%s:%d' % (source_addr[0], source_addr[1], server_af)


class UDPRelay(object):
    def __init__(self, config, dns_resolver, is_local, stat_callback=None):
        self._config = config
        if is_local:
            self._listen_addr = config['local_address']
            self._listen_port = config['local_port']
            self._remote_addr = config['server']
            self._remote_port = config['server_port']
        else:
            self._listen_addr = config['server']
            self._listen_port = config['server_port']
            self._remote_addr = None
            self._remote_port = None
        self._dns_resolver = dns_resolver
        self._password = common.to_bytes(config['password'])
        self._method = config['method']
        self._timeout = config['timeout']
        if 'one_time_auth' in config and config['one_time_auth']:
            self._one_time_auth_enable = True
        else:
            self._one_time_auth_enable = False
        self._is_local = is_local
        self._cache = lru_cache.LRUCache(timeout=config['timeout'],
                                         close_callback=self._close_client)
        self._client_fd_to_server_addr = \
            lru_cache.LRUCache(timeout=config['timeout'])
        self._dns_cache = lru_cache.LRUCache(timeout=300)
        self._eventloop = None
        self._closed = False
        self._sockets = set()
        if 'forbidden_ip' in config:
            self._forbidden_iplist = config['forbidden_ip']
        else:
            self._forbidden_iplist = None

        addrs = socket.getaddrinfo(self._listen_addr, self._listen_port, 0,
                                   socket.SOCK_DGRAM, socket.SOL_UDP)
        if len(addrs) == 0:
            raise Exception("UDP can't get addrinfo for %s:%d" %
                            (self._listen_addr, self._listen_port))
        af, socktype, proto, canonname, sa = addrs[0]
        server_socket = socket.socket(af, socktype, proto)
        server_socket.bind((self._listen_addr, self._listen_port))
        server_socket.setblocking(False)
        self._server_socket = server_socket
        self._stat_callback = stat_callback

    def _get_a_server(self):
        server = self._config['server']
        server_port = self._config['server_port']
        if type(server_port) == list:
            server_port = random.choice(server_port)
        if type(server) == list:
            server = random.choice(server)
        logging.debug('chosen server: %s:%d', server, server_port)
        return server, server_port

    def _close_client(self, client):
        if hasattr(client, 'close'):
            self._sockets.remove(client.fileno())
            self._eventloop.remove(client)
            client.close()
        else:
            # just an address
            pass

    def _handle_server(self):
        server = self._server_socket
        data, r_addr = server.recvfrom(BUF_SIZE)
        key = None
        iv = None
        if not data:
            logging.debug('UDP handle_server: data is empty')
        if self._stat_callback:
            self._stat_callback(self._listen_port, len(data))
        if self._is_local:
            frag = common.ord(data[2])
            if frag != 0:
                logging.warn('UDP drop a message since frag is not 0')
                return
            else:
                data = data[3:]
        else:
            data, key, iv = encrypt.dencrypt_all(self._password,
                                                 self._method,
                                                 data)
            # decrypt data
            if not data:
                logging.debug(
                    'UDP handle_server: data is empty after decrypt'
                )
                return
        header_result = parse_header(data)
        if header_result is None:
            return
        addrtype, dest_addr, dest_port, header_length = header_result

        if self._is_local:
            server_addr, server_port = self._get_a_server()
        else:
            server_addr, server_port = dest_addr, dest_port
            # spec https://shadowsocks.org/en/spec/one-time-auth.html
            if self._one_time_auth_enable or addrtype & ADDRTYPE_AUTH:
                if len(data) < header_length + ONETIMEAUTH_BYTES:
                    logging.warn('UDP one time auth header is too short')
                    return
                _hash = data[-ONETIMEAUTH_BYTES:]
                data = data[: -ONETIMEAUTH_BYTES]
                _key = iv + key
                if onetimeauth_verify(_hash, data, _key) is False: