#!/usr/bin/env python
#
# Copyright 2015-2015 breakwa11
#
# 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.

from __future__ import absolute_import, division, print_function, \
    with_statement

import os
import sys
import hashlib
import logging
import binascii
import base64
import datetime
import struct

from shadowsocks.obfsplugin import plain
from shadowsocks import common
from shadowsocks.common import to_bytes, to_str, ord

def create_verify_obfs(method):
    return verify_simple(method)

obfs = {
        'verify_simple': (create_verify_obfs,),
}

def match_begin(str1, str2):
    if len(str1) >= len(str2):
        if str1[:len(str2)] == str2:
            return True
    return False

class verify_simple(plain.plain):
    def __init__(self, method):
        self.method = method
        self.recv_buf = b''
        self.unit_len = 8100

    def pack_data(self, buf):
        if len(buf) == 0:
            return b''
        rnd_data = os.urandom(common.ord(os.urandom(1)[0]) % 16)
        data = common.chr(len(rnd_data) + 1) + rnd_data + buf
        data = struct.pack('>H', len(data) + 6) + data
        crc = (0xffffffff - binascii.crc32(data)) & 0xffffffff
        data += struct.pack('<I', crc)
        return data

    def client_pre_encrypt(self, buf):
        ret = b''
        while len(buf) > self.unit_len:
            ret += self.pack_data(buf[:self.unit_len])
            buf = buf[self.unit_len:]
        ret += self.pack_data(buf)
        return ret

    def client_encode(self, buf):
        return buf

    def client_decode(self, buf):
        # (buffer_to_recv, is_need_to_encode_and_send_back)
        return (buf, False)

    def client_post_decrypt(self, buf):
        return buf

    def server_pre_encrypt(self, buf):
        ret = b''
        while len(buf) > self.unit_len:
            ret += self.pack_data(buf[:self.unit_len])
            buf = buf[self.unit_len:]
        ret += self.pack_data(buf)
        return ret

    def server_encode(self, buf):
        return buf

    def server_decode(self, buf):
        # (buffer_to_recv, is_need_decrypt, is_need_to_encode_and_send_back)
        return (buf, True, False)

    def server_post_decrypt(self, buf):
        self.recv_buf += buf
        out_buf = b''
        while len(self.recv_buf) > 2:
            length = struct.unpack('>H', self.recv_buf[:2])[0]
            if length >= 8192:
                raise Exception('server_post_decrype data error')
            if length > len(self.recv_buf):
                break

            if (binascii.crc32(self.recv_buf[:length]) & 0xffffffff) != 0xffffffff:
                raise Exception('server_post_decrype data uncorrect CRC32')

            pos = common.ord(self.recv_buf[2]) + 2
            out_buf += self.recv_buf[pos:length - 4]
            self.recv_buf = self.recv_buf[length:]

        return out_buf