# -*- test-case-name: twisted.conch.test.test_ssh -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Common functions for the SSH classes.

Maintainer: Paul Swartz
"""
from __future__ import absolute_import, division

import struct

from twisted.conch.ssh._cryptography_backports import (
    intFromBytes as int_from_bytes, intToBytes as int_to_bytes)

from twisted.python.compat import _PY3, long


def NS(t):
    """
    net string
    """
    return struct.pack('!L', len(t)) + t



def getNS(s, count=1):
    """
    get net string
    """
    ns = []
    c = 0
    for i in range(count):
        l, = struct.unpack('!L', s[c:c + 4])
        ns.append(s[c + 4:4 + l + c])
        c += 4 + l
    return tuple(ns) + (s[c:],)



def MP(number):
    if number == 0:
        return b'\000' * 4
    assert number > 0
    bn = int_to_bytes(number)
    if ord(bn[0:1]) & 128:
        bn = b'\000' + bn
    return struct.pack('>L', len(bn)) + bn



def getMP(data, count=1):
    """
    Get multiple precision integer out of the string.  A multiple precision
    integer is stored as a 4-byte length followed by length bytes of the
    integer.  If count is specified, get count integers out of the string.
    The return value is a tuple of count integers followed by the rest of
    the data.
    """
    mp = []
    c = 0
    for i in range(count):
        length, = struct.unpack('>L', data[c:c + 4])
        mp.append(int_from_bytes(data[c + 4:c + 4 + length], 'big'))
        c += 4 + length
    return tuple(mp) + (data[c:],)



def _MPpow(x, y, z):
    """
    Return the MP version of C{(x ** y) % z}.
    """
    return MP(pow(x, y, z))



def ffs(c, s):
    """
    first from second
    goes through the first list, looking for items in the second, returns the first one
    """
    for i in c:
        if i in s:
            return i



getMP_py = getMP
MP_py = MP
_MPpow_py = _MPpow
pyPow = pow



def _fastgetMP(data, count=1):
    mp = []
    c = 0
    for i in range(count):
        length = struct.unpack('!L', data[c:c + 4])[0]
        mp.append(long(
            gmpy.mpz(data[c + 4:c + 4 + length][::-1] + b'\x00', 256)))
        c += length + 4
    return tuple(mp) + (data[c:],)



def _fastMP(i):
    i2 = gmpy.mpz(i).binary()[::-1]
    return struct.pack('!L', len(i2)) + i2



def _fastMPpow(x, y, z=None):
    r = pyPow(gmpy.mpz(x), y, z).binary()[::-1]
    return struct.pack('!L', len(r)) + r



def install():
    global getMP, MP, _MPpow
    getMP = _fastgetMP
    MP = _fastMP
    _MPpow = _fastMPpow
    # XXX: We override builtin pow so that other code can benefit too.
    # This is monkeypatching, and therefore VERY BAD.
    def _fastpow(x, y, z=None, mpz=gmpy.mpz):
        if type(x) in (long, int):
            x = mpz(x)
        return pyPow(x, y, z)
    if _PY3:
        __builtins__['pow'] = _fastpow
    else:
        import __builtin__
        __builtin__.pow = _fastpow

try:
    import gmpy
    install()
except ImportError:
    pass