"""
Helper module around the system's libssl library if available for IGE mode.
"""
import ctypes
import ctypes.util
import platform
import sys
try:
    import ctypes.macholib.dyld
except ImportError:
    pass
import logging
import os

__log__ = logging.getLogger(__name__)


def _find_ssl_lib():
    lib = ctypes.util.find_library('ssl')
    # macOS 10.15 segfaults on  unversioned crypto libraries.
    # We therefore pin the current stable version here
    # Credit for fix goes to Sarah Harvey (@worldwise001)
    # https://www.shh.sh/2020/01/04/python-abort-trap-6.html
    if sys.platform == 'darwin':
        _, major, minor = platform.mac_ver()[0].split('.')
        # macOS 10.14 "mojave" is the last known major release
        # to support unversioned libssl.dylib. Anything above
        # needs specific versions
        if int(major) > 14:
            lib = (
                ctypes.util.find_library('libssl.46') or
                ctypes.util.find_library('libssl.44') or
                ctypes.util.find_library('libssl.42')
            )
    if not lib:
        raise OSError('no library called "ssl" found')

    # First, let ctypes try to handle it itself.
    try:
        libssl = ctypes.cdll.LoadLibrary(lib)
    except OSError:
        pass
    else:
        return libssl

    # This is a best-effort attempt at finding the full real path of lib.
    #
    # Unfortunately ctypes doesn't tell us *where* it finds the library,
    # so we have to do that ourselves.
    try:
        # This is not documented, so it could fail. Be on the safe side.
        paths = ctypes.macholib.dyld.DEFAULT_LIBRARY_FALLBACK
    except AttributeError:
        paths = [
            os.path.expanduser("~/lib"),
            "/usr/local/lib",
            "/lib",
            "/usr/lib",
        ]

    for path in paths:
        if os.path.isdir(path):
            for root, _, files in os.walk(path):
                if lib in files:
                    # Manually follow symbolic links on *nix systems.
                    # Fix for https://github.com/LonamiWebs/Telethon/issues/1167
                    lib = os.path.realpath(os.path.join(root, lib))
                    return ctypes.cdll.LoadLibrary(lib)
    else:
        raise OSError('no absolute path for "%s" and cannot load by name' % lib)


try:
    _libssl = _find_ssl_lib()
except OSError as e:
    # See https://github.com/LonamiWebs/Telethon/issues/1167
    # Sometimes `find_library` returns improper filenames.
    __log__.info('Failed to load SSL library: %s (%s)', type(e), e)
    _libssl = None

if not _libssl:
    decrypt_ige = None
    encrypt_ige = None
else:
    # https://github.com/openssl/openssl/blob/master/include/openssl/aes.h
    AES_ENCRYPT = ctypes.c_int(1)
    AES_DECRYPT = ctypes.c_int(0)
    AES_MAXNR = 14

    class AES_KEY(ctypes.Structure):
        """Helper class representing an AES key"""
        _fields_ = [
            ('rd_key', ctypes.c_uint32 * (4 * (AES_MAXNR + 1))),
            ('rounds', ctypes.c_uint),
        ]

    def decrypt_ige(cipher_text, key, iv):
        aes_key = AES_KEY()
        key_len = ctypes.c_int(8 * len(key))
        key = (ctypes.c_ubyte * len(key))(*key)
        iv = (ctypes.c_ubyte * len(iv))(*iv)

        in_len = ctypes.c_size_t(len(cipher_text))
        in_ptr = (ctypes.c_ubyte * len(cipher_text))(*cipher_text)
        out_ptr = (ctypes.c_ubyte * len(cipher_text))()

        _libssl.AES_set_decrypt_key(key, key_len, ctypes.byref(aes_key))
        _libssl.AES_ige_encrypt(
            ctypes.byref(in_ptr),
            ctypes.byref(out_ptr),
            in_len,
            ctypes.byref(aes_key),
            ctypes.byref(iv),
            AES_DECRYPT
        )

        return bytes(out_ptr)

    def encrypt_ige(plain_text, key, iv):
        aes_key = AES_KEY()
        key_len = ctypes.c_int(8 * len(key))
        key = (ctypes.c_ubyte * len(key))(*key)
        iv = (ctypes.c_ubyte * len(iv))(*iv)

        in_len = ctypes.c_size_t(len(plain_text))
        in_ptr = (ctypes.c_ubyte * len(plain_text))(*plain_text)
        out_ptr = (ctypes.c_ubyte * len(plain_text))()

        _libssl.AES_set_encrypt_key(key, key_len, ctypes.byref(aes_key))
        _libssl.AES_ige_encrypt(
            ctypes.byref(in_ptr),
            ctypes.byref(out_ptr),
            in_len,
            ctypes.byref(aes_key),
            ctypes.byref(iv),
            AES_ENCRYPT
        )

        return bytes(out_ptr)