"""
This module holds an AES IGE class, if libssl is available on the system.
"""
import os
import ctypes
from ctypes.util import find_library

lib = find_library('ssl')
if not lib:
    AES = None
else:
    """ <aes.h>
    # define AES_ENCRYPT     1
    # define AES_DECRYPT     0
    # define AES_MAXNR 14
    struct aes_key_st {
    # ifdef AES_LONG
        unsigned long rd_key[4 * (AES_MAXNR + 1)];
    # else
        unsigned int rd_key[4 * (AES_MAXNR + 1)];
    # endif
        int rounds;
    };
    typedef struct aes_key_st AES_KEY;

    int AES_set_encrypt_key(const unsigned char *userKey, const int bits,
                            AES_KEY *key);
    int AES_set_decrypt_key(const unsigned char *userKey, const int bits,
                            AES_KEY *key);
    void AES_ige_encrypt(const unsigned char *in, unsigned char *out,
                         size_t length, const AES_KEY *key,
                         unsigned char *ivec, const int enc);
    """
    _libssl = ctypes.cdll.LoadLibrary(lib)

    AES_MAXNR = 14
    AES_ENCRYPT = ctypes.c_int(1)
    AES_DECRYPT = ctypes.c_int(0)

    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),
        ]

    class AES:
        """
        Class that servers as an interface to encrypt and decrypt
        text through the AES IGE mode, using the system's libssl.
        """
        @staticmethod
        def decrypt_ige(cipher_text, key, iv):
            """
            Decrypts the given text in 16-bytes blocks by using the
            given key and 32-bytes initialization vector.
            """
            aeskey = AES_KEY()
            ckey = (ctypes.c_ubyte * len(key))(*key)
            cklen = ctypes.c_int(len(key)*8)
            cin = (ctypes.c_ubyte * len(cipher_text))(*cipher_text)
            ctlen = ctypes.c_size_t(len(cipher_text))
            cout = (ctypes.c_ubyte * len(cipher_text))()
            civ = (ctypes.c_ubyte * len(iv))(*iv)

            _libssl.AES_set_decrypt_key(ckey, cklen, ctypes.byref(aeskey))
            _libssl.AES_ige_encrypt(
                ctypes.byref(cin),
                ctypes.byref(cout),
                ctlen,
                ctypes.byref(aeskey),
                ctypes.byref(civ),
                AES_DECRYPT
            )

            return bytes(cout)

        @staticmethod
        def encrypt_ige(plain_text, key, iv):
            """
            Encrypts the given text in 16-bytes blocks by using the
            given key and 32-bytes initialization vector.
            """
            # Add random padding iff it's not evenly divisible by 16 already
            if len(plain_text) % 16 != 0:
                padding_count = 16 - len(plain_text) % 16
                plain_text += os.urandom(padding_count)

            aeskey = AES_KEY()
            ckey = (ctypes.c_ubyte * len(key))(*key)
            cklen = ctypes.c_int(len(key)*8)
            cin = (ctypes.c_ubyte * len(plain_text))(*plain_text)
            ctlen = ctypes.c_size_t(len(plain_text))
            cout = (ctypes.c_ubyte * len(plain_text))()
            civ = (ctypes.c_ubyte * len(iv))(*iv)

            _libssl.AES_set_encrypt_key(ckey, cklen, ctypes.byref(aeskey))
            _libssl.AES_ige_encrypt(
                ctypes.byref(cin),
                ctypes.byref(cout),
                ctlen,
                ctypes.byref(aeskey),
                ctypes.byref(civ),
                AES_ENCRYPT
            )

            return bytes(cout)