"""
AES IGE implementation in Python. This module may use libssl if available.
"""
import os
import pyaes
from . import libssl


if libssl.AES is not None:
    # Use libssl if available, since it will be faster
    AES = libssl.AES
else:
    # Fallback to a pure Python implementation
    class AES:
        """
        Class that servers as an interface to encrypt and decrypt
        text through the AES IGE mode.
        """
        @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.
            """
            iv1 = iv[:len(iv) // 2]
            iv2 = iv[len(iv) // 2:]

            aes = pyaes.AES(key)

            plain_text = []
            blocks_count = len(cipher_text) // 16

            cipher_text_block = [0] * 16
            for block_index in range(blocks_count):
                for i in range(16):
                    cipher_text_block[i] = \
                        cipher_text[block_index * 16 + i] ^ iv2[i]

                plain_text_block = aes.decrypt(cipher_text_block)

                for i in range(16):
                    plain_text_block[i] ^= iv1[i]

                iv1 = cipher_text[block_index * 16:block_index * 16 + 16]
                iv2 = plain_text_block

                plain_text.extend(plain_text_block)

            return bytes(plain_text)

        @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)

            iv1 = iv[:len(iv) // 2]
            iv2 = iv[len(iv) // 2:]

            aes = pyaes.AES(key)

            cipher_text = []
            blocks_count = len(plain_text) // 16

            for block_index in range(blocks_count):
                plain_text_block = list(
                    plain_text[block_index * 16:block_index * 16 + 16]
                )
                for i in range(16):
                    plain_text_block[i] ^= iv1[i]

                cipher_text_block = aes.encrypt(plain_text_block)

                for i in range(16):
                    cipher_text_block[i] ^= iv2[i]

                iv1 = cipher_text_block
                iv2 = plain_text[block_index * 16:block_index * 16 + 16]

                cipher_text.extend(cipher_text_block)

            return bytes(cipher_text)
