import secrets
from Cryptodome.Cipher import AES
import base64
import struct
import subprocess
import binascii
import os

FILE_ID_LENGTH = 22
TOKEN_LENGTH = 22

def encrypt_file(filename_in, chunk_size=1000000//16):
    file_id = secrets.token_urlsafe(16)
    auth_secret = secrets.token_bytes(16)
    key = secrets.token_bytes(16)
    data_nonce = secrets.token_bytes(8)

    token_cipher = AES.new(auth_secret, AES.MODE_GCM)
    ciphertext, token_tag = token_cipher.encrypt_and_digest(key)
    token = base64.b64encode(ciphertext).rstrip(b'=').decode()

    with open(f'{file_id}.enc', 'wb') as fout, open(filename_in, 'rb') as fin:
        fout.write(token_cipher.nonce) # 16 bytes
        fout.write(token_tag) # 16 bytes
        fout.write(auth_secret) # 16 bytes
        fout.write(data_nonce) # 8 bytes

        cipher = AES.new(key, AES.MODE_CTR,
                initial_value=struct.pack('<Q', 0), nonce=data_nonce)

        block = fin.read(cipher.block_size*chunk_size)
        while block:
            data = cipher.encrypt(block)
            fout.write(data)
            block = fin.read(cipher.block_size*chunk_size)

    return file_id, token

def payload_size(path):
    return os.stat(path).st_size - 56

def decrypt_generator(filename, token, seek=0, end=None, chunk_size=1000000//16):
    with open(filename, 'rb') as fin:
        token_nonce = fin.read(16)
        token_tag = fin.read(16)
        auth_secret = fin.read(16)
        data_nonce = fin.read(8)

        ciphertext = base64.b64decode(token + '='*((3-len(token)%3)%3))
        token_cipher = AES.new(auth_secret, AES.MODE_GCM, nonce=token_nonce)
        key = token_cipher.decrypt_and_verify(ciphertext, token_tag)

        # Use token cipher's block size assuming the two are the same
        cipher = AES.new(key, AES.MODE_CTR,
                initial_value=struct.pack('>Q', seek // token_cipher.block_size), nonce=data_nonce)
        print('Seeking to position', seek, 'iv', seek // token_cipher.block_size, 'pos', seek - seek %
                cipher.block_size, 'offset', seek % cipher.block_size)
        fin.seek(seek - seek % cipher.block_size, 1)
        offset = seek % cipher.block_size

        to_send = end - seek + 1 if end else None
        block = fin.read(cipher.block_size*chunk_size)
        while block and (to_send is None or to_send > 0):
            data = cipher.decrypt(block)
            out = data[offset:to_send]
            yield out
            if to_send is not None:
                to_send -= len(out)
            offset = 0
            block = fin.read(cipher.block_size*chunk_size)