use aes::{
    cipher::{consts::U16, generic_array::GenericArray, BlockCipherMut, NewBlockCipher},
    Aes128,
};
use thiserror::Error;

pub type CraftCipherResult<T> = Result<T, CipherError>;

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub enum CipherComponent {
    Key,
    Iv,
}

#[derive(Debug, Error)]
pub enum CipherError {
    #[error("encryption is already enabled and cannot be enabled again")]
    AlreadyEnabled,
    #[error("bad size '{1}' for '{0:?}'")]
    BadSize(CipherComponent, usize),
}

const BYTES_SIZE: usize = 16;

pub struct CraftCipher {
    iv: GenericArray<u8, U16>,
    tmp: GenericArray<u8, U16>,
    cipher: Aes128,
}

impl CraftCipher {
    pub fn new(key: &[u8], iv: &[u8]) -> CraftCipherResult<Self> {
        if iv.len() != BYTES_SIZE {
            return Err(CipherError::BadSize(CipherComponent::Iv, iv.len()));
        }

        if key.len() != BYTES_SIZE {
            return Err(CipherError::BadSize(CipherComponent::Key, iv.len()));
        }

        let mut iv_out = [0u8; BYTES_SIZE];
        iv_out.copy_from_slice(iv);

        let mut key_out = [0u8; BYTES_SIZE];
        key_out.copy_from_slice(key);

        let tmp = [0u8; BYTES_SIZE];

        Ok(Self {
            iv: GenericArray::from(iv_out),
            tmp: GenericArray::from(tmp),
            cipher: Aes128::new(&GenericArray::from(key_out)),
        })
    }

    pub fn encrypt(&mut self, data: &mut [u8]) {
        unsafe { self.crypt(data, false) }
    }

    pub fn decrypt(&mut self, data: &mut [u8]) {
        unsafe { self.crypt(data, true) }
    }

    unsafe fn crypt(&mut self, data: &mut [u8], decrypt: bool) {
        let iv = &mut self.iv;
        const IV_SIZE: usize = 16;
        const IV_SIZE_MINUS_ONE: usize = IV_SIZE - 1;
        let iv_ptr = iv.as_mut_ptr();
        let iv_end_ptr = iv_ptr.offset(IV_SIZE_MINUS_ONE as isize);
        let tmp_ptr = self.tmp.as_mut_ptr();
        let tmp_offset_one_ptr = tmp_ptr.offset(1);
        let cipher = &mut self.cipher;
        let n = data.len();
        let mut data_ptr = data.as_mut_ptr();
        let data_end_ptr = data_ptr.offset(n as isize);

        while data_ptr != data_end_ptr {
            std::ptr::copy_nonoverlapping(iv_ptr, tmp_ptr, IV_SIZE);
            cipher.encrypt_block(iv);
            let orig = *data_ptr;
            let updated = orig ^ *iv_ptr;
            std::ptr::copy_nonoverlapping(tmp_offset_one_ptr, iv_ptr, IV_SIZE_MINUS_ONE);
            if decrypt {
                *iv_end_ptr = orig;
            } else {
                *iv_end_ptr = updated;
            }
            *data_ptr = updated;
            data_ptr = data_ptr.offset(1);
        }
    }
}

pub(crate) fn setup_craft_cipher(
    target: &mut Option<CraftCipher>,
    key: &[u8],
    iv: &[u8],
) -> Result<(), CipherError> {
    if target.is_some() {
        Err(CipherError::AlreadyEnabled)
    } else {
        *target = Some(CraftCipher::new(key, iv)?);
        Ok(())
    }
}