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use nettle_sys::{
    des_ctx, nettle_des_check_parity, nettle_des_decrypt, nettle_des_encrypt,
    nettle_des_fix_parity, nettle_des_set_key,
};
use std::cmp::min;
use std::mem::zeroed;
use std::os::raw::c_void;

use crate::cipher::RawCipherFunctionPointer;
use crate::{cipher::Cipher, Error, Result};

/// The Data Encryption Standard (DES) defined in FIPS 46-3.
/// # Note
/// DES is no longer considered a secure cipher. Only use it for legacy applications.
pub struct Des {
    context: des_ctx,
}

impl Des {
    /// Creates a new instance with `key` that can be used for both encryption and decryption.
    pub fn with_key(key: &[u8]) -> Result<Self> {
        if key.len() != Des::KEY_SIZE {
            return Err(Error::InvalidArgument { argument_name: "key" }.into());
        }
        let mut ctx = unsafe { zeroed() };
        unsafe {
            nettle_des_set_key(&mut ctx as *mut _, key.as_ptr());
        }

        Ok(Des { context: ctx })
    }

    /// Checks the parity bits of the given DES key. Returns `true` if parity is correct, `false`
    /// otherwise.
    pub fn check_parity(key: &[u8]) -> bool {
        unsafe { nettle_des_check_parity(key.len(), key.as_ptr()) == 1 }
    }

    /// Sets the parity bits in the given DES key.
    pub fn fix_parity(key: &mut [u8]) {
        unsafe {
            nettle_des_fix_parity(key.len(), key.as_mut_ptr(), key.as_ptr());
        }
    }
}

impl Cipher for Des {
    const BLOCK_SIZE: usize = ::nettle_sys::DES_BLOCK_SIZE as usize;
    const KEY_SIZE: usize = ::nettle_sys::DES_KEY_SIZE as usize;

    fn with_encrypt_key(key: &[u8]) -> Result<Des> {
        Des::with_key(key)
    }

    fn with_decrypt_key(key: &[u8]) -> Result<Des> {
        Des::with_key(key)
    }

    fn encrypt(&mut self, dst: &mut [u8], src: &[u8]) {
        unsafe {
            nettle_des_encrypt(
                &mut self.context as *mut _,
                min(src.len(), dst.len()),
                dst.as_mut_ptr(),
                src.as_ptr(),
            )
        };
    }

    fn decrypt(&mut self, dst: &mut [u8], src: &[u8]) {
        unsafe {
            nettle_des_decrypt(
                &mut self.context as *mut _,
                min(src.len(), dst.len()),
                dst.as_mut_ptr(),
                src.as_ptr(),
            )
        };
    }

    fn context(&mut self) -> *mut c_void {
        ((&mut self.context) as *mut des_ctx) as *mut c_void
    }

    fn raw_encrypt_function() -> RawCipherFunctionPointer {
        RawCipherFunctionPointer::new(nettle_des_encrypt)
    }

    fn raw_decrypt_function() -> RawCipherFunctionPointer {
        RawCipherFunctionPointer::new(nettle_des_decrypt)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn set_key() {
        let key = &(b"\x01\x02\x03\x04\x05\x06\x07\x08"[..]);
        let _ = Des::with_encrypt_key(key).unwrap();
        let _ = Des::with_decrypt_key(key).unwrap();
    }

    #[test]
    fn round_trip() {
        let key = vec![0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08];
        let input = vec![
            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x10, 0x11,
            0x12, 0x13, 0x14, 0x15, 0x16,
        ];
        let mut cipher = vec![0; 16];
        let mut output = vec![0; 16];

        let mut enc = Des::with_encrypt_key(&key).unwrap();
        let mut dec = Des::with_decrypt_key(&key).unwrap();

        enc.encrypt(&mut cipher, &input);
        dec.decrypt(&mut output, &cipher);

        assert_eq!(output, input);
    }

    #[test]
    fn key_parity() {
        let mut key = b"\x01\x02\x03\x04\x05\x06\x07\x08"[..]
            .iter()
            .cloned()
            .collect::<Vec<_>>();

        assert!(!Des::check_parity(&key));
        Des::fix_parity(&mut key);
        assert!(Des::check_parity(&key));
    }
}