//! Salsa20 Stream Cipher
//!
//! # Examples
//!
//! Combine a simple input using a 128 bits key and 64 bit nonce:
//!
//! ```
//! use cryptoxide::salsa20::Salsa20;
//!
//! let key : [u8; 16] = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15];
//! let nonce : [u8; 8] = [1,2,3,4,5,6,7,8];
//! let input : &[u8; 12] = b"hello world!";
//! let mut out : [u8; 12] = [0u8; 12];
//!
//! // create a new cipher
//! let mut cipher = Salsa20::new(&key, &nonce);
//!
//! // encrypt the msg
//! cipher.process(input, &mut out);
//! ```
//!

// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use crate::cryptoutil::{read_u32_le, write_u32_le, xor_keystream};
use crate::simd::u32x4;

use core::cmp;

#[derive(Clone)]
struct SalsaState {
    a: u32x4,
    b: u32x4,
    c: u32x4,
    d: u32x4,
}

#[derive(Clone)]
pub struct Salsa20 {
    state: SalsaState,
    output: [u8; 64],
    offset: usize,
}

const S7: u32x4 = u32x4(7, 7, 7, 7);
const S9: u32x4 = u32x4(9, 9, 9, 9);
const S13: u32x4 = u32x4(13, 13, 13, 13);
const S18: u32x4 = u32x4(18, 18, 18, 18);
const S32: u32x4 = u32x4(32, 32, 32, 32);

macro_rules! prepare_rowround {
    ($a: expr, $b: expr, $c: expr) => {{
        let u32x4(a10, a11, a12, a13) = $a;
        $a = u32x4(a13, a10, a11, a12);
        let u32x4(b10, b11, b12, b13) = $b;
        $b = u32x4(b12, b13, b10, b11);
        let u32x4(c10, c11, c12, c13) = $c;
        $c = u32x4(c11, c12, c13, c10);
    }};
}

macro_rules! prepare_columnround {
    ($a: expr, $b: expr, $c: expr) => {{
        let u32x4(a13, a10, a11, a12) = $a;
        $a = u32x4(a10, a11, a12, a13);
        let u32x4(b12, b13, b10, b11) = $b;
        $b = u32x4(b10, b11, b12, b13);
        let u32x4(c11, c12, c13, c10) = $c;
        $c = u32x4(c10, c11, c12, c13);
    }};
}

macro_rules! add_rotate_xor {
    ($dst: expr, $a: expr, $b: expr, $shift: expr) => {{
        let v = $a + $b;
        let r = S32 - $shift;
        let right = v >> r;
        $dst = $dst ^ (v << $shift) ^ right
    }};
}

fn columnround(state: &mut SalsaState) {
    add_rotate_xor!(state.a, state.d, state.c, S7);
    add_rotate_xor!(state.b, state.a, state.d, S9);
    add_rotate_xor!(state.c, state.b, state.a, S13);
    add_rotate_xor!(state.d, state.c, state.b, S18);
}

fn rowround(state: &mut SalsaState) {
    add_rotate_xor!(state.c, state.d, state.a, S7);
    add_rotate_xor!(state.b, state.c, state.d, S9);
    add_rotate_xor!(state.a, state.c, state.b, S13);
    add_rotate_xor!(state.d, state.a, state.b, S18);
}

impl Salsa20 {
    pub fn new(key: &[u8], nonce: &[u8]) -> Salsa20 {
        assert!(key.len() == 16 || key.len() == 32);
        assert!(nonce.len() == 8);
        Salsa20 {
            state: Salsa20::expand(key, nonce),
            output: [0; 64],
            offset: 64,
        }
    }

    pub fn new_xsalsa20(key: &[u8], nonce: &[u8]) -> Salsa20 {
        assert!(key.len() == 32);
        assert!(nonce.len() == 24);
        let mut xsalsa20 = Salsa20 {
            state: Salsa20::expand(key, &nonce[0..16]),
            output: [0; 64],
            offset: 64,
        };

        let mut new_key = [0; 32];
        xsalsa20.hsalsa20_hash(&mut new_key);
        xsalsa20.state = Salsa20::expand(&new_key, &nonce[16..24]);

        xsalsa20
    }

    fn expand(key: &[u8], nonce: &[u8]) -> SalsaState {
        let constant = match key.len() {
            16 => b"expand 16-byte k",
            32 => b"expand 32-byte k",
            _ => unreachable!(),
        };

        // The state vectors are laid out to facilitate SIMD operation,
        // instead of the natural matrix ordering.
        //
        //  * Constant (x0, x5, x10, x15)
        //  * Key (x1, x2, x3, x4, x11, x12, x13, x14)
        //  * Input (x6, x7, x8, x9)

        // (x11, x12, x13, x14)
        let key_tail = if key.len() == 16 { key } else { &key[16..32] };

        // (x8, x9)
        let (x8, x9) = if nonce.len() == 16 {
            // HSalsa uses the full 16 byte nonce.
            (read_u32_le(&nonce[8..12]), read_u32_le(&nonce[12..16]))
        } else {
            (0, 0)
        };

        SalsaState {
            a: u32x4(
                read_u32_le(&key[12..16]),      // x4
                x9,                             // x9
                read_u32_le(&key_tail[12..16]), // x14
                read_u32_le(&key[8..12]),       // x3
            ),
            b: u32x4(
                x8,                            // x8
                read_u32_le(&key_tail[8..12]), // x13
                read_u32_le(&key[4..8]),       // x2
                read_u32_le(&nonce[4..8]),     // x7
            ),
            c: u32x4(
                read_u32_le(&key_tail[4..8]), // x12
                read_u32_le(&key[0..4]),      // x1
                read_u32_le(&nonce[0..4]),    // x6
                read_u32_le(&key_tail[0..4]), // x11
            ),
            d: u32x4(
                read_u32_le(&constant[0..4]),   // x0
                read_u32_le(&constant[4..8]),   // x5
                read_u32_le(&constant[8..12]),  // x10
                read_u32_le(&constant[12..16]), // x15
            ),
        }
    }

    fn hash(&mut self) {
        let mut state = self.state.clone();
        for _ in 0..10 {
            columnround(&mut state);
            prepare_rowround!(state.a, state.b, state.c);
            rowround(&mut state);
            prepare_columnround!(state.a, state.b, state.c);
        }
        let u32x4(x4, x9, x14, x3) = self.state.a + state.a;
        let u32x4(x8, x13, x2, x7) = self.state.b + state.b;
        let u32x4(x12, x1, x6, x11) = self.state.c + state.c;
        let u32x4(x0, x5, x10, x15) = self.state.d + state.d;
        let lens = [
            x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15,
        ];
        for (i, lensi) in lens.iter().enumerate() {
            write_u32_le(&mut self.output[i * 4..(i + 1) * 4], *lensi);
        }

        self.state.b = self.state.b + u32x4(1, 0, 0, 0);
        let u32x4(_, _, _, ctr_lo) = self.state.b;
        if ctr_lo == 0 {
            self.state.a = self.state.a + u32x4(0, 1, 0, 0);
        }

        self.offset = 0;
    }

    fn hsalsa20_hash(&mut self, out: &mut [u8]) {
        let mut state = self.state.clone();
        for _ in 0..10 {
            columnround(&mut state);
            prepare_rowround!(state.a, state.b, state.c);
            rowround(&mut state);
            prepare_columnround!(state.a, state.b, state.c);
        }
        let u32x4(_, x9, _, _) = state.a;
        let u32x4(x8, _, _, x7) = state.b;
        let u32x4(_, _, x6, _) = state.c;
        let u32x4(x0, x5, x10, x15) = state.d;
        let lens = [x0, x5, x10, x15, x6, x7, x8, x9];
        for i in 0..lens.len() {
            write_u32_le(&mut out[i * 4..(i + 1) * 4], lens[i]);
        }
    }

    /// Process the input through the cipher, xoring the byte one-by-one
    ///
    /// the output need to be the same size as the input otherwise
    /// this function will panic.
    pub fn process(&mut self, input: &[u8], output: &mut [u8]) {
        assert!(input.len() == output.len());
        let len = input.len();
        let mut i = 0;
        while i < len {
            // If there is no keystream available in the output buffer,
            // generate the next block.
            if self.offset == 64 {
                self.hash();
            }

            // Process the min(available keystream, remaining input length).
            let count = cmp::min(64 - self.offset, len - i);
            xor_keystream(
                &mut output[i..i + count],
                &input[i..i + count],
                &self.output[self.offset..],
            );
            i += count;
            self.offset += count;
        }
    }
}

pub fn hsalsa20(key: &[u8], nonce: &[u8], out: &mut [u8]) {
    assert!(key.len() == 32);
    assert!(nonce.len() == 16);
    let mut h = Salsa20 {
        state: Salsa20::expand(key, nonce),
        output: [0; 64],
        offset: 64,
    };
    h.hsalsa20_hash(out);
}

#[cfg(test)]
mod test {
    use alloc::vec::Vec;
    use std::iter::repeat;

    use super::Salsa20;

    use crate::digest::Digest;
    use crate::sha2::Sha256;

    #[test]
    fn test_salsa20_128bit_ecrypt_set_1_vector_0() {
        let key = [128u8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
        let nonce = [0u8; 8];
        let input = [0u8; 64];
        let mut stream = [0u8; 64];
        let result = [
            0x4D, 0xFA, 0x5E, 0x48, 0x1D, 0xA2, 0x3E, 0xA0, 0x9A, 0x31, 0x02, 0x20, 0x50, 0x85,
            0x99, 0x36, 0xDA, 0x52, 0xFC, 0xEE, 0x21, 0x80, 0x05, 0x16, 0x4F, 0x26, 0x7C, 0xB6,
            0x5F, 0x5C, 0xFD, 0x7F, 0x2B, 0x4F, 0x97, 0xE0, 0xFF, 0x16, 0x92, 0x4A, 0x52, 0xDF,
            0x26, 0x95, 0x15, 0x11, 0x0A, 0x07, 0xF9, 0xE4, 0x60, 0xBC, 0x65, 0xEF, 0x95, 0xDA,
            0x58, 0xF7, 0x40, 0xB7, 0xD1, 0xDB, 0xB0, 0xAA,
        ];

        let mut salsa20 = Salsa20::new(&key, &nonce);
        salsa20.process(&input, &mut stream);
        assert!(stream[..] == result[..]);
    }

    #[test]
    fn test_salsa20_256bit_ecrypt_set_1_vector_0() {
        let key = [
            128u8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0,
        ];
        let nonce = [0u8; 8];
        let input = [0u8; 64];
        let mut stream = [0u8; 64];
        let result = [
            0xE3, 0xBE, 0x8F, 0xDD, 0x8B, 0xEC, 0xA2, 0xE3, 0xEA, 0x8E, 0xF9, 0x47, 0x5B, 0x29,
            0xA6, 0xE7, 0x00, 0x39, 0x51, 0xE1, 0x09, 0x7A, 0x5C, 0x38, 0xD2, 0x3B, 0x7A, 0x5F,
            0xAD, 0x9F, 0x68, 0x44, 0xB2, 0x2C, 0x97, 0x55, 0x9E, 0x27, 0x23, 0xC7, 0xCB, 0xBD,
            0x3F, 0xE4, 0xFC, 0x8D, 0x9A, 0x07, 0x44, 0x65, 0x2A, 0x83, 0xE7, 0x2A, 0x9C, 0x46,
            0x18, 0x76, 0xAF, 0x4D, 0x7E, 0xF1, 0xA1, 0x17,
        ];

        let mut salsa20 = Salsa20::new(&key, &nonce);
        salsa20.process(&input, &mut stream);
        assert!(stream[..] == result[..]);
    }

    #[test]
    fn test_salsa20_256bit_nacl_vector_2() {
        let key = [
            0xdc, 0x90, 0x8d, 0xda, 0x0b, 0x93, 0x44, 0xa9, 0x53, 0x62, 0x9b, 0x73, 0x38, 0x20,
            0x77, 0x88, 0x80, 0xf3, 0xce, 0xb4, 0x21, 0xbb, 0x61, 0xb9, 0x1c, 0xbd, 0x4c, 0x3e,
            0x66, 0x25, 0x6c, 0xe4,
        ];
        let nonce = [0x82, 0x19, 0xe0, 0x03, 0x6b, 0x7a, 0x0b, 0x37];
        let input: Vec<u8> = repeat(0).take(4194304).collect();
        let mut stream: Vec<u8> = repeat(0).take(input.len()).collect();
        let output_str = "662b9d0e3463029156069b12f918691a98f7dfb2ca0393c96bbfc6b1fbd630a2";

        let mut salsa20 = Salsa20::new(&key, &nonce);
        salsa20.process(input.as_ref(), &mut stream);

        let mut sh = Sha256::new();
        sh.input(stream.as_ref());
        let out_str = sh.result_str();
        assert!(&out_str[..] == output_str);
    }

    #[test]
    fn test_xsalsa20_cryptopp() {
        let key = [
            0x1b, 0x27, 0x55, 0x64, 0x73, 0xe9, 0x85, 0xd4, 0x62, 0xcd, 0x51, 0x19, 0x7a, 0x9a,
            0x46, 0xc7, 0x60, 0x09, 0x54, 0x9e, 0xac, 0x64, 0x74, 0xf2, 0x06, 0xc4, 0xee, 0x08,
            0x44, 0xf6, 0x83, 0x89,
        ];
        let nonce = [
            0x69, 0x69, 0x6e, 0xe9, 0x55, 0xb6, 0x2b, 0x73, 0xcd, 0x62, 0xbd, 0xa8, 0x75, 0xfc,
            0x73, 0xd6, 0x82, 0x19, 0xe0, 0x03, 0x6b, 0x7a, 0x0b, 0x37,
        ];
        let input = [0u8; 139];
        let mut stream = [0u8; 139];
        let result = [
            0xee, 0xa6, 0xa7, 0x25, 0x1c, 0x1e, 0x72, 0x91, 0x6d, 0x11, 0xc2, 0xcb, 0x21, 0x4d,
            0x3c, 0x25, 0x25, 0x39, 0x12, 0x1d, 0x8e, 0x23, 0x4e, 0x65, 0x2d, 0x65, 0x1f, 0xa4,
            0xc8, 0xcf, 0xf8, 0x80, 0x30, 0x9e, 0x64, 0x5a, 0x74, 0xe9, 0xe0, 0xa6, 0x0d, 0x82,
            0x43, 0xac, 0xd9, 0x17, 0x7a, 0xb5, 0x1a, 0x1b, 0xeb, 0x8d, 0x5a, 0x2f, 0x5d, 0x70,
            0x0c, 0x09, 0x3c, 0x5e, 0x55, 0x85, 0x57, 0x96, 0x25, 0x33, 0x7b, 0xd3, 0xab, 0x61,
            0x9d, 0x61, 0x57, 0x60, 0xd8, 0xc5, 0xb2, 0x24, 0xa8, 0x5b, 0x1d, 0x0e, 0xfe, 0x0e,
            0xb8, 0xa7, 0xee, 0x16, 0x3a, 0xbb, 0x03, 0x76, 0x52, 0x9f, 0xcc, 0x09, 0xba, 0xb5,
            0x06, 0xc6, 0x18, 0xe1, 0x3c, 0xe7, 0x77, 0xd8, 0x2c, 0x3a, 0xe9, 0xd1, 0xa6, 0xf9,
            0x72, 0xd4, 0x16, 0x02, 0x87, 0xcb, 0xfe, 0x60, 0xbf, 0x21, 0x30, 0xfc, 0x0a, 0x6f,
            0xf6, 0x04, 0x9d, 0x0a, 0x5c, 0x8a, 0x82, 0xf4, 0x29, 0x23, 0x1f, 0x00, 0x80,
        ];

        let mut xsalsa20 = Salsa20::new_xsalsa20(&key, &nonce);
        xsalsa20.process(&input, &mut stream);
        assert!(stream[..] == result[..]);
    }
}

#[cfg(all(test, feature = "with-bench"))]
mod bench {
    use super::Salsa20;
    use crate::symmetriccipher::SynchronousStreamCipher;
    use test::Bencher;

    #[bench]
    pub fn salsa20_10(bh: &mut Bencher) {
        let mut salsa20 = Salsa20::new(&[0; 32], &[0; 8]);
        let input = [1u8; 10];
        let mut output = [0u8; 10];
        bh.iter(|| {
            salsa20.process(&input, &mut output);
        });
        bh.bytes = input.len() as u64;
    }

    #[bench]
    pub fn salsa20_1k(bh: &mut Bencher) {
        let mut salsa20 = Salsa20::new(&[0; 32], &[0; 8]);
        let input = [1u8; 1024];
        let mut output = [0u8; 1024];
        bh.iter(|| {
            salsa20.process(&input, &mut output);
        });
        bh.bytes = input.len() as u64;
    }

    #[bench]
    pub fn salsa20_64k(bh: &mut Bencher) {
        let mut salsa20 = Salsa20::new(&[0; 32], &[0; 8]);
        let input = [1u8; 65536];
        let mut output = [0u8; 65536];
        bh.iter(|| {
            salsa20.process(&input, &mut output);
        });
        bh.bytes = input.len() as u64;
    }
}