//! Various utility to write/read in buffers

// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// 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 core::{mem::size_of, ptr};

macro_rules! write_type {
    ($C: ident, $T: ident, $F: ident) => {
        /// Write a $T into a vector, which must be of the correct size. The value is written using $F for endianness
        pub fn $C(dst: &mut [u8], input: $T) {
            const SZ: usize = size_of::<$T>();
            assert!(dst.len() == SZ);
            let as_bytes = input.$F();
            unsafe {
                let tmp = &as_bytes as *const u8;
                ptr::copy_nonoverlapping(tmp, dst.get_unchecked_mut(0), SZ);
            }
        }
    };
}

write_type!(write_u128_be, u128, to_be_bytes);
//write_type!(write_u128_le, u128, to_le_bytes);
write_type!(write_u64_be, u64, to_be_bytes);
write_type!(write_u64_le, u64, to_le_bytes);
write_type!(write_u32_be, u32, to_be_bytes);
write_type!(write_u32_le, u32, to_le_bytes);

macro_rules! write_array_type {
    ($C: ident, $T: ident, $F: ident) => {
        /// Write a $T into a vector, which must be of the correct size. The value is written using $F for endianness
        pub fn $C(dst: &mut [u8], input: &[$T]) {
            const SZ: usize = size_of::<$T>();
            assert!(dst.len() == SZ * input.len());
            unsafe {
                let mut x: *mut u8 = dst.get_unchecked_mut(0);
                for v in input.iter() {
                    let tmp = v.$F();
                    ptr::copy_nonoverlapping(&tmp as *const u8, x, SZ);
                    x = x.add(SZ);
                }
            }
        }
    };
}

write_array_type!(write_u64v_le, u64, to_le_bytes);
write_array_type!(write_u64v_be, u64, to_be_bytes);
write_array_type!(write_u32v_le, u32, to_le_bytes);
write_array_type!(write_u32v_be, u32, to_be_bytes);

macro_rules! read_array_type {
    ($C: ident, $T: ident, $F: ident) => {
        /// Read an array of bytes into an array of $T. The values are read with $F for endianness.
        pub fn $C(dst: &mut [$T], input: &[u8]) {
            const SZ: usize = size_of::<$T>();
            assert!(dst.len() * SZ == input.len());

            unsafe {
                let mut x: *mut $T = dst.get_unchecked_mut(0);
                let mut y: *const u8 = input.get_unchecked(0);

                for _ in 0..dst.len() {
                    let mut tmp = [0u8; SZ];
                    ptr::copy_nonoverlapping(y, &mut tmp as *mut _ as *mut u8, SZ);
                    *x = $T::$F(tmp);
                    x = x.add(1);
                    y = y.add(SZ);
                }
            }
        }
    };
}

read_array_type!(read_u64v_be, u64, from_be_bytes);
read_array_type!(read_u64v_le, u64, from_le_bytes);
read_array_type!(read_u32v_be, u32, from_be_bytes);
read_array_type!(read_u32v_le, u32, from_le_bytes);

/// Read the value of a vector of bytes as a u32 value in little-endian format.
pub fn read_u32_le(input: &[u8]) -> u32 {
    assert!(input.len() == 4);
    let mut tmp = [0u8; 4];
    unsafe {
        ptr::copy_nonoverlapping(input.get_unchecked(0), &mut tmp as *mut _ as *mut u8, 4);
    }
    u32::from_le_bytes(tmp)
}

/*
/// Read the value of a vector of bytes as a u32 value in big-endian format.
pub fn read_u32_be(input: &[u8]) -> u32 {
    assert!(input.len() == 4);
    unsafe {
        let mut tmp: u32 = mem::uninitialized();
        ptr::copy_nonoverlapping(input.get_unchecked(0), &mut tmp as *mut _ as *mut u8, 4);
        u32::from_be(tmp)
    }
}
*/

/// XOR plaintext and keystream, storing the result in dst.
pub fn xor_keystream(dst: &mut [u8], plaintext: &[u8], keystream: &[u8]) {
    assert!(dst.len() == plaintext.len());
    assert!(plaintext.len() <= keystream.len());

    // Do one byte at a time, using unsafe to skip bounds checking.
    let p = plaintext.as_ptr();
    let k = keystream.as_ptr();
    let d = dst.as_mut_ptr();
    for i in 0isize..plaintext.len() as isize {
        unsafe { *d.offset(i) = *p.offset(i) ^ *k.offset(i) };
    }
}

/// XOR a keystream in a buffer
pub fn xor_keystream_mut(buf: &mut [u8], keystream: &[u8]) {
    assert!(buf.len() <= keystream.len());

    // Do one byte at a time, using unsafe to skip bounds checking.
    let k = keystream.as_ptr();
    let d = buf.as_mut_ptr();
    for i in 0isize..buf.len() as isize {
        unsafe { *d.offset(i) = *d.offset(i) ^ *k.offset(i) };
    }
}

/// Copy bytes from src to dest
#[inline]
pub fn copy_memory(src: &[u8], dst: &mut [u8]) {
    assert!(dst.len() >= src.len());
    unsafe {
        let srcp = src.as_ptr();
        let dstp = dst.as_mut_ptr();
        ptr::copy_nonoverlapping(srcp, dstp, src.len());
    }
}

/// Zero all bytes in dst
#[inline]
pub fn zero(dst: &mut [u8]) {
    unsafe {
        ptr::write_bytes(dst.as_mut_ptr(), 0, dst.len());
    }
}

/// A fixed size buffer of N bytes useful for cryptographic operations.
#[derive(Clone)]
pub(crate) struct FixedBuffer<const N: usize> {
    buffer: [u8; N],
    buffer_idx: usize,
}

impl<const N: usize> FixedBuffer<N> {
    /// Create a new buffer
    pub const fn new() -> Self {
        Self {
            buffer: [0u8; N],
            buffer_idx: 0,
        }
    }

    pub fn input<F: FnMut(&[u8])>(&mut self, input: &[u8], mut func: F) {
        let mut i = 0;

        // If there is already data in the buffer, copy as much as we can into it and process
        // the data if the buffer becomes full.
        if self.buffer_idx != 0 {
            let buffer_remaining = N - self.buffer_idx;
            if input.len() >= buffer_remaining {
                copy_memory(
                    &input[..buffer_remaining],
                    &mut self.buffer[self.buffer_idx..N],
                );
                self.buffer_idx = 0;
                func(&self.buffer);
                i += buffer_remaining;
            } else {
                copy_memory(
                    input,
                    &mut self.buffer[self.buffer_idx..self.buffer_idx + input.len()],
                );
                self.buffer_idx += input.len();
                return;
            }
        }

        // While we have at least a full buffer size chunks's worth of data, process that data
        // without copying it into the buffer
        if input.len() - i >= N {
            let remaining = input.len() - i;
            let block_bytes = (remaining / N) * N;
            func(&input[i..i + block_bytes]);
            i += block_bytes;
        }

        // Copy any input data into the buffer. At this point in the method, the ammount of
        // data left in the input vector will be less than the buffer size and the buffer will
        // be empty.
        let input_remaining = input.len() - i;
        copy_memory(&input[i..], &mut self.buffer[0..input_remaining]);
        self.buffer_idx += input_remaining;
    }

    pub fn reset(&mut self) {
        self.buffer_idx = 0;
    }

    fn zero_until(&mut self, idx: usize) {
        assert!(idx >= self.buffer_idx);
        zero(&mut self.buffer[self.buffer_idx..idx]);
        self.buffer_idx = idx;
    }

    pub fn next(&mut self, len: usize) -> &mut [u8] {
        self.buffer_idx += len;
        &mut self.buffer[self.buffer_idx - len..self.buffer_idx]
    }

    pub fn full_buffer(&mut self) -> &[u8; N] {
        assert!(self.buffer_idx == N);
        self.buffer_idx = 0;
        &self.buffer
    }

    /// Add standard padding to the buffer. The buffer must not be full when this method is called
    /// and is guaranteed to have exactly rem remaining bytes when it returns. If there are not at
    /// least rem bytes available, the buffer will be zero padded, processed, cleared, and then
    /// filled with zeros again until only rem bytes are remaining.
    pub fn standard_padding<F: FnMut(&[u8; N])>(&mut self, rem: usize, mut func: F) {
        self.next(1)[0] = 128;

        if (N - self.buffer_idx) < rem {
            self.zero_until(N);
            func(self.full_buffer());
        }

        self.zero_until(N - rem);
    }
}

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

    use crate::digest::Digest;

    /// Feed 1,000,000 'a's into the digest with varying input sizes and check that the result is
    /// correct.
    pub fn test_digest_1million_random<D: Digest>(
        digest: &mut D,
        blocksize: usize,
        expected: &str,
    ) {
        let total_size = 1000000;
        let buffer: Vec<u8> = repeat(b'a').take(blocksize * 2).collect();
        //let mut rng = IsaacRng::new_unseeded();
        //let range = Range::new(0, 2 * blocksize + 1);
        let mut count = 0;

        digest.reset();

        while count < total_size {
            //let next = range.ind_sample(&mut rng);
            let next = 10;
            let remaining = total_size - count;
            let size = if next > remaining { remaining } else { next };
            digest.input(&buffer[..size]);
            count += size;
        }

        let result_str = digest.result_str();

        assert!(expected == &result_str[..]);
    }
}