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#![no_std]
extern crate generic_array;
extern crate byte_tools;
use generic_array::{GenericArray, ArrayLength};
use byte_tools::{zero, write_u64_le};

mod paddings;

pub use paddings::*;

type Block<N> = GenericArray<u8, N>;

#[derive(Default, Clone, Copy)]
pub struct BlockBuffer<N: ArrayLength<u8>> where N::ArrayType: Copy {
    buffer: GenericArray<u8, N>,
    pos: usize,
}

impl <N: ArrayLength<u8>> BlockBuffer<N> where N::ArrayType: Copy {
    #[inline]
    pub fn input<F: FnMut(&Block<N>)>(&mut self, mut input: &[u8], mut func: F) {
        // 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.pos != 0 {
            let rem = self.remaining();

            if input.len() >= rem {
                let (l, r) = input.split_at(rem);
                input = r;
                self.buffer[self.pos..].copy_from_slice(l);
                self.pos = 0;
                func(&self.buffer);
            } else {
                let end = self.pos + input.len();
                self.buffer[self.pos..end].copy_from_slice(input);
                self.pos = end;
                return;
            }
        }

        // While we have at least a full buffer size chunks's worth of data,
        // process that data without copying it into the buffer
        while input.len() >= self.size() {
            let (l, r) = input.split_at(self.size());
            input = r;
            func(GenericArray::from_slice(&l));
        }

        // 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.
        self.buffer[..input.len()].copy_from_slice(input);
        self.pos = input.len();
    }

    #[inline]
    fn digest_pad<F>(&mut self, up_to: usize, mut func: &mut F)
        where F: FnMut(&Block<N>)
    {
        self.buffer[self.pos] = 0x80;
        self.pos += 1;

        zero(&mut self.buffer[self.pos..]);

        if self.remaining() < up_to {
            func(&self.buffer);
            zero(&mut self.buffer[..self.pos]);
        }
    }

    #[inline]
    /// Will pad message with message length in little-endian format
    pub fn len_padding<F>(&mut self, data_len: u64, mut func: F)
        where F: FnMut(&Block<N>)
    {
        self.digest_pad(8, &mut func);
        let s = self.size();
        write_u64_le(&mut self.buffer[s-8..], data_len);
        func(&self.buffer);
        self.pos = 0;
    }

    #[inline]
    pub fn len_padding_u128<F>(&mut self, hi: u64, lo: u64, mut func: F)
        where F: FnMut(&Block<N>)
    {
        self.digest_pad(16, &mut func);
        let s = self.size();
        write_u64_le(&mut self.buffer[s-16..s-8], hi);
        write_u64_le(&mut self.buffer[s-8..], lo);
        func(&self.buffer);
        self.pos = 0;
    }

    #[inline]
    pub fn pad_with<P: Padding>(&mut self) -> &mut GenericArray<u8, N> {
        P::pad(self.buffer.as_mut_slice(), self.pos);
        self.pos = 0;
        &mut self.buffer
    }

    #[inline]
    pub fn size(&self) -> usize {
        N::to_usize()
    }

    #[inline]
    pub fn position(&self) -> usize {
        self.pos
    }

    #[inline]
    pub fn remaining(&self) -> usize {
        self.size() - self.pos
    }
}