use rand::{Error, RngCore, SeedableRng};

pub struct LaggedFibonacciPRNG {

    circular_buffer: [u32; 64],

    index: usize,

}

impl LaggedFibonacciPRNG {

    pub fn new(init_values: &[u8]) -> Self {

        let mut buf = [0xa98765; 64];

        for i in 0..std::cmp::min(init_values.len(), 54) {

            buf[i] = init_values[i] as u32;

        }

        let mut prng = Self {

            circular_buffer: buf,

        };

        prng.discard(2048);

        prng

    }

    #[inline]

    pub fn discard(&mut self, count: usize) {

        for _i in 0..count {

            self.get_next();

        }

    }

    #[inline]

    fn get_next(&mut self) -> u32 {

        self.index = (self.index + 1) & 0x3f;

        let next_value = self.circular_buffer[(self.index + 40) & 0x3f]

    }

    #[inline]

    pub fn get_random(&mut self, modulo: u32) -> u32 {

        self.get_next();

        self.get_next() % modulo

    }

    #[inline]

    pub fn add_randomness(&mut self, value: u32) {

        self.index = (self.index + 1) & 0x3f;

        self.circular_buffer[self.index] ^= value;

    }

}

impl Iterator for LaggedFibonacciPRNG {

    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {

        self.get_next();

        Some(self.get_next())

    }

}

impl RngCore for LaggedFibonacciPRNG {

    fn next_u32(&mut self) -> u32 {

        self.get_next().wrapping_add(self.get_next())

    }

    fn next_u64(&mut self) -> u64 {

        ((self.next_u32() as u64) << 32) | self.next_u32() as u64

    }

    fn fill_bytes(&mut self, dest: &mut [u8]) {

        dest.iter_mut().for_each(|x| *x = self.next_u32() as u8);

    }

    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {

        Ok(self.fill_bytes(dest))

    }

}

impl SeedableRng for LaggedFibonacciPRNG {

    type Seed = [u8; 32];

    fn from_seed(seed: Self::Seed) -> Self {

        LaggedFibonacciPRNG::new(&seed)

    }

}

#[cfg(test)]

#[test]

fn compatibility() {

    let mut prng = LaggedFibonacciPRNG::new("{052e2aee-ce41-4720-97bd-559a413bf866}".as_bytes());

    prng.add_randomness(123);

        prng.get_random(2);

    }

}