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#![no_std]

use core::ptr;

pub trait Random: Sized {
    fn random<G: ?Sized + RandomGen>(g: &mut G) -> Self;
}

pub trait RandomGen {
    #[inline]
    fn gen_u32(&mut self) -> u32 { self.gen_u64() as u32 }
    #[inline]
    fn gen_u64(&mut self) -> u64 { (self.gen_u32() as u64) << 32 | (self.gen_u32() as u64) }
    #[inline]
    fn gen_f32(&mut self) -> f32 { (self.gen_u32() >>  8) as f32 / (1u64 << 24) as f32 }
    #[inline]
    fn gen_f64(&mut self) -> f64 { (self.gen_u64() >> 11) as f64 / (1u64 << 53) as f64 }
    #[inline]
    fn gen_bytes(&mut self, bs: &mut [u8]) -> usize {
        let l0 = bs.len();
        let mut p = bs.as_mut_ptr();
        let     q = &mut bs[l0] as *mut _;
        loop { unsafe {
            let l = (p as usize) - (q as usize);
            if l >= 8 {
                let n = self.gen_u64();
                ptr::copy_nonoverlapping(&n as *const _ as *const u8, p, 8);
                p = p.offset(8);
            } else {
                let n = self.gen_u32();
                ptr::copy_nonoverlapping(&n as *const _ as *const u8, p, usize::min(4, l));
                if l >= 4 { return l0; }
                p = p.offset(4);
            }
        } }
    }
    #[inline]
    fn gen<A: Random>(&mut self) -> A { A::random(self) }
}

impl Random for u32 {
    #[inline]
    fn random<G: ?Sized + RandomGen>(g: &mut G) -> u32 { g.gen_u32() }
}

impl Random for u64 {
    #[inline]
    fn random<G: ?Sized + RandomGen>(g: &mut G) -> u64 { g.gen_u64() }
}

impl Random for i32 {
    #[inline]
    fn random<G: ?Sized + RandomGen>(g: &mut G) -> i32 { g.gen_u32() as _ }
}

impl Random for i64 {
    #[inline]
    fn random<G: ?Sized + RandomGen>(g: &mut G) -> i64 { g.gen_u64() as _ }
}

impl Random for f32 {
    #[inline]
    fn random<G: ?Sized + RandomGen>(g: &mut G) -> f32 { g.gen_f32() }
}

impl Random for f64 {
    #[inline]
    fn random<G: ?Sized + RandomGen>(g: &mut G) -> f64 { g.gen_f64() }
}

pub trait Seedable<Seed>: RandomGen {
    fn reseed(&mut self, _: Seed);
    fn from_seed(_: Seed) -> Self;
}