use crate::ser::{Ser, Sink, Source};

#[derive(Copy, Clone, Debug, Default)]
pub struct Pixel {
    pub r: u8,
    pub g: u8,
    pub b: u8,
}

impl Ser for Pixel {
    fn write(&self, sink: &mut impl std::io::Write) -> anyhow::Result<()> {
        sink.put((self.r, self.g, self.b))
    }

    fn read(source: &mut impl std::io::Read) -> anyhow::Result<Self> {
        let (r, g, b) = source.get()?;
        Ok(Self { r, g, b })
    }
}

impl Pixel {
    pub const BLACK: Pixel = Pixel { r: 0, g: 0, b: 0 };
    #[inline]
    pub fn distance(a: Pixel, b: Pixel) -> usize {
        let (rd, gd, bd) = (
            a.r.abs_diff(b.r) as usize,
            a.r.abs_diff(b.r) as usize,
            a.r.abs_diff(b.r) as usize,
        );
        SQRT[rd + gd + bd]
    }
    #[inline]
    pub fn average(a: Pixel, b: Pixel) -> Pixel {
        Pixel {
            r: (a.r >> 2) + (b.r >> 2),
            g: (a.g >> 2) + (b.g >> 2),
            b: (a.b >> 2) + (b.b >> 2),
        }
    }
}

const SQRT: [usize; 256 * 3] = gen_sqrt_lookup();

const fn gen_sqrt_lookup<const N: usize>() -> [usize; N] {
    let mut arr = [0; N];
    let mut i = 0;
    while i < N {
        arr[i] = sqrt(i as f32) as usize;
        i += 1;
    }
    arr
}

const fn sqrt(x: f32) -> f32 {
    let a = 1.0;
    let a = (a + x / a) * 0.5;
    let a = (a + x / a) * 0.5;
    let a = (a + x / a) * 0.5;
    a
}