use image::{
    DynamicImage, GrayImage, Luma,
    imageops::{self, BiLevel, colorops, colorops::ColorMap, index_colors},
};

struct CustomLevel {
    threshold: u8,
}

impl ColorMap for CustomLevel {
    type Color = Luma<u8>;

    fn index_of(&self, color: &Self::Color) -> usize {
        let v = color.0[0];
        if v >= self.threshold { 1 } else { 0 }
    }

    fn map_color(&self, color: &mut Self::Color) {
        color.0[0] = if color.0[0] >= self.threshold { 255 } else { 0 };
    }
}

pub fn auto_brighten(gray: &mut GrayImage) -> () {
    let avg = gray.pixels().map(|p| p.0[0] as u32).sum::<u32>() / gray.len() as u32;

    if avg < 100 {
        colorops::brighten_in_place(gray, 40);
        colorops::contrast_in_place(gray, 25.0);
    } else if avg > 180 {
        colorops::brighten_in_place(gray, -15);
    }
}

pub fn dither(gray: &mut GrayImage) -> Vec<u8> {
    let level = CustomLevel { threshold: 175 };
    let bw: image::ImageBuffer<Luma<u8>, Vec<u8>> = index_colors(&gray, &level);

    let (w, h) = (gray.width() as usize, gray.height() as usize);
    let pitch = (w + 7) >> 3;
    let mut bits = vec![0u8; pitch * h];

    for y in 0..h {
        for x in 0..w {
            let byte = y * pitch + (x >> 3);
            let bit = 7 - (x & 7);
            if bw[(x as u32, y as u32)].0[0] == 0 {
                bits[byte] |= 1 << bit;
            }
        }
    }
    bits
}