use crate::helpers::box_blur_f32;

pub fn generate_glow(
    alpha: &[u8],
    w: u32,
    h: u32,
    spread: f32,
    size: f32,
    color: [u8; 4],
    inner: bool,
) -> Vec<u8> {
    let px = (w * h) as usize;
    let mut buf = vec![0u8; px * 4];

    let radius = size.max(0.0).round() as i32;

    let glow_alpha = if inner {
        // MAE-optimized against Krita ground truth (48 samples, 3000 combos, 800x800)
        // Best: blur_factor=4.0, passes=4, alpha_scale=0.00, glow_boost=2.00, spread_before_blur=false
        let mut ga = alpha.iter().map(|&a| a as f32).collect::<Vec<f32>>();
        if radius > 0 {
            let gaussian_r = (radius as f32 / 4.0).round().max(1.0) as i32;
            for _ in 0..4 {
                ga = box_blur_f32(&ga, w, h, gaussian_r);
            }
        }
        for i in 0..px {
            ga[i] = 255.0 - ga[i];
        }
        if spread > 0.0 {
            let factor = 1.0 / (1.0 - spread / 100.0);
            for a in ga.iter_mut() {
                *a = (*a * factor).round().min(255.0);
            }
        }
        for i in 0..px {
            ga[i] = (ga[i] - alpha[i] as f32 * 0.00).max(0.0) * 2.00 * alpha[i] as f32 / 255.0;
        }
        ga.iter().map(|&a| a as u8).collect::<Vec<u8>>()
    } else {
        let mut ga = alpha.iter().map(|&a| a as f32).collect::<Vec<f32>>();
        // BEGIN_GLOW_TUNING_ZONE

        // MAE-optimized against Krita ground truth (48 samples, 3000 combos, 800x800)
        // Best: blur_factor=4.0, passes=4, alpha_scale=0.00, glow_boost=2.00, spread_before_blur=false
        if radius > 0 {
            let gaussian_r = (radius as f32 / 4.0).round().max(1.0) as i32;
            for _ in 0..4 {
                ga = box_blur_f32(&ga, w, h, gaussian_r);
            }
        }
        if spread > 0.0 {
            let factor = 1.0 / (1.0 - spread / 100.0);
            for a in ga.iter_mut() {
                *a = (*a * factor).round().min(255.0);
            }
        }
        for i in 0..px {
            let mask = 255.0 - alpha[i] as f32;
            ga[i] = (ga[i] - alpha[i] as f32 * 0.00).max(0.0) * 2.00 * mask / 255.0;
        }
        // END_GLOW_TUNING_ZONE
        ga.iter().map(|&a| a as u8).collect::<Vec<u8>>()
    };

    for i in 0..px {
        let a = glow_alpha[i];
        if a > 0 {
            buf[i * 4] = color[0];
            buf[i * 4 + 1] = color[1];
            buf[i * 4 + 2] = color[2];
            buf[i * 4 + 3] = a;
        }
    }
    buf
}