use crate::qr::QrCode;
use image::{ImageBuffer, Luma};

/// 将单个模块填充到图像缓冲区（module_size × module_size 像素块）
fn fill_module(
    img: &mut ImageBuffer<Luma<u8>, Vec<u8>>,
    x: u32,
    y: u32,
    module_size: u32,
    is_dark: bool,
) {
    let px_val = if is_dark { 0u8 } else { 255u8 };
    let x0 = x * module_size;
    let y0 = y * module_size;
    for dy in 0..module_size {
        for dx in 0..module_size {
            img.put_pixel(x0 + dx, y0 + dy, Luma([px_val]));
        }
    }
}

pub fn render_png(qr: &QrCode, module_size: u8) -> Result<Vec<u8>, image::ImageError> {
    let matrix_size = qr.size() as u32;
    let margin = qr.margin as u32;
    let total_size = matrix_size + 2 * margin;
    let img_size = total_size * module_size as u32;

    let mut img = ImageBuffer::new(img_size, img_size);

    for y in 0..total_size {
        for x in 0..total_size {
            // 直接比较坐标与 margin 边界，避免 saturating_sub 在边界处回绕到 0
            let is_dark = if x >= margin
                && x < margin + matrix_size
                && y >= margin
                && y < margin + matrix_size
            {
                let mx = (x - margin) as usize;
                let my = (y - margin) as usize;
                qr.modules()[my][mx]
            } else {
                false // 白边 (quiet zone)
            };

            fill_module(&mut img, x, y, module_size as u32, is_dark);
        }
    }

    let mut buf = Vec::new();
    img.write_to(&mut std::io::Cursor::new(&mut buf), image::ImageFormat::Png)?;
    Ok(buf)
}