extern crate image;

use image::{Pixel, GenericImage, ImageResult, Rgba};

/// Compute a MSE between an image and its color.
///
/// Will panic an error if the two images don't have the same size.
pub fn mse_color<P: Pixel<Subpixel=u8>, T: GenericImage<Pixel=P>>(img: &T, color: &Rgba<u8>) -> f64 {

    let mut mse = 0.0;

    for x in 0 .. img.dimensions().0 {
        for y in 0 .. img.dimensions().1 {

            let p1 = img.get_pixel(x, y).to_rgba();

            let dx = p1.data[0] as f64 - color.data[0] as f64;
            let dy = p1.data[1] as f64 - color.data[1] as f64;
            let dz = p1.data[2] as f64 - color.data[2] as f64;

            let dx = dx * dx;
            let dy = dy * dy;
            let dz = dz * dz;

            mse += dx + dy + dz;
        }
    }

    mse / (img.dimensions().0 * img.dimensions().1 * 3) as f64
}
/// Compute a MSE between two images.
///
/// Will panic an error if the two images don't have the same size.
pub fn mse<P: Pixel<Subpixel=u8>, T: GenericImage<Pixel=P>>(img1: &T, img2: &T) -> f64 {

    assert_eq!(img1.dimensions(), img2.dimensions());

    let mut mse = 0.0;

    for x in 0 .. img1.dimensions().0 {
        for y in 0 .. img1.dimensions().1 {

            let p1 = img1.get_pixel(x, y).to_rgba();
            let p2 = img2.get_pixel(x, y).to_rgba();

            let dx = p1.data[0] as f64 - p2.data[0] as f64;
            let dy = p1.data[1] as f64 - p2.data[1] as f64;
            let dz = p1.data[2] as f64 - p2.data[2] as f64;

            let dx = dx * dx;
            let dy = dy * dy;
            let dz = dz * dz;

            mse += dx + dy + dz;
        }
    }

    mse / (img1.dimensions().0 * img1.dimensions().1 * 3) as f64
}

pub fn psnr<P: Pixel<Subpixel=u8>, T: GenericImage<Pixel=P>>(img1: &T, img2: &T) -> f64 {
    let twenty_log10_max: f64 = 20.0 * (std::u8::MAX as f64).log10();
    twenty_log10_max - 10.0 * mse(img1, img2).log10()
}

pub fn psnr_files(path1: &str, path2: &str) -> ImageResult<f64> {
    let img1 = image::open(path1)?;
    let img2 = image::open(path2)?;
    Ok(psnr(&img1, &img2))
}