//! Utils for testing and debugging.

use definitions::{
    VecBuffer
};

use image::{
    DynamicImage,
    GenericImage,
    GrayImage,
    ImageBuffer,
    Luma,
    open,
    Pixel,
    Primitive,
    Rgb,
    RgbImage
};

use quickcheck::{
    Arbitrary,
    Gen
};

use rand::{
    Rand
};

use std::fmt;
use std::path::Path;

/// Panics if any pixels differ between the two input images.
#[macro_export]
macro_rules! assert_pixels_eq {
    ($actual:expr, $expected:expr) => ({
        assert_dimensions_match!($actual, $expected);
        let diffs = $crate::utils::pixel_diffs(&$actual, &$expected, |p, q| p != q);
        if !diffs.is_empty() {
            panic!($crate::utils::describe_pixel_diffs(diffs.into_iter()))
        }
     })
}

/// Panics if any pixels differ between the two images by more than the
/// given tolerance in a single channel.
#[macro_export]
macro_rules! assert_pixels_eq_within {
    ($actual:expr, $expected:expr, $channel_tolerance:expr) => ({

        assert_dimensions_match!($actual, $expected);
        let diffs = $crate::utils::pixel_diffs(&$actual, &$expected, |p, q| {

            use image::Pixel;
            let cp = p.2.channels();
            let cq = q.2.channels();
            if cp.len() != cq.len() {
                panic!("pixels have different channel counts. \
                    actual: {:?}, expected: {:?}", cp.len(), cq.len())
            }

            let mut large_diff = false;
            for i in 0..cp.len() {
                let sp = cp[i];
                let sq = cq[i];
                // Handle unsigned subpixels
                let diff = if sp > sq {sp - sq} else {sq - sp};
                if diff > $channel_tolerance {
                    large_diff = true;
                    break;
                }
            }

            large_diff
        });
        if !diffs.is_empty() {
            panic!($crate::utils::describe_pixel_diffs(diffs.into_iter()))
        }
    })
}

/// Panics if image dimensions do not match.
#[macro_export]
macro_rules! assert_dimensions_match {
    ($actual:expr, $expected:expr) => ({

        let actual_dim = $actual.dimensions();
        let expected_dim = $expected.dimensions();

        if actual_dim != expected_dim {
            panic!("dimensions do not match. \
                actual: {:?}, expected: {:?}", actual_dim, expected_dim)
        }
     })
}

/// Lists pixels that differ between left and right images.
pub fn pixel_diffs<I, F>(left: &I, right: &I, is_diff: F)
        -> Vec<((u32, u32, I::Pixel), (u32, u32, I::Pixel))>
    where I: GenericImage,
          I::Pixel: PartialEq,
          F: Fn((u32, u32, I::Pixel), (u32, u32, I::Pixel)) -> bool {

    // Can't just call $image.pixels(), as that needn't hit the
    // trait pixels method - ImageBuffer defines its own pixels
    // method with a different signature
    GenericImage::pixels(left)
        .zip(GenericImage::pixels(right))
        .filter(|&(p, q)| is_diff(p, q))//p != q)
        .collect::<Vec<_>>()
}

/// Gives a summary description of a list of pixel diffs for use in error messages.
pub fn describe_pixel_diffs<I, P>(diffs: I) -> String
    where I: Iterator<Item=(P, P)>,
          P: fmt::Debug {

    let mut err = "pixels do not match. ".to_string();
    err.push_str(&(diffs
        .take(5)
        .map(|d| format!("\nactual: {:?}, expected {:?} ", d.0, d.1))
        .collect::<Vec<_>>()
        .join("")));
    err
}

/// Loads image at given path, panicking on failure.
pub fn load_image_or_panic(path: &Path) -> DynamicImage {
     open(path)
         .ok()
         .expect(&format!("Could not load image at {:?}", path))
}

/// Gray image to use in benchmarks. This is neither noise nor
/// similar to natural images - it's just a convenience method
/// to produce an image that's not constant.
pub fn gray_bench_image(width: u32, height: u32) -> GrayImage {
    let mut image = GrayImage::new(width, height);
    for y in 0..image.height() {
        for x in 0..image.width() {
            let intensity = (x % 7 + y % 6) as u8;
            image.put_pixel(x, y, Luma([intensity]));
        }
    }
    image
}

/// RGB image to use in benchmarks. See comment on gray_bench_image.
pub fn rgb_bench_image(width: u32, height: u32) -> RgbImage {
    use std::cmp;
    let mut image = RgbImage::new(width, height);
    for y in 0..image.height() {
        for x in 0..image.width() {
            let r = (x % 7 + y % 6) as u8;
            let g = 255u8 - r;
            let b = cmp::min(r, g);
            image.put_pixel(x, y, Rgb([r, g, b]));
        }
    }
    image
}

/// Wrapper for image buffers to allow us to write an Arbitrary instance.
#[derive(Clone)]
pub struct TestBuffer<T: Pixel>(pub VecBuffer<T>);

/// 8bpp grayscale TestBuffer.
pub type GrayTestImage = TestBuffer<Luma<u8>>;

/// 24bpp RGB TestBuffer.
pub type RgbTestImage = TestBuffer<Rgb<u8>>;

impl<T: Pixel + ArbitraryPixel + Send + 'static> Arbitrary for TestBuffer<T>
    where <T as Pixel>::Subpixel: Send
{
    fn arbitrary<G: Gen>(g: &mut G) -> Self {
        let (width, height) = small_image_dimensions(g);
        let mut image = ImageBuffer::new(width, height);
        for y in 0..height {
            for x in 0..width {
                let pix: T = ArbitraryPixel::arbitrary(g);
                image.put_pixel(x, y, pix);
            }
        }
        TestBuffer(image)
    }

    fn shrink(&self) -> Box<Iterator<Item=TestBuffer<T>>> {
        Box::new(shrink(&self.0).map(|x| TestBuffer(x)))
    }
}

/// Workaround for not being able to define Arbitrary instances for pixel types
/// defines in other modules.
pub trait ArbitraryPixel {
    fn arbitrary<G: Gen>(g: &mut G) -> Self;
}

fn shrink<I>(image: &I) -> Box<Iterator<Item=VecBuffer<I::Pixel>>>
    where I: GenericImage,
          I::Pixel: 'static
{
    let mut subs = vec![];

    let w = image.width();
    let h = image.height();

    if w > 0 {
        let left = copy_sub(image, 0, 0, w - 1, h);
        subs.push(left);
        let right = copy_sub(image, 1, 0, w - 1, h);
        subs.push(right);
    }
    if h > 0 {
        let top = copy_sub(image, 0, 0, w, h - 1);
        subs.push(top);
        let bottom = copy_sub(image, 0, 1, w, h - 1);
        subs.push(bottom);
    }

    Box::new(subs.into_iter())
}

fn copy_sub<I>(image: &I, x: u32, y: u32, width: u32, height: u32) -> VecBuffer<I::Pixel>
    where I: GenericImage,
          I::Pixel: 'static
{
    let mut out = ImageBuffer::new(width, height);
    for dy in 0..height {
        let oy = y + dy;
        for dx in 0..width {
            let ox = x + dx;
            out.put_pixel(dx, dy, image.get_pixel(ox, oy));
        }
    }
    out
}

impl<T: fmt::Debug + Pixel + 'static> fmt::Debug for TestBuffer<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "width: {}, height: {}, data: {:?}",
            self.0.width(), self.0.height(), self.0.enumerate_pixels().collect::<Vec<_>>())
    }
}

fn small_image_dimensions<G: Gen>(g: &mut G) -> (u32, u32) {
    let dims: (u8, u8) = Arbitrary::arbitrary(g);
    ((dims.0 % 10) as u32, (dims.1 % 10) as u32)
}

impl<T: Rand + Send + Primitive> ArbitraryPixel for Rgb<T> {
    fn arbitrary<G: Gen>(g: &mut G) -> Self {
        let red: T = g.gen();
        let green: T = g.gen();
        let blue: T = g.gen();
        Rgb([red, green, blue])
    }
}

impl<T: Rand + Send + Primitive> ArbitraryPixel for Luma<T> {
    fn arbitrary<G: Gen>(g: &mut G) -> Self {
        let val: T = g.gen();
        Luma([val])
    }
}

#[cfg(test)]
mod test {

    use image::{
        GrayImage,
        ImageBuffer
    };

    #[test]
    fn test_assert_pixels_eq_passes() {
        let image: GrayImage = ImageBuffer::from_raw(3, 2, vec![
            00, 01, 02,
            10, 11, 12]).unwrap();

        assert_pixels_eq!(image, image);
    }

    #[test]
    #[should_panic]
    fn test_assert_pixels_eq_fails() {
        let image: GrayImage = ImageBuffer::from_raw(3, 2, vec![
            00, 01, 02,
            10, 11, 12]).unwrap();

        let diff: GrayImage = ImageBuffer::from_raw(3, 2, vec![
            00, 11, 02,
            10, 11, 12]).unwrap();

        assert_pixels_eq!(diff, image);
    }

    #[test]
    fn test_assert_pixels_eq_within_passes() {
        let image: GrayImage = ImageBuffer::from_raw(3, 2, vec![
            00, 01, 02,
            10, 11, 12]).unwrap();

        let diff: GrayImage = ImageBuffer::from_raw(3, 2, vec![
            00, 02, 02,
            10, 11, 12]).unwrap();

        assert_pixels_eq_within!(diff, image, 1);
    }

    #[test]
    #[should_panic]
    fn test_assert_pixels_eq_within_fails() {
        let image: GrayImage = ImageBuffer::from_raw(3, 2, vec![
            00, 01, 02,
            10, 11, 12]).unwrap();

        let diff: GrayImage = ImageBuffer::from_raw(3, 2, vec![
            00, 03, 02,
            10, 11, 12]).unwrap();

        assert_pixels_eq_within!(diff, image, 1);
    }
}