//! Reference plots for different backends.
//!
//! Use the `SNAPSHOT_UPDATE` to generate / update snapshot images:
//!
//! ```bash
//! SNAPSHOT_UPDATE=1 cargo run test --test references --features cpu_backend
//! ```

use image::{DynamicImage, ImageError};

use std::{env, io, path::Path};

use julia_set::{Backend, ImageBuffer, Params, Render};

const IMAGE_SIZE: [u32; 2] = [360, 360];

fn generate_image<F, B: Backend<F> + Default>(function: F, params: &Params) -> ImageBuffer {
    B::default()
        .create_program(function)
        .unwrap()
        .render(params)
        .unwrap()
}

fn compare_to_reference(reference_filename: &str, image: &ImageBuffer) {
    const ROOT_PATH: &str = env!("CARGO_MANIFEST_DIR");
    let reference_path = Path::new(ROOT_PATH)
        .join("tests")
        .join("__snapshots__")
        .join(reference_filename);

    let reference_image = match image::open(&reference_path) {
        Ok(DynamicImage::ImageLuma8(image)) => Some(image),
        Ok(_) => panic!("Unexpected image format"),

        Err(ImageError::IoError(ref io_error)) if io_error.kind() == io::ErrorKind::NotFound => {
            None
        }
        Err(other_error) => panic!("Error opening reference file: {:?}", other_error),
    };

    if let Some(ref reference_image) = reference_image {
        let image_diff = ImageDiff::new(reference_image, &image);
        println!("{}: {:?}", reference_filename, image_diff);
        image_diff.assert_is_sound();
        return;
    } else if let Ok(snapshot_update) = env::var("SNAPSHOT_UPDATE") {
        if snapshot_update == "1" {
            // Store the reference image.
            image
                .save(&reference_path)
                .expect("Cannot save reference image");
            return;
        }
    }

    panic!("Snapshot `{}` not found", reference_filename);
}

#[derive(Debug)]
struct ImageDiff {
    /// Percentage of differing image pixels.
    differing_pixels: f32,
    /// Mean difference in pixel luma across all pixels in the image.
    mean_difference: f32,
}

impl ImageDiff {
    const MAX_DIFFERING_PIXELS: f32 = 0.1;
    const MAX_MEAN_DIFFERENCE: f32 = 2.0;

    fn pixel_quantity(image: &ImageBuffer, quantity: u32) -> f32 {
        let pixel_count = image.width() * image.height();
        quantity as f32 / pixel_count as f32
    }

    fn new(expected: &ImageBuffer, actual: &ImageBuffer) -> Self {
        assert_eq!(expected.width(), actual.width());
        assert_eq!(expected.height(), actual.height());

        let mut differing_count = 0_u32;
        let mut total_diff = 0_u32;

        for (expected_pixel, actual_pixel) in expected.pixels().zip(actual.pixels()) {
            let diff = if expected_pixel[0] > actual_pixel[0] {
                expected_pixel[0] - actual_pixel[0]
            } else {
                actual_pixel[0] - expected_pixel[0]
            };

            if diff > 0 {
                differing_count += 1;
                total_diff += diff as u32;
            }
        }

        let differing_pixels = Self::pixel_quantity(&expected, differing_count);
        let mean_difference = Self::pixel_quantity(&expected, total_diff);
        Self {
            differing_pixels,
            mean_difference,
        }
    }

    fn assert_is_sound(&self) {
        assert!(
            self.differing_pixels <= Self::MAX_DIFFERING_PIXELS,
            "{:?}",
            self
        );
        assert!(
            self.mean_difference <= Self::MAX_MEAN_DIFFERENCE,
            "{:?}",
            self
        );
    }
}

mod cubic {
    use super::*;

    #[cfg(any(
        feature = "dyn_cpu_backend",
        feature = "opencl_backend",
        feature = "vulkan_backend"
    ))]
    fn create_function() -> julia_set::Function {
        "z * z * z - 0.39".parse().unwrap()
    }

    const SNAPSHOT_FILENAME: &str = "cubic.png";

    fn render_params() -> Params {
        Params::new(IMAGE_SIZE, 2.5).with_infinity_distance(2.5)
    }

    #[test]
    #[cfg(feature = "dyn_cpu_backend")]
    fn cpu_backend() {
        let image = generate_image::<_, julia_set::Cpu>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "cpu_backend")]
    fn cpu_backend_with_native_function() {
        let image = generate_image::<_, julia_set::Cpu>(|z| z * z * z - 0.39, &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "vulkan_backend")]
    fn vulkan_backend() {
        let image = generate_image::<_, julia_set::Vulkan>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "opencl_backend")]
    fn opencl_backend() {
        let image = generate_image::<_, julia_set::OpenCl>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }
}

mod exp {
    use super::*;
    use num_complex::Complex32;

    #[cfg(any(
        feature = "dyn_cpu_backend",
        feature = "opencl_backend",
        feature = "vulkan_backend"
    ))]
    fn create_function() -> julia_set::Function {
        "exp(z ^ -4) + 0.15i".parse().unwrap()
    }

    const SNAPSHOT_FILENAME: &str = "exp.png";

    fn render_params() -> Params {
        Params::new(IMAGE_SIZE, 4.0).with_infinity_distance(9.0)
    }

    #[test]
    #[cfg(feature = "dyn_cpu_backend")]
    fn cpu_backend() {
        let image = generate_image::<_, julia_set::Cpu>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "cpu_backend")]
    fn cpu_backend_with_native_function() {
        let image = generate_image::<_, julia_set::Cpu>(
            |z: Complex32| z.powi(-4).exp() + Complex32::new(0.0, 0.15),
            &render_params(),
        );
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "vulkan_backend")]
    fn vulkan_backend() {
        let image = generate_image::<_, julia_set::Vulkan>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "opencl_backend")]
    fn opencl_backend() {
        let image = generate_image::<_, julia_set::OpenCl>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }
}

mod flower {
    use super::*;
    use num_complex::Complex32;

    #[cfg(any(
        feature = "dyn_cpu_backend",
        feature = "opencl_backend",
        feature = "vulkan_backend"
    ))]
    fn create_function() -> julia_set::Function {
        "0.8*z + z/atanh(z^-4)".parse().unwrap()
    }

    const SNAPSHOT_FILENAME: &str = "flower.png";

    fn render_params() -> Params {
        Params::new(IMAGE_SIZE, 2.0).with_infinity_distance(10.0)
    }

    #[test]
    #[cfg(feature = "dyn_cpu_backend")]
    fn cpu_backend() {
        let image = generate_image::<_, julia_set::Cpu>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "cpu_backend")]
    fn cpu_backend_with_native_function() {
        let image = generate_image::<_, julia_set::Cpu>(
            |z: Complex32| z * 0.8 + z / z.powi(-4).atanh(),
            &render_params(),
        );
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "vulkan_backend")]
    fn vulkan_backend() {
        let image = generate_image::<_, julia_set::Vulkan>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "opencl_backend")]
    fn opencl_backend() {
        let image = generate_image::<_, julia_set::OpenCl>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }
}

mod hills {
    use super::*;
    use num_complex::Complex32;

    #[cfg(any(
        feature = "dyn_cpu_backend",
        feature = "opencl_backend",
        feature = "vulkan_backend"
    ))]
    fn create_function() -> julia_set::Function {
        "1i * acosh(cosh(1i * z) - arg(z)^-2) - 0.05 + 0.05i"
            .parse()
            .unwrap()
    }

    const SNAPSHOT_FILENAME: &str = "hills.png";

    fn render_params() -> Params {
        Params::new(IMAGE_SIZE, 8.0)
            .with_view_center([-9.41, 0.0])
            .with_infinity_distance(5.0)
    }

    #[test]
    #[cfg(feature = "dyn_cpu_backend")]
    fn cpu_backend() {
        let image = generate_image::<_, julia_set::Cpu>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "cpu_backend")]
    fn cpu_backend_with_native_function() {
        let image = generate_image::<_, julia_set::Cpu>(
            |z: Complex32| {
                Complex32::i() * ((Complex32::i() * z).cosh() - z.arg().powi(-2)).acosh()
                    + Complex32::new(-0.05, 0.05)
            },
            &render_params(),
        );
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "vulkan_backend")]
    fn vulkan_backend() {
        let image = generate_image::<_, julia_set::Vulkan>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "opencl_backend")]
    fn opencl_backend() {
        let image = generate_image::<_, julia_set::OpenCl>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }
}

mod spiral {
    use super::*;
    use num_complex::Complex32;

    #[cfg(any(
        feature = "dyn_cpu_backend",
        feature = "opencl_backend",
        feature = "vulkan_backend"
    ))]
    fn create_function() -> julia_set::Function {
        "z + tanh(sqrt(z)) - 0.18 + 0.5i".parse().unwrap()
    }

    const SNAPSHOT_FILENAME: &str = "spiral.png";

    fn render_params() -> Params {
        Params::new(IMAGE_SIZE, 2.3)
            .with_view_center([-6.84, 1.15])
            .with_infinity_distance(9.0)
    }

    #[test]
    #[cfg(feature = "dyn_cpu_backend")]
    fn cpu_backend() {
        let image = generate_image::<_, julia_set::Cpu>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "cpu_backend")]
    fn cpu_backend_with_native_function() {
        let image = generate_image::<_, julia_set::Cpu>(
            |z: Complex32| z + z.sqrt().tanh() + Complex32::new(-0.18, 0.5),
            &render_params(),
        );
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "vulkan_backend")]
    fn vulkan_backend() {
        let image = generate_image::<_, julia_set::Vulkan>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }

    #[test]
    #[cfg(feature = "opencl_backend")]
    fn opencl_backend() {
        let image = generate_image::<_, julia_set::OpenCl>(&create_function(), &render_params());
        compare_to_reference(SNAPSHOT_FILENAME, &image);
    }
}