//! Image Processing Functions
use std::cmp;

use num_traits::{NumCast};

use crate::image::{GenericImage, GenericImageView, SubImage};
use crate::traits::{Lerp, Primitive, Pixel};

pub use self::sample::FilterType;

pub use self::sample::FilterType::{CatmullRom, Gaussian, Lanczos3, Nearest, Triangle};

/// Affine transformations
pub use self::affine::{
    flip_horizontal, flip_horizontal_in_place, flip_vertical, flip_vertical_in_place, rotate180,
    rotate180_in_place, rotate270, rotate90, rotate180_in, rotate90_in, rotate270_in, flip_horizontal_in, flip_vertical_in
};

/// Image sampling
pub use self::sample::{blur, filter3x3, resize, thumbnail, unsharpen};

/// Color operations
pub use self::colorops::{brighten, contrast, dither, grayscale, huerotate, index_colors, invert,
                         BiLevel, ColorMap};

mod affine;
// Public only because of Rust bug:
// https://github.com/rust-lang/rust/issues/18241
pub mod colorops;
mod sample;

/// Return a mutable view into an image
pub fn crop<I: GenericImageView>(
    image: &mut I,
    x: u32,
    y: u32,
    width: u32,
    height: u32,
) -> SubImage<&mut I> {
    let (x, y, width, height) = crop_dimms(image, x, y, width, height);
    SubImage::new(image, x, y, width, height)
}

/// Return an immutable view into an image
pub fn crop_imm<I: GenericImageView>(
    image: &I,
    x: u32,
    y: u32,
    width: u32,
    height: u32,
) -> SubImage<&I> {
    let (x, y, width, height) = crop_dimms(image, x, y, width, height);
    SubImage::new(image, x, y, width, height)
}

fn crop_dimms<I: GenericImageView>(
    image: &I,
    x: u32,
    y: u32,
    width: u32,
    height: u32,
) -> (u32, u32, u32, u32) {
    let (iwidth, iheight) = image.dimensions();

    let x = cmp::min(x, iwidth);
    let y = cmp::min(y, iheight);

    let height = cmp::min(height, iheight - y);
    let width = cmp::min(width, iwidth - x);

    (x, y, width, height)
}

/// Calculate the region that can be copied from top to bottom.
///
/// Given image size of bottom and top image, and a point at which we want to place the top image
/// onto the bottom image, how large can we be? Have to wary of the following issues:
/// * Top might be larger than bottom
/// * Overflows in the computation
/// * Coordinates could be completely out of bounds
///
/// The main idea is to make use of inequalities provided by the nature of `saturing_add` and
/// `saturating_sub`. These intrinsically validate that all resulting coordinates will be in bounds
/// for both images.
///
/// We want that all these coordinate accesses are safe:
/// 1. `bottom.get_pixel(x + [0..x_range), y + [0..y_range))`
/// 2. `top.get_pixel([0..x_range), [0..y_range))`
///
/// Proof that the function provides the necessary bounds for width. Note that all unaugmented math
/// operations are to be read in standard arithmetic, not integer arithmetic. Since no direct
/// integer arithmetic occurs in the implementation, this is unambiguous.
///
/// ```text
/// Three short notes/lemmata:
/// - Iff `(a - b) <= 0` then `a.saturating_sub(b) = 0`
/// - Iff `(a - b) >= 0` then `a.saturating_sub(b) = a - b`
/// - If  `a <= c` then `a.saturating_sub(b) <= c.saturating_sub(b)`
///
/// 1.1 We show that if `bottom_width <= x`, then `x_range = 0` therefore `x + [0..x_range)` is empty.
///
/// x_range
///  = (top_width.saturating_add(x).min(bottom_width)).saturating_sub(x)
/// <= bottom_width.saturating_sub(x)
///
/// bottom_width <= x
/// <==> bottom_width - x <= 0
/// <==> bottom_width.saturating_sub(x) = 0
///  ==> x_range <= 0
///  ==> x_range  = 0
///
/// 1.2 If `x < bottom_width` then `x + x_range < bottom_width`
///
/// x + x_range
/// <= x + bottom_width.saturating_sub(x)
///  = x + (bottom_width - x)
///  = bottom_width
///
/// 2. We show that `x_range <= top_width`
///
/// x_range
///  = (top_width.saturating_add(x).min(bottom_width)).saturating_sub(x)
/// <= top_width.saturating_add(x).saturating_sub(x)
/// <= (top_wdith + x).saturating_sub(x)
///  = top_width (due to `top_width >= 0` and `x >= 0`)
/// ```
///
/// Proof is the same for height.
pub fn overlay_bounds(
    (bottom_width, bottom_height): (u32, u32),
    (top_width, top_height): (u32, u32),
    x: u32,
    y: u32
)
    -> (u32, u32)
{
    let x_range = top_width.saturating_add(x) // Calculate max coordinate
        .min(bottom_width) // Restrict to lower width
        .saturating_sub(x); // Determinate length from start `x`
    let y_range = top_height.saturating_add(y)
        .min(bottom_height)
        .saturating_sub(y);
    (x_range, y_range)
}

/// Overlay an image at a given coordinate (x, y)
pub fn overlay<I, J>(bottom: &mut I, top: &J, x: u32, y: u32)
where
    I: GenericImage,
    J: GenericImageView<Pixel = I::Pixel>,
{
    let bottom_dims = bottom.dimensions();
    let top_dims = top.dimensions();

    // Crop our top image if we're going out of bounds
    let (range_width, range_height) = overlay_bounds(bottom_dims, top_dims, x, y);

    for top_y in 0..range_height {
        for top_x in 0..range_width {
            let p = top.get_pixel(top_x, top_y);
            let mut bottom_pixel = bottom.get_pixel(x + top_x, y + top_y);
            bottom_pixel.blend(&p);

            bottom.put_pixel(x + top_x, y + top_y, bottom_pixel);
        }
    }
}

/// Tile an image by repeating it multiple times
///
/// # Examples
/// ```no_run
/// use image::{RgbaImage};
///
/// fn main() {
///      let mut img = RgbaImage::new(1920, 1080);
///      let tile = image::open("tile.png").unwrap();
///
///      image::imageops::tile(&mut img, &tile);
///      img.save("tiled_wallpaper.png").unwrap();
/// }
/// ```
pub fn tile<I, J>(bottom: &mut I, top: &J)
where
    I: GenericImage,
    J: GenericImageView<Pixel = I::Pixel>,
{
    for x in (0..bottom.width()).step_by(top.width() as usize) {
        for y in (0..bottom.height()).step_by(top.height() as usize) {
            overlay(bottom, top, x, y);
        }
    }
}

/// Fill the image with a linear vertical gradient
/// 
/// This function assumes a linear color space.
/// 
/// # Examples
/// ```no_run
/// use image::{Rgba, RgbaImage, Pixel};
/// 
/// fn main() {
///     let mut img = RgbaImage::new(100, 100);
///     let start = Rgba::from_slice(&[0, 128, 0, 0]);
///     let end = Rgba::from_slice(&[255, 255, 255, 255]);
/// 
///     image::imageops::vertical_gradient(&mut img, start, end);
///     img.save("vertical_gradient.png").unwrap();
/// }
pub fn vertical_gradient<S, P, I>(img: &mut I, start: &P, stop: &P)
where
    I: GenericImage<Pixel = P>,
    P: Pixel<Subpixel = S> + 'static,
    S: Primitive + Lerp + 'static
{
    for y in 0..img.height() {
        let pixel = start.map2(stop, |a, b| {
            let y = <S::Ratio as NumCast>::from(y).unwrap();
            let height = <S::Ratio as NumCast>::from(img.height() - 1).unwrap();
            S::lerp(a, b, y / height)
        });
        
        for x in 0..img.width() {
            img.put_pixel(x, y, pixel);
        }
    }
}

/// Fill the image with a linear horizontal gradient
/// 
/// This function assumes a linear color space.
///
/// # Examples
/// ```no_run
/// use image::{Rgba, RgbaImage, Pixel};
/// 
/// fn main() {
///     let mut img = RgbaImage::new(100, 100);
///     let start = Rgba::from_slice(&[0, 128, 0, 0]);
///     let end = Rgba::from_slice(&[255, 255, 255, 255]);
/// 
///     image::imageops::horizontal_gradient(&mut img, start, end);
///     img.save("horizontal_gradient.png").unwrap();
/// }
pub fn horizontal_gradient<S, P, I>(img: &mut I, start: &P, stop: &P)
where
    I: GenericImage<Pixel = P>,
    P: Pixel<Subpixel = S> + 'static,
    S: Primitive + Lerp + 'static
{
    for x in 0..img.width() {
        let pixel = start.map2(stop, |a, b| {
            let x = <S::Ratio as NumCast>::from(x).unwrap();
            let width = <S::Ratio as NumCast>::from(img.width() - 1).unwrap();
            S::lerp(a, b, x / width)
        });
        
        for y in 0..img.height() {
            img.put_pixel(x, y, pixel);
        }
    }
}

/// Replace the contents of an image at a given coordinate (x, y)
pub fn replace<I, J>(bottom: &mut I, top: &J, x: u32, y: u32)
where
    I: GenericImage,
    J: GenericImageView<Pixel = I::Pixel>,
{
    let bottom_dims = bottom.dimensions();
    let top_dims = top.dimensions();

    // Crop our top image if we're going out of bounds
    let (range_width, range_height) = overlay_bounds(bottom_dims, top_dims, x, y);

    for top_y in 0..range_height {
        for top_x in 0..range_width {
            let p = top.get_pixel(top_x, top_y);
            bottom.put_pixel(x + top_x, y + top_y, p);
        }
    }
}

#[cfg(test)]
mod tests {

    use super::overlay;
    use crate::RgbaImage;
    use crate::ImageBuffer;
    use crate::color::Rgb;

    #[test]
    /// Test that images written into other images works
    fn test_image_in_image() {
        let mut target = ImageBuffer::new(32, 32);
        let source = ImageBuffer::from_pixel(16, 16, Rgb([255u8, 0, 0]));
        overlay(&mut target, &source, 0, 0);
        assert!(*target.get_pixel(0, 0) == Rgb([255u8, 0, 0]));
        assert!(*target.get_pixel(15, 0) == Rgb([255u8, 0, 0]));
        assert!(*target.get_pixel(16, 0) == Rgb([0u8, 0, 0]));
        assert!(*target.get_pixel(0, 15) == Rgb([255u8, 0, 0]));
        assert!(*target.get_pixel(0, 16) == Rgb([0u8, 0, 0]));
    }

    #[test]
    /// Test that images written outside of a frame doesn't blow up
    fn test_image_in_image_outside_of_bounds() {
        let mut target = ImageBuffer::new(32, 32);
        let source = ImageBuffer::from_pixel(32, 32, Rgb([255u8, 0, 0]));
        overlay(&mut target, &source, 1, 1);
        assert!(*target.get_pixel(0, 0) == Rgb([0, 0, 0]));
        assert!(*target.get_pixel(1, 1) == Rgb([255u8, 0, 0]));
        assert!(*target.get_pixel(31, 31) == Rgb([255u8, 0, 0]));
    }

    #[test]
    /// Test that images written to coordinates out of the frame doesn't blow up
    /// (issue came up in #848)
    fn test_image_outside_image_no_wrap_around() {
        let mut target = ImageBuffer::new(32, 32);
        let source = ImageBuffer::from_pixel(32, 32, Rgb([255u8, 0, 0]));
        overlay(&mut target, &source, 33, 33);
        assert!(*target.get_pixel(0, 0) == Rgb([0, 0, 0]));
        assert!(*target.get_pixel(1, 1) == Rgb([0, 0, 0]));
        assert!(*target.get_pixel(31, 31) == Rgb([0, 0, 0]));
    }

    #[test]
    /// Test that images written to coordinates with overflow works
    fn test_image_coordinate_overflow() {
        let mut target = ImageBuffer::new(16, 16);
        let source = ImageBuffer::from_pixel(32, 32, Rgb([255u8, 0, 0]));
        // Overflows to 'sane' coordinates but top is larger than bot.
        overlay(&mut target, &source, u32::max_value() - 31, u32::max_value() - 31);
        assert!(*target.get_pixel(0, 0) == Rgb([0, 0, 0]));
        assert!(*target.get_pixel(1, 1) == Rgb([0, 0, 0]));
        assert!(*target.get_pixel(15, 15) == Rgb([0, 0, 0]));
    }

    use super::{horizontal_gradient, vertical_gradient};

    #[test]
    /// Test that horizontal gradients are correctly generated
    fn test_image_horizontal_gradient_limits() {
        let mut img = ImageBuffer::new(100, 1);

        let start = Rgb([0u8, 128, 0]);
        let end = Rgb([255u8, 255, 255]);

        horizontal_gradient(&mut img, &start, &end);

        assert_eq!(img.get_pixel(0, 0), &start);
        assert_eq!(img.get_pixel(img.width() - 1, 0), &end);
    }

    #[test]
    /// Test that vertical gradients are correctly generated
    fn test_image_vertical_gradient_limits() {
        let mut img = ImageBuffer::new(1, 100);

        let start = Rgb([0u8, 128, 0]);
        let end = Rgb([255u8, 255, 255]);

        vertical_gradient(&mut img, &start, &end);

        assert_eq!(img.get_pixel(0, 0), &start);
        assert_eq!(img.get_pixel(0, img.height() - 1), &end);
    }

    #[test]
    /// Test blur doens't panick when passed 0.0
    fn test_blur_zero() {
        let image = RgbaImage::new(50, 50);
        let _ = super::blur(&image, 0.0);
    }
}