//! Shared mathematical utility functions.

use std::cmp::max;

/// Calculates the width and height an image should be resized to.

/// This preserves aspect ratio, and based on the `fill` parameter

/// will either fill the dimensions to fit inside the smaller constraint

/// (will overflow the specified bounds on one axis to preserve

/// aspect ratio), or will shrink so that both dimensions are

/// completely contained within the given `width` and `height`,

/// with empty space on one axis.

pub(crate) fn resize_dimensions(

    width: u32,

    height: u32,

    nwidth: u32,

    nheight: u32,

    fill: bool,

) -> (u32, u32) {

    let wratio = f64::from(nwidth) / f64::from(width);

    let hratio = f64::from(nheight) / f64::from(height);

    let ratio = if fill {

        f64::max(wratio, hratio)

    } else {

        f64::min(wratio, hratio)

    };

    let nw = max((f64::from(width) * ratio).round() as u64, 1);

    let nh = max((f64::from(height) * ratio).round() as u64, 1);

    if nw > u64::from(u32::MAX) {

        let ratio = f64::from(u32::MAX) / f64::from(width);

        (u32::MAX, max((f64::from(height) * ratio).round() as u32, 1))

    } else if nh > u64::from(u32::MAX) {

        let ratio = f64::from(u32::MAX) / f64::from(height);

        (max((f64::from(width) * ratio).round() as u32, 1), u32::MAX)

    } else {

        (nw as u32, nh as u32)

    }

}

#[cfg(test)]

mod test {

    quickcheck! {

        fn resize_bounds_correctly_width(old_w: u32, new_w: u32) -> bool {

            if old_w == 0 || new_w == 0 { return true; }

            // In this case, the scaling is limited by scaling of height.

            // We could check that case separately but it does not conform to the same expectation.

            if u64::from(new_w) * 400u64 >= u64::from(old_w) * u64::from(u32::MAX) { return true; }

            let result = super::resize_dimensions(old_w, 400, new_w, u32::MAX, false);

            let exact = (400_f64 * f64::from(new_w) / f64::from(old_w)).round() as u32;

            result.0 == new_w && result.1 == exact.max(1)

        }

    }

    quickcheck! {

        fn resize_bounds_correctly_height(old_h: u32, new_h: u32) -> bool {

            if old_h == 0 || new_h == 0 { return true; }

            // In this case, the scaling is limited by scaling of width.

            // We could check that case separately but it does not conform to the same expectation.

            if 400u64 * u64::from(new_h) >= u64::from(old_h) * u64::from(u32::MAX) { return true; }

            let result = super::resize_dimensions(400, old_h, u32::MAX, new_h, false);

            let exact = (400_f64 * f64::from(new_h) / f64::from(old_h)).round() as u32;

            result.1 == new_h && result.0 == exact.max(1)

        }

    }

    #[test]

    fn resize_handles_fill() {

        let result = super::resize_dimensions(100, 200, 200, 500, true);

        assert!(result.0 == 250);

        assert!(result.1 == 500);

        let result = super::resize_dimensions(200, 100, 500, 200, true);

        assert!(result.0 == 500);

        assert!(result.1 == 250);

    }

    #[test]

    fn resize_never_rounds_to_zero() {

        let result = super::resize_dimensions(1, 150, 128, 128, false);

        assert!(result.0 > 0);

        assert!(result.1 > 0);

    }

    #[test]

    fn resize_handles_overflow() {

        let result = super::resize_dimensions(100, u32::MAX, 200, u32::MAX, true);

        assert!(result.0 == 100);

        assert!(result.1 == u32::MAX);

        let result = super::resize_dimensions(u32::MAX, 100, u32::MAX, 200, true);

        assert!(result.0 == u32::MAX);

        assert!(result.1 == 100);

    }

    #[test]

    fn resize_rounds() {

        // Only truncation will result in (3840, 2229) and (2160, 3719)

        let result = super::resize_dimensions(4264, 2476, 3840, 2160, true);

        assert_eq!(result, (3840, 2230));

        let result = super::resize_dimensions(2476, 4264, 2160, 3840, false);

        assert_eq!(result, (2160, 3720));

    }

    #[test]

    fn resize_handles_zero() {

        let result = super::resize_dimensions(0, 100, 100, 100, false);

        assert_eq!(result, (1, 100));

        let result = super::resize_dimensions(100, 0, 100, 100, false);

        assert_eq!(result, (100, 1));

        let result = super::resize_dimensions(100, 100, 0, 100, false);

        assert_eq!(result, (1, 1));

        let result = super::resize_dimensions(100, 100, 100, 0, false);

        assert_eq!(result, (1, 1));

    }

}