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use crate::Coord;

pub trait Lerp {
    /// calculate the point at `percent` between `self` and `end`
    ///
    /// e.g. 10.lerp(20, 0.5) returns 15 and
    ///      10.lerp(20, 0.1) returns 11
    ///
    /// internally the values are cast as f32 and rounded before being returned
    fn lerp(self, end: Self, percent: f32) -> Self;
}

/// This method has to be separate and named differently because
/// f32::lerp already exists but is unstable
///
/// see [f32::lerp]
#[inline]
pub fn flerp(start: f32, end: f32, percent: f32) -> f32 {
    start + ((end - start) * percent)
}

macro_rules! impl_lerp {
    ($num_type: ty) => {
        impl Lerp for $num_type {
            #[inline]
            fn lerp(self, end: $num_type, percent: f32) -> $num_type {
                let start = self as f32;
                let end = end as f32;
                flerp(start, end, percent).round() as $num_type
            }
        }
    };
}

impl_lerp!(u8);
impl_lerp!(i8);
impl_lerp!(u16);
impl_lerp!(i16);
impl_lerp!(u32);
impl_lerp!(i32);
impl_lerp!(u64);
impl_lerp!(i64);
impl_lerp!(u128);
impl_lerp!(i128);
impl_lerp!(usize);
impl_lerp!(isize);

impl Lerp for Coord {
    #[inline]
    fn lerp(self, end: Coord, percent: f32) -> Coord {
        Coord {
            x: self.x.lerp(end.x, percent),
            y: self.y.lerp(end.y, percent),
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn isize_simple() {
        assert_eq!(0_isize.lerp(10, 0.), 0);
        assert_eq!(0_isize.lerp(10, 0.5), 5);
        assert_eq!(0_isize.lerp(10, 1.), 10);
        assert_eq!(0_isize.lerp(10, 0.2), 2);

        assert_eq!(5_isize.lerp(10, 0.), 5);
        assert_eq!(5_isize.lerp(10, 1.), 10);

        assert_eq!(785_isize.lerp(787, 0.), 785);
        assert_eq!(785_isize.lerp(787, 0.5), 786);
        assert_eq!(785_isize.lerp(787, 1.), 787);

        assert_eq!(21_isize.lerp(21, 0.), 21);
        assert_eq!(21_isize.lerp(21, 0.5), 21);
        assert_eq!(21_isize.lerp(21, 1.), 21);

        assert_eq!(10_isize.lerp(1, 1.), 1);
        assert_eq!(10_isize.lerp(1, 0.5), 6);
        assert_eq!(10_isize.lerp(1, 0.), 10);

        assert_eq!((-5_isize).lerp(5, 1.), 5);
        assert_eq!((-5_isize).lerp(5, 0.5), 0);
        assert_eq!((-5_isize).lerp(5, 0.), -5);

        assert_eq!(5_isize.lerp(-5, 1.), -5);
        assert_eq!(5_isize.lerp(-5, 0.5), 0);
        assert_eq!(5_isize.lerp(-5, 0.), 5);
    }

    #[test]
    fn point_simple() {
        let start1 = Coord { x: 0, y: 0 };
        let end1 = Coord { x: 10, y: 10 };

        let start2 = Coord { x: -1, y: -1 };
        let end2 = Coord { x: 1, y: 1 };

        let start3 = Coord { x: 1, y: -1 };
        let end3 = Coord { x: -1, y: 1 };

        assert_eq!(start1.lerp(end1, 0.), Coord { x: 0, y: 0 });
        assert_eq!(start1.lerp(end1, 0.5), Coord { x: 5, y: 5 });
        assert_eq!(start1.lerp(end1, 1.), Coord { x: 10, y: 10 });

        assert_eq!(end1.lerp(start1, 0.), Coord { x: 10, y: 10 });
        assert_eq!(end1.lerp(start1, 0.5), Coord { x: 5, y: 5 });
        assert_eq!(end1.lerp(start1, 1.), Coord { x: 0, y: 0 });

        assert_eq!(start2.lerp(end2, 0.), Coord { x: -1, y: -1 });
        assert_eq!(start2.lerp(end2, 0.5), Coord { x: 0, y: 0 });
        assert_eq!(start2.lerp(end2, 1.), Coord { x: 1, y: 1 });

        assert_eq!(end2.lerp(start2, 0.), Coord { x: 1, y: 1 });
        assert_eq!(end2.lerp(start2, 0.5), Coord { x: 0, y: 0 });
        assert_eq!(end2.lerp(start2, 1.), Coord { x: -1, y: -1 });

        assert_eq!(start3.lerp(end3, 0.), Coord { x: 1, y: -1 });
        assert_eq!(start3.lerp(end3, 0.5), Coord { x: 0, y: 0 });
        assert_eq!(start3.lerp(end3, 1.), Coord { x: -1, y: 1 });

        assert_eq!(end3.lerp(start3, 0.), Coord { x: -1, y: 1 });
        assert_eq!(end3.lerp(start3, 0.5), Coord { x: 0, y: 0 });
        assert_eq!(end3.lerp(start3, 1.), Coord { x: 1, y: -1 });

        assert_eq!(start1.lerp(end1, 2.), Coord { x: 20, y: 20 });
        assert_eq!(start1.lerp(end1, -1.), Coord { x: -10, y: -10 });
    }
}