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use num_traits::{Float, FromPrimitive};
use types::Point;

/// Returns a new Point using the distance to the existing Point and a bearing for the direction

pub trait HaversineDestination<T: Float> {
    /// Returns a new Point using distance to the existing Point and a bearing for the direction
    ///
    /// ```
    /// use geo::Point;
    /// use geo::algorithm::haversine_destination::HaversineDestination;
    ///
    /// let p_1 = Point::<f64>::new(9.177789688110352, 48.776781529534965);
    /// let p_2 = p_1.haversine_destination(45., 10000.);
    /// assert_eq!(p_2, Point::<f64>::new(9.274410083250379, 48.84033282787534))
    /// ```
    fn haversine_destination(&self, bearing: T, distance: T) -> Point<T>;
}

impl<T> HaversineDestination<T> for Point<T>
    where T: Float + FromPrimitive
{
    fn haversine_destination(&self, bearing: T, distance: T) -> Point<T> {
        let center_lng = self.x().to_radians();
        let center_lat = self.y().to_radians();
        let bearing_rad = bearing.to_radians();

        // WGS84 equatorial radius is 6378137.0
        let rad = distance / T::from(6371000.0).unwrap();

        let lat = {
                center_lat.sin() * rad.cos() + center_lat.cos() * rad.sin() * bearing_rad.cos()
            }
            .asin();
        let lng = {
                bearing_rad.sin() * rad.sin() * center_lat.cos()
            }
            .atan2(rad.cos() - center_lat.sin() * lat.sin()) + center_lng;

        Point::new(lng.to_degrees(), lat.to_degrees())
    }
}

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

    #[test]
    fn returns_a_new_point() {
        let p_1 = Point::<f64>::new(9.177789688110352, 48.776781529534965);
        let p_2 = p_1.haversine_destination(45., 10000.);
        assert_eq!(p_2, Point::<f64>::new(9.274410083250379, 48.84033282787534));
        let distance = p_1.haversine_distance(&p_2);
        assert_relative_eq!(distance, 10000., epsilon = 1.0e-6)
    }
}