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use crate::{Coordinate, GeoNum, LineString, MultiLineString, MultiPoint, MultiPolygon, Polygon};

/// Returns the convex hull of a Polygon. The hull is always oriented counter-clockwise.
///
/// This implementation uses the QuickHull algorithm,
/// based on [Barber, C. Bradford; Dobkin, David P.; Huhdanpaa, Hannu (1 December 1996)](https://dx.doi.org/10.1145%2F235815.235821)
/// Original paper here: http://www.cs.princeton.edu/~dpd/Papers/BarberDobkinHuhdanpaa.pdf
///
/// # Examples
///
/// ```
/// use geo::{line_string, polygon};
/// use geo::algorithm::convex_hull::ConvexHull;
///
/// // an L shape
/// let poly = polygon![
///     (x: 0.0, y: 0.0),
///     (x: 4.0, y: 0.0),
///     (x: 4.0, y: 1.0),
///     (x: 1.0, y: 1.0),
///     (x: 1.0, y: 4.0),
///     (x: 0.0, y: 4.0),
///     (x: 0.0, y: 0.0),
/// ];
///
/// // The correct convex hull coordinates
/// let correct_hull = line_string![
///     (x: 4.0, y: 0.0),
///     (x: 4.0, y: 1.0),
///     (x: 1.0, y: 4.0),
///     (x: 0.0, y: 4.0),
///     (x: 0.0, y: 0.0),
///     (x: 4.0, y: 0.0),
/// ];
///
/// let res = poly.convex_hull();
/// assert_eq!(res.exterior(), &correct_hull);
/// ```
pub trait ConvexHull {
    type Scalar: GeoNum;
    fn convex_hull(&self) -> Polygon<Self::Scalar>;
}

impl<T> ConvexHull for Polygon<T>
where
    T: GeoNum,
{
    type Scalar = T;
    fn convex_hull(&self) -> Polygon<T> {
        Polygon::new(quick_hull(&mut self.exterior().0.clone()), vec![])
    }
}

impl<T> ConvexHull for MultiPolygon<T>
where
    T: GeoNum,
{
    type Scalar = T;
    fn convex_hull(&self) -> Polygon<T> {
        let mut aggregated: Vec<_> = self
            .0
            .iter()
            .flat_map(|elem| elem.exterior().0.iter().copied())
            .collect();
        Polygon::new(quick_hull(&mut aggregated), vec![])
    }
}

impl<T> ConvexHull for LineString<T>
where
    T: GeoNum,
{
    type Scalar = T;
    fn convex_hull(&self) -> Polygon<T> {
        Polygon::new(quick_hull(&mut self.0.clone()), vec![])
    }
}

impl<T> ConvexHull for MultiLineString<T>
where
    T: GeoNum,
{
    type Scalar = T;
    fn convex_hull(&self) -> Polygon<T> {
        let mut aggregated: Vec<_> = self.iter().flat_map(|elem| elem.clone().0).collect();
        Polygon::new(quick_hull(&mut aggregated), vec![])
    }
}

impl<T> ConvexHull for MultiPoint<T>
where
    T: GeoNum,
{
    type Scalar = T;
    fn convex_hull(&self) -> Polygon<T> {
        let mut aggregated: Vec<_> = self.iter().map(|p| p.0).collect();
        Polygon::new(quick_hull(&mut aggregated), vec![])
    }
}

pub mod qhull;
pub use qhull::quick_hull;

pub mod graham;
pub use graham::graham_hull;

// Helper function that outputs the convex hull in the
// trivial case: input with at most 3 points. It ensures the
// output is ccw, and does not repeat points unless
// required.
fn trivial_hull<T>(points: &mut [Coordinate<T>], include_on_hull: bool) -> LineString<T>
where
    T: GeoNum,
{
    assert!(points.len() < 4);

    // Remove repeated points unless collinear points
    // are to be included.
    let mut ls: Vec<Coordinate<T>> = points.iter().copied().collect();
    if !include_on_hull {
        ls.dedup();
    }

    // A linestring with a single point is invalid.
    if ls.len() == 1 {
        ls.push(ls[0]);
    }

    let mut ls = LineString(ls);
    ls.close();

    // Maintain the CCW invariance
    use super::winding_order::Winding;
    ls.make_ccw_winding();
    ls
}

// Utility function: swap idx to head(0th position), remove
// head (modifies the slice), and return head as a reference
fn swap_remove_to_first<'a, T>(slice: &mut &'a mut [T], idx: usize) -> &'a mut T {
    let tmp = std::mem::replace(slice, &mut []);
    tmp.swap(0, idx);
    let (h, t) = tmp.split_first_mut().unwrap();
    *slice = t;
    h
}

#[cfg(test)]
mod test;