# -*- mode: snippet -*-
# name: convex hull
# contributor: Nakamura Kenko
# key: convexhull
# --

pub fn extract_convex_hull(points: &[Point], contain_on_segment: bool) -> Vec<usize> {
    let n = points.len();
    if n <= 1 {
        return vec![0];
    }

    let mut ps: Vec<usize> = (0..n).collect();
    ps.sort_by(|&a, &b| {
        if (points[a].x - points[b].x).abs() < std::f64::EPSILON {
            points[a].y.partial_cmp(&points[b].y).unwrap()
        } else {
            points[a].x.partial_cmp(&points[b].x).unwrap()
        }
    });

    let mut qs: Vec<usize> = Vec::new();
    for &i in &ps {
        while qs.len() > 1 {
            let k = qs.len();
            let det = (points[qs[k - 1]] - points[qs[k - 2]]).det(&(points[i] - points[qs[k - 1]]));
            if det < 0.0 || (det <= 0.0 && !contain_on_segment) {
                qs.pop();
            } else {
                break;
            }
        }
        qs.push(i);
    }

    let t = qs.len();
    for i in (0..(n - 1)).rev() {
        let i = ps[i];
        while qs.len() > t {
            let k = qs.len();
            let det = (points[qs[k - 1]] - points[qs[k - 2]]).det(&(points[i] - points[qs[k - 1]]));
            if det < 0.0 || (det <= 0.0 && !contain_on_segment) {
                qs.pop();
            } else {
                break;
            }
        }
        qs.push(i);
    }

    qs.pop();
    qs
}

#[derive(Debug, Copy, Clone)]
pub struct Point {
    x: f64,
    y: f64,
}

impl std::ops::Sub for Point {
    type Output = Point;
    fn sub(self, other: Point) -> Point {
        Point {
            x: self.x - other.x,
            y: self.y - other.y,
        }
    }
}

impl Point {
    pub fn det(&self, other: &Point) -> f64 {
        self.x * other.y - self.y * other.x
    }
}

