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use crate::math::{Point, Vector};
use crate::procedural::path::{CurveSampler, PathSample};
use na::RealField;

/// A path with its sample points given by a polyline.
///
/// This will return sequencially each vertex of the polyline.
pub struct PolylinePath<'a, N: 'a + RealField> {
    curr_len: N,
    curr_dir: Vector<N>,
    curr_pt_id: usize,
    curr_pt: Point<N>,
    polyline: &'a Vec<Point<N>>,
}

impl<'a, N: RealField> PolylinePath<'a, N> {
    /// Creates a new polyline-based path.
    pub fn new(polyline: &'a Vec<Point<N>>) -> PolylinePath<'a, N> {
        assert!(
            polyline.len() > 1,
            "The polyline must have at least two points."
        );

        let mut dir: Vector<N> = polyline[1] - polyline[0];
        let len: N = dir.normalize_mut();

        PolylinePath {
            curr_len: len,
            curr_dir: dir,
            curr_pt_id: 0,
            curr_pt: polyline[0].clone(),
            polyline: polyline,
        }
    }
}

impl<'a, N: RealField> CurveSampler<N> for PolylinePath<'a, N> {
    fn next(&mut self) -> PathSample<N> {
        let poly_coords = self.polyline;

        let result = if self.curr_pt_id == 0 {
            PathSample::StartPoint(self.curr_pt.clone(), self.curr_dir.clone())
        } else if self.curr_pt_id < poly_coords.len() - 1 {
            PathSample::InnerPoint(self.curr_pt.clone(), self.curr_dir.clone())
        } else if self.curr_pt_id == poly_coords.len() - 1 {
            PathSample::EndPoint(self.curr_pt.clone(), self.curr_dir.clone())
        } else {
            PathSample::EndOfSample
        };

        self.curr_pt_id = self.curr_pt_id + 1;

        if self.curr_pt_id < poly_coords.len() {
            self.curr_pt = poly_coords[self.curr_pt_id].clone();

            if self.curr_pt_id < poly_coords.len() - 1 {
                let mut curr_diff = poly_coords[self.curr_pt_id + 1] - poly_coords[self.curr_pt_id];
                self.curr_len = curr_diff.normalize_mut();
                self.curr_dir = curr_diff;
            }
        }

        result
    }
}