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use std::iter;
use std::ptr;
use na;
use super::{TriMesh, Polyline};
use math::{Point, Vect};

// De-Casteljau algorithm.
// Evaluates the bezier curve with control points `control_points`.
#[doc(hidden)]
pub fn bezier_curve_at<P>(control_points: &[P], t: <P::Vect as Vect>::Scalar, cache: &mut Vec<P>) -> P
    where P: Point {
    if control_points.len() > cache.len() {
        let diff = control_points.len() - cache.len();
        cache.extend(iter::repeat(na::orig::<P>()).take(diff))
    }

    let cache = &mut cache[..];

    let _1: <P::Vect as Vect>::Scalar = na::cast(1.0);
    let t_1 = _1 - t;

    // XXX: not good if the objects are not POD.
    unsafe {
        ptr::copy_nonoverlapping(control_points.as_ptr(), cache.as_mut_ptr(), control_points.len());
    }

    for i in 1usize .. control_points.len() {
        for j in 0usize .. control_points.len() - i {
            cache[j] = cache[j] * t_1 + *cache[j + 1].as_vec() * t;
        }
    }

    cache[0].clone()
}

// Evaluates the bezier curve with control points `control_points`.
#[doc(hidden)]
pub fn bezier_surface_at<P>(
                         control_points: &[P],
                         nupoints:       usize,
                         nvpoints:       usize,
                         u:              <P::Vect as Vect>::Scalar,
                         v:              <P::Vect as Vect>::Scalar,
                         ucache:         &mut Vec<P>,
                         vcache:         &mut Vec<P>)
                         -> P
    where P: Point {
    if vcache.len() < nvpoints {
        let diff = nvpoints - vcache.len();
        vcache.extend(iter::repeat(na::orig::<P>()).take(diff));
    }

    // FIXME: start with u or v, depending on which dimension has more control points.
    let vcache = &mut vcache[..];

    for i in 0 .. nvpoints {
        let start = i * nupoints;
        let end   = start + nupoints;

        vcache[i] = bezier_curve_at(&control_points[start .. end], u, ucache);
    }

    bezier_curve_at(&vcache[0 .. nvpoints], v, ucache)
}

/// Given a set of control points, generates a (non-rational) Bezier curve.
pub fn bezier_curve<P>(control_points: &[P], nsubdivs: usize) -> Polyline<P>
    where P: Point {
    let mut coords = Vec::with_capacity(nsubdivs);
    let mut cache  = Vec::new();
    let tstep      = na::cast(1.0 / (nsubdivs as f64));
    let mut t      = na::zero::<<P::Vect as Vect>::Scalar>();

    while t <= na::one() {
        coords.push(bezier_curve_at(control_points, t, &mut cache));
        t = t + tstep;
    }

    // FIXME: normals

    Polyline::new(coords, None)
}

/// Given a set of control points, generates a (non-rational) Bezier surface.
pub fn bezier_surface<P>(
                      control_points: &[P],
                      nupoints:       usize,
                      nvpoints:       usize,
                      usubdivs:       usize,
                      vsubdivs:       usize)
                      -> TriMesh<P>
    where P: Point {
    assert!(nupoints * nvpoints == control_points.len());

    let mut surface = super::unit_quad::<P>(usubdivs, vsubdivs);

    {
        let uvs    = &surface.uvs.as_ref().unwrap()[..];
        let coords = &mut surface.coords[..];

        let mut ucache = Vec::new();
        let mut vcache = Vec::new();

        for j in 0 .. vsubdivs + 1 {
            for i in 0 .. usubdivs + 1 {
                let id = i + j * (usubdivs + 1);
                coords[id] = bezier_surface_at(control_points,
                                               nupoints,
                                               nvpoints,
                                               uvs[id].x,
                                               uvs[id].y,
                                               &mut ucache,
                                               &mut vcache)
            }
        }

        // XXX: compute the normals manually.
        surface.normals = None;
    }

    surface
}