use crate::*;
use Direction::*;

/// A split or layer.
pub struct Bsp<A, B>(
    pub(crate) Direction,
    pub(crate) A,
    pub(crate) B,
);
impl<A, B> Bsp<A, B> {
    #[inline] pub const fn n (a: A, b: B) -> Self { Self(North, a, b) }
    #[inline] pub const fn s (a: A, b: B) -> Self { Self(South, a, b) }
    #[inline] pub const fn e (a: A, b: B) -> Self { Self(East,  a, b) }
    #[inline] pub const fn w (a: A, b: B) -> Self { Self(West,  a, b) }
    #[inline] pub const fn a (a: A, b: B) -> Self { Self(Above, a, b) }
    #[inline] pub const fn b (a: A, b: B) -> Self { Self(Below, a, b) }
}
impl<E: Output, A: Render<E>, B: Render<E>> Render<E> for Bsp<A, B> {
    fn layout (&self, outer: E::Area) -> E::Area { let [_, _, c] = self.areas(outer); c }
    fn render (&self, to: &mut E) {
        let [area_a, area_b, _] = self.areas(to.area());
        let (a, b) = self.contents();
        match self.0 {
            Below => { to.place(area_a, a); to.place(area_b, b); },
            _     => { to.place(area_b, b); to.place(area_a, a); }
        }
    }
}
impl<E: Output, A: Render<E>, B: Render<E>> BspAreas<E, A, B> for Bsp<A, B> {
    fn direction (&self) -> Direction { self.0 }
    fn contents (&self) -> (&A, &B) { (&self.1, &self.2) }
}
pub trait BspAreas<E: Output, A: Render<E>, B: Render<E>> {
    fn direction (&self) -> Direction;
    fn contents (&self) -> (&A, &B);
    fn areas (&self, outer: E::Area) -> [E::Area;3] {
        let direction = self.direction();
        let [x, y, w, h] = outer.xywh();
        let (a, b) = self.contents();
        let [aw, ah] = a.layout(outer).wh();
        let [bw, bh] = b.layout(match direction {
            Above | Below => outer,
            South => [x, y + ah, w, h.minus(ah)].into(),
            North => [x, y, w, h.minus(ah)].into(),
            East  => [x + aw, y, w.minus(aw), h].into(),
            West  => [x, y, w.minus(aw), h].into(),
        }).wh();
        match direction {
            Above | Below => {
                let [x, y, w, h] = outer.center_xy([aw.max(bw), ah.max(bh)]);
                let a = [(x + w/2.into()).minus(aw/2.into()), (y + h/2.into()).minus(ah/2.into()), aw, ah];
                let b = [(x + w/2.into()).minus(bw/2.into()), (y + h/2.into()).minus(bh/2.into()), bw, bh];
                [a.into(), b.into(), [x, y, w, h].into()]
            },
            South => {
                let [x, y, w, h] = outer.center_xy([aw.max(bw), ah + bh]);
                let a = [(x + w/2.into()).minus(aw/2.into()), y, aw, ah];
                let b = [(x + w/2.into()).minus(bw/2.into()), y + ah, bw, bh];
               [a.into(), b.into(), [x, y, w, h].into()]
            },
            North => {
                let [x, y, w, h] = outer.center_xy([aw.max(bw), ah + bh]);
                let a = [(x + (w/2.into())).minus(aw/2.into()), y + bh, aw, ah];
                let b = [(x + (w/2.into())).minus(bw/2.into()), y, bw, bh];
                [a.into(), b.into(), [x, y, w, h].into()]
            },
            East => {
                let [x, y, w, h] = outer.center_xy([aw + bw, ah.max(bh)]);
                let a = [x,      (y + h/2.into()).minus(ah/2.into()), aw, ah];
                let b = [x + aw, (y + h/2.into()).minus(bh/2.into()), bw, bh];
                [a.into(), b.into(), [x, y, w, h].into()]
            },
            West => {
                let [x, y, w, h] = outer.center_xy([aw + bw, ah.max(bh)]);
                let a = [x + bw, (y + h/2.into()).minus(ah/2.into()), aw, ah];
                let b = [x,      (y + h/2.into()).minus(bh/2.into()), bw, bh];
                [a.into(), b.into(), [x, y, w, h].into()]
            },
        }
    }
}

/// Stack things on top of each other,
#[macro_export] macro_rules! lay (($($expr:expr),* $(,)?) =>
    {{ let bsp = (); $(let bsp = Bsp::b(bsp, $expr);)*; bsp }});

/// Stack southward.
#[macro_export] macro_rules! col (($($expr:expr),* $(,)?) =>
    {{ let bsp = (); $(let bsp = Bsp::s(bsp, $expr);)*; bsp }});

/// Stack northward.
#[macro_export] macro_rules! col_up (($($expr:expr),* $(,)?) =>
    {{ let bsp = (); $(let bsp = Bsp::n(bsp, $expr);)*; bsp }});

/// Stack eastward.
#[macro_export] macro_rules! row (($($expr:expr),* $(,)?) =>
    {{ let bsp = (); $(let bsp = Bsp::e(bsp, $expr);)*; bsp }});