use crate::*;

/// Defines an enum that wraps the same renderable item
/// but discriminates on the variant which wraps it.
///
/// It also has a special `_Unused` variant which wraps
/// the engine type using `PhantomData` to permit the
/// double generic.
macro_rules! content_enum {
    ($Enum:ident: $($Variant:ident),+ $(,)?) => {
        pub enum $Enum<E: Engine, T: Content<E>> {
            _Unused(PhantomData<E>), $($Variant(T)),+
        }
    }
}

/// Defines an enum that transforms its content
/// along either the X axis, the Y axis, or both.
macro_rules! transform_xy {
    ($self:ident : $Enum:ident |$to:ident|$area:expr) => {
        content_enum!($Enum: X, Y, XY);
        impl<E: Engine, T: Content<E>> $Enum<E, T> {
            pub fn x (item: T) -> Self { Self::X(item) }
            pub fn y (item: T) -> Self { Self::Y(item) }
            pub fn xy (item: T) -> Self { Self::XY(item) }
        }
        impl<E: Engine, T: Content<E>> Content<E> for $Enum<E, T> {
            fn content (&self) -> Option<impl Content<E>> {
                Some(match self {
                    Self::X(item)    => item,
                    Self::Y(item)    => item,
                    Self::XY(item)   => item,
                    _ => unreachable!()
                })
            }
            fn area (&$self, $to: <E as Engine>::Area) -> <E as Engine>::Area {
                $area
            }
        }
    }
}

transform_xy!(self: Fill |to|{
    let [x0, y0, wmax, hmax] = to.xywh();
    let [x, y, w, h] = self.content().unwrap().area(to).xywh();
    return match self {
        Self::X(_)  => [x0, y, wmax, h],
        Self::Y(_)  => [x, y0, w, hmax],
        Self::XY(_) => [x0, y0, wmax, hmax],
        _ => unreachable!()
    }.into()
});

/// Defines an enum that transforms its content parametrically
/// along either the X axis, the Y axis, or both
macro_rules! transform_xy_unit {
    (|$self:ident : $Enum:ident, $to:ident|$area:expr) => {
        pub enum $Enum<E: Engine, T: Content<E>> {
            X(E::Unit, T), Y(E::Unit, T), XY(E::Unit, E::Unit, T),
        }
        impl<E: Engine, T: Content<E>> $Enum<E, T> {
            pub fn x (x: E::Unit, item: T) -> Self { Self::X(x, item) }
            pub fn y (y: E::Unit, item: T) -> Self { Self::Y(y, item) }
            pub fn xy (x: E::Unit, y: E::Unit, item: T) -> Self { Self::XY(x, y, item) }
            pub fn dx (&self) -> E::Unit {
                match self {
                    Self::X(x, _)     => *x,
                    Self::Y(_, _)     => E::Unit::zero(),
                    Self::XY(x, _, _) => *x,
                }
            }
            pub fn dy (&self) -> E::Unit {
                match self {
                    Self::X(_, _)     => E::Unit::zero(),
                    Self::Y(y, _)     => *y,
                    Self::XY(_, y, _) => *y,
                }
            }
        }
        impl<E: Engine, T: Content<E>> Content<E> for $Enum<E, T> {
            fn content (&self) -> Option<impl Content<E>> {
                Some(match self {
                    Self::X(_, content)     => content,
                    Self::Y(_, content)     => content,
                    Self::XY(_, _, content) => content,
                })
            }
            fn area (&$self, $to: E::Area) -> E::Area {
                $area.into()
            }
        }
    }
}

transform_xy_unit!(|self: Fixed, to|match self {
    Self::X(fw, _) => [to.x(), to.y(), *fw, to.h()],
    Self::Y(fh, _) => [to.x(), to.y(), to.w(), *fh],
    Self::XY(fw, fh, _) => [to.x(), to.y(), *fw, *fh], // tagn
});

transform_xy_unit!(|self: Shrink, to|
    [to.x(), to.y(), to.w().minus(self.dx()), to.h().minus(self.dy())]);

transform_xy_unit!(|self: Expand, to|
    [to.x(), to.y(), to.w() + self.dx(), to.h() + self.dy()]);

transform_xy_unit!(|self: Min, to|match self {
    Self::X(mw, _)      => [to.x(), to.y(), to.w().max(*mw), to.h()],
    Self::Y(mh, _)      => [to.x(), to.y(), to.w(),          to.h().max(*mh)],
    Self::XY(mw, mh, _) => [to.x(), to.y(), to.w().max(*mw), to.h().max(*mh)]
});

transform_xy_unit!(|self: Max, to|match self {
    Self::X(mw, _)      => [to.x(), to.y(), to.w().min(*mw), to.h()],
    Self::Y(mh, _)      => [to.x(), to.y(), to.w(),          to.h().min(*mh)],
    Self::XY(mw, mh, _) => [to.x(), to.y(), to.w().min(*mw), to.h().min(*mh)],
});

transform_xy_unit!(|self: Push, to|
    [to.x() + self.dx(), to.y() + self.dy(), to.w(), to.h()]);

transform_xy_unit!(|self: Pull, to|
    [to.x().minus(self.dx()), to.y().minus(self.dy()), to.w(), to.h()]);

transform_xy_unit!(|self: Margin, to|{
    let dx = self.dx();
    let dy = self.dy();
    [to.x().minus(dx), to.y().minus(dy), to.w() + dy + dy, to.h() + dy + dy]
});

transform_xy_unit!(|self: Padding, to|{
    let dx = self.dx();
    let dy = self.dy();
    [to.x() + dx, to.y() + dy, to.w().minus(dy + dy), to.h().minus(dy + dy), ]
});

content_enum!(Align: Center, X, Y, NW, N, NE, E, SE, S, SW, W);
impl<E: Engine, T: Content<E>> Align<E, T> {
    pub fn c  (w: T) -> Self { Self::Center(w) }
    pub fn x  (w: T) -> Self { Self::X(w)      }
    pub fn y  (w: T) -> Self { Self::Y(w)      }
    pub fn n  (w: T) -> Self { Self::N(w)      }
    pub fn s  (w: T) -> Self { Self::S(w)      }
    pub fn e  (w: T) -> Self { Self::E(w)      }
    pub fn w  (w: T) -> Self { Self::W(w)      }
    pub fn nw (w: T) -> Self { Self::NW(w)     }
    pub fn sw (w: T) -> Self { Self::SW(w)     }
    pub fn ne (w: T) -> Self { Self::NE(w)     }
    pub fn se (w: T) -> Self { Self::SE(w)     }
}

fn align<E: Engine, T: Content<E>, N: Coordinate, R: Area<N> + From<[N;4]>> (align: &Align<E, T>, outer: R, content: R) -> Option<R> {
    if outer.w() < content.w() || outer.h() < content.h() {
        None
    } else {
        let [ox, oy, ow, oh] = outer.xywh();
        let [ix, iy, iw, ih] = content.xywh();
        Some(match align {
            Align::Center(_) => [ox + (ow - iw) / 2.into(), oy + (oh - ih) / 2.into(), iw, ih,].into(),
            Align::X(_)  => [ox + (ow - iw) / 2.into(), iy, iw, ih,].into(),
            Align::Y(_)  => [ix, oy + (oh - ih) / 2.into(), iw, ih,].into(),
            Align::NW(_) => [ox, oy, iw, ih,].into(),
            Align::N(_)  => [ox + (ow - iw) / 2.into(), oy, iw, ih,].into(),
            Align::NE(_) => [ox + ow - iw, oy, iw, ih,].into(),
            Align::W(_)  => [ox, oy + (oh - ih) / 2.into(), iw, ih,].into(),
            Align::E(_)  => [ox + ow - iw, oy + (oh - ih) / 2.into(), iw, ih,].into(),
            Align::SW(_) => [ox, oy + oh - ih, iw, ih,].into(),
            Align::S(_)  => [ox + (ow - iw) / 2.into(), oy + oh - ih, iw, ih,].into(),
            Align::SE(_) => [ox + ow - iw, oy + oh - ih, iw, ih,].into(),
            _ => unreachable!()
        })
    }
}

impl<E: Engine, T: Content<E>> Content<E> for Align<E, T> {
    fn render (&self, to: &mut E::Output) {
        let outer_area = to.area();
        let content    = self.content();
        let inner_area = content.area(outer_area);
        if let Some(aligned) = align(&self, outer_area.into(), inner_area.into()) {
            to.place(aligned, &content)
        }
    }
}