use crate::*;
/// Show an item only when a condition is true.
pub struct When<A>(pub bool, pub A);
impl<A> When<A> { pub fn new (c: bool, a: A) -> Self { Self(c, a) } }
/// Show one item if a condition is true and another if the condition is false
pub struct Either<A, B>(pub bool, pub A, pub B);
impl<A, B> Either<A, B> { pub fn new (c: bool, a: A, b: B) -> Self { Self(c, a, b) } }
try_from_expr!(<'a, E>: When<RenderBox<'a, E>>: |state, iter| {
    if let Some((Token { value: Value::Key("when"), .. }, _)) = iter.next() {
        let iter = iter.clone();
        let condition = iter.next();
        if let Some((ref condition, _)) = condition {
            let condition = state.get_bool(&condition.value).expect("no condition");
            if let Some((ref content, _)) = iter.next() {
                let content = state.get_content(&content.value).expect("no atom");
                return Some(Self(condition, content))
            }
        }
    }
});
try_from_expr!(<'a, E>: Either<RenderBox<'a, E>, RenderBox<'a, E>>: |state, iter| {
    if let Some((Token { value: Value::Key("either"), .. }, _)) = iter.next() {
        let iter = iter.clone();
        let condition = iter.next();
        if let Some((ref condition, _)) = condition {
            let condition = state.get_bool(&condition.value).expect("no condition");
            if let Some((ref content1, _)) = iter.next() {
                let content1 = state.get_content(&content1.value).expect("no content1");
                if let Some((ref content2, _)) = iter.next() {
                    let content2 = state.get_content(&content2.value).expect("no content2");
                    return Some(Self(condition, content1, content2))
                }
            }
        }
    }
});
impl<E: Output, A: Render<E>> Content<E> for When<A> {
    fn layout (&self, to: E::Area) -> E::Area {
        let Self(cond, item) = self;
        let mut area = E::Area::zero();
        if *cond {
            let item_area = item.layout(to);
            area[0] = item_area.x();
            area[1] = item_area.y();
            area[2] = item_area.w();
            area[3] = item_area.h();
        }
        area.into()
    }
    fn render (&self, to: &mut E) {
        let Self(cond, item) = self;
        if *cond { item.render(to) }
    }
}
impl<E: Output, A: Render<E>, B: Render<E>> Content<E> for Either<A, B> {
    fn layout (&self, to: E::Area) -> E::Area {
        let Self(cond, a, b) = self;
        if *cond { a.layout(to) } else { b.layout(to) }
    }
    fn render (&self, to: &mut E) {
        let Self(cond, a, b) = self;
        if *cond { a.render(to) } else { b.render(to) }
    }
}