tek/output/src/when.rs

use crate::*;
/// Show an item only when a condition is true.
pub struct When<E, A>(pub PhantomData<E>, pub bool, pub A);
impl<E, A> When<E, A> {
    pub fn new (c: bool, a: A) -> Self {
        Self(Default::default(), c, a)
    }
}
impl<'a, E: Output + 'a, T: EdnViewData<'a, E>> TryFromEdn<'a, T> for When<E, RenderBox<'a, E>> {
    fn try_from_edn (
        state: &'a T, head: &EdnItem<&str>, tail: &'a [EdnItem<&str>]
    ) -> Option<Self> {
        use EdnItem::*;
        if let (Key("when"), [condition, content]) = (head, tail) {
            Some(Self(
                Default::default(),
                state.get_bool(condition).expect("when: no condition"),
                state.get_content(content).expect("when: no content")
            ))
        } else {
            None
        }
    }
}
impl<E: Output, A: Render<E>> Content<E> for When<E, 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) }
    }
}