use crate::*;

/// Show an item only when a condition is true.
pub struct When<A>(pub bool, pub A);
impl<A> When<A> {
    /// Create a binary condition.
    pub const 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> {
    /// Create a ternary condition.
    pub const fn new (c: bool, a: A, b: B) -> Self {
        Self(c, a, b) 
    }
}

#[cfg(feature = "dsl")]
try_from_expr!(<'source, 'state, E>: When<RenderBox<'state, E>>: |state, iter| {
    if let Some(Token { value: Value::Key("when"), .. }) = iter.peek() {
        let _ = iter.next().unwrap();
        let content = iter.next().expect("no content specified").value;
        return Some(Self(
            state.get(&mut iter)
                .expect("no condition provided"),
            state.get_content(&content)
                .unwrap_or_else(||panic!("no content corresponding to for {:?}", &content))
        ))
    }
});

#[cfg(feature = "dsl")]
try_from_expr!(<'source, 'state, E>: Either<RenderBox<'state, E>, RenderBox<'state, E>>: |state, iter| {
    if let Some(Token { value: Value::Key("either"), .. }) = iter.peek() {
        let _ = iter.next().unwrap();
        let content   = iter.next().expect("no content specified").value;
        let alternate = iter.next().expect("no alternate specified").value;
        return Some(Self(
            state.get(&mut iter)
                .expect("no condition provided"),
            state.get_content(&content)
                .unwrap_or_else(||panic!("no content 1 corresponding to {:?}", &content)),
            state.get_content(&alternate)
                .unwrap_or_else(||panic!("no content 2 corresponding to {:?}", &alternate)),
        ))
    }
});

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) }
    }
}