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use crate::{Node, Bind, Context, Event, IdPath, Id, IdentifyExt};

/// The primary view trait. Represents a lightweight UI component.
pub trait View: Bind {
    type Body: View = NeverView;

    fn body(&self) -> Self::Body {
        panic!("View does not have a body!")
    }

    // TODO: Return an error type from fire to avoid panicking on wrong paths?

    fn fire(&self, event: &Event, id_path: &IdPath) {
        self.body().fire(event, id_path);
    }

    fn render(&self, context: &Context) -> Node {
        self.bind(context);
        self.body().render(context)
    }
}

macro_rules! impl_tuple_view {
    ($($tvs:ident),*) => {
        impl<$($tvs),*> View for ($($tvs,)*) where $($tvs: View),* {
            fn fire(&self, event: &Event, id_path: &IdPath) {
                if let Some(head) = id_path.head() {
                    match head {
                        $(${ignore($tvs)} Id::Index(${index()}) => self.${index()}.fire(event, &id_path.tail()),)*
                        i => panic!("Cannot fire event for child id {} on a {}-tuple", i, ${count($tvs, 0)})
                    }
                }
            }

            fn render(&self, context: &Context) -> Node {
                Node::Group {
                    children: vec![
                        $(${ignore($tvs)} self.${index()}.render(&context.child(${index()})).identify(${index()}),)*
                    ]
                }
            }
        }
    };
}

/// A view type that can never be constructed.
pub enum NeverView {}

impl Bind for NeverView {}
impl View for NeverView {}

// Note: We explicitly implement the 0 (unit) and 1 tuples to avoid e.g. the
// overhead of using a Group requiring a Vec.

impl View for () {
    fn fire(&self, _event: &Event, _id_path: &IdPath) {}

    fn render(&self, _context: &Context) -> Node {
        Node::Empty {}
    }
}

impl<T> View for (T,) where T: View {
    type Body = T::Body;

    fn body(&self) -> Self::Body {
        self.0.body()
    }

    fn fire(&self, event: &Event, id_path: &IdPath) {
        if let Some(head) = id_path.head() {
            match head {
                Id::Index(0) => self.0.fire(event, &id_path.tail()),
                i => panic!("Cannot fire event for child id {} on 1-tuple", i)
            }
        }
    }

    fn render(&self, context: &Context) -> Node {
        Node::Child { wrapped: Box::new(self.0.render(&context.child(0)).identify(0)) }
    }
}

// TODO: Generate with variadic generics once available

impl_tuple_view!(T1, T2);
impl_tuple_view!(T1, T2, T3);
impl_tuple_view!(T1, T2, T3, T4);
impl_tuple_view!(T1, T2, T3, T4, T5);
impl_tuple_view!(T1, T2, T3, T4, T5, T6);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22, T23);
impl_tuple_view!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22, T23, T24);