use crate::*;
use std::{sync::Arc, marker::PhantomData};
/// Define an EDN-backed view.
///
/// This consists of:
/// * render callback (implementation of [Content])
/// * value providers (implementations of [Context])
#[macro_export] macro_rules! view {
    ($Output:ty: |$self:ident: $App:ty| $content:expr; {
        $( $type:ty { $($sym:literal => $value:expr),* } );*
    }) => {
        impl Content<$Output> for $App {
            fn content(&$self) -> impl Render<$Output> { $content }
        }
        $(
            impl<'a> Context<'a, $type> for $App {
                fn get (&'a $self, edn: &'a impl Atom) -> Option<$type> {
                    Some(match edn.to_ref() { $(Atom::Sym($sym) => $value,)* _ => return None })
                }
            }
        )*
    }
}
/// Implements `Context` for content components and expressions
#[macro_export] macro_rules! provide_content {
    (|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
        impl<'a, E: Output> Context<'a, Box<dyn Render<E> + 'a>> for $State {
            fn get (&'a $self, edn: &'a impl Atom) -> Option<Box<dyn Render<E> + 'a>> {
                Some(match edn.to_ref() {
                    $(Atom::Sym($pat) => $expr),*,
                    _ => return None
                })
            }
        }
    };
    ($Output:ty: |$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
        impl<'a> Context<'a, Box<dyn Render<$Output> + 'a>> for $State {
            fn get (&'a $self, edn: &'a impl Atom) -> Option<Box<dyn Render<$Output> + 'a>> {
                Some(match edn.to_ref() {
                    $(Atom::Sym($pat) => $expr),*,
                    _ => return None
                })
            }
        }
    }
}
/// Renders from EDN source and context.
#[derive(Default)] pub enum EdnView<'a, E: Output, T: ViewContext<'a, E> + std::fmt::Debug> {
    #[default] Inert,
    Ok(T, Atom<Arc<str>>),
    //render: Box<dyn Fn(&'a T)->Box<dyn Render<E> + Send + Sync + 'a> + Send + Sync + 'a>
    Err(String),
    _Unused(PhantomData<&'a E>),
}
impl<'a, E: Output, T: ViewContext<'a, E> + std::fmt::Debug> std::fmt::Debug for EdnView<'a, E, T> {
    fn fmt (&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
        match self {
            Self::Inert | Self::_Unused(_) =>
                write!(f, "EdnView::Inert"),
            Self::Ok(state, view) =>
                write!(f, "EdnView::Ok(state={state:?} view={view:?}"),
            Self::Err(error) =>
                write!(f, "EdnView::Err({error})"),
            _ => unreachable!()
        }
    }
}
impl<'a, E: Output, T> ViewContext<'a, E> for T where T:
    Context<'a, bool> +
    Context<'a, usize> +
    Context<'a, E::Unit> +
    Context<'a, Box<dyn Render<E> + 'a>>
{}
impl<'a, E: Output, T: ViewContext<'a, E> + std::fmt::Debug> EdnView<'a, E, T> {
    pub fn from_source (state: T, source: &'a str) -> Self {
        match Atom::read_one(&source) {
            Ok((layout, _)) => Self::Ok(state, layout),
            Err(error) => Self::Err(format!("{error} in {source}"))
        }
    }
    pub fn from_items (state: T, items: Vec<impl Atom>) -> Self {
        Self::Ok(state, Atom::Exp(items).to_arc())
    }
}
impl<E: Output, T: for<'a>ViewContext<'a, E> + Send + Sync + std::fmt::Debug> Content<E> for EdnView<'_, E, T> {
    fn content (&self) -> impl Render<E> {
        match self {
            Self::Ok(state, layout) => state.get_content(layout),
            Self::Err(_error) => {
                panic!("{self:?}");
                //TODO:&format!("EdnView error: {error:?}")) // FIXME: String is not Render
            },
            _ => todo!()
        }
    }
}

macro_rules! edn_try_delegate {
    ($s:ident, $e:expr, $T:ty) => {
        if let [head, tail @ ..] = $e.as_slice() {
            if let Some(content) = <$T>::try_from_edn($s, head, tail) {
                return Some(content.boxed())
            }
        }
    }
}

/// Provides values to the template
pub trait ViewContext<'a, E: Output>:
    Context<'a, bool> +
    Context<'a, usize> +
    Context<'a, E::Unit> +
    Context<'a, Box<dyn Render<E> + 'a>>
{
    fn get_bool (&'a self, item: &'a impl Atom) -> Option<bool> {
        Some(match &item {
            Sym(s) => match s.as_ref() {
                ":false" | ":f" => false,
                ":true"  | ":t" => true,
                _ => return Context::get(self, item)
            },
            Num(0) => false,
            Num(_) => true,
            _ => return Context::get(self, item)
        })
    }
    fn get_usize (&'a self, item: &'a impl Atom) -> Option<usize> {
        Some(match &item { Num(n) => *n, _ => return Context::get(self, item) })
    }
    fn get_unit (&'a self, item: &'a impl Atom) -> Option<E::Unit> {
        Some(match &item { Num(n) => (*n as u16).into(), _ => return Context::get(self, item) })
    }
    fn get_content (&'a self, item: &'a impl Atom) -> Option<Box<dyn Render<E> + 'a>> where E: 'a {
        Some(match item {
            Nil => Box::new(()),
            Exp(ref e) => {
                edn_try_delegate!(self, e, When::<_, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Either::<_, RenderBox<'a, E>, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Align::<_, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Bsp::<_, RenderBox<'a, E>, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Fill::<_, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Fixed::<_, _, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Min::<_, _, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Max::<_, _, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Shrink::<_, _, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Expand::<_, _, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Push::<_, _, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Pull::<_, _, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Margin::<_, _, RenderBox<'a, E>>);
                edn_try_delegate!(self, e, Padding::<_, _, RenderBox<'a, E>>);
                Context::get_or_fail(self, &item)
            },
            _ => Context::get_or_fail(self, &item)
        })
        //panic!("no content")
    }
}
// A function that returns a `RenderBox.
pub type EdnCallback<'a, O, State> =
    dyn Fn(&'a State)-> RenderBox<'a, O> + Send + Sync + 'a;
// A box containing a function that returns a `RenderBox.
pub type EdnRenderCallback<'a, O, State> =
    Box<EdnCallback<'a, O, State>>;