use crate::*;
/// Map EDN tokens to parameters of a given type for a given context
pub trait Context<U>: Sized {
    fn get (&self, _atom: &impl Atom) -> Option<U> {
        None
    }
    fn get_or_fail (&self, atom: &impl Atom) -> U {
        self.get(atom).expect("no value")
    }
}
impl<T: Context<U>, U> Context<U> for &T {
    fn get (&self, atom: &impl Atom) -> Option<U> {
        (*self).get(atom)
    }
    fn get_or_fail (&self, atom: &impl Atom) -> U {
        (*self).get_or_fail(atom)
    }
}
impl<T: Context<U>, U> Context<U> for Option<T> {
    fn get (&self, atom: &impl Atom) -> Option<U> {
        self.as_ref().map(|s|s.get(atom)).flatten()
    }
    fn get_or_fail (&self, atom: &impl Atom) -> U {
        self.as_ref().map(|s|s.get_or_fail(atom)).expect("no provider")
    }
}
/// Implement `Context` for a context and type.
#[macro_export] macro_rules! provide {
    // Provide a value to the EDN template
    ($type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
        impl Context<$type> for $State {
            fn get (&$self, atom: &impl Atom) -> Option<$type> {
                Some(match (atom.kind(), atom.text()) {
                    $((TokenKind::Sym, $pat) => $expr,)*
                    _ => return None
                })
            }
        }
    };
    // Provide a value more generically
    ($lt:lifetime: $type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
        impl<$lt> Context<$lt, $type> for $State {
            fn get (&$lt $self, atom: &impl Atom) -> Option<$type> {
                Some(match (atom.kind(), atom.text()) {
                    $((TokenKind::Sym, $pat) => $expr,)*
                    _ => return None
                })
            }
        }
    };
}
/// Implement `Context` for a context and numeric type.
///
/// This enables support for numeric literals.
#[macro_export] macro_rules! provide_num {
    // Provide a value that may also be a numeric literal in the EDN, to a generic implementation.
    ($type:ty:|$self:ident:<$T:ident:$Trait:path>|{ $($pat:pat => $expr:expr),* $(,)? }) => {
        impl<$T: $Trait> Context<$type> for $T {
            fn get (&$self, atom: &impl Atom) -> Option<$type> {
                Some(match (atom.kind(), atom.text()) {
                    $((TokenKind::Sym, $pat) => $expr,)*
                    (TokenKind::Num, _) => atom.num() as $type,
                    _ => return None
                })
            }
        }
    };
    // Provide a value that may also be a numeric literal in the EDN, to a concrete implementation.
    ($type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
        impl Context<$type> for $State {
            fn get (&$self, atom: &impl Atom) -> Option<$type> {
                Some(match (atom.kind(), atom.text()) {
                    $((TokenKind::Sym, $pat) => $expr,)*
                    (TokenKind::Num, _) => atom.num() as $type,
                    _ => return None
                })
            }
        }
    };
}
/// Implement `Context` for a context and content type.
///
/// This enables support for layout expressions.
#[macro_export] macro_rules! provide_content {
    (|$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, atom: &'a impl Atom) -> Option<Box<dyn Render<E> + 'a>> {
                use RefAtom::*;
                Some(match atom.to_ref() { $(RefAtom::Sym($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 $self, atom: &'a impl Atom) -> Option<Box<dyn Render<$Output> + 'a>> {
                use RefAtom::*;
                Some(match atom.to_ref() { $(Sym($pat) => $expr),*, _ => return None })
            }
        }
    }
}