use crate::*;
use std::marker::PhantomData;

/// Lazily-evaluated [Render]able.
pub struct Thunk<E: Output, T: Render<E>, F: Fn()->T + Send + Sync>(
    PhantomData<E>,
    F
);
impl<E: Output, T: Render<E>, F: Fn()->T + Send + Sync> Thunk<E, T, F> {
    pub const fn new (thunk: F) -> Self {
        Self(PhantomData, thunk)
    }
}
impl<E: Output, T: Render<E>, F: Fn()->T + Send + Sync> Content<E> for Thunk<E, T, F> {
    fn content (&self) -> impl Render<E> { (self.1)() }
}

pub struct ThunkBox<'a, E: Output>(
    PhantomData<E>,
    Box<dyn Fn()->RenderBox<'a, E> + Send + Sync + 'a>
);
impl<'a, E: Output> ThunkBox<'a, E> {
    pub const fn new (thunk: Box<dyn Fn()->RenderBox<'a, E> + Send + Sync + 'a>) -> Self {
        Self(PhantomData, thunk)
    }
}
impl<'a, E: Output> Content<E> for ThunkBox<'a, E> {
    fn content (&self) -> impl Render<E> { (self.1)() }
}
impl<'a, E, F, T> From<F> for ThunkBox<'a, E>
where
    E: Output,
    F: Fn()->T + Send + Sync + 'a,
    T: Render<E> + Send + Sync + 'a
{
    fn from (f: F) -> Self {
        Self(PhantomData, Box::new(move||f().boxed()))
    }
}
//impl<'a, E: Output, F: Fn()->Box<dyn Render<E> + 'a> + Send + Sync + 'a> From<F> for ThunkBox<'a, E> {
    //fn from (f: F) -> Self {
        //Self(Default::default(), Box::new(f))
    //}
//}

pub struct ThunkRender<E: Output, F: Fn(&mut E) + Send + Sync>(PhantomData<E>, F);
impl<E: Output, F: Fn(&mut E) + Send + Sync> ThunkRender<E, F> {
    pub fn new (render: F) -> Self { Self(PhantomData, render) }
}
impl<E: Output, F: Fn(&mut E) + Send + Sync> Content<E> for ThunkRender<E, F> {
    fn render (&self, to: &mut E) { (self.1)(to) }
}

pub struct ThunkLayout<
    E: Output,
    F1: Fn(E::Area)->E::Area + Send + Sync, 
    F2: Fn(&mut E) + Send + Sync
>(
    PhantomData<E>, 
    F1,
    F2
);
impl<E: Output, F1: Fn(E::Area)->E::Area + Send + Sync, F2: Fn(&mut E) + Send + Sync> ThunkLayout<E, F1, F2> {
    pub fn new (layout: F1, render: F2) -> Self { Self(PhantomData, layout, render) }
}
impl<E, F1, F2> Content<E> for ThunkLayout<E, F1, F2>
where
    E:  Output,
    F1: Fn(E::Area)->E::Area + Send + Sync,
    F2: Fn(&mut E) + Send + Sync
{
    fn layout (&self, to: E::Area) -> E::Area { (self.1)(to) }
    fn render (&self, to: &mut E) { (self.2)(to) }
}