use crate::*;
use std::ops::Deref;
/// Render target.
pub trait Output: Send + Sync + Sized {
    /// Unit of length
    type Unit: Coordinate;
    /// Rectangle without offset
    type Size: Size<Self::Unit>;
    /// Rectangle with offset
    type Area: Area<Self::Unit>;
    /// Current output area
    fn area (&self) -> Self::Area;
    /// Mutable pointer to area
    fn area_mut (&mut self) -> &mut Self::Area;
    /// Render widget in area
    fn place (&mut self, area: Self::Area, content: &impl Render<Self>);
    #[inline] fn x (&self) -> Self::Unit { self.area().x() }
    #[inline] fn y (&self) -> Self::Unit { self.area().y() }
    #[inline] fn w (&self) -> Self::Unit { self.area().w() }
    #[inline] fn h (&self) -> Self::Unit { self.area().h() }
    #[inline] fn wh (&self) -> Self::Size { self.area().wh().into() }
}

/// Renderable with dynamic dispatch.
pub trait Render<E: Output> {
    /// Compute layout.
    fn layout (&self, area: E::Area) -> E::Area;
    /// Write data to display.
    fn render (&self, output: &mut E);
    /// Perform type erasure, turning `self` into an opaque [RenderBox].
    fn boxed <'a> (self) -> RenderBox<'a, E> where Self: Send + Sync + Sized + 'a {
        Box::new(self) as RenderBox<'a, E>
    }
}

/// Most importantly, every [Content] is also a [Render].
///
/// However, the converse does not hold true.
/// Instead, the [Content::content] method returns an
/// opaque [Render] pointer.
impl<E: Output, C: Content<E>> Render<E> for C {
    fn layout (&self, area: E::Area) -> E::Area { Content::layout(self, area) }
    fn render (&self, output: &mut E) { Content::render(self, output) }
}

/// Opaque pointer to a renderable living on the heap.
///
/// Return this from [Content::content] to use dynamic dispatch.
pub type RenderBox<'a, E> = Box<RenderDyn<'a, E>>;

/// You can render from a box.
impl<'a, E: Output> Content<E> for RenderBox<'a, E> {
    fn content (&self) -> impl Render<E> { self.deref() }
    //fn boxed <'b> (self) -> RenderBox<'b, E> where Self: Sized + 'b { self }
}

/// Opaque pointer to a renderable.
pub type RenderDyn<'a, E> = dyn Render<E> + Send + Sync + 'a;

/// You can render from an opaque pointer.
impl<'a, E: Output> Content<E> for &RenderDyn<'a, E> where Self: Sized {
    fn content (&self) -> impl Render<E> {
        #[allow(suspicious_double_ref_op)]
        self.deref()
    }
    fn layout (&self, area: E::Area) -> E::Area {
        #[allow(suspicious_double_ref_op)]
        Render::layout(self.deref(), area)
    }
    fn render (&self, output: &mut E) {
        #[allow(suspicious_double_ref_op)]
        Render::render(self.deref(), output)
    }
}

/// Composable renderable with static dispatch.
pub trait Content<E: Output> {
    /// Return a [Render]able of a specific type.
    fn content (&self) -> impl Render<E> { () }
    /// Perform layout. By default, delegates to [Self::content].
    fn layout (&self, area: E::Area) -> E::Area { self.content().layout(area) }
    /// Draw to output. By default, delegates to [Self::content].
    fn render (&self, output: &mut E) { self.content().render(output) }
}

/// Every pointer to [Content] is a [Content].
impl<E: Output, C: Content<E>> Content<E> for &C {
    fn content (&self) -> impl Render<E> { (*self).content() }
    fn layout (&self, area: E::Area) -> E::Area { (*self).layout(area) }
    fn render (&self, output: &mut E) { (*self).render(output) }
}

/// The platonic ideal unit of [Content]: total emptiness at dead center (e=1vg^sqrt(-1))
impl<E: Output> Content<E> for () {
    fn layout (&self, area: E::Area) -> E::Area { area.center().to_area_pos().into() }
    fn render (&self, _: &mut E) {}
}

impl<E: Output, T: Content<E>> Content<E> for Option<T> {
    fn content (&self) -> impl Render<E> {
        self.as_ref()
    }
    fn layout (&self, area: E::Area) -> E::Area {
        self.as_ref()
            .map(|content|content.layout(area))
            .unwrap_or([0.into(), 0.into(), 0.into(), 0.into(),].into())
    }
    fn render (&self, output: &mut E) {
        self.as_ref()
            .map(|content|content.render(output));
    }
}

/// Implement [Content] with composable content for a struct.
#[macro_export] macro_rules! content {
    // Implement for all [Output]s.
    (|$self:ident:$Struct:ty| $content:expr) => {
        impl<E: Output> Content<E> for $Struct {
            fn content (&$self) -> impl Render<E> { Some($content) }
        }
    };
    // Implement for specific [Output].
    ($Output:ty:|
        $self:ident:
        $Struct:ident$(<$($($L:lifetime)? $($T:ident)? $(:$Trait:path)?),+>)?
    |$content:expr) => {
        impl $(<$($($L)? $($T)? $(:$Trait)?),+>)? Content<$Output>
        for $Struct $(<$($($L)? $($T)?),+>)? {
            fn content (&$self) -> impl Render<$Output> { $content }
        }
    };
}

/// Implement [Content] with custom rendering for a struct.
#[macro_export] macro_rules! render {
    (|$self:ident:$Struct:ident $(<
        $($L:lifetime),* $($T:ident $(:$Trait:path)?),*
    >)?, $to:ident | $render:expr) => {
        impl <$($($L),*)? E: Output, $($T$(:$Trait)?),*> Content<E>
        for $Struct $(<$($L),* $($T),*>>)? {
            fn render (&$self, $to: &mut E) { $render }
        }
    };
    ($Output:ty:|
        $self:ident:
        $Struct:ident $(<$($($L:lifetime)? $($T:ident)? $(:$Trait:path)?),+>)?, $to:ident
    |$render:expr) => {
        impl $(<$($($L)? $($T)? $(:$Trait)?),+>)? Content<$Output>
        for $Struct $(<$($($L)? $($T)?),+>)? {
            fn render (&$self, $to: &mut $Output) { $render }
        }
    };
}