use crate::*;

/// A component that may contain [Focusable] components.
pub trait Focus <const N: usize, E: Engine>: Render<E> + Handle<E> {
    fn focus (&self) -> usize;
    fn focus_mut (&mut self) -> &mut usize;
    fn focusable (&self) -> [&dyn Focusable<E>;N];
    fn focusable_mut (&mut self) -> [&mut dyn Focusable<E>;N];

    fn focused (&self) -> &dyn Focusable<E> {
        let focus = self.focus();
        self.focusable()[focus]
    }
    fn focused_mut (&mut self) -> &mut dyn Focusable<E> {
        let focus = self.focus();
        self.focusable_mut()[focus]
    }
    fn focus_prev (&mut self) {
        let focus = self.focus();
        self.focus_set(if focus > 0 { focus - 1 } else { N - 1 });
    }
    fn focus_next (&mut self) {
        let focus = self.focus();
        self.focus_set(if focus < N - 1 { focus + 1 } else { 0 });
    }
    fn focus_set (&mut self, focus: usize) {
        *self.focus_mut() = focus;
        let focusable = self.focusable_mut();
        for index in 0..N {
            focusable[index].set_focused(index == focus);
        }
    }
}

/// A component that may be focused.
pub trait Focusable<E: Engine>: Render<E> + Handle<E> {
    fn is_focused (&self) -> bool;
    fn set_focused (&mut self, focused: bool);
}

impl<F: Focusable<E>, E: Engine> Focusable<E> for Option<F>
    where Option<F>: Render<E>
{
    fn is_focused (&self) -> bool {
        match self {
            Some(focusable) => focusable.is_focused(),
            None => false
        }
    }
    fn set_focused (&mut self, focused: bool) {
        if let Some(focusable) = self {
            focusable.set_focused(focused)
        }
    }
}

/// Implement the [Focus] trait for a component.
#[macro_export] macro_rules! focus {
    ($struct:ident ($focus:ident) : $count:expr => [
       $($focusable:ident),*
    ]) => {
        impl Focus<$count, E> for $struct {
            fn focus (&self) -> usize {
                self.$focus
            }
            fn focus_mut (&mut self) -> &mut usize {
                &mut self.$focus
            }
            fn focusable (&self) -> [&dyn Focusable<E>;$count] {
                [
                    $(&self.$focusable as &dyn Focusable<E>,)*
                ]
            }
            fn focusable_mut (&mut self) -> [&mut dyn Focusable<E>;$count] {
                [
                    $(&mut self.$focusable as &mut dyn Focusable<E>,)*
                ]
            }
        }
    }
}

/// Implement the [Focusable] trait for a component.
#[macro_export] macro_rules! focusable {
    ($struct:ident) => {
        focusable!($struct (focused));
    };
    ($struct:ident ($focused:ident)) => {
        impl Focusable for $struct {
            fn is_focused (&self) -> bool {
                self.$focused
            }
            fn set_focused (&mut self, focused: bool) {
                self.$focused = focused
            }
        }
    }
}