use crate::*;

/// Platform backend.
pub trait Engine: Send + Sync + Sized {
    /// Input event type
    type Input: Input;
    /// Render target
    type Output: Output;
    /// Prepare before run
    fn setup (&mut self) -> Usually<()> { Ok(()) }
    /// True if done
    fn exited (&self) -> bool;
    /// Clean up after run
    fn teardown (&mut self) -> Usually<()> { Ok(()) }
}

/// Event source
pub trait Input: Send + Sync + Sized {
    /// Type of input event
    type Event;
    /// Result of handling input
    type Handled;
    /// Currently handled event
    fn event (&self) -> &Self::Event;
    /// Whether component should exit
    fn is_done (&self) -> bool;
    /// Mark component as done
    fn done (&self);
}

/// 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() }
}