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use viewport::Viewport;

use { Event, GenericEvent, Input };

/// Render arguments
#[derive(Copy, Clone, PartialEq, Debug)]
pub struct RenderArgs {
    /// Extrapolated time in seconds, used to do smooth animation.
    pub ext_dt: f64,
    /// The width of rendered area in points.
    pub width: u32,
    /// The height of rendered area in points.
    pub height: u32,
    /// The width of rendered area in pixels.
    pub draw_width: u32,
    /// The height of rendered area in pixels.
    pub draw_height: u32,
}

impl RenderArgs {
    /// Returns viewport information filling entire render area.
    pub fn viewport(&self) -> Viewport {
        Viewport {
            rect: [0, 0, self.draw_width as i32, self.draw_height as i32],
            window_size: [self.width, self.height],
            draw_size: [self.draw_width, self.draw_height],
        }
    }
}

/// When the next frame should be rendered
pub trait RenderEvent: Sized {
    /// Creates a render event.
    fn from_render_args(args: &RenderArgs, old_event: &Self) -> Option<Self>;
    /// Calls closure if this is a render event.
    fn render<U, F>(&self, f: F) -> Option<U>
        where F: FnMut(&RenderArgs) -> U;
    /// Returns render arguments.
    fn render_args(&self) -> Option<RenderArgs> {
        self.render(|args| args.clone())
    }
}

/* TODO: Enable when specialization gets stable.
impl<T: GenericEvent> RenderEvent for T {
    fn from_render_args(args: &RenderArgs, old_event: &Self) -> Option<Self> {
        GenericEvent::from_args(RENDER, args as &Any, old_event)
    }

    fn render<U, F>(&self, mut f: F) -> Option<U>
        where F: FnMut(&RenderArgs) -> U
    {
        if self.event_id() != RENDER {
            return None;
        }
        self.with_args(|any| {
            if let Some(args) = any.downcast_ref::<RenderArgs>() {
                Some(f(args))
            } else {
                panic!("Expected RenderArgs")
            }
        })
    }
}
*/

impl RenderEvent for Input {
    fn from_render_args(_args: &RenderArgs, _old_event: &Self) -> Option<Self> {
        None
    }

    fn render<U, F>(&self, mut _f: F) -> Option<U>
        where F: FnMut(&RenderArgs) -> U
    {
        None
    }
}

impl<I: GenericEvent> RenderEvent for Event<I> {
    fn from_render_args(args: &RenderArgs, _old_event: &Self) -> Option<Self> {
        Some(Event::Render(*args))
    }

    fn render<U, F>(&self, mut f: F) -> Option<U>
        where F: FnMut(&RenderArgs) -> U
    {
        match *self {
            Event::Render(ref args) => Some(f(args)),
            _ => None
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_event_render() {
        use Event;
        use RenderArgs;

        let e = Event::Render(RenderArgs { ext_dt: 0.0, width: 0, height: 0,
            draw_width: 0, draw_height: 0 });
        let x: Option<Event> = RenderEvent::from_render_args(
            &RenderArgs {
                ext_dt: 1.0,
                width: 10,
                height: 10,
                draw_width: 10,
                draw_height: 10,
            }, &e
        );
        let y: Option<Event> = x.clone().unwrap().render(|args|
            RenderEvent::from_render_args(args, x.as_ref().unwrap())).unwrap();
        assert_eq!(x, y);
    }
}