use crate::{
    UiRegion, WidgetId, Widgets,
    primitive::{PrimitiveData, PrimitiveInstance, Primitives},
};

pub struct Painter<'a, Ctx> {
    nodes: &'a Widgets<Ctx>,
    ctx: &'a mut Ctx,
    primitives: Primitives,
    pub region: UiRegion,
}

impl<'a, Ctx> Painter<'a, Ctx> {
    pub fn new(nodes: &'a Widgets<Ctx>, ctx: &'a mut Ctx) -> Self {
        Self {
            nodes,
            ctx,
            primitives: Primitives::default(),
            region: UiRegion::full(),
        }
    }
    pub fn write<Data: PrimitiveData>(&mut self, data: Data) {
        let ptr = self.primitives.data.len() as u32;
        let region = self.region;
        self.primitives
            .instances
            .push(PrimitiveInstance { region, ptr });
        self.primitives.data.push(Data::DISCRIM);
        self.primitives
            .data
            .extend_from_slice(bytemuck::cast_slice::<_, u32>(&[data]));
    }

    pub fn draw(&mut self, id: &WidgetId) where Ctx: 'static {
        self.nodes.get_dyn(id).draw(self);
    }

    pub fn draw_within(&mut self, node: &WidgetId, region: UiRegion) where Ctx: 'static {
        let old = self.region;
        self.region.select(&region);
        self.draw(node);
        self.region = old;
    }

    pub fn finish(self) -> Primitives {
        self.primitives
    }

    pub fn ctx_mut(&mut self) -> &mut Ctx {
        self.ctx
    }
}