use std::error::Error;
use async_trait::async_trait;
use web_sys::{CanvasRenderingContext2d, HtmlCanvasElement};
use crate::rendering::Renderer;
use wasm_bindgen::{JsCast, JsValue};
use crate::CLIENT;

#[derive(Debug)]
pub struct WebRenderer {
    canvas_element_id: String
}

#[async_trait]
impl Renderer for WebRenderer {
    async fn get(canvas_element_id: &str) -> Result<Self, Box<dyn Error>> {
        Ok(Self {
            canvas_element_id: canvas_element_id.to_string()
        })
    }

    async fn render_frame(&self, _time_delta_ms: f64) -> Result<(), Box<dyn Error>> {
        // TODO
        // time_delta_ms is the delta, in ms, from when the last render_frame was called by the browser
        let window = web_sys::window().ok_or("window needs to exist")?;
        let document = window.document().ok_or("window.document needs to exist")?;
        let canvas_element = document.get_element_by_id(&self.canvas_element_id).ok_or("canvas element does not exist")?;
        let typed_canvas_element: HtmlCanvasElement = canvas_element.dyn_into::<web_sys::HtmlCanvasElement>().map_err(|_| ()).unwrap();
        let context = typed_canvas_element.get_context("2d").unwrap().unwrap().dyn_into::<CanvasRenderingContext2d>().unwrap();
        let client = CLIENT.read()?;

        context.set_transform(1f64, 0f64, 0f64, 1f64, 0f64, 0f64).map_err(|e: JsValue| e.as_string().unwrap())?;
        context.clear_rect(0f64, 0f64, typed_canvas_element.width() as f64, typed_canvas_element.height() as f64);

        let camera_translate_x = -client.x + (typed_canvas_element.width() / 2) as f64;
        let camera_translate_y = -client.y + (typed_canvas_element.height() / 2) as f64;

        context.translate(camera_translate_x, camera_translate_y).map_err(|e: JsValue| e.as_string().unwrap())?;

        Ok(())
    }
}