use wasm_bindgen::prelude::*;
use web_sys::HtmlCanvasElement;
mod func_plot;

#[global_allocator]
static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;

pub type DrawResult<T> = Result<T, Box<dyn std::error::Error>>;

/// Result of screen to chart coordinates conversion.
#[wasm_bindgen]
pub struct Point {
    pub x: f32,
    pub y: f32,
}

#[wasm_bindgen]
impl Point {
    pub fn new(x: f32, y: f32) -> Self { Self { x, y } }
}

#[wasm_bindgen]
pub struct Chart {
    convert: Box<dyn Fn((i32, i32)) -> Option<(f32, f32)>>,
    area: f32,
}

#[wasm_bindgen]
impl Chart {
    pub fn draw(
        canvas: HtmlCanvasElement, func_str: &str, min_x: f32, max_x: f32, min_y: f32, max_y: f32,
        num_interval: usize, resolution: i32,
    ) -> Result<Chart, JsValue> {
        let draw_output = func_plot::draw(
            canvas,
            func_str,
            min_x,
            max_x,
            min_y,
            max_y,
            num_interval,
            resolution,
        )
        .map_err(|err| err.to_string())?;
        let map_coord = draw_output.0;

        Ok(Chart {
            convert: Box::new(move |coord| map_coord(coord).map(|(x, y)| (x, y))),
            area: draw_output.1,
        })
    }

    pub fn get_area(&self) -> f32 { self.area }

    pub fn coord(&self, x: i32, y: i32) -> Option<Point> {
        (self.convert)((x, y)).map(|(x, y)| Point::new(x, y))
    }
}