use plotters::prelude::*;

fn snowflake_iter(points: &[(f64, f64)]) -> Vec<(f64, f64)> {
    let mut ret = vec![];
    for i in 0..points.len() {
        let (start, end) = (points[i], points[(i + 1) % points.len()]);
        let t = ((end.0 - start.0) / 3.0, (end.1 - start.1) / 3.0);
        let s = (
            t.0 * 0.5 - t.1 * (0.75f64).sqrt(),
            t.1 * 0.5 + (0.75f64).sqrt() * t.0,
        );
        ret.push(start);
        ret.push((start.0 + t.0, start.1 + t.1));
        ret.push((start.0 + t.0 + s.0, start.1 + t.1 + s.1));
        ret.push((start.0 + t.0 * 2.0, start.1 + t.1 * 2.0));
    }
    ret
}

const OUT_FILE_NAME: &str = "plotters-doc-data/animation.gif";
fn main() -> Result<(), Box<dyn std::error::Error>> {
    let root = BitMapBackend::gif(OUT_FILE_NAME, (800, 600), 1_000)?.into_drawing_area();

    for i in 0..8 {
        root.fill(&WHITE)?;

        let mut chart = ChartBuilder::on(&root)
            .caption(
                format!("Koch's Snowflake (n_iter = {})", i),
                ("sans-serif", 50),
            )
            .build_cartesian_2d(-2.0..2.0, -1.5..1.5)?;

        let mut snowflake_vertices = {
            let mut current: Vec<(f64, f64)> = vec![
                (0.0, 1.0),
                ((3.0f64).sqrt() / 2.0, -0.5),
                (-(3.0f64).sqrt() / 2.0, -0.5),
            ];
            for _ in 0..i {
                current = snowflake_iter(&current[..]);
            }
            current
        };

        chart.draw_series(std::iter::once(Polygon::new(
            snowflake_vertices.clone(),
            RED.mix(0.2),
        )))?;

        snowflake_vertices.push(snowflake_vertices[0]);
        chart.draw_series(std::iter::once(PathElement::new(snowflake_vertices, RED)))?;

        root.present()?;
    }

    println!("Result has been saved to {}", OUT_FILE_NAME);

    Ok(())
}

#[test]
fn entry_point() {
    main().unwrap()
}