use mathru::special::gamma;
use plotters::prelude::*;

fn main() {
    let x_start: f64 = -3.50;
    let x_end: f64 = 5.0;
    let length: usize = 2000;

    let mut graph_1: Vec<(f64, f64)> = Vec::with_capacity(length);
    for i in 0..length {
        let x: f64 = (x_end - x_start) / (length as f64) * (i as f64) + x_start;
        graph_1.push((x, gamma::gamma(x)));
    }

    let root_area = BitMapBackend::new("./figures/gamma.png", (600, 400)).into_drawing_area();
    root_area.fill(&WHITE).unwrap();

    let mut ctx = ChartBuilder::on(&root_area)
        .margin(20)
        .set_label_area_size(LabelAreaPosition::Left, 40)
        .set_label_area_size(LabelAreaPosition::Bottom, 40)
        .build_cartesian_2d(x_start..x_end, -10.0f64..25.0f64)
        .unwrap();

    ctx.configure_mesh()
        .x_desc("x")
        .y_desc("gamma(x)")
        .axis_desc_style(("sans-serif", 15).into_font())
        .draw()
        .unwrap();

    ctx.draw_series(LineSeries::new(graph_1, &BLUE)).unwrap();
}