Volume profile

fn volume_profile() -> Chart {
    let bars = walk(23, 120);
    let lookback = 70;
    let mut vp = build_checked(
        "volume_profile",
        &params(&[("lookback", lookback as f64), ("num_bins", 30.0)]),
    )?;

    let mut last = None;
    for bar in &bars {
        if let Some(out) = vp.on_bar(bar) {
            last = Some(out);
        }
    }
    let out = last.ok_or("volume profile produced no output")?;
    let (poc, vah, val) = (out.extra["vpoc"], out.extra["vah"], out.extra["val"]);

    let from = bars[bars.len() - lookback].timestamp;
    let to = bars[bars.len() - 1].timestamp;
    let data = ChartRenderData {
        title: "Volume profile, last 70 bars".to_string(),
        bars: candles(&bars),
        series: vec![line(
            "Point of control",
            "#ffb74d",
            vec![(from, poc), (to, poc)],
        )],
        zones: vec![ChartZoneData {
            name: format!("Value area {val:.2} to {vah:.2}"),
            price_top: vah,
            price_bottom: val,
            color: "#29b6f6".to_string(),
        }],
        markers: Vec::new(),
    };
    Ok(render_chart_svg(&data, 800, 400))
}