Supertrend

fn supertrend() -> Chart {
    let bars = market_legs();
    let mut st = build_checked(
        "supertrend",
        &params(&[("period", 10.0), ("multiplier", 3.0)]),
    )?;

    // One line segment per trend run, a marker wherever the trend flips.
    let mut segments: Vec<ChartSeries> = Vec::new();
    let mut markers = Vec::new();
    let mut prev_trend = 0.0;
    for bar in &bars {
        let Some(out) = st.on_bar(bar) else { continue };
        let trend = out.extra["trend"];
        if trend != prev_trend {
            let (name, color, label, action) = if trend > 0.0 {
                ("Supertrend long", "#26a69a", "flip up", TriggerAction::Buy)
            } else {
                (
                    "Supertrend short",
                    "#ef5350",
                    "flip down",
                    TriggerAction::Sell,
                )
            };
            if prev_trend != 0.0 {
                markers.push(ChartMarkerData {
                    timestamp: bar.timestamp,
                    price: bar.close,
                    label: label.to_string(),
                    action,
                });
            }
            segments.push(line(name, color, Vec::new()));
            prev_trend = trend;
        }
        if let Some(segment) = segments.last_mut() {
            segment.points.push((bar.timestamp, out.value));
        }
    }

    let data = ChartRenderData {
        title: "Supertrend (10, 3)".to_string(),
        bars: candles(&bars),
        series: segments,
        zones: Vec::new(),
        markers,
    };
    Ok(render_chart_svg(&data, 800, 400))
}