Bollinger Bands

// overlay = true
const length = input.int("Length", 20, { min: 2, max: 500 });
const mult   = input.float("StdDev Mult", 2.0, { min: 0.1, max: 10, step: 0.1 });
const src    = input.source("Source", "close");

const upperPlot  = plot("BB Upper",  null, { color: "#3b82f6FF", linewidth: 1 });
const middlePlot = plot("BB Basis",  null, { color: "#3b82f680", linewidth: 1 });
const lowerPlot  = plot("BB Lower",  null, { color: "#3b82f6FF", linewidth: 1 });

fill(upperPlot, lowerPlot, { color: "#3b82f615" });

onBar(() => {
  const bb = ta.bb(src, length, mult);
  if (na(bb.upper)) return;

  plot("BB Upper",  bb.upper);
  plot("BB Basis",  bb.middle);
  plot("BB Lower",  bb.lower);
});

// overlay = true
const length = input.int("Length", 20, { min: 2 });
const mult   = input.float("Mult", 2.0, { min: 0.1 });
const src    = input.source("Source", "close");

const upperP = plot("BB Upper", null, { color: "#3b82f6FF" });
const lowerP = plot("BB Lower", null, { color: "#3b82f6FF" });
plot("BB Middle", null, { color: "#3b82f650" });

fill(upperP, lowerP, { color: "#3b82f615" });

// %B and bandwidth require their own sub-pane plots
plot("BB %B",    null, { color: "#f59e0bFF" });
plot("BB Width", null, { color: "#a78bfaFF" });

hline(1, { color: "#ef4444FF", style: "dashed" });
hline(0, { color: "#22c55eFF", style: "dashed" });

onBar(() => {
  const bb = ta.bb(src, length, mult);
  if (na(bb.upper)) return;

  plot("BB Upper",  bb.upper);
  plot("BB Middle", bb.middle);
  plot("BB Lower",  bb.lower);

  // %B: where is price within the band?
  const width   = bb.upper - bb.lower;
  const pctB    = width > 0 ? (src() - bb.lower) / width : 0.5;
  const bbWidth = width / bb.middle * 100;

  plot("BB %B",    pctB);
  plot("BB Width", bbWidth);
});