Ichimoku

// Ichimoku Kinko Hyo, drawn as TradingView's built-in draws it: the two leading spans, and the
// cloud between them, shifted 25 bars ahead, into the space past the newest bar; the lagging
// span, the close, shifted 25 bars back. Each line is the midpoint of the highest high and the
// lowest low over its window.
indicator('Ichimoku', { overlay: true });

const conversionLength = input.int('Conversion line length', 9, { min: 1 });
const baseLength = input.int('Base line length', 26, { min: 1 });
const spanBLength = input.int('Leading span B length', 52, { min: 1 });
const displacement = input.int('Displacement', 26, { min: 1 });

const chart = bars();
const conversionHigh = ta.highest(conversionLength);
const conversionLow = ta.lowest(conversionLength);
const baseHigh = ta.highest(baseLength);
const baseLow = ta.lowest(baseLength);
const spanBHigh = ta.highest(spanBLength);
const spanBLow = ta.lowest(spanBLength);

// Blue, red and green as on TradingView, from the theme's study colours.
const conversion = plot.line('Conversion line', { color: color.study(12) });
const base = plot.line('Base line', { color: color.study(6) });
// TradingView counts the displacement from the current bar, so the shift is one bar less.
const lagging = plot.line('Lagging span', { color: color.study(10), offset: 1 - displacement });
const spanA = plot.line('Leading span A', { color: color.withAlpha(color.up, 0.75), offset: displacement - 1 });
const spanB = plot.line('Leading span B', { color: color.withAlpha(color.down, 0.75), offset: displacement - 1 });
const cloud = plot.fill('Cloud', spanA, spanB);

chart.onBar(() => {
  const c = (conversionHigh.update(chart.high) + conversionLow.update(chart.low)) / 2;
  const b = (baseHigh.update(chart.high) + baseLow.update(chart.low)) / 2;
  const a = (c + b) / 2;
  const s = (spanBHigh.update(chart.high) + spanBLow.update(chart.low)) / 2;
  conversion.set(c);
  base.set(b);
  lagging.set(chart.close);
  spanA.set(a);
  spanB.set(s);
  cloud.set(a > s ? color.withAlpha(color.up, 0.12) : color.withAlpha(color.down, 0.12));
});