Trend bars

// Candles coloured by trend, as Pine's barcolor() colours them: the up colour while the close
// holds above a rising EMA, the down colour below a falling one, grey in between. A label marks
// a flip of the close across the EMA that holds for two bars, drawn on the first of them, and
// no sooner than a set number of bars after the last label, so chop does not stack them. A dot
// marks a bar twice as wide as the recent average.
indicator('Trend bars', { overlay: true });

const length = input.int('EMA length', 34, { min: 2 });
// How labels are spaced is not what the script computes, so it stays out of the legend name.
const gap = input.int('Bars between labels', 10, { min: 1, legend: false });

const chart = bars();
const ema = ta.ema(length);
const rising = ta.rising(1);
const falling = ta.falling(1);
const range = ta.sma(20);
// Which side of the EMA the close has held, the side it was on one bar ago, and bars since a label.
const held = state.bar<number>(0);
const before = state.bar<number>(0);
const quiet = state.bar<number>(1e9);

const line = plot.line('EMA', { width: 2 });
const trend = plot.barColor('Trend');
// Set on the second bar of a flip, drawn one bar back on its first.
const up = plot.shape('Flips up', { shape: 'labelUp', location: 'below', color: color.up, text: 'Up', offset: -1 });
const down = plot.shape('Flips down', { shape: 'labelDown', location: 'above', color: color.down, text: 'Down', offset: -1 });
const wide = plot.shape('Wide bar', { char: '•', location: 'above', color: color.neutral, size: 'normal' });

chart.onBar(() => {
  const e = ema.update(chart.close);
  const isRising = rising.update(e);
  const isFalling = falling.update(e);
  const average = range.update(chart.high - chart.low);
  line.set(e);
  if (isNa(e)) trend.set(null);
  else if (chart.close > e && isRising) trend.set(color.up);
  else if (chart.close < e && isFalling) trend.set(color.down);
  else trend.set(color.withAlpha(color.neutral, 0.55));

  const side = isNa(e) ? 0 : chart.close > e ? 1 : chart.close < e ? -1 : 0;
  const flipped = side !== 0 && side === before.value && side !== held.value;
  const labelled = flipped && held.value !== 0 && quiet.value >= gap;
  up.set(labelled && side > 0);
  down.set(labelled && side < 0);
  if (flipped) held.value = side;
  quiet.value = labelled ? 1 : quiet.value + 1;
  before.value = side;
  wide.set(chart.high - chart.low > 2 * average);
});