Trend candles

// Trend Candles: the chart's own candles tinted by where the close sits against two moving averages. Above both,
// the candle turns sky; below both, violet; between them it keeps the chart's own colours. The two averages are drawn
// as thin lines (fast teal, slow slate), a dot marks each bar where the trend flipped from one side to the other
// (under the bar for a flip up, over it for a flip down), and a counter at the top right reads how long the current
// state has held ("12 bars up").

param.int("fast_len", 21, { min: 2, max: 200, label: "Fast EMA", row: "lengths", description: "Fast EMA length in bars" }); // two whole numbers on one dialog line
param.int("slow_len", 50, { min: 2, max: 400, label: "Slow EMA", row: "lengths", description: "Slow EMA length in bars" });
param.color("up_color", "#38bdf8", { label: "Up tint", row: "tints" }); // two colour settings on one line: each paints the dot and the candle tint of its side below, by name
param.color("down_color", "#a78bfa", { label: "Down tint", row: "tints" });
const fastLine = output("fast_ema", line, overlay, { color: "#2dd4bf", width: 1, label: "Fast EMA", format: "price", description: "EMA of the close over fast_len bars" }); // the handle names it for the hover card
output("slow_ema", line, overlay, { color: "#94a3b8", width: 1, label: "Slow EMA", format: "price", description: "EMA of the close over slow_len bars" });
output("trend", none, overlay, { description: "+1 above both averages, -1 below both, 0 between" });
output("tinted", none, overlay, { description: "1 when the candle is tinted (above or below both averages): the tint's gate" });
output("tint", none, overlay, { description: "1 above both averages (sky), 0 below both (violet): the tint's colour index" });
output("run", none, overlay, { description: "Bars the current state has held" });
output("flip_up", shape, overlay, { color: "@up_color", description: "A dot under the bar where the trend turned up" }); // the up tint setting paints it
output("flip_down", shape, overlay, { color: "@down_color", description: "A dot over the bar where the trend turned down" });
string("text", { max_bytes: 24 }); // the counter's one line
handles.label({ anchor: "top_right", align: "right", size: 12 }); // the counter, in pane pixels from the chart's top-right corner
render.barcolor("trend_tint", { where: "tinted", color_by: "tint", colors: ["@down_color", "@up_color"] }); // the bar's own candle, body and wick, in the two tint settings
hover(fastLine, [block.value("Fast EMA", "fast_ema", { format: "price" }), block.rows([["Slow EMA", "slow_ema", "price"], ["Trend", "trend", "int"], ["Run", "run", "int"]])]); // the card the fast average opens under the cursor

const SLATE = rgba(148, 163, 184, 255);
const counter = draw.label(0);

let fastLen = 21; // settings, read in onStart()
let slowLen = 50;
let upInk = rgba(56, 189, 248, 255); // the two tint settings: the counter reads in the side's tint
let downInk = rgba(167, 139, 250, 255);
let fastEma = new Ema(21); // rebuilt in onStart()
let slowEma = new Ema(50);
let trend = 0; // +1 above both, -1 below both, 0 between
let lastTinted = 0; // the last side the close was on (+1 or -1): a flip is a change of side
let run = 0; // bars the current state has held
let rangeAvg: f64 = NaN; // a running mean of high - low: the dot's distance from the bar

function onStart(): void {
  fastLen = i32(p_fast_len());
  slowLen = i32(p_slow_len());
  fastEma = new Ema(fastLen);
  slowEma = new Ema(slowLen);
  upInk = fromPacked(p_up_color());
  downInk = fromPacked(p_down_color());
}

// onBar() runs once per bar: feed both averages, place the close against them, count the run, catch a flip;
// then write the averages, the state and the dots on every bar, and the counter on the live bar only.
function onBar(): void {
  const close = bar.close();
  const high = bar.high();
  const low = bar.low();
  const fast = fastEma.update(close);
  const slow = slowEma.update(close);
  const range = high - low;
  rangeAvg = isNaN(rangeAvg) ? range : rangeAvg + (range - rangeAvg) * 0.1;
  let flipUpY: f64 = NaN; // this bar's dots, NaN when the side held
  let flipDownY: f64 = NaN;
  if (isNaN(fast) || isNaN(slow)) return; // warm-up rows draw nothing
  const next = close > fast && close > slow ? 1 : close < fast && close < slow ? -1 : 0;
  run = next == trend ? run + 1 : 1;
  trend = next;
  if (trend != 0 && trend != lastTinted) { // the close crossed to the other side of both averages
    if (lastTinted != 0) {
      if (trend > 0) flipUpY = low - rangeAvg * 0.6;
      else flipDownY = high + rangeAvg * 0.6;
    }
    lastTinted = trend;
  }
  out_fast_ema(fast);
  out_slow_ema(slow);
  out_trend(f64(trend));
  out_tinted(trend != 0 ? 1.0 : 0.0);
  out_tint(trend > 0 ? 1.0 : 0.0);
  out_run(f64(run));
  out_flip_up(flipUpY);
  out_flip_down(flipDownY);
  if (bar.isLast()) {
    sb_clear();
    sb_int(run);
    sb_text(run == 1 ? " bar " : " bars ");
    sb_text(trend > 0 ? "up" : trend < 0 ? "down" : "between");
    counter.set(60, 14).text(str_text_sb).align(ALIGN_RIGHT).color(trend > 0 ? upInk : trend < 0 ? downInk : SLATE); // inward past the price-axis tags, in the side's tint
  }
}