export async function createStreamVisualizer(stream, { maxPoints, alpha, width, height, yDomain }) {
  const d3 = await import('d3');
  const data = [];
  let ema = null;
  
  for await (const { timestamp, value } of stream) {
    ema = ema === null ? value : alpha * value + (1 - alpha) * ema;
    data.push({ timestamp, value, ema });
    if (data.length > maxPoints) data.shift();
  }
  
  if (!data.length) return { data, path: '' };
  
  const x = d3.scaleLinear().domain([data[0].timestamp, data[data.length - 1].timestamp]).range([0, width]);
  const y = d3.scaleLinear().domain(yDomain).range([height, 0]);
  const path = d3.line().x(d => x(d.timestamp)).y(d => y(d.ema))(data);
  
  return { data, path };
}
export default createStreamVisualizer;