function round(value) {
  return Math.round(value * 100) / 100;
}
function sign(value) {
  return value < 0 ? -1 : 1;
}
function innerTangent([x0, y0], [x1, y1], [x2, y2]) {
  const h0 = x1 - x0;
  const h1 = x2 - x1;
  const s0 = (y1 - y0) / (h0 || (h1 < 0 ? -0 : 0));
  const s1 = (y2 - y1) / (h1 || (h0 < 0 ? -0 : 0));
  const p = (s0 * h1 + s1 * h0) / (h0 + h1);
  return (sign(s0) + sign(s1)) * Math.min(Math.abs(s0), Math.abs(s1), 0.5 * Math.abs(p)) || 0;
}
function edgeTangent([x0, y0], [x1, y1], tangent) {
  const h = x1 - x0;
  return h ? (3 * (y1 - y0) / h - tangent) / 2 : tangent;
}
function monotoneSegments(points) {
  if (points.length < 3) {
    return points.slice(1).map(([x, y]) => `L${round(x)},${round(y)}`).join("");
  }
  const tangents = points.map((point, i) => i > 0 && i < points.length - 1 ? innerTangent(points[i - 1], point, points[i + 1]) : 0);
  tangents[0] = edgeTangent(points[0], points[1], tangents[1]);
  tangents[points.length - 1] = edgeTangent(points[points.length - 2], points[points.length - 1], tangents[points.length - 2]);
  return points.slice(1).map(([x1, y1], i) => {
    const [x0, y0] = points[i];
    const dx = (x1 - x0) / 3;
    return `C${round(x0 + dx)},${round(y0 + dx * tangents[i])},${round(x1 - dx)},${round(y1 - dx * tangents[i + 1])},${round(x1)},${round(y1)}`;
  }).join("");
}
function stepSegments(points) {
  return points.slice(1).map(([x1, y1], i) => {
    const [x0, y0] = points[i];
    const x = round((x0 + x1) / 2);
    return `L${x},${round(y0)}L${x},${round(y1)}L${round(x1)},${round(y1)}`;
  }).join("");
}
function createCurve(segments) {
  const line = (points) => points.length ? `M${round(points[0][0])},${round(points[0][1])}${segments(points)}` : "";
  return {
    line,
    area: (top, bottom) => {
      if (!top.length) {
        return "";
      }
      const reversed = [...bottom].reverse();
      return `${line(top)}L${round(reversed[0][0])},${round(reversed[0][1])}${segments(reversed)}Z`;
    }
  };
}
export const chartCurves = {
  monotone: createCurve(monotoneSegments),
  step: createCurve(stepSegments)
};