// Vector Math
const vectorDot = (u, v) => u.map((x, i) => x * v[i]).reduce((x, y) => x + y);
const vectorMag = (v) => Math.sqrt(vectorDot(v, v));

// Angle Math
const rad2deg = 180 / Math.PI;

// Contrast
const getContrastingTextColor = (hex) => {
  const { r, g, b } = d3.color(hex);
  return vectorDot([r, g, b], [0.3, 0.6, 0.1]) >= 128 ? "#222" : "#ddd";
};