/**
 * Calculate tick step.
 * Implementation from d3-array (ticks.js)
 * https://github.com/d3/d3-array/blob/master/src/ticks.js
 * @param start Start value
 * @param stop End value
 * @param count Ticks count
 */
export function tickStep(start: number, stop: number, count: number): number {
  let e10 = Math.sqrt(50),
    e5 = Math.sqrt(10),
    e2 = Math.sqrt(2);

  let step0 = Math.abs(stop - start) / Math.max(0, count),
    step1 = Math.pow(10, Math.floor(Math.log(step0) / Math.LN10)),
    error = step0 / step1;

  if (error >= e10) {
    step1 *= 10;
  } else if (error >= e5) {
    step1 *= 5;
  } else if (error >= e2) {
    step1 *= 2;
  }

  return stop < start ? -step1 : step1;
}