RavelLaw/e3

const {abs, ceil, floor, pow, log, LN10} = Math;

export default function e3Ticks(domain, ticks) {
  if(domain) {
    return linearTickRange(domain, ticks);
  } else {
    return [];
  }
}

function linearTickRange(extent, m = 10) {
  let span = extent[1] - extent[0],
      step = pow(10, floor(log(span / m) / LN10)),
      err = m / span * step;

  // Filter ticks to get closer to the desired count.
  if (err <= 0.15) {
    step *= 10;
  } else if (err <= 0.35) {
    step *= 5;
  } else if (err <= 0.75) {
    step *= 2;
  }

  // Round start and stop values to step interval.
  return range(ceil(extent[0] / step) * step, floor(extent[1] / step) * step + step * 0.5, step);
}

function range(start, stop, step) {
  if (arguments.length < 3) {
    step = 1;
    if (arguments.length < 2) {
      stop = start;
      start = 0;
    }
  }
  if ((stop - start) / step === Infinity) {
    throw new Error("infinite range");
  }

  let usedRage = [], k = integerScale(abs(step)), i = -1, j;

  start *= k;
  stop *= k;
  step *= k;

  if (step < 0) {
    while ((j = start + step * ++i) > stop) {
      usedRage.push(j / k);
    }
  } else {
    while ((j = start + step * ++i) < stop) {
      usedRage.push(j / k);
    }
  }
  return usedRage;
}

function integerScale(x) {
  let k = 1;
  while (x * k % 1) {
    k *= 10;
  }
  return k;
}