band.js

import {range as sequence} from "d3-array";
import ordinal from "./ordinal";

export default function band() {
  var scale = ordinal().unknown(undefined),
      domain = scale.domain,
      ordinalRange = scale.range,
      range = [0, 1],
      step,
      bandwidth,
      round = false,
      paddingInner = 0,
      paddingOuter = 0,
      align = 0.5;

  delete scale.unknown;

  function rescale() {
    var n = domain().length,
        reverse = range[1] < range[0],
        start = range[reverse - 0],
        stop = range[1 - reverse];
    step = (stop - start) / Math.max(1, n - paddingInner + paddingOuter * 2);
    if (round) step = Math.floor(step);
    start += (stop - start - step * (n - paddingInner)) * align;
    bandwidth = step * (1 - paddingInner);
    if (round) start = Math.round(start), bandwidth = Math.round(bandwidth);
    var values = sequence(n).map(function(i) { return start + step * i; });
    return ordinalRange(reverse ? values.reverse() : values);
  }

  scale.domain = function(_) {
    return arguments.length ? (domain(_), rescale()) : domain();
  };

  scale.range = function(_) {
    return arguments.length ? (range = [+_[0], +_[1]], rescale()) : range.slice();
  };

  scale.rangeRound = function(_) {
    return range = [+_[0], +_[1]], round = true, rescale();
  };

  scale.bandwidth = function() {
    return bandwidth;
  };

  scale.step = function() {
    return step;
  };

  scale.round = function(_) {
    return arguments.length ? (round = !!_, rescale()) : round;
  };

  scale.padding = function(_) {
    return arguments.length ? (paddingInner = paddingOuter = Math.max(0, Math.min(1, _)), rescale()) : paddingInner;
  };

  scale.paddingInner = function(_) {
    return arguments.length ? (paddingInner = Math.max(0, Math.min(1, _)), rescale()) : paddingInner;
  };

  scale.paddingOuter = function(_) {
    return arguments.length ? (paddingOuter = Math.max(0, Math.min(1, _)), rescale()) : paddingOuter;
  };

  scale.align = function(_) {
    return arguments.length ? (align = Math.max(0, Math.min(1, _)), rescale()) : align;
  };

  scale.copy = function() {
    return band()
        .domain(domain())
        .range(range)
        .round(round)
        .paddingInner(paddingInner)
        .paddingOuter(paddingOuter)
        .align(align);
  };

  return rescale();
}

function pointish(scale) {
  var copy = scale.copy;

  scale.padding = scale.paddingOuter;
  delete scale.paddingInner;
  delete scale.paddingOuter;

  scale.copy = function() {
    return pointish(copy());
  };

  return scale;
}

export function point() {
  return pointish(band().paddingInner(1));
}