distribute.js

import _ from 'lodash';

_.mixin({
  splitOn: (array, needSplit) => {
    function splitting(chunks, current) {
      const [init, last] = [_.initial(chunks) || [], _.last(chunks) || []];
      const previous = _.last(last);
      return needSplit(current, previous) ? [ ...chunks, [current] ] : [ ...init, [ ...last, current ] ];
    }

    return _.isEmpty(array) ? [] : _.reduce(_.tail(array), splitting, [ [ _.first(array) ] ]);
  }
});

export function distribute(points, locator) {
  function spread(clump) {
    const size = _.sumBy(clump, 'size');
    const middle = (_.first(clump)[locator] + _.last(clump)[locator]) / 2;
    const locating = ({ distributed, edge }, item) => ({
        distributed: [...distributed, { ...item, [locator]: edge + item.size / 2} ],
        edge: edge + item.size
    });
    const { distributed } = _.reduce(clump, locating, { distributed: [], edge: middle - size / 2 });
    return { items: distributed, size, [locator]: middle };
  }

  function iterate(clumps) {
    const needsRedistribution = _.some(clumps, clump => clump.length > 1);
    return needsRedistribution ? iterate(_.map(clumps, spread)) : _.chain(clumps).map('items').flatten().value();
  }

  const hasSpareSpace = (left, right) => (left[locator] - left.size / 2) - (right[locator] + right.size / 2) >= 0;
  const clumps = _.chain(points).sortBy(locator).splitOn(hasSpareSpace).map(spread).value();
  return iterate(clumps);
}