source: node_modules/d3-hierarchy/src/pack/index.js

import {optional} from "../accessors.js";
import constant, {constantZero} from "../constant.js";
import lcg from "../lcg.js";
import {packSiblingsRandom} from "./siblings.js";

function defaultRadius(d) {
  return Math.sqrt(d.value);
}

export default function() {
  var radius = null,
      dx = 1,
      dy = 1,
      padding = constantZero;

  function pack(root) {
    const random = lcg();
    root.x = dx / 2, root.y = dy / 2;
    if (radius) {
      root.eachBefore(radiusLeaf(radius))
          .eachAfter(packChildrenRandom(padding, 0.5, random))
          .eachBefore(translateChild(1));
    } else {
      root.eachBefore(radiusLeaf(defaultRadius))
          .eachAfter(packChildrenRandom(constantZero, 1, random))
          .eachAfter(packChildrenRandom(padding, root.r / Math.min(dx, dy), random))
          .eachBefore(translateChild(Math.min(dx, dy) / (2 * root.r)));
    }
    return root;
  }

  pack.radius = function(x) {
    return arguments.length ? (radius = optional(x), pack) : radius;
  };

  pack.size = function(x) {
    return arguments.length ? (dx = +x[0], dy = +x[1], pack) : [dx, dy];
  };

  pack.padding = function(x) {
    return arguments.length ? (padding = typeof x === "function" ? x : constant(+x), pack) : padding;
  };

  return pack;
}

function radiusLeaf(radius) {
  return function(node) {
    if (!node.children) {
      node.r = Math.max(0, +radius(node) || 0);
    }
  };
}

function packChildrenRandom(padding, k, random) {
  return function(node) {
    if (children = node.children) {
      var children,
          i,
          n = children.length,
          r = padding(node) * k || 0,
          e;

      if (r) for (i = 0; i < n; ++i) children[i].r += r;
      e = packSiblingsRandom(children, random);
      if (r) for (i = 0; i < n; ++i) children[i].r -= r;
      node.r = e + r;
    }
  };
}

function translateChild(k) {
  return function(node) {
    var parent = node.parent;
    node.r *= k;
    if (parent) {
      node.x = parent.x + k * node.x;
      node.y = parent.y + k * node.y;
    }
  };
}