source: node_modules/d3-hierarchy/src/stratify.js@ e4c61dd

import {optional} from "./accessors.js";
import {Node, computeHeight} from "./hierarchy/index.js";

var preroot = {depth: -1},
    ambiguous = {},
    imputed = {};

function defaultId(d) {
  return d.id;
}

function defaultParentId(d) {
  return d.parentId;
}

export default function() {
  var id = defaultId,
      parentId = defaultParentId,
      path;

  function stratify(data) {
    var nodes = Array.from(data),
        currentId = id,
        currentParentId = parentId,
        n,
        d,
        i,
        root,
        parent,
        node,
        nodeId,
        nodeKey,
        nodeByKey = new Map;

    if (path != null) {
      const I = nodes.map((d, i) => normalize(path(d, i, data)));
      const P = I.map(parentof);
      const S = new Set(I).add("");
      for (const i of P) {
        if (!S.has(i)) {
          S.add(i);
          I.push(i);
          P.push(parentof(i));
          nodes.push(imputed);
        }
      }
      currentId = (_, i) => I[i];
      currentParentId = (_, i) => P[i];
    }

    for (i = 0, n = nodes.length; i < n; ++i) {
      d = nodes[i], node = nodes[i] = new Node(d);
      if ((nodeId = currentId(d, i, data)) != null && (nodeId += "")) {
        nodeKey = node.id = nodeId;
        nodeByKey.set(nodeKey, nodeByKey.has(nodeKey) ? ambiguous : node);
      }
      if ((nodeId = currentParentId(d, i, data)) != null && (nodeId += "")) {
        node.parent = nodeId;
      }
    }

    for (i = 0; i < n; ++i) {
      node = nodes[i];
      if (nodeId = node.parent) {
        parent = nodeByKey.get(nodeId);
        if (!parent) throw new Error("missing: " + nodeId);
        if (parent === ambiguous) throw new Error("ambiguous: " + nodeId);
        if (parent.children) parent.children.push(node);
        else parent.children = [node];
        node.parent = parent;
      } else {
        if (root) throw new Error("multiple roots");
        root = node;
      }
    }

    if (!root) throw new Error("no root");

    // When imputing internal nodes, only introduce roots if needed.
    // Then replace the imputed marker data with null.
    if (path != null) {
      while (root.data === imputed && root.children.length === 1) {
        root = root.children[0], --n;
      }
      for (let i = nodes.length - 1; i >= 0; --i) {
        node = nodes[i];
        if (node.data !== imputed) break;
        node.data = null;
      }
    }

    root.parent = preroot;
    root.eachBefore(function(node) { node.depth = node.parent.depth + 1; --n; }).eachBefore(computeHeight);
    root.parent = null;
    if (n > 0) throw new Error("cycle");

    return root;
  }

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

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

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

  return stratify;
}

// To normalize a path, we coerce to a string, strip the trailing slash if any
// (as long as the trailing slash is not immediately preceded by another slash),
// and add leading slash if missing.
function normalize(path) {
  path = `${path}`;
  let i = path.length;
  if (slash(path, i - 1) && !slash(path, i - 2)) path = path.slice(0, -1);
  return path[0] === "/" ? path : `/${path}`;
}

// Walk backwards to find the first slash that is not the leading slash, e.g.:
// "/foo/bar" ⇥ "/foo", "/foo" ⇥ "/", "/" ↦ "". (The root is special-cased
// because the id of the root must be a truthy value.)
function parentof(path) {
  let i = path.length;
  if (i < 2) return "";
  while (--i > 1) if (slash(path, i)) break;
  return path.slice(0, i);
}

// Slashes can be escaped; to determine whether a slash is a path delimiter, we
// count the number of preceding backslashes escaping the forward slash: an odd
// number indicates an escaped forward slash.
function slash(path, i) {
  if (path[i] === "/") {
    let k = 0;
    while (i > 0 && path[--i] === "\\") ++k;
    if ((k & 1) === 0) return true;
  }
  return false;
}