mesh.js

import {object} from "./feature.js";
import stitch from "./stitch.js";

export default function(topology) {
  return object(topology, meshArcs.apply(this, arguments));
}

export function meshArcs(topology, object, filter) {
  var arcs, i, n;
  if (arguments.length > 1) arcs = extractArcs(topology, object, filter);
  else for (i = 0, arcs = new Array(n = topology.arcs.length); i < n; ++i) arcs[i] = i;
  return {type: "MultiLineString", arcs: stitch(topology, arcs)};
}

function extractArcs(topology, object, filter) {
  var arcs = [],
      geomsByArc = [],
      geom;

  function extract0(i) {
    var j = i < 0 ? ~i : i;
    (geomsByArc[j] || (geomsByArc[j] = [])).push({i: i, g: geom});
  }

  function extract1(arcs) {
    arcs.forEach(extract0);
  }

  function extract2(arcs) {
    arcs.forEach(extract1);
  }

  function extract3(arcs) {
    arcs.forEach(extract2);
  }

  function geometry(o) {
    switch (geom = o, o.type) {
      case "GeometryCollection": o.geometries.forEach(geometry); break;
      case "LineString": extract1(o.arcs); break;
      case "MultiLineString": case "Polygon": extract2(o.arcs); break;
      case "MultiPolygon": extract3(o.arcs); break;
    }
  }

  geometry(object);

  geomsByArc.forEach(filter == null
      ? function(geoms) { arcs.push(geoms[0].i); }
      : function(geoms) { if (filter(geoms[0].g, geoms[geoms.length - 1].g)) arcs.push(geoms[0].i); });

  return arcs;
}