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import {object} from "./feature.js";
import stitch from "./stitch.js";
function planarRingArea(ring) {
var i = -1, n = ring.length, a, b = ring[n - 1], area = 0;
while (++i < n) a = b, b = ring[i], area += a[0] * b[1] - a[1] * b[0];
return Math.abs(area); // Note: doubled area!
}
export default function(topology) {
return object(topology, mergeArcs.apply(this, arguments));
}
export function mergeArcs(topology, objects) {
var polygonsByArc = {},
polygons = [],
groups = [];
objects.forEach(geometry);
function geometry(o) {
switch (o.type) {
case "GeometryCollection": o.geometries.forEach(geometry); break;
case "Polygon": extract(o.arcs); break;
case "MultiPolygon": o.arcs.forEach(extract); break;
}
}
function extract(polygon) {
polygon.forEach(function(ring) {
ring.forEach(function(arc) {
(polygonsByArc[arc = arc < 0 ? ~arc : arc] || (polygonsByArc[arc] = [])).push(polygon);
});
});
polygons.push(polygon);
}
function area(ring) {
return planarRingArea(object(topology, {type: "Polygon", arcs: [ring]}).coordinates[0]);
}
polygons.forEach(function(polygon) {
if (!polygon._) {
var group = [],
neighbors = [polygon];
polygon._ = 1;
groups.push(group);
while (polygon = neighbors.pop()) {
group.push(polygon);
polygon.forEach(function(ring) {
ring.forEach(function(arc) {
polygonsByArc[arc < 0 ? ~arc : arc].forEach(function(polygon) {
if (!polygon._) {
polygon._ = 1;
neighbors.push(polygon);
}
});
});
});
}
}
});
polygons.forEach(function(polygon) {
delete polygon._;
});
return {
type: "MultiPolygon",
arcs: groups.map(function(polygons) {
var arcs = [], n;
// Extract the exterior (unique) arcs.
polygons.forEach(function(polygon) {
polygon.forEach(function(ring) {
ring.forEach(function(arc) {
if (polygonsByArc[arc < 0 ? ~arc : arc].length < 2) {
arcs.push(arc);
}
});
});
});
// Stitch the arcs into one or more rings.
arcs = stitch(topology, arcs);
// If more than one ring is returned,
// at most one of these rings can be the exterior;
// choose the one with the greatest absolute area.
if ((n = arcs.length) > 1) {
for (var i = 1, k = area(arcs[0]), ki, t; i < n; ++i) {
if ((ki = area(arcs[i])) > k) {
t = arcs[0], arcs[0] = arcs[i], arcs[i] = t, k = ki;
}
}
}
return arcs;
}).filter(function(arcs) {
return arcs.length > 0;
})
};
}