const geomSdf = await import("@thi.ng/geom-sdf");

import { asSvg, bounds, circle, group, svgDoc } from "@thi.ng/geom";
import { asPolygons, asSDF, sample2d } from "@thi.ng/geom-sdf";
import { range, repeatedly } from "@thi.ng/transducers";
import { randMinMax2 } from "@thi.ng/vectors";
import { writeFileSync } from "fs";

const RES = [256, 256];

// create a group of 20 random circle shapes
// the special `__sdf` attrib object is used to control the conversion later
// the `smooth` option will combine the circles using the `smoothUnion()` operator
// see: https://docs.thi.ng/umbrella/geom-sdf/interfaces/SDFAttribs.html
const scene = group({ stroke: "red", __sdf: { smooth: 20 } }, [
    ...repeatedly(
        () =>
            circle(
                randMinMax2([], [-100, -100], [100, 100]),
                5 + Math.random() * 15
            ),
        20
    ),
]);

// compute bounding box + some extra margin
// the extra margin is to ensure the SDF can be fully sampled
// at some distance from the original boundary (see further below)
const sceneBounds = bounds(scene, 40);

// convert to an SDF distance function
// more information about supported shape types:
// https://docs.thi.ng/umbrella/geom-sdf/functions/asSDF.html
const sdf = asSDF(scene);

// sample SDF in given bounding rect and resolution
const image = sample2d(sdf, sceneBounds, RES);

// extract contour polygons from given image
// in this case the contours extracted are at distances in the [0..32) interval
// the function also simplifies the resulting polygons using the Douglas-Peucker algorithm
// with the given threshold (0.25) - the default setting only removes co-linear vertices...
// see: https://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm
const contours = asPolygons(image, sceneBounds, RES, range(0, 32, 4), 0.25);

// convert to SVG and output as file
writeFileSync(
    "export/metaballs.svg",
    asSvg(
        svgDoc(
            { fill: "none" },
            // contour polygons
            group({ stroke: "#000" }, contours),
            // original geometry
            scene
        )
    )
);