add waterways to relation using scripting plugin

waterways2relations.js

import josm from "josm";
import { RelationBuilder } from "josm/builder";

const byName = {};

const ds = josm.layers.activeLayer.getDataSet();

const ways = ds.getWays();

for (const way of ways) {
  if (way.hasKey("waterway")) {
    const name = way.get("name");

    let ways = byName[name];

    if (!ways) {
      ways = byName[name] = new Set();
    }

    ways.add(way);
  }
}

for (const name in byName) {
  josm.console.println(name);

  const ways = byName[name];

  while (ways.size) {
    const [way] = ways;

    const collected = [way];

    ways.delete(way);

    collect(collected, ways, way);

    if (collected.length > 1) {
      const tags = { type: "waterway" };

      for (const w of collected) {
        const waterway = w.get("waterway");

        if (
          (tags.waterway !== "stream" && tags.waterway !== "river") ||
          waterway == "river"
        ) {
          tags.waterway = waterway;
        }

        for (const tagname of w.keySet()) {
          if (
            tagname.includes("_name") ||
            tagname == "name" ||
            tagname.startsWith("name:")
          ) {
            tags[tagname] = w.get(tagname);
          }
        }
      }

      josm.console.println(Object.keys(tags));

      const rb = new RelationBuilder(ds);

      rb.withTags(tags).withMembers(collected).create();
    }
  }
}

function collect(collected, ways, way1) {
  const newCollected = [];

  for (const way2 of ways) {
    const nodeIds = new Set(way2.getNodeIds());

    if ([...way1.getNodeIds()].some((n) => nodeIds.has(n))) {
      newCollected.push(way2);
    }
  }

  for (const w of newCollected) {
    ways.delete(w);
  }

  for (const w of newCollected) {
    collect(collected, ways, w);
  }

  collected.push(...newCollected);
}