import { feature } from "topojson-client";
// 110m (not 50m) resolution - coastline detail beyond this isn't visible on
// a full-globe kiosk view, and it's 7x smaller to fetch/parse (108KB vs
// 756KB).
import worldTopology from "world-atlas/countries-110m.json";
import { countryMetaByCcn3, ALASKA_REGION_ID } from "./countryMeta";

// Ported from globe-proto/src/lib/countryPolygons.ts.
let cached = null;

/**
 * Converts the world-atlas topology into GeoJSON country features (once,
 * then cached in-module), decorated with the metadata (name/cca3/continent)
 * countryMeta.js knows for each ccn3 - consumed by InteractiveGlobe's polygon
 * layer. Also splits out French Guiana (from France's MultiPolygon) and
 * Alaska (from the USA's) into their own features, see the inline comments
 * below, so they can be colored independently via countryColors.js.
 *
 * @returns {Array<Object>} GeoJSON Feature objects, each with `properties:
 *   {ccn3, name, cca3, continent}`.
 */
export function loadCountryPolygons() {
  if (cached) return cached;

  const collection = feature(worldTopology, worldTopology.objects.countries);

  cached = collection.features.flatMap((f) => {
    // A handful of territories (Kosovo, Somaliland, N. Cyprus, ...) ship
    // without an ISO numeric id in this topology; fall back to a name-based
    // key so they don't all collapse onto the same "undefined" identity.
    const ccn3 = f.id !== undefined ? String(f.id) : `unclassified-${f.properties.name}`;

    // world-atlas bakes French Guiana into France's MultiPolygon as an extra
    // ring (coordinates[0], with mainland France and Corsica following)
    // instead of giving it its own topology feature - Natural Earth treats
    // it as French territory, not a separate country. Left alone, its South
    // American landmass would render and color as Europe/"France". Split it
    // into its own feature so continent-based coloring is accurate.
    if (ccn3 === "250" && f.geometry.type === "MultiPolygon") {
      const [guianaRing, ...metropolitanRings] = f.geometry.coordinates;
      const guianaMeta = countryMetaByCcn3("254");
      const franceMeta = countryMetaByCcn3(ccn3);
      return [
        {
          ...f,
          id: "254",
          geometry: { type: "Polygon", coordinates: guianaRing },
          properties: {
            ccn3: "254",
            name: guianaMeta?.commonName ?? "French Guiana",
            cca3: guianaMeta?.cca3 ?? null,
            continent: guianaMeta?.continent ?? null,
          },
        },
        {
          ...f,
          geometry: { type: "MultiPolygon", coordinates: metropolitanRings },
          properties: {
            ccn3,
            name: franceMeta?.commonName ?? f.properties.name,
            cca3: franceMeta?.cca3 ?? null,
            continent: franceMeta?.continent ?? null,
          },
        },
      ];
    }

    // The USA MultiPolygon bundles its states into one set of coordinates
    // with no per-state breakdown - rings 6/7/8/9 are (respectively) St.
    // Lawrence Island, Kodiak Island, the Alaska mainland+Aleutians and a
    // Seward Peninsula islet, identified by inspecting their bounding boxes
    // (ring 0 is CONUS, rings 1-5 are Hawaii). Splitting these out under
    // ALASKA_REGION_ID lets countryDisplay color Alaska independently of the
    // rest of the country instead of it always following the US's color.
    if (ccn3 === "840" && f.geometry.type === "MultiPolygon") {
      const alaskaRingIndices = new Set([6, 7, 8, 9]);
      const alaskaRings = f.geometry.coordinates.filter((_, i) => alaskaRingIndices.has(i));
      const usRings = f.geometry.coordinates.filter((_, i) => !alaskaRingIndices.has(i));
      const usMeta = countryMetaByCcn3(ccn3);
      return [
        {
          ...f,
          id: ALASKA_REGION_ID,
          geometry: { type: "MultiPolygon", coordinates: alaskaRings },
          properties: {
            ccn3: ALASKA_REGION_ID,
            name: "Alaska",
            cca3: null,
            continent: usMeta?.continent ?? null,
          },
        },
        {
          ...f,
          geometry: { type: "MultiPolygon", coordinates: usRings },
          properties: {
            ccn3,
            name: usMeta?.commonName ?? f.properties.name,
            cca3: usMeta?.cca3 ?? null,
            continent: usMeta?.continent ?? null,
          },
        },
      ];
    }

    const meta = countryMetaByCcn3(ccn3);
    return [
      {
        ...f,
        properties: {
          ccn3,
          name: meta?.commonName ?? f.properties.name,
          cca3: meta?.cca3 ?? null,
          continent: meta?.continent ?? null,
        },
      },
    ];
  });

  return cached;
}