import { geoEqualEarth, geoPath, type GeoPermissibleObjects, type GeoProjection } from 'd3-geo';
import { feature } from 'topojson-client';
import type { Topology, GeometryCollection } from 'topojson-specification';
import type { Feature, FeatureCollection, Geometry } from 'geojson';
import world from 'world-atlas/countries-110m.json';
import { atlasGeometryIso3 } from './iso-numeric';

/**
 * World geometry for the Choropleth: world-atlas 110m TopoJSON → Equal Earth projected SVG paths keyed by
 * ISO3. Computed once per server process (module scope); ≈ 90 KB of path data shipped to the client view.
 * The numeric → alpha-3 lookup prefers the API's `iso_numeric` (registry) and falls back to the static table.
 */
export const MAP_WIDTH = 960;
export const MAP_HEIGHT = 470;

export interface CountryPath {
  iso3: string | null;
  /** ISO numeric id from the TopoJSON (3 digits) when present. */
  numeric: string | null;
  name: string;
  d: string;
}

type CountriesTopology = Topology<{ countries: GeometryCollection<{ name: string }> }>;

function fitProjection(width: number, height: number, pad = 4): GeoProjection {
  return geoEqualEarth().fitExtent(
    [
      [pad, pad],
      [width - pad, height - pad],
    ],
    { type: 'Sphere' } as GeoPermissibleObjects,
  );
}

let cache: { paths: CountryPath[]; sphere: string } | null = null;

export function worldPaths(): { paths: CountryPath[]; sphere: string } {
  if (cache) return cache;
  const topology = world as unknown as CountriesTopology;
  const fc = feature(topology, topology.objects.countries) as FeatureCollection<Geometry, { name: string }>;
  const projection = fitProjection(MAP_WIDTH, MAP_HEIGHT);
  const path = geoPath(projection).digits(1);
  const paths: CountryPath[] = [];
  for (const f of fc.features as Array<Feature<Geometry, { name: string }>>) {
    if (f.id === '010') continue; // Antarctica: no data, dominates the lower band
    const d = path(f);
    if (!d) continue;
    const numeric = f.id != null && f.id !== '' ? String(f.id).padStart(3, '0') : null;
    paths.push({ iso3: atlasGeometryIso3(f.id as string | number | undefined, f.properties?.name), numeric, name: f.properties?.name ?? '', d });
  }
  const sphere = path({ type: 'Sphere' }) ?? '';
  cache = { paths, sphere };
  return cache;
}

/** Re-key a path's ISO3 using the registry's iso_numeric when available (API `/countries` → iso_numeric). */
export function isoLookupFromCountries(countries: Array<{ id: string; iso_numeric?: string | null }>): Map<string, string> {
  const m = new Map<string, string>();
  for (const c of countries) if (c.iso_numeric) m.set(String(c.iso_numeric).padStart(3, '0'), c.id);
  return m;
}

/** Class index 0..k for a value against sorted quantile breaks (k = breaks.length). */
export function classIndex(value: number, breaks: number[]): number {
  let i = 0;
  while (i < breaks.length && value >= breaks[i]!) i++;
  return i;
}