star-map/tools/etl/build.ts

import { statSync } from 'node:fs';

import { BodyRecord, OrbitalElements } from '../../src/app/shared/models/body.model';
import { eclipticToEquatorial, laplacePlaneToEquatorial, raDecToUnitVector } from '../../src/app/shared/astro/coordinates';
import { meanElementsAt, positionAtEpoch } from '../../src/app/shared/astro/kepler';
import { orientationAt } from '../../src/app/shared/astro/rotational-elements';
import { DeepSkyRecord } from '../../src/app/shared/models/deepsky.model';
import { ExoplanetRecord } from '../../src/app/shared/models/exoplanet.model';
import { StarRecord, SUN_STAR_ID } from '../../src/app/shared/models/star.model';
import { fetchDeepSky } from './fetchDeepSky';
import { fetchExoplanets } from './fetchExoplanets';
import { fetchSolarSystem, FREELY_SPINNING_MOONS } from './fetchSolarSystem';
import { BYTES_PER_STAR_META, BYTES_PER_STAR_POSITION, decodeStarCatalog, encodeStarCatalog } from '../../src/app/shared/models/star-catalog';
import { fetchStars } from './fetchStars';
import { describeSources } from './sources/registry';
import { dataPath } from './lib/paths';

class ValidationError extends Error {}

function assertCondition(condition: boolean, message: string): void {
  if (!condition) {
    throw new ValidationError(message);
  }
}

function validateStars(stars: StarRecord[]): void {
  assertCondition(stars.length > 0, 'No stars were produced.');

  const ids = new Set<number>();
  for (const star of stars) {
    assertCondition(Number.isFinite(star.id), `Star has a non-numeric id: ${JSON.stringify(star)}`);
    assertCondition(!ids.has(star.id), `Duplicate star id: ${star.id}`);
    ids.add(star.id);
    assertCondition(!!star.name, `Star ${star.id} has no name.`);
    assertCondition([star.x, star.y, star.z].every(Number.isFinite), `Star ${star.id} has a non-finite position.`);
  }

  const positionBytes = statSync(dataPath('stars.bin')).size;
  assertCondition(positionBytes === stars.length * BYTES_PER_STAR_POSITION, `stars.bin size (${positionBytes}) does not match ${stars.length} stars.`);
  const metaBytes = statSync(dataPath('stars-meta.bin')).size;
  assertCondition(metaBytes === stars.length * BYTES_PER_STAR_META, `stars-meta.bin size (${metaBytes}) does not match ${stars.length} stars.`);

  // Round-trips the written assets back through the decoder the app uses, so a format change
  // that only half-lands fails here rather than as a silently wrong star map.
  const { index, positions, meta } = encodeStarCatalog(stars);
  const decoded = decodeStarCatalog(index, positions, meta);
  assertCondition(decoded.length === stars.length, `Star catalogue round-trip lost records: ${decoded.length} of ${stars.length}.`);
  for (let i = 0; i < stars.length; i++) {
    assertCondition(decoded[i].id === stars[i].id && decoded[i].name === stars[i].name, `Star catalogue round-trip altered record ${i}.`);
    assertCondition(decoded[i].spectralType === stars[i].spectralType, `Star catalogue round-trip lost the spectral type of star ${stars[i].id}.`);
    assertCondition(decoded[i].colorIndex === null === (stars[i].colorIndex === null), `Star catalogue round-trip changed whether star ${stars[i].id} has a colour index.`);
  }
}

/**
 * What a good merge looks like, in two numbers the unit suite cannot see.
 *
 * The catalogues are regenerated by a scheduled job that pushes straight to `main` once the unit
 * tests and a production build pass — and both passed, for weeks, on a catalogue carrying 23 000
 * stars twice: the suite tests code against fixtures, and no fixture is 400 000 real stars. The
 * two ways the merge has actually failed both show up here.
 *
 * A star kept twice leaves its two entries near each other on the sky, from *different* sources —
 * one catalogue does not list a star twice. Under an arcsecond that is never two stars at this
 * depth, so every such pair is a miss. Nineteen survive today, all of them a second HYG row
 * wanting a Gaia entry that already absorbed one (Gliese lists some doubles twice); the merge
 * that trusted a Hipparcos parallax over direction left 1 112.
 *
 * The other failure leaves no close pair at all, because proper motion had already carried the
 * two entries tens of arcseconds apart — the 2026-08-24 refresh, where HYG sat at epoch 2000.0
 * and Gaia at J2016.0. What it does leave is HYG rows that found no counterpart: 36 056 of them
 * against the 10 886 today, and no counterpart was possible for most of those. Two thirds of them,
 * 6 835, are the stars Gaia measures but the main query never downloads, because Gaia's parallax
 * puts them past `ETL_GAIA_DISTANCE_PC` while Hipparcos put them inside `ETL_STAR_DISTANCE_PC`;
 * they are every star in the published catalogue beyond 250 pc. The rest are what Gaia genuinely
 * lacks: bright stars it saturates on, red dwarfs past its magnitude cut. So the headroom left to
 * the ceiling tracks the gap between those two cutoffs as much as Gaia's completeness.
 *
 * This bounds a merge that went wrong, and — loosely — a Gaia download that came back short: a
 * truncated answer leaves the HYG rows whose counterpart it dropped without one, so survivors go
 * *up*, not down. Measured against the published catalogue: 10 886 today, 11 004 at nine tenths of
 * the rows, 12 711 at half, 16 258 at a third. So this ceiling only catches a truncation past about
 * two thirds, and `fetchGaiaStars` catches the shallower ones with its own row floor.
 */
const MAX_UNMERGED_TWINS = 100;
const MAX_HYG_SURVIVORS = 15_000;
const TWIN_TOLERANCE_RAD = (1 / 3600) * (Math.PI / 180);

function validateMerge(stars: StarRecord[]): void {
  // Checked first and on its own: an unreachable Gaia is skipped rather than thrown, and would
  // otherwise surface below as "68 000 HYG stars found no counterpart" — true, and no help.
  assertCondition(
    stars.some((star) => star.source === 'gaia'),
    'Gaia DR3 contributed no stars — the archive was unreachable or returned nothing, and a catalogue without it is not one to publish.'
  );
  const survivors = stars.filter((star) => star.source === 'hyg').length;
  assertCondition(
    survivors <= MAX_HYG_SURVIVORS,
    `${survivors} HYG stars found no Gaia counterpart (at most ${MAX_HYG_SURVIVORS} expected) — the two catalogues are not being matched.`
  );

  // Sorted by declination, so each star is only compared against the handful sharing its
  // parallel — an arcsecond of declination holds one or two of 400 000 stars.
  const byDec = stars
    .map((star) => {
      const distance = Math.hypot(star.x, star.y, star.z);
      return { star, distance, dec: distance === 0 ? 0 : Math.asin(Math.max(-1, Math.min(1, star.z / distance))) };
    })
    .filter((entry) => entry.distance > 0)
    .sort((a, b) => a.dec - b.dec);

  const cosTolerance = Math.cos(TWIN_TOLERANCE_RAD);
  let twins = 0;
  let example = '';
  for (let i = 0; i < byDec.length; i++) {
    const a = byDec[i];
    for (let j = i + 1; j < byDec.length && byDec[j].dec - a.dec <= TWIN_TOLERANCE_RAD; j++) {
      const b = byDec[j];
      if (a.star.source === b.star.source) {
        continue;
      }
      const cosine = (a.star.x * b.star.x + a.star.y * b.star.y + a.star.z * b.star.z) / (a.distance * b.distance);
      if (cosine >= cosTolerance) {
        twins++;
        example ||= `${a.star.name} (${a.star.source}) and ${b.star.name} (${b.star.source})`;
      }
    }
  }
  assertCondition(
    twins <= MAX_UNMERGED_TWINS,
    `${twins} stars from different catalogues sit within an arcsecond of each other (at most ${MAX_UNMERGED_TWINS} expected), starting with ${example} — the merge is keeping the same star twice.`
  );
  console.log(`  ${survivors} HYG stars have no Gaia counterpart; ${twins} unmerged cross-catalogue pairs within an arcsecond.`);
}

/**
 * How far a body's mean elements may put it from where Horizons has it, on the one date the ETL
 * asks Horizons about (2025-01-01), seen from the Sun for a planet and from its planet for a moon.
 *
 * Measured on this catalogue: the planets at most 0.10 degrees (Uranus; Standish's own stated
 * error for his fit is 2 000 arcseconds, 0.56 degrees), the moons at most 1.41 (the Moon, whose
 * evection and variation, 1.27 and 0.66 degrees, no mean ellipse has). What this catches is a
 * table read wrongly: a moon read against the ecliptic instead of its Laplace plane, a precession
 * run the wrong way, or a column taken for its neighbour, which put Triton 26 degrees out and Io
 * 0.9.
 */
const MAX_PLANET_OFFSET_DEG = 0.25;
const MAX_MOON_OFFSET_DEG = 2.5;
const KM_PER_AU = 149597870.7;
const DEG_TO_RAD = Math.PI / 180;

/**
 * The moons whose table row cannot come within that on this one date, each for a reason no mean
 * ellipse carries, with a ceiling just above its offset here. What each reaches elsewhere is
 * larger, and neither this check nor twelve New Year's Days sampled from 1980 to 2100 see it:
 *
 * - Hyperion, 9.4 degrees here and 22.2 at worst, sampled every other day from 1980 to 2100: held
 *   in a 4:3 resonance by Titan; the row's eccentricity, 0.0232, is less than a quarter of the
 *   0.105 JPL's current table gives.
 * - Iapetus, 9.6 here and 10.1 at worst: the row sits 9.4 degrees behind Horizons at its own epoch,
 *   2000 Jan 1.5, and keeps that offset; its plane agrees with Horizons' to 0.07 degrees and its
 *   period to 0.001 per cent, so the fault is in the row's longitude, which this has no second
 *   source to correct.
 * - Nereid, 2.6 here and 11.2 at worst, sampled daily: an eccentricity of 0.75, the largest here,
 *   which a mean ellipse follows least well near periapsis, where the true anomaly runs ten times
 *   faster than the mean. Its 360-day year put all twelve New Year's Days, under 2.6, far from
 *   periapsis; sampled daily it is past 2.6 on 92 days in 2010-2020 and on 295 in 2040-2050, each
 *   near a periapsis, and under 0.4 on most days.
 *
 * Mimas's swing of 44 degrees either way, the libration of its resonance with Tethys, which also
 * needed a ceiling here once, is now in its orbit; see `orbitFromW` in `fetchSolarSystem.ts`.
 */
const MOON_OFFSET_CEILINGS_DEG: Record<string, number> = { hyperion: 21, iapetus: 11, nereid: 3 };

/**
 * The bodies the IAU WGCCRE 2015 report gives no rotational elements for: Hyperion tumbles, and
 * Nereid, Eris, Haumea and Makemake have no model. Every other body must carry them, or the
 * kernel was read wrongly and the body would be drawn on an invented pole.
 */
const WITHOUT_ROTATIONAL_ELEMENTS = new Set(['hyperion', 'nereid', 'eris', 'haumea', 'makemake']);

/**
 * How far the IAU's day, 360 degrees over W's rate, may be from the one Horizons states, as a
 * fraction of it. Measured on this catalogue: at most 1.8e-5 (Jupiter's System III, 9.92492 hours
 * against 9.92510). Neptune is 0.89 per cent out, because the report takes 15.9663 hours from the
 * cloud features Karkoschka (2011) tracked, where Horizons keeps Voyager's radio period, 16.11. What
 * this catches is a rate read in the wrong unit or for the wrong body: Oberon's day for Titania's is
 * 55 per cent out.
 */
const MAX_DAY_OFFSET = 1e-4;
const DAY_OFFSET_CEILINGS: Record<string, number> = { neptune: 0.01 };

/**
 * How far the tilt of the IAU's spin axis from the orbit may be from the obliquity Horizons
 * states. The axis is the IAU's pole, turned end for end where W runs backwards: the report names
 * a planet's north pole by the side of the solar system it lies on, whichever way the planet turns.
 * Measured on this catalogue: at most 0.058 degrees (Venus, 177.358 against 177.3). Taken as the
 * pole alone, Venus comes out at 2.6 degrees and Uranus at 82.2, which is what this catches.
 */
const MAX_OBLIQUITY_OFFSET_DEG = 0.1;

/**
 * How far from its planet a locked moon's drawn face may turn: the east longitude, on the IAU's
 * body-fixed frame, of the direction to the planet from where the mean elements put the moon,
 * sampled every 135 days from 1950 to 2100, where both the tables and the IAU's elements hold.
 *
 * Measured on this catalogue: at most 6.70 degrees (the Moon, whose longitude swings 6.3 either
 * way with its eccentricity; Horizons has the same). Three need their own: Mimas 10.15, whose
 * physical libration W carries and Horizons shows as 5 to 9 degrees at its true place; Iapetus
 * 18.33, whose row sits 9.4 degrees behind Horizons; and Proteus 8.18, whose W turns 6.3e-7 of
 * its rate slower than its orbit, a drift of 74 degrees by AD 3000. What this catches is an orbit
 * and a W that go round at different rates: the tidal acceleration W carried and the orbit did not
 * turned Phobos 13.8 degrees from Mars by 2100, and the Mimas-Tethys libration Mimas 54.5.
 */
const MAX_SUB_PLANET_LONGITUDE_DEG = 7;
const SUB_PLANET_CEILINGS_DEG: Record<string, number> = { mimas: 11, iapetus: 19, proteus: 9 };
const LOCK_DATES_JD = Array.from({ length: 407 }, (_, index) => 2433282.5 + index * 135);

/** The planet's east longitude on a moon's IAU body-fixed frame, from the moon's mean place, at a TDB date. */
function subPlanetLongitudeDeg(body: BodyRecord, jd: number): number {
  const own = positionAtEpoch(meanElementsAt(body.orbit, body.rates, jd));
  const place = body.laplacePole ? laplacePlaneToEquatorial(own, body.laplacePole) : eclipticToEquatorial(own);
  const { poleRaDeg, poleDecDeg, primeMeridianDeg } = orientationAt(body.rotationalElements!, jd);
  const pole = { raDeg: poleRaDeg, decDeg: poleDecDeg };
  const w = primeMeridianDeg * DEG_TO_RAD;
  const meridian = laplacePlaneToEquatorial({ x: Math.cos(w), y: Math.sin(w), z: 0 }, pole);
  const east = laplacePlaneToEquatorial({ x: -Math.sin(w), y: Math.cos(w), z: 0 }, pole);
  const along = (axis: { x: number; y: number; z: number }) => -(place.x * axis.x + place.y * axis.y + place.z * axis.z);
  return Math.atan2(along(east), along(meridian)) / DEG_TO_RAD;
}

function angleBetweenDeg(a: { x: number; y: number; z: number }, b: { x: number; y: number; z: number }): number {
  const cosine = (a.x * b.x + a.y * b.y + a.z * b.z) / (Math.hypot(a.x, a.y, a.z) * Math.hypot(b.x, b.y, b.z));
  return (Math.acos(Math.min(1, Math.max(-1, cosine))) * 180) / Math.PI;
}

function validateBodies(bodies: BodyRecord[], horizonsOrbits: Map<string, OrbitalElements>): void {
  assertCondition(bodies.length > 0, 'No solar-system bodies were produced.');

  const ids = new Set(bodies.map((body) => body.id));
  assertCondition(ids.size === bodies.length, 'Duplicate body ids were found.');

  const offsets: string[] = [];
  const spins: string[] = [];
  for (const body of bodies) {
    const orbitValues = Object.values(body.orbit);
    assertCondition(orbitValues.every(Number.isFinite), `Body ${body.id} has non-finite orbital elements.`);
    assertCondition(body.rates.meanMotionDegPerDay > 0, `Body ${body.id} has no mean motion.`);

    // Horizons' elements are osculating, exact at their own epoch; both sets are placed there.
    const horizons = horizonsOrbits.get(body.id);
    assertCondition(horizons !== undefined, `Body ${body.id} has no Horizons elements to be checked against.`);
    const truth = eclipticToEquatorial(positionAtEpoch(horizons!));
    const mean = positionAtEpoch(meanElementsAt(body.orbit, body.rates, horizons!.epochJd));
    const offset = angleBetweenDeg(body.laplacePole ? laplacePlaneToEquatorial(mean, body.laplacePole) : eclipticToEquatorial(mean), truth);
    const ceiling = body.kind === 'moon' ? (MOON_OFFSET_CEILINGS_DEG[body.id] ?? MAX_MOON_OFFSET_DEG) : MAX_PLANET_OFFSET_DEG;
    assertCondition(
      offset <= ceiling,
      `${body.name}'s mean elements put it ${offset.toFixed(2)} degrees from where Horizons has it (at most ${ceiling} expected) — the elements were read wrongly.`
    );
    offsets.push(`${body.id} ${offset.toFixed(3)}`);

    // A radius of 0 is what a page whose radius no pattern reads comes out as — Charon's did.
    assertCondition(body.radiusKm > 0, `Body ${body.id} has no radius; its page states it in a form the ETL does not read.`);

    const rotation = body.rotationalElements;
    assertCondition(
      (rotation === undefined) === WITHOUT_ROTATIONAL_ELEMENTS.has(body.id),
      `Body ${body.id} ${rotation ? 'has' : 'has no'} IAU rotational elements, which the report ${rotation ? 'does not give' : 'gives'} for it.`
    );
    if (rotation) {
      const rate = rotation.primeMeridianDeg[1];
      if (body.rotationPeriodHours !== undefined) {
        const dayOffset = Math.abs(((360 / Math.abs(rate)) * 24) / Math.abs(body.rotationPeriodHours) - 1);
        const dayCeiling = DAY_OFFSET_CEILINGS[body.id] ?? MAX_DAY_OFFSET;
        assertCondition(
          dayOffset <= dayCeiling,
          `${body.name}'s IAU day, ${((360 / Math.abs(rate)) * 24).toFixed(5)} hours, is ${dayOffset.toExponential(2)} of its length from Horizons' ${Math.abs(body.rotationPeriodHours).toFixed(5)} (at most ${dayCeiling} expected).`
        );
        spins.push(`${body.id} day ${dayOffset.toExponential(1)}`);
      }
      if (body.obliquityDeg !== undefined) {
        const pole = orientationAt(rotation, horizons!.epochJd);
        const pointing = raDecToUnitVector(pole.poleRaDeg / 15, pole.poleDecDeg);
        const axis = { x: Math.sign(rate) * pointing.x, y: Math.sign(rate) * pointing.y, z: Math.sign(rate) * pointing.z };
        const { inclinationDeg, longitudeOfAscendingNodeDeg } = meanElementsAt(body.orbit, body.rates, horizons!.epochJd);
        const tilt = inclinationDeg * DEG_TO_RAD;
        const node = longitudeOfAscendingNodeDeg * DEG_TO_RAD;
        const normal = { x: Math.sin(tilt) * Math.sin(node), y: -Math.sin(tilt) * Math.cos(node), z: Math.cos(tilt) };
        const obliquity = angleBetweenDeg(axis, body.laplacePole ? laplacePlaneToEquatorial(normal, body.laplacePole) : eclipticToEquatorial(normal));
        assertCondition(
          Math.abs(obliquity - body.obliquityDeg) <= MAX_OBLIQUITY_OFFSET_DEG,
          `${body.name}'s IAU spin axis is ${obliquity.toFixed(3)} degrees from its orbit's pole, where Horizons gives an obliquity of ${body.obliquityDeg} (at most ${MAX_OBLIQUITY_OFFSET_DEG} apart expected) — the pole or the sense of W was read wrongly.`
        );
        spins.push(`${body.id} tilt ${obliquity.toFixed(3)}`);
      }
    }

    if (body.kind === 'moon') {
      const parent = bodies.find((candidate) => candidate.id === body.parentBodyId);
      assertCondition(parent !== undefined, `Moon ${body.id} has no valid parentBodyId.`);
      const orbitHours = (360 / body.rates.meanMotionDegPerDay) * 24;
      if (FREELY_SPINNING_MOONS.has(body.id)) {
        // Hyperion tumbles and Nereid's page gives no spin, so they have none; Phoebe turns in
        // 9.27 hours against a 550-day orbit. A lock here would be the rule below misapplied.
        assertCondition(
          body.rotationPeriodHours === undefined || Math.abs(body.rotationPeriodHours - orbitHours) > orbitHours * 0.1,
          `Moon ${body.id} does not keep one face to its planet, yet turns once in ${body.rotationPeriodHours} hours against an orbit of ${orbitHours}.`
        );
      } else {
        // Every other moon here is tidally locked, and drawn by its orbit and its IAU W: the two
        // have to agree, or its face turns away from its planet.
        assertCondition(rotation !== undefined, `Moon ${body.id} is locked but has no W to keep its face to its planet by.`);
        const ceiling = SUB_PLANET_CEILINGS_DEG[body.id] ?? MAX_SUB_PLANET_LONGITUDE_DEG;
        const worst = Math.max(...LOCK_DATES_JD.map((jd) => Math.abs(subPlanetLongitudeDeg(body, jd))));
        assertCondition(
          worst <= ceiling,
          `Moon ${body.id} turns its face up to ${worst.toFixed(2)} degrees from its planet between 1950 and 2100 (at most ${ceiling} expected) — its orbit and its W disagree.`
        );
        spins.push(`${body.id} faces ${worst.toFixed(2)}`);
      }
      if (body.massRatio !== undefined) {
        // The pair's barycentre, which the planet's elements place, must lie outside the planet —
        // that is why the two are drawn going round it — and nearer the planet than the moon.
        const offsetKm = (body.orbit.semiMajorAxisAu * KM_PER_AU * body.massRatio) / (1 + body.massRatio);
        assertCondition(
          body.massRatio > 0 && body.massRatio < 1 && offsetKm > parent!.radiusKm,
          `${body.name}'s mass ratio ${body.massRatio} puts its barycentre ${offsetKm.toFixed(0)} km from ${parent!.name}'s centre, which is not between its surface, ${parent!.radiusKm} km out, and the moon.`
        );
      }
    }
  }

  const planetCount = bodies.filter((body) => body.kind === 'planet').length;
  assertCondition(planetCount === 8, `Expected 8 planets, found ${planetCount}.`);
  const dwarfCount = bodies.filter((body) => body.kind === 'dwarf').length;
  assertCondition(dwarfCount === 5, `Expected the IAU's 5 dwarf planets, found ${dwarfCount}.`);
  console.log(`  mean elements against Horizons, degrees: ${offsets.join(', ')}.`);
  console.log(`  IAU rotation against Horizons (day as a fraction of it, tilt in degrees): ${spins.join(', ')}.`);
}

function validateExoplanets(exoplanets: ExoplanetRecord[], starIds: Set<number>): void {
  assertCondition(exoplanets.length > 0, 'No exoplanets were produced.');

  let crossReferenced = 0;
  for (const exoplanet of exoplanets) {
    assertCondition(!!exoplanet.name, `Exoplanet ${exoplanet.id} has no name.`);
    if (exoplanet.hostStarId !== null) {
      assertCondition(starIds.has(exoplanet.hostStarId), `Exoplanet ${exoplanet.id} references unknown star id ${exoplanet.hostStarId}.`);
      // The Sun has no exoplanets, so any match to it is a matching failure — historically a
      // blank distance column parsing as 0, which puts the host at the origin and matches Sol
      // exactly. Free, permanent tripwire for that whole class of bug.
      assertCondition(
        exoplanet.hostStarId !== SUN_STAR_ID,
        `Exoplanet ${exoplanet.id} was matched to the Sun, which has no exoplanets — the host-star match is wrong.`
      );
      crossReferenced++;
    }

    assertCondition(
      exoplanet.periodDays === undefined || exoplanet.periodDays > 0,
      `Exoplanet ${exoplanet.id} has a non-positive orbital period.`
    );
    assertCondition(
      exoplanet.hostStarMassSolar === undefined || exoplanet.hostStarMassSolar > 0,
      `Exoplanet ${exoplanet.id} has a non-positive host star mass.`
    );
  }

  console.log(`  ${crossReferenced}/${exoplanets.length} exoplanets cross-referenced to a HYG host star.`);

  // How many can be propagated at their real rate rather than as if the host were the Sun.
  const withPeriod = exoplanets.filter((exoplanet) => exoplanet.periodDays !== undefined).length;
  const withHostMass = exoplanets.filter((exoplanet) => exoplanet.hostStarMassSolar !== undefined).length;
  console.log(`  ${withPeriod}/${exoplanets.length} have a measured period, ${withHostMass} a host star mass.`);
}

const UNIT_VECTOR_TOLERANCE = 1e-6;

function validateDeepSky(objects: DeepSkyRecord[]): void {
  assertCondition(objects.length > 0, 'No deep-sky objects were produced.');

  const ids = new Set<string>();
  for (const object of objects) {
    assertCondition(!!object.id, `Deep-sky object has no id: ${JSON.stringify(object)}`);
    assertCondition(!ids.has(object.id), `Duplicate deep-sky id: ${object.id}`);
    ids.add(object.id);
    assertCondition(!!object.name, `Deep-sky object ${object.id} has no name.`);

    // Positions are directions, so every one of them must be a unit vector — a zero-length
    // or mis-scaled entry would silently collapse onto the origin on the backdrop shell.
    const length = Math.hypot(object.x, object.y, object.z);
    assertCondition(Math.abs(length - 1) < UNIT_VECTOR_TOLERANCE, `Deep-sky object ${object.id} has a non-unit direction (length ${length}).`);

    assertCondition(object.angularSizeDeg >= 0, `Deep-sky object ${object.id} has a negative angular size.`);
    assertCondition(object.distancePc === null || object.distancePc > 0, `Deep-sky object ${object.id} has a non-positive distance.`);
    // The distance and its provenance have to travel together, or the UI cannot say where a
    // number came from.
    assertCondition(
      (object.distancePc === null) === (object.distanceMethod === null),
      `Deep-sky object ${object.id} has a distance/method mismatch.`
    );
  }

  const kinds = new Set(objects.map((object) => object.kind));
  for (const kind of ['galaxy', 'nebula', 'cluster'] as const) {
    assertCondition(kinds.has(kind), `No deep-sky objects of kind "${kind}" were produced.`);
  }

  const withDistance = objects.filter((object) => object.distancePc !== null).length;
  console.log(`  ${withDistance}/${objects.length} deep-sky objects have a derived distance.`);
}

/**
 * Orchestrates the whole ETL pipeline: fetches every source (each caches its own raw
 * responses under `tools/etl/.cache/`), writes the static assets under `src/assets/data/`,
 * then validates the combined output for completeness before declaring success.
 */
async function build(): Promise<void> {
  console.log('=== NASA star map ETL ===\n');
  console.log('Catalogues:');
  console.log(describeSources());
  console.log();

  const stars = await fetchStars();
  console.log();
  const { bodies, horizonsOrbits } = await fetchSolarSystem();
  console.log();
  const exoplanets = await fetchExoplanets(stars);
  console.log();
  const deepSky = await fetchDeepSky();
  console.log();

  console.log('Validating output...');
  validateStars(stars);
  validateMerge(stars);
  validateBodies(bodies, horizonsOrbits);
  validateExoplanets(exoplanets, new Set(stars.map((star) => star.id)));
  validateDeepSky(deepSky);

  console.log('\nETL completed successfully:');
  console.log(`  stars:      ${stars.length}`);
  console.log(`  bodies:     ${bodies.length}`);
  console.log(`  exoplanets: ${exoplanets.length}`);
  console.log(`  deep sky:   ${deepSky.length}`);
}

build().catch((error) => {
  console.error('\nETL failed:', error instanceof Error ? error.message : error);
  process.exitCode = 1;
});