KSP-MissionControl/apps/live-map/tests/scene.test.ts

import { describe, it, expect } from 'vitest';
import {
  bodyPositionAt,
  vesselPositionAt,
  findBodyMu,
  logScale,
  inverseLogScale,
} from '../src/scene/layout.js';
import type { CelestialBody, Vessel } from '@kerbal-rt/shared-types';

const kerbol: CelestialBody = {
  id: 'kerbol',
  name: 'Kerbol',
  kind: 'star',
  parentId: null,
  radius: 261_600_000,
  sphereOfInfluence: 1e30,
  gravitationalParameter: 1.172e18,
  rotationPeriod: 432_000,
  axialTilt: 0,
  orbit: {
    semiMajorAxis: 0,
    eccentricity: 0,
    inclination: 0,
    longitudeOfAscendingNode: 0,
    argumentOfPeriapsis: 0,
    meanAnomalyAtEpoch: 0,
    epoch: 0,
  },
};

const kerbin: CelestialBody = {
  id: 'kerbin',
  name: 'Kerbin',
  kind: 'planet',
  parentId: 'kerbol',
  radius: 600_000,
  sphereOfInfluence: 84_159_286,
  gravitationalParameter: 3.5316e12,
  rotationPeriod: 21_600,
  axialTilt: 0,
  orbit: {
    semiMajorAxis: 13_599_840_256,
    eccentricity: 0, // circular for predictable test math
    inclination: 0,
    longitudeOfAscendingNode: 0,
    argumentOfPeriapsis: 0,
    meanAnomalyAtEpoch: 0,
    epoch: 0,
  },
};

const mun: CelestialBody = {
  id: 'mun',
  name: 'Mun',
  kind: 'moon',
  parentId: 'kerbin',
  radius: 200_000,
  sphereOfInfluence: 2_429_559,
  gravitationalParameter: 6.514e10,
  rotationPeriod: 138_984,
  axialTilt: 0,
  orbit: {
    semiMajorAxis: 12_000_000,
    eccentricity: 0,
    inclination: 0,
    longitudeOfAscendingNode: 0,
    argumentOfPeriapsis: 0,
    meanAnomalyAtEpoch: 0,
    epoch: 0,
  },
};

const bodies: CelestialBody[] = [kerbol, kerbin, mun];

describe('bodyPositionAt', () => {
  it('returns origin for the star', () => {
    const p = bodyPositionAt(bodies, 'kerbol', 100);
    expect(p.x).toBe(0);
    expect(p.y).toBe(0);
    expect(p.z).toBe(0);
  });

  it('returns a non-zero position for a planet at t > 0', () => {
    const p = bodyPositionAt(bodies, 'kerbin', 1_000_000);
    const dist = Math.hypot(p.x, p.y, p.z);
    // SMA is 13.6 billion meters, so position is on that order
    expect(dist).toBeGreaterThan(1e10);
    expect(dist).toBeLessThan(2e10);
  });

  it('returns origin for a body not in the catalog', () => {
    const p = bodyPositionAt(bodies, 'unknown', 1);
    expect(p).toEqual({ x: 0, y: 0, z: 0 });
  });

  it('is periodic (returns near the same position after one full orbit)', () => {
    // Kerbin orbits Kerbol, so the period is computed with kerbol's μ
    const p1 = bodyPositionAt(bodies, 'kerbin', 0);
    const period =
      (2 * Math.PI) / Math.sqrt(kerbol.gravitationalParameter / Math.pow(13_599_840_256, 3));
    const p2 = bodyPositionAt(bodies, 'kerbin', period);
    expect(p1.x).toBeCloseTo(p2.x, -2);
    expect(p1.y).toBeCloseTo(p2.y, -2);
  });
});

describe('vesselPositionAt', () => {
  const vessel: Vessel = {
    id: 'v1',
    name: 'Test',
    type: 'Probe',
    owner: 'KASA',
    situation: 'ORBITING',
    status: 'ACTIVE',
    orbit: {
      semiMajorAxis: 7_000_000,
      eccentricity: 0,
      inclination: 0,
      longitudeOfAscendingNode: 0,
      argumentOfPeriapsis: 0,
      meanAnomalyAtEpoch: 0,
      epoch: 0,
    },
    referenceBodyId: 'kerbin',
    createdAt: '2026-01-01T00:00:00Z',
    retiredAt: null,
  };

  it('returns the kerbin-centered position when reference body is kerbin', () => {
    // At t=0, vessel is at (7e6, 0, 0) in kerbin frame
    const p = vesselPositionAt(bodies, vessel, 0);
    // kerbin is at (sma, 0, 0) = (13.6e9, 0, 0)
    // so vessel should be at roughly (13.6e9 + 7e6, 0, 0)
    expect(p.x).toBeCloseTo(13_599_840_256 + 7_000_000, -2);
    expect(p.y).toBeCloseTo(0, 2);
  });
});

describe('findBodyMu', () => {
  it("returns the body's own gravitational parameter", () => {
    expect(findBodyMu(bodies, 'kerbin')).toBe(kerbin.gravitationalParameter);
  });
  it('returns 0 for null id', () => {
    expect(findBodyMu(bodies, null)).toBe(0);
  });
  it('returns 0 for unknown id', () => {
    expect(findBodyMu(bodies, 'nope')).toBe(0);
  });
});

describe('logScale', () => {
  it('is the inverse of inverseLogScale', () => {
    for (const t of [0, 4, 8, 12]) {
      const d = logScale(t);
      expect(inverseLogScale(d)).toBeCloseTo(t, 6);
    }
  });
  it('produces reasonable distances for camera placement', () => {
    // t=4 → ~5.5e9 m (good for showing Kerbin at 13.6e9)
    expect(logScale(4)).toBeGreaterThan(1e9);
    expect(logScale(4)).toBeLessThan(1e10);
    // t=10 → ~22e12 m (good for showing all planets)
    expect(logScale(10)).toBeGreaterThan(1e12);
  });
});