Flight-Ops/lib/sim/movement.test.ts

import { describe, expect, it } from 'vitest';
import { haversineKm } from '@/lib/geo';
import {
  arrivalTimeFor,
  burnRateConstant,
  FUEL_DENSITY_KG_PER_L,
  fuelAtWeighted,
  positionAt,
  progressAt,
  requiredFuelFor,
  travelDurationMs,
} from './movement';

// Synthetic in-flight fixtures — no DB needed: everything is a pure function of
// the sim clock. ATR 72-600 numbers from lib/game/catalog.ts.
const DEP = 1_750_000_000_000; // departure sim time (ms)
const SPEED = 510; // km/h
const BURN = 1.75; // L/km at a full tank
const WE = 9_300; // kg, operating empty weight
const TANK = 6_300; // liters, full tank

// Frankfurt → Madrid, real coordinates from the CSV dataset.
const FROM = { lat: 50.0333, lon: 8.5706 };
const TO = { lat: 40.47, lon: -3.56 };
const KM = haversineKm(FROM.lat, FROM.lon, TO.lat, TO.lon); // ≈ 2190 km

describe('travelDurationMs / arrivalTimeFor', () => {
  it('duration is distance/speed converted to ms', () => {
    expect(travelDurationMs(510, SPEED)).toBe(3_600_000); // one hour at cruise
    expect(travelDurationMs(KM, SPEED)).toBeCloseTo((KM / SPEED) * 3_600_000, 9);
  });

  it('rejects a non-positive speed', () => {
    expect(() => travelDurationMs(100, 0)).toThrow();
  });

  it('arrival is departure + duration', () => {
    const arrival = arrivalTimeFor(DEP, KM, SPEED);
    expect(arrival).toBeCloseTo(DEP + (KM / SPEED) * 3_600_000, 9);
    expect(arrival).toBeGreaterThan(DEP);
  });
});

describe('progressAt', () => {
  const duration = travelDurationMs(KM, SPEED);

  it('is 0 before departure and at departure', () => {
    expect(progressAt(DEP, KM, SPEED, DEP - 1)).toBe(0);
    expect(progressAt(DEP, KM, SPEED, DEP)).toBe(0);
  });

  it('is linear in the middle of the flight', () => {
    // Precision 9: clock values sit at ~1.75e12 ms, so (clock - DEP) loses a few
    // ulps to cancellation — 1e-9 progress is still sub-millisecond on this leg.
    expect(progressAt(DEP, KM, SPEED, DEP + duration / 2)).toBeCloseTo(0.5, 9);
    expect(progressAt(DEP, KM, SPEED, DEP + duration * 0.25)).toBeCloseTo(0.25, 9);
  });

  it('is exactly 1 at arrival and stays 1 after', () => {
    const arrival = DEP + duration;
    expect(progressAt(DEP, KM, SPEED, arrival)).toBe(1);
    expect(progressAt(DEP, KM, SPEED, arrival + 10_000)).toBe(1);
  });

  it('a zero-distance leg is complete immediately', () => {
    expect(progressAt(DEP, 0, SPEED, DEP - 5)).toBe(1);
  });
});

describe('positionAt (great-circle slerp)', () => {
  it('returns the exact endpoints at progress 0 and 1', () => {
    expect(positionAt(FROM.lat, FROM.lon, TO.lat, TO.lon, 0)).toEqual({ lat: FROM.lat, lon: FROM.lon });
    expect(positionAt(FROM.lat, FROM.lon, TO.lat, TO.lon, 1)).toEqual({ lat: TO.lat, lon: TO.lon });
  });

  it('clamps out-of-range progress to the endpoints', () => {
    expect(positionAt(FROM.lat, FROM.lon, TO.lat, TO.lon, -0.5)).toEqual({ lat: FROM.lat, lon: FROM.lon });
    expect(positionAt(FROM.lat, FROM.lon, TO.lat, TO.lon, 1.5)).toEqual({ lat: TO.lat, lon: TO.lon });
  });

  it('stays on the great circle: arc lengths add up to the total distance', () => {
    for (const t of [0.1, 0.37, 0.5, 0.9]) {
      const p = positionAt(FROM.lat, FROM.lon, TO.lat, TO.lon, t);
      const d1 = haversineKm(FROM.lat, FROM.lon, p.lat, p.lon);
      const d2 = haversineKm(p.lat, p.lon, TO.lat, TO.lon);
      expect(d1 + d2).toBeCloseTo(KM, 6); // slerp keeps the point on the arc
    }
  });

  it('the midpoint is equidistant from both ends', () => {
    const m = positionAt(FROM.lat, FROM.lon, TO.lat, TO.lon, 0.5);
    expect(haversineKm(FROM.lat, FROM.lon, m.lat, m.lon)).toBeCloseTo(KM / 2, 6);
    expect(haversineKm(m.lat, m.lon, TO.lat, TO.lon)).toBeCloseTo(KM / 2, 6);
  });

  it('is exact along the equator (great circle = constant latitude)', () => {
    for (const t of [0.25, 0.5, 0.75]) {
      const p = positionAt(0, -10, 0, 10, t);
      expect(p.lat).toBeCloseTo(0, 9);
      expect(p.lon).toBeCloseTo(-10 + 20 * t, 9);
    }
  });

  it('handles the same-point route without dividing by zero', () => {
    const p = positionAt(48.85, 2.35, 48.85, 2.35, 0.5);
    expect(p).toEqual({ lat: 48.85, lon: 2.35 });
  });
});

describe('weighted burn model (v0.16.0)', () => {
  it('calibrates so a full tank burns exactly the old constant rate', () => {
    const k = burnRateConstant(BURN, WE, TANK);
    expect(k * (WE + FUEL_DENSITY_KG_PER_L * TANK)).toBeCloseTo(BURN, 12);

    // Over a short hop from full, weighted ≈ constant — divergence only grows as fuel drops off.
    const d = 100;
    const consumed = TANK - fuelAtWeighted(TANK, BURN, WE, TANK, d, 1);
    expect(Math.abs(consumed - BURN * d)).toBeLessThan(1); // < 1 L over 100 km from full
  });

  it('consumption matches numeric integration of r(F) = k·(We + ρF)', () => {
    const k = burnRateConstant(BURN, WE, TANK);
    const rho = FUEL_DENSITY_KG_PER_L;
    // Euler-integrate dF/dx = −k(We + ρF) from a full tank over the whole leg.
    const steps = 200_000;
    const h = KM / steps;
    let f = TANK;
    for (let i = 0; i < steps; i++) f -= k * (WE + rho * f) * h;
    expect(Math.abs(fuelAtWeighted(TANK, BURN, WE, TANK, KM, 1) - f)).toBeLessThan(0.001); // Euler drift is sub-milliliter here
  });

  it('requiredFuelFor is zero for a zero leg and strictly increasing in distance', () => {
    expect(requiredFuelFor(BURN, WE, TANK, 0)).toBe(0);
    let prev = requiredFuelFor(BURN, WE, TANK, 100);
    for (const d of [500, 1_000, 2_000, 3_000, 4_000]) {
      const cur = requiredFuelFor(BURN, WE, TANK, d);
      expect(cur).toBeGreaterThan(prev);
      prev = cur;
    }
  });

  it('a lighter start burns less over the same distance', () => {
    const burnFromFull = TANK - fuelAtWeighted(TANK, BURN, WE, TANK, KM, 1);
    const burnFromHalf = TANK / 2 - fuelAtWeighted(TANK / 2, BURN, WE, TANK, KM, 1);
    expect(burnFromFull).toBeGreaterThan(burnFromHalf);
  });

  it('starting with exactly the required fuel arrives on empty', () => {
    const req = requiredFuelFor(BURN, WE, TANK, KM);
    expect(fuelAtWeighted(req, BURN, WE, TANK, KM, 1)).toBeCloseTo(0, 6);
  });

  it('clamps at zero instead of going negative', () => {
    expect(fuelAtWeighted(100, BURN, WE, TANK, KM, 1)).toBe(0); // needs ~2800 L from full, has 100
    expect(fuelAtWeighted(TANK, BURN, WE, TANK, KM, 0)).toBe(TANK);
    expect(fuelAtWeighted(TANK, BURN, WE, TANK, 0, 1)).toBe(TANK);
  });

  it('composes with progressAt for a just-before-arrival snapshot', () => {
    const duration = travelDurationMs(KM, SPEED);
    const clock = DEP + duration - 1; // one ms before arrival
    const p = positionAt(FROM.lat, FROM.lon, TO.lat, TO.lon, progressAt(DEP, KM, SPEED, clock));
    expect(haversineKm(p.lat, p.lon, TO.lat, TO.lon)).toBeGreaterThan(0); // not yet at the gate
    expect(fuelAtWeighted(TANK, BURN, WE, TANK, KM, progressAt(DEP, KM, SPEED, clock))).toBeGreaterThan(0);
  });
});