Environment: gravity, ambient pressure and temperature

/**
 * Figures a preset starts from. `source` says where each comes from; the temperature of a world with no atmosphere to speak of is a
 * mean the designer is expected to replace with the case that matters (`range` is the swing to check against).
 */
export const PRESETS = {
  earth: { g: 9.80665, pressure: 101325, temperature: 20, range: [-89, 57], source: 'standard gravity (CGPM 1901), standard atmosphere (exact), 20 °C reference temperature (ISO 1)' },
  moon: { g: 1.62, pressure: 0, temperature: -23, range: [-173, 123], source: 'NASA lunar fact sheet: surface gravity 1.62 m/s², mean surface temperature about 250 K, 100–396 K between night and day' },
  mars: { g: 3.71, pressure: 636, temperature: -63, range: [-143, 27], source: 'NASA Mars fact sheet: surface gravity 3.71 m/s², mean surface pressure about 636 Pa, mean temperature about 210 K' },
  orbit: { g: 0, pressure: 0, temperature: 20, range: [-65, 125], source: 'free fall (no apparent weight; tidal terms ignored); no ambient pressure; 20 °C is an assumed interior temperature, not a figure' },
};

/** Gravity in mm/s², the unit the solvers use. */
export const gravityMM = (env) => env.g * 1000;

/** Ambient pressure in MPa (N/mm²). */
export const pressureMPa = (env) => env.pressure / 1e6;

/** Gauge pressure for a sealed volume at `absoluteMPa` inside: what loads the walls. Negative = the outside pushes harder. */
export const gaugeMPa = (env, absoluteMPa) => absoluteMPa - pressureMPa(env);

/** Weight in newtons of a mass in kg. */
export const weightN = (env, kg) => kg * env.g;

/**
 * Fill in everything the environment decides. Returns a copy of `job` (the argument is not changed); a job with no `env` is
 * returned as it came. Safe to call twice (a second call finds nothing left to fill). The job shape is the solvers':
 *   job.bcs.loads[]  {type 'gravity', dir, g?} | {type 'pressure', p, absolute?} | …
 *   job.heat[]       {type 'convection'|'radiation', Tamb?} | …
 *   job.thermalLoad  {mode, dT, Tref?}
 *   job.env          the environment (readEnv shape)
 * `job.envApplied` is set to the key that was applied.
 */
export function applyEnv(job) {
  if (!job || !job.env) return job;
  const env = job.env, key = envKey(env);
  if (job.envApplied === key) return job;
  const out = { ...job, envApplied: key };
  if (job.bcs && Array.isArray(job.bcs.loads)) {
    out.bcs = { ...job.bcs, loads: job.bcs.loads.map((l) => {
      if (l.type === 'gravity' && (l.g === undefined || l.g === null)) return { ...l, g: gravityMM(env) };
      if (l.type === 'pressure' && l.absolute === true) { const { absolute, ...rest } = l; return { ...rest, p: gaugeMPa(env, l.p), gaugeOf: l.p }; }
      return l;
    }) };
  }
  if (Array.isArray(job.heat)) out.heat = job.heat.map((h) => ((h.type === 'convection' || h.type === 'radiation') && (h.Tamb === undefined || h.Tamb === null) ? { ...h, Tamb: env.temperature } : h));
  if (job.thermalLoad && (job.thermalLoad.Tref === undefined || job.thermalLoad.Tref === null)) out.thermalLoad = { ...job.thermalLoad, Tref: env.temperature };
  return out;
}

/** A short stable string for caching ("did the environment change since this result?"). */
export const envKey = (env) => (env ? [env.g, env.pressure, env.temperature].map((v) => +v.toPrecision(10)).join('|') : 'none');