probability/src/sim/npc.js

import { GOODS, DOCK_DELAY, VIS_BAND } from './constants.js';
import { advancePlanet, priceOf, applyTrade } from './economy.js';
import { findRoute, otherEnd } from './galaxy.js';
import { rollFor } from './rng.js';

// Leg duration = lane.days * uniform(JIT_MIN, JIT_MIN+JIT_SPAN); delayed legs x DELAY_MULT.
export const JIT_MIN = 0.85;
export const JIT_SPAN = 0.3;
export const DELAY_MULT = 1.6;
const LOCAL_HOP_DAYS = 0.4; // same-system planet-to-planet trade run
const MAX_JUMPS = 3;

export function hazardProbs(h) {
  return { destroyed: h * 0.06, cargoLost: h * 0.2, delayed: h * 0.3 };
}

// Resolve the whole journey from the NPC's seed: route timing and hazard
// outcomes are fixed at plan time, revealed only when something observes them.
export function buildItinerary(galaxy, npc, routeLanes, startSys, t0, planId) {
  let t = t0, sys = startSys, finalOutcome = 'ok';
  const legs = [];
  for (let i = 0; i < routeLanes.length; i++) {
    const lane = galaxy.lanes[routeLanes[i]];
    const toSys = otherEnd(lane, sys);
    let dur = lane.days * (JIT_MIN + JIT_SPAN * rollFor(npc.seed, `${planId}:leg${i}:jit`));
    const p = hazardProbs(lane.hazard);
    const r = rollFor(npc.seed, `${planId}:leg${i}:hazard`);
    let outcome = 'safe';
    if (r < p.destroyed) outcome = 'destroyed';
    else if (r < p.destroyed + p.cargoLost) outcome = 'cargoLost';
    else if (r < p.destroyed + p.cargoLost + p.delayed) { outcome = 'delayed'; dur *= DELAY_MULT; }
    legs.push({ laneId: lane.id, fromSys: sys, toSys, depart: t, arrive: t + dur, outcome });
    t += dur;
    sys = toSys;
    if (outcome === 'destroyed') { finalOutcome = 'destroyed'; break; }
    if (outcome === 'cargoLost') finalOutcome = 'cargoLost';
  }
  return { legs, finalOutcome, arriveTime: t };
}

// Score arbitrage options using stale news, buy cargo, fix the itinerary,
// and schedule the arrival event. Falls back to a retry if nothing pays.
export function planNpc(world, npc) {
  const t = world.t;
  npc.planCount = (npc.planCount || 0) + 1;
  const planId = `p${npc.planCount}`;
  const origin = world.galaxy.planets[npc.planetId];
  advancePlanet(origin, t);

  let best = null;
  for (const dest of world.galaxy.planets) {
    if (dest.id === origin.id) continue;
    const hops = world.hops[origin.systemId][dest.systemId];
    if (hops > MAX_JUMPS) continue;
    const known = world.news.knownPrices(dest.id, hops, t);
    if (!known) continue;
    const route = hops === 0
      ? { lanes: [], days: LOCAL_HOP_DAYS }
      : findRoute(world.galaxy, origin.systemId, dest.systemId);
    if (!route) continue;

    let survival = 1;
    for (const laneId of route.lanes) {
      const p = hazardProbs(world.galaxy.lanes[laneId].hazard);
      survival *= 1 - p.destroyed - p.cargoLost;
    }
    for (const good of GOODS) {
      const buyP = priceOf(good, origin.stock[good]);
      const sellP = known.prices[good];
      if (sellP <= buyP * 1.15) continue; // demand a margin over price noise
      const qty = Math.min(npc.capacity, Math.floor(npc.credits / buyP), Math.floor(origin.stock[good] * 0.5));
      if (qty < 1) continue;
      const profit = (sellP * survival - buyP) * qty; // EV: buy cost is sunk even if cargo is lost
      if (profit <= 0) continue;
      const days = Math.max(LOCAL_HOP_DAYS, route.days);
      const noise = 0.9 + 0.2 * rollFor(npc.seed, `${planId}:noise:${dest.id}:${good}`);
      const score = (profit / days) * noise;
      if (!best || score > best.score) best = { score, dest, good, qty, route };
    }
  }

  if (!best) {
    npc.plan = null;
    npc.state = 'docked';
    world.queue.push(t + 2, 'npc-replan', { npcId: npc.id });
    return;
  }

  const price = applyTrade(origin, t, best.good, -best.qty);
  npc.credits = Math.round((npc.credits - price * best.qty) * 100) / 100;
  npc.cargo = { good: best.good, qty: best.qty };

  const itin = best.route.lanes.length > 0
    ? buildItinerary(world.galaxy, npc, best.route.lanes, origin.systemId, t, planId)
    : { legs: [], finalOutcome: 'ok', arriveTime: t + LOCAL_HOP_DAYS };

  npc.plan = {
    id: planId, good: best.good, qty: best.qty,
    originPlanet: origin.id, destPlanet: best.dest.id,
    // Planned route (public knowledge for clouds) — unlike legs, never
    // truncated by a hidden 'destroyed' roll.
    routeLanes: best.route.lanes, startSys: origin.systemId,
    startTime: t, ...itin,
  };
  npc.lastPlan = null; // superseded; v1 simplification: a fresh cloud implies the previous run ended
  npc.state = 'transit';
  world.queue.push(itin.arriveTime, 'npc-arrive', { npcId: npc.id, planId });
}

// Arrival: reveal the journey's outcome and commit its market effects.
export function onNpcArrive(world, { npcId, planId }) {
  const npc = world.npcs[npcId];
  if (!npc.alive || !npc.plan || npc.plan.id !== planId) return;
  const plan = npc.plan;
  if (plan.finalOutcome === 'destroyed') {
    npc.alive = false;
    npc.lastPlan = plan; // cloud persists from the envelope until observed/expired
    npc.plan = null;
    npc.cargo = null;
    npc.state = 'destroyed';
    world.stats.npcDestroyed++;
    return;
  }
  const dest = world.galaxy.planets[plan.destPlanet];
  npc.planetId = dest.id;
  npc.systemId = dest.systemId;
  npc.state = 'docked';
  if (plan.finalOutcome !== 'cargoLost' && npc.cargo) {
    const price = applyTrade(dest, world.t, npc.cargo.good, npc.cargo.qty);
    npc.credits = Math.round((npc.credits + price * npc.cargo.qty) * 100) / 100;
    world.stats.trades++;
  }
  npc.lastPlan = plan; // unobserved arrival: the player's cloud persists a while
  npc.cargo = null;
  npc.plan = null;
  world.queue.push(world.t + DOCK_DELAY, 'npc-replan', { npcId });
}

// Concrete ships present in a system right now: docked ones, local hops,
// and ships within the VIS_BAND fraction of a lane adjacent to the system.
export function shipsIn(world, systemId) {
  const out = [];
  for (const npc of world.npcs) {
    if (!npc.alive) continue;
    if (npc.state === 'docked') {
      if (npc.systemId === systemId) out.push({ npc, kind: 'docked', planetId: npc.planetId });
      continue;
    }
    if (!npc.plan) continue;
    if (npc.plan.legs.length === 0) {
      // same-system hop between planets
      if (world.galaxy.planets[npc.plan.originPlanet].systemId === systemId) {
        const f = (world.t - npc.plan.startTime) / (npc.plan.arriveTime - npc.plan.startTime);
        out.push({ npc, kind: 'local-hop', progress: Math.min(1, Math.max(0, f)) });
      }
      continue;
    }
    const leg = npc.plan.legs.find((l) => l.depart <= world.t && world.t < l.arrive);
    if (!leg) continue;
    const f = (world.t - leg.depart) / (leg.arrive - leg.depart);
    if (leg.fromSys === systemId && f < VIS_BAND) {
      out.push({ npc, kind: 'departing', laneId: leg.laneId, progress: f / VIS_BAND });
    } else if (leg.toSys === systemId && f > 1 - VIS_BAND) {
      out.push({ npc, kind: 'arriving', laneId: leg.laneId, progress: (f - (1 - VIS_BAND)) / VIS_BAND });
    }
  }
  return out;
}