feat: news ledger with lane-delayed price snapshots

src/sim/news.js

@@ -0,0 +1,35 @@
+import { GOODS, NEWS_DAYS_PER_LANE, SNAPSHOT_KEEP } from './constants.js';
+import { advancePlanet, priceOf } from './economy.js';
+
+// Daily price snapshots per planet. Knowledge from `hops` lanes away
+// is the snapshot from hops * NEWS_DAYS_PER_LANE days ago.
+export class NewsLedger {
+  constructor() {
+    this.history = new Map(); // planetId -> [{time, prices}]
+  }
+
+  record(galaxy, t) {
+    for (const planet of galaxy.planets) {
+      advancePlanet(planet, t);
+      const prices = Object.fromEntries(GOODS.map((g) => [g, priceOf(g, planet.stock[g])]));
+      let arr = this.history.get(planet.id);
+      if (!arr) this.history.set(planet.id, (arr = []));
+      arr.push({ time: t, prices });
+      if (arr.length > SNAPSHOT_KEEP) arr.shift();
+    }
+  }
+
+  // Latest snapshot of planetId that has had time to travel `hops` lanes by time t.
+  // Clamped to t=0: the initial state is universally known.
+  knownPrices(planetId, hops, t) {
+    const arr = this.history.get(planetId);
+    if (!arr || arr.length === 0) return null;
+    const asOf = Math.max(0, t - hops * NEWS_DAYS_PER_LANE);
+    let best = null;
+    for (const snap of arr) {
+      if (snap.time <= asOf) best = snap;
+      else break;
+    }
+    return best ?? arr[0];
+  }
+}