feat: economy with lazy stock advancement and price curve

2026-06-12 13:58:54 +00:00
parent 3682205580
commit 922926cc6d
3 changed files with 111 additions and 0 deletions
@@ -0,0 +1,58 @@
+import { describe, it, expect } from 'vitest';
+import { priceOf, advancePlanet, marketView, applyTrade } from '../src/sim/economy.js';
+import { BASE_PRICE, GOODS, TYPICAL_STOCK } from '../src/sim/constants.js';
+
+function makePlanet() {
+  return {
+    id: 0, systemId: 0, name: 'Test Prime',
+    produces: { food: 10 }, consumes: { fuel: 5 },
+    stock: { ore: 100, food: 100, fuel: 100, tech: 100, meds: 100, luxury: 100 },
+    stockTime: 0,
+  };
+}
+
+describe('economy', () => {
+  it('price falls as stock rises, clamped to [0.25x, 4x] base', () => {
+    expect(priceOf('ore', TYPICAL_STOCK)).toBeCloseTo(BASE_PRICE.ore, 1);
+    expect(priceOf('ore', 10)).toBeGreaterThan(priceOf('ore', 500));
+    expect(priceOf('ore', 0)).toBe(BASE_PRICE.ore * 4);
+    expect(priceOf('ore', 1e9)).toBe(BASE_PRICE.ore * 0.25);
+  });
+
+  it('advancePlanet applies production/consumption over elapsed time', () => {
+    const p = makePlanet();
+    advancePlanet(p, 10);
+    expect(p.stock.food).toBeCloseTo(200, 5); // +10/day
+    expect(p.stock.fuel).toBeCloseTo(50, 5);  // -5/day
+    expect(p.stock.ore).toBeCloseTo(100, 5);  // untouched
+    expect(p.stockTime).toBe(10);
+  });
+
+  it('advancePlanet never goes negative and is idempotent', () => {
+    const p = makePlanet();
+    advancePlanet(p, 100);
+    expect(p.stock.fuel).toBe(0);
+    const snapshot = { ...p.stock };
+    advancePlanet(p, 100); // same time again: no change
+    expect(p.stock).toEqual(snapshot);
+  });
+
+  it('applyTrade returns pre-trade price and mutates stock', () => {
+    const p = makePlanet();
+    const price = applyTrade(p, 0, 'ore', -20); // a buyer removes 20
+    expect(price).toBeCloseTo(priceOf('ore', 100), 5);
+    expect(p.stock.ore).toBe(80);
+    applyTrade(p, 0, 'ore', 50); // a seller delivers 50
+    expect(p.stock.ore).toBe(130);
+  });
+
+  it('marketView lists all goods with integer stock and price', () => {
+    const p = makePlanet();
+    const view = marketView(p, 5);
+    expect(view.map((r) => r.good)).toEqual(GOODS);
+    for (const row of view) {
+      expect(Number.isInteger(row.stock)).toBe(true);
+      expect(row.price).toBeGreaterThan(0);
+    }
+  });
+});