fix: Changing way to sell with demand

tests/engine.test.js

@@ -13,7 +13,7 @@ import {
   simulateOffline,
   upgradeVisible,
 } from '../public/js/engine/engine.js';
-import { bulkCost, demandPerSecond, maxAffordable } from '../public/js/engine/formulas.js';
+import { balancedPrice, bulkCost, demandPerSecond, maxAffordable } from '../public/js/engine/formulas.js';
 import { createState, sanitizeState, serializeState } from '../public/js/engine/state.js';
 import { loadContext } from './helpers.js';
 
@@ -35,11 +35,24 @@ test('maxAffordable never overspends and is maximal', () => {
   }
 });
 
-test('demand is flat at/below the fair price and drops above it', () => {
+test('lower prices sell more, higher prices sell less, with no ceiling at the reference price', () => {
   const { market } = ctx.rules;
-  const atFair = demandPerSecond(market, market.fairPrice, 1);
-  assert.equal(demandPerSecond(market, market.fairPrice / 5, 1), atFair);
-  assert.ok(demandPerSecond(market, market.fairPrice * 2, 1) < atFair / 3);
+  const at = (price, mult = 1) => demandPerSecond(market, price, mult);
+  const ref = at(market.referencePrice);
+  assert.equal(ref, market.baseDemand);
+  assert.ok(at(market.referencePrice / 2) > ref * 2, 'half price sells more than double');
+  assert.ok(at(market.minPrice) > at(market.referencePrice / 2));
+  assert.ok(at(market.referencePrice * 2) < ref / 2);
+  assert.equal(at(market.referencePrice, 3), ref * 3, 'bonuses scale demand');
+});
+
+test('the balanced price moves with output and demand bonuses', () => {
+  const { market } = ctx.rules;
+  const balanced = (supply, mult) => balancedPrice(market, supply, mult);
+  const p = balanced(10, 1);
+  assert.ok(Math.abs(demandPerSecond(market, p, 1) - 10) < 1e-9, 'demand equals supply there');
+  assert.ok(balanced(100, 1) < p, 'more output -> lower balanced price');
+  assert.ok(balanced(10, 4) > p, 'more demand -> higher balanced price');
 });
 
 test('click makes a unit from material', () => {
@@ -139,12 +152,12 @@ test('auto-buy restocks material when funds allow', () => {
 });
 
 test('material is costly at first and cheaper relative to the sale price as production grows', () => {
-  const { fairPrice } = ctx.rules.market;
+  const { referencePrice } = ctx.rules.market;
   const costShare = (totalProduced) => {
     const s = fresh();
     s.totalProduced = totalProduced;
     const d = derive(s, ctx);
-    return d.batchCost / d.batchSize / fairPrice;
+    return d.batchCost / d.batchSize / referencePrice;
   };
   assert.ok(costShare(0) > 0.25, 'expensive at the start');
   assert.ok(costShare(1e4) < costShare(0));
@@ -178,6 +191,24 @@ test('the material market is erratic but stays within its bounds', () => {
   assert.ok(new Set(seen.map((f) => f.toFixed(2))).size > 100, 'does not sit still');
 });
 
+test('material prices have cents, not just whole numbers', () => {
+  const s = fresh();
+  s.materialFactor = 0.8137;
+  const { batchCost } = derive(s, ctx);
+  assert.notEqual(batchCost, Math.round(batchCost));
+  assert.equal(batchCost, Math.round(batchCost * 100) / 100);
+});
+
+test('the material price changes every 10 seconds, not before', () => {
+  const m = ctx.rules.materialMarket;
+  assert.equal(m.updateEverySeconds, 10);
+  const s = fresh();
+  advance(s, ctx, 9.5, () => 0.9);
+  assert.equal(s.materialFactor, 1);
+  advance(s, ctx, 1, () => 0.9);
+  assert.notEqual(s.materialFactor, 1);
+});
+
 test('auto-buy waits for a fair price unless stock is nearly gone', () => {
   const s = fresh();
   s.upgrades = ['auto_buy'];