idle_clicker/public/js/engine/engine.js

// Game rules. Every function takes the mutable `state` and the static `ctx`
// (see context.js) and never touches the DOM, so it runs the same in the
// browser and in Node (tests, balance simulations).

import { computeModifiers } from './effects.js';
import { bulkCost, clamp, demandPerSecond, materialBatch, maxAffordable } from './formulas.js';

const MAX_STEP_SECONDS = 1;

// ---------------------------------------------------------------- conditions

export function isUnlocked(state, condition = {}) {
  if (condition.totalProduced != null && state.totalProduced < condition.totalProduced) return false;
  if (condition.generator != null && (state.generators[condition.generator] ?? 0) < (condition.count ?? 1)) {
    return false;
  }
  return true;
}

export function upgradeVisible(state, upgrade) {
  if (state.upgrades.includes(upgrade.id)) return false;
  if (upgrade.requires && !state.upgrades.includes(upgrade.requires)) return false;
  return isUnlocked(state, upgrade.unlock);
}

// ------------------------------------------------------------------- derived

/** Everything computed from the state (rates, multipliers, current prices). */
export function derive(state, ctx) {
  const { rules } = ctx;
  const mods = computeModifiers(state.upgrades, ctx.upgradesById);

  const perGenerator = {};
  let rate = 0;
  for (const g of ctx.generators) {
    perGenerator[g.id] = g.baseRate * (mods.generators[g.id] ?? 1) * mods.global;
    rate += perGenerator[g.id] * (state.generators[g.id] ?? 0);
  }

  const demandMultiplier = mods.demand * rules.marketing.demandPerLevel ** state.marketing;
  const batch = materialBatch(
    rules.materialMarket,
    state.totalProduced,
    rate,
    state.materialFactor,
    mods.batchDiscount,
  );
  return {
    clickYield: rules.click.yield * mods.click,
    perGenerator,
    rate,
    demandMultiplier,
    demand: demandPerSecond(rules.market, state.price, demandMultiplier),
    valueMultiplier: mods.value,
    materialPerUnit: rules.unit.materialPerUnit / mods.materialEfficiency,
    batchSize: batch.size,
    batchCost: batch.cost,
    autoBuyMaterial: mods.autoBuyMaterial,
    marketingCost: Math.ceil(rules.marketing.baseCost * rules.marketing.costGrowth ** state.marketing),
  };
}

// ------------------------------------------------------------------- actions
// Each returns true when the action was performed.

export function click(state, ctx) {
  const d = derive(state, ctx);
  if (state.material < d.materialPerUnit) return false;
  const made = Math.min(d.clickYield, state.material / d.materialPerUnit);
  state.material -= made * d.materialPerUnit;
  state.units += made;
  state.totalProduced += made;
  return true;
}

export function buyMaterial(state, ctx) {
  const d = derive(state, ctx);
  if (state.funds < d.batchCost) return false;
  state.funds -= d.batchCost;
  state.material += d.batchSize;
  return true;
}

export function buyMarketing(state, ctx) {
  const d = derive(state, ctx);
  if (state.funds < d.marketingCost) return false;
  state.funds -= d.marketingCost;
  state.marketing += 1;
  return true;
}

/** How many generators the player gets for `amount` ("max" or a number). */
export function generatorQuote(state, ctx, id, amount) {
  const g = ctx.generatorsById.get(id);
  const owned = state.generators[id] ?? 0;
  const count = amount === 'max' ? maxAffordable(g.baseCost, g.costGrowth, owned, state.funds) : amount;
  return { count, cost: bulkCost(g.baseCost, g.costGrowth, owned, count) };
}

export function buyGenerator(state, ctx, id, amount = 1) {
  if (!ctx.generatorsById.has(id)) return false;
  const { count, cost } = generatorQuote(state, ctx, id, amount);
  if (count <= 0 || state.funds < cost) return false;
  state.funds -= cost;
  state.generators[id] += count;
  return true;
}

export function buyUpgrade(state, ctx, id) {
  const upgrade = ctx.upgradesById.get(id);
  if (!upgrade || !upgradeVisible(state, upgrade) || state.funds < upgrade.cost) return false;
  state.funds -= upgrade.cost;
  state.upgrades.push(id);
  return true;
}

export function setPrice(state, ctx, price) {
  const { minPrice, maxPrice } = ctx.rules.market;
  if (!Number.isFinite(price)) return false;
  state.price = Math.round(clamp(price, minPrice, maxPrice) * 100) / 100;
  return true;
}

// ---------------------------------------------------------------------- time

function stepMaterialMarket(state, ctx, dt, rng) {
  const m = ctx.rules.materialMarket;
  state.materialTimer += dt;
  while (state.materialTimer >= m.updateEverySeconds) {
    state.materialTimer -= m.updateEverySeconds;
    let shock = 1 + (rng() - 0.5) * 2 * m.volatility;
    if (rng() < m.spikeChance) shock *= rng() < 0.5 ? m.spikeSize : 1 / m.spikeSize; // shortage or glut
    const pulled = state.materialFactor + (1 - state.materialFactor) * m.reversion;
    const next = clamp(pulled * shock, m.minFactor, m.maxFactor);
    state.materialTrend = Math.sign(next - state.materialFactor);
    state.materialFactor = next;
  }
}

function step(state, ctx, dt, rng, totals) {
  stepMaterialMarket(state, ctx, dt, rng);
  const d = derive(state, ctx);

  // Production, limited by the material in stock.
  const made = Math.min(d.rate * dt, state.material / d.materialPerUnit);
  state.material -= made * d.materialPerUnit;
  state.units += made;
  state.totalProduced += made;

  // Automatic restock: patient while the price is high, urgent when nearly out.
  if (d.autoBuyMaterial && state.funds >= d.batchCost) {
    const { autoBuyBelowFactor } = ctx.rules.materialMarket;
    const low = state.material < d.batchSize / 2 && state.materialFactor <= autoBuyBelowFactor;
    if (low || state.material < d.batchSize / 10) buyMaterial(state, ctx);
  }

  // Customers buy what they want, up to what is in stock.
  const sold = Math.min(state.units, d.demand * dt);
  const revenue = sold * state.price * d.valueMultiplier;
  state.units -= sold;
  state.funds += revenue;
  state.totalSold += sold;

  totals.produced += made;
  totals.sold += sold;
  totals.revenue += revenue;
}

/** Advance the simulation by `seconds`. Returns what happened during that time. */
export function advance(state, ctx, seconds, rng = Math.random) {
  const totals = { produced: 0, sold: 0, revenue: 0 };
  let left = Math.max(0, seconds);
  while (left > 1e-9) {
    const dt = Math.min(left, MAX_STEP_SECONDS);
    step(state, ctx, dt, rng, totals);
    left -= dt;
  }
  return totals;
}

/**
 * Catch up on the time the game was closed. Deterministic (no price noise)
 * and discounted by `offline.efficiency`. Returns null if too short to matter.
 */
export function simulateOffline(state, ctx, elapsedSeconds) {
  const { maxSeconds, efficiency, minSeconds } = ctx.rules.offline;
  if (elapsedSeconds < minSeconds) return null;
  const seconds = Math.min(elapsedSeconds, maxSeconds) * efficiency;
  const totals = advance(state, ctx, seconds, () => 0.5);
  return { ...totals, seconds: Math.min(elapsedSeconds, maxSeconds) };
}