elysium/apps/api/src/services/offlineProgress.ts

import type { GameState } from "@elysium/types";

const MAX_OFFLINE_SECONDS = 8 * 60 * 60; // 8 hours

/**
 * Calculates the gold and essence earned whilst the player was offline.
 * Capped at 8 hours to prevent exploit via system clock manipulation.
 * Applies the same multipliers as the client-side tick engine.
 */
export const calculateOfflineEarnings = (
  state: GameState,
  nowMs: number,
): { offlineGold: number; offlineEssence: number; offlineSeconds: number } => {
  const elapsedSeconds = Math.min(
    (nowMs - state.lastTickAt) / 1000,
    MAX_OFFLINE_SECONDS,
  );

  const equipmentGoldMultiplier = (state.equipment ?? [])
    .filter((e) => e.equipped)
    .reduce((mult, e) => mult * (e.bonus.goldMultiplier ?? 1), 1);

  const runestonesIncome = state.prestige.runestonesIncomeMultiplier ?? 1;
  const runestonesEssence = state.prestige.runestonesEssenceMultiplier ?? 1;

  let goldPerSecond = 0;
  let essencePerSecond = 0;

  for (const adventurer of state.adventurers) {
    if (!adventurer.unlocked || adventurer.count === 0) {
      continue;
    }

    const upgradeMultiplier = state.upgrades
      .filter(
        (u) =>
          u.purchased &&
          (u.target === "global" ||
            (u.target === "adventurer" && u.adventurerId === adventurer.id)),
      )
      .reduce((mult, u) => mult * u.multiplier, 1);

    const prestige = state.prestige.productionMultiplier;

    goldPerSecond +=
      adventurer.goldPerSecond *
      adventurer.count *
      upgradeMultiplier *
      prestige *
      runestonesIncome *
      equipmentGoldMultiplier;

    essencePerSecond +=
      adventurer.essencePerSecond *
      adventurer.count *
      upgradeMultiplier *
      prestige *
      runestonesEssence;
  }

  return {
    offlineGold: goldPerSecond * elapsedSeconds,
    offlineEssence: essencePerSecond * elapsedSeconds,
    offlineSeconds: elapsedSeconds,
  };
};