Battle-for-Tismo/shared/game_state/taxes.js

// Trade taxes: the government's only revenue. There is no GDP tax, so the
// state lives on what crosses its borders and what its regions trade among
// themselves:
//
//   - a national sales tax on every purchase a region makes from another region
//     of the same country, paid by the buyer on top of the price;
//   - an export tariff a foreign buyer pays to the seller's government, in the
//     seller's currency, on top of what the seller receives;
//   - an import tariff a region pays its own government on the national
//     currency it spends acquiring a foreign currency for a purchase.
//
// Rates are set per nation, with an optional per-resource override, so a
// government can protect or tax one commodity differently from the rest.

import { RESOURCE_IDS, TAXES } from "../data.js";
import { NEWS_TARIFF } from "../data/relations.js";

function defaultTaxConfig() {
  return {
    sales: TAXES.defaultSales,
    export: TAXES.defaultExport,
    import: TAXES.defaultImport,
    // Per-resource overrides, keyed resource id -> { sales?, export?, import? }.
    overrides: {},
  };
}

export const taxMethods = {
  _initTaxes() {
    this.taxRates = new Map();
    // The current day's tax take per nation, in treasury units, reset by the
    // resource tick alongside the other daily ledgers.
    this.taxLedger = new Map();
    // The current day's tax take per region that generated it, so the region
    // tables can show what each contributes.
    this.cityTaxLedger = new Map();
    // The world commodity price index move of the last day, a fraction.
    this.commodityInflation = 0;
    this._prevResourcePrices = null;
  },

  // A nation's live tax config, created with the defaults on first read.
  getTaxConfig(civ) {
    if (civ < 0) return null;
    let config = this.taxRates ? this.taxRates.get(civ) : null;
    if (!config) {
      config = defaultTaxConfig();
      if (!this.taxRates) this.taxRates = new Map();
      this.taxRates.set(civ, config);
    }
    return config;
  },

  // The rate a nation charges for one tax kind, on one resource: the resource
  // override when it has one, otherwise the nation's default rate.
  getTaxRate(civ, kind, resource = null) {
    const config = this.getTaxConfig(civ);
    if (!config) return 0;
    const override = resource && config.overrides[resource]
      ? config.overrides[resource][kind]
      : undefined;
    return override === undefined ? (config[kind] || 0) : override;
  },

  // Sets a nation's default rate for a kind, or a single resource's override.
  // Returns the value applied.
  setTaxRate(civ, kind, rate, resource = null) {
    if (civ < 0 || !TAXES.kinds.includes(kind)) return null;
    const value = Math.max(0, Math.min(TAXES.maxRate, Number(rate) || 0));
    const config = this.getTaxConfig(civ);
    if (resource) {
      const entry = config.overrides[resource] || (config.overrides[resource] = {});
      entry[kind] = value;
    } else {
      config[kind] = value;
    }
    return value;
  },

  // A player changes a tax. Changing an import or export tariff notifies the
  // other nations; the sales tax is purely domestic and passes quietly.
  requestSetTaxRate(civ, kind, rate, resource = null) {
    if (civ < 0 || civ >= this.civilisations.length) return false;
    const value = Number(rate);
    if (!Number.isFinite(value) || value < 0) return false;
    if (!TAXES.kinds.includes(kind)) return false;
    if (resource !== null && !RESOURCE_IDS.includes(resource)) return false;
    const before = this.getTaxRate(civ, kind, resource);
    const applied = this.setTaxRate(civ, kind, value, resource);
    if (applied === null) return false;
    // A no-op apply (the box was left unchanged) is not news.
    if (applied !== before && (kind === "import" || kind === "export")) {
      this._addNews({ type: NEWS_TARIFF, civ, kind, rate: applied, resource: resource || null });
    }
    this._emitChanged();
    return true;
  },

  // The viewer's tax config, as plain data: each kind's default rate and the
  // resource overrides that differ from it.
  getTaxConfigView(civ) {
    const config = this.getTaxConfig(civ);
    const result = {};
    for (const kind of TAXES.kinds) {
      const resources = {};
      for (const id of RESOURCE_IDS) {
        const override = config.overrides[id] ? config.overrides[id][kind] : undefined;
        if (override !== undefined) resources[id] = override;
      }
      result[kind] = { rate: config[kind] || 0, resources };
    }
    return result;
  },

  // Books a tax payment into the treasury and the day's ledgers. `city` is the
  // region that generated it (the buyer, or the seller for an export tariff).
  _recordTax(civ, kind, resource, amount, city = null) {
    if (civ < 0 || !(amount > 0)) return;
    this.budgets.set(civ, this.getBudget(civ) + amount);
    const category = kind === "sales" ? "taxSales" : kind === "export" ? "taxExport" : "taxImport";
    this._recordBudgetCash(civ, category, amount);
    if (!this.taxLedger) this.taxLedger = new Map();
    let day = this.taxLedger.get(civ);
    if (!day) {
      day = { sales: 0, export: 0, import: 0 };
      this.taxLedger.set(civ, day);
    }
    day[kind] += amount;
    if (city) {
      if (!this.cityTaxLedger) this.cityTaxLedger = new Map();
      let region = this.cityTaxLedger.get(city.id);
      if (!region) {
        region = { cityId: city.id, sales: 0, export: 0, import: 0 };
        this.cityTaxLedger.set(city.id, region);
      }
      region[kind] += amount;
    }
  },

  // The taxes one nation collected over the last day, in treasury units.
  getTaxTake(civ) {
    const day = this.taxLedger ? this.taxLedger.get(civ) : null;
    return {
      sales: day ? day.sales : 0,
      export: day ? day.export : 0,
      import: day ? day.import : 0,
    };
  },

  // The taxes one region generated over the last day, in treasury units.
  getCityTaxTake(city) {
    const region = this.cityTaxLedger ? this.cityTaxLedger.get(city.id) : null;
    return {
      sales: region ? region.sales : 0,
      export: region ? region.export : 0,
      import: region ? region.import : 0,
    };
  },

  // Clears the daily tax ledgers, called from the resource day tick.
  _resetTaxLedger() {
    this.taxLedger = new Map();
    this.cityTaxLedger = new Map();
  },
};