Battle-for-Tismo/shared/rules.js

// Catalogue maths shared by the server (which charges costs) and the browser
// (which displays and disables buttons) so the numbers always agree.

import { effectValue, CITY_DEFENSE_BONUS, ECONOMY } from "./data.js";

// Fixed cost of raising a building to `level` (0-indexed: the cost of the next
// level). It grows only with the level, never with the nation's GDP.
export function buildingBuildCost(proto, level) {
  return proto.baseCost * Math.pow(proto.costAlpha, Math.max(level, 0));
}

export function buildingRefund(proto, level) {
  return buildingBuildCost(proto, level - 1) * proto.refundFraction;
}

// Recurring upkeep of a building kept at `level`, as a fraction of the cost of
// that level. Like the build cost it follows the level alone, never the GDP.
export const BUILDING_UPKEEP_FRACTION = 0.01;

export function buildingUpkeep(proto, level) {
  if (level <= 0) return 0;
  return buildingBuildCost(proto, level - 1) * BUILDING_UPKEEP_FRACTION;
}

export function buildingEffectValue(proto, stat, level) {
  let total = 0;
  for (const e of proto.effects) {
    if (e.stat === stat) total += effectValue(e, level);
  }
  return total;
}

export function governmentChangeCost(proto, gdp) {
  return proto.baseCost + proto.costGdpFraction * Math.max(gdp, 0);
}

// Combined effect totals for a catalogue entry whose effects do not scale
// (governments and technologies are always applied at level 1).
function effectsTotal(proto) {
  const totals = {};
  for (const e of proto.effects) {
    totals[e.stat] = (totals[e.stat] || 0) + effectValue(e, 1);
  }
  return totals;
}

export function governmentEffects(proto) {
  return effectsTotal(proto);
}

export function technologyEffects(proto) {
  return effectsTotal(proto);
}

// True when every prerequisite technology is in the researched set. The set
// holds catalogue indices, so each prerequisite id is first resolved against
// the catalogue.
export function prerequisitesMet(technology, researchedSet, catalogue) {
  for (const id of technology.prerequisites) {
    const index = catalogue ? catalogue.findIndex((t) => t.id === id) : -1;
    if (index < 0 || !researchedSet.has(index)) return false;
  }
  return true;
}

// Every defense modifier of the tile a unit stands on, in display order. The
// tile carries its own terrain bonus and a city adds another; each entry is a
// fraction of the unit's base defense. Shared by the server (which fights with
// them) and the browser (which shows them) so the numbers always agree.
export function defenseFactors(tile, hasCity) {
  const factors = [];
  if (tile && tile.defenseBonus) {
    factors.push({ label: tile.terrainType, bonus: tile.defenseBonus });
  }
  if (hasCity) factors.push({ label: "City", bonus: CITY_DEFENSE_BONUS });
  return factors;
}

// Multiplier applied to a unit's base defense for the tile it occupies.
export function defenseMultiplier(tile, hasCity) {
  let total = 0;
  for (const factor of defenseFactors(tile, hasCity)) total += factor.bonus;
  return 1 + total;
}

// A unit's defense on a tile, before any role bonus (the attacker/defender
// distinction is a combat rule, not part of the stat shown to the player).
export function unitDefense(baseDefense, tile, hasCity) {
  return baseDefense * defenseMultiplier(tile, hasCity);
}

// Every GDP-per-capita modifier of a tile, in display order. `tile` supplies the
// terrain multiplier and its name; `cityKind` is "capital", "city" or null and
// `nextToCity` is true when the tile borders one of its owner's cities. The
// pillage penalty and battle deficit are the lasting marks of war. Shared by the
// server (which derives each tile's GDP) and the browser (which explains it), so
// the numbers always agree.
export function gdpPerCapitaFactors(tile, {
  cityKind = null,
  nextToCity = false,
  pillagePenalty = 1,
  battleDeficit = 0,
  regionalMultiplier = 1,
  regionalLabel = null,
  nationalMultiplier = 1,
} = {}) {
  const factors = [];
  const terrainMultiplier = tile ? tile.gdpMultiplier || 0 : 0;
  factors.push({ label: tile ? tile.terrainType : "Unknown", multiplier: terrainMultiplier });
  if (cityKind === "capital") {
    factors.push({ label: "Capital", multiplier: ECONOMY.capitalTileGdpMultiplier });
  } else if (cityKind === "city") {
    factors.push({ label: "City", multiplier: ECONOMY.cityTileGdpMultiplier });
  } else if (nextToCity) {
    factors.push({ label: "Near city", multiplier: 1 + ECONOMY.citySurroundingGdpBonus });
  }
  if (pillagePenalty !== 1) {
    factors.push({ label: "Pillaging", multiplier: pillagePenalty });
  }
  // City improvements only shape the region their city controls, so a tile's
  // GDP per capita carries its region's multiplier plus the nation-wide one
  // from government and research. Both are factors on the per-capita figure,
  // never an adjustment to the final GDP. They are applied before the absolute
  // war damage below, so a scar stays proportional to the tile's productivity.
  if (regionalMultiplier !== 1) {
    factors.push({
      label: regionalLabel ? `${regionalLabel} improvements` : "Regional improvements",
      multiplier: regionalMultiplier,
    });
  }
  if (nationalMultiplier !== 1) {
    factors.push({ label: "National modifiers", multiplier: nationalMultiplier });
  }
  if (battleDeficit > 0) {
    factors.push({ label: "Battle damage", amount: -battleDeficit });
  }
  return factors;
}

// Applies the `gdpPerCapitaFactors` list to `base`, in order, never falling
// below zero.
export function gdpPerCapitaFromFactors(base, factors) {
  let total = base;
  for (const factor of factors) {
    if (factor.amount !== undefined) total += factor.amount;
    else total *= factor.multiplier;
  }
  return total > 0 ? total : 0;
}