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, POPULARITY, TRENCH } from "./data.js";

// The popularity scale shared by the server (which simulates it) and the
// browser (which shows it). Opinions live on the 0..1 scale; popularity is the
// same figure in integer points centred on neutral 0, and what the player sees
// is a logistic of those points.
export function popularityPoints(opinion) {
  return Math.round((opinion - 0.5) / POPULARITY.opinionPerPoint);
}

export function popularityDisplay(points) {
  return 1 / (1 + Math.exp(-POPULARITY.logisticScale * points));
}

// The hourly pace at which a population at `points` returns to neutral: one
// point an hour, so the estimate is simply the distance left.
export function hoursToNeutral(points) {
  return Math.abs(points);
}

// 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 production 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 production) and the browser (which explains
// it), so the numbers always agree.
export function productionFactors(tile, {
  cityKind = null,
  nextToCity = false,
  pillagePenalty = 1,
  battleDeficit = 0,
  trench = false,
  regionalMultiplier = 1,
  regionalLabel = null,
  nationalMultiplier = 1,
  portProduction = 0,
  naturalGrowth = 0,
} = {}) {
  const factors = [];
  const terrainMultiplier = tile ? tile.productionMultiplier || 0 : 0;
  factors.push({ label: tile ? tile.terrainType : "Unknown", multiplier: terrainMultiplier });
  if (cityKind === "capital") {
    factors.push({ label: "Capital", multiplier: ECONOMY.capitalTileProductionMultiplier });
  } else if (cityKind === "city") {
    factors.push({ label: "City", multiplier: ECONOMY.cityTileProductionMultiplier });
  } else if (nextToCity) {
    factors.push({ label: "Near city", multiplier: 1 + ECONOMY.citySurroundingProductionBonus });
  }
  if (pillagePenalty !== 1) {
    factors.push({ label: "Pillaging", multiplier: pillagePenalty });
  }
  if (trench) {
    factors.push({ label: "Trenches", multiplier: TRENCH.productionMultiplier });
  }
  // City improvements only shape the region their city controls, so a tile's
  // production carries its region's multiplier plus the nation-wide one
  // from government and research. Both are factors on the production 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 });
  }
  // A warm-water port adds a flat production-per-head figure to its whole
  // region, scaled by the sea tiles beside the city, before war damage is taken
  // off.
  if (portProduction > 0) {
    factors.push({ label: "Port", amount: portProduction });
  }
  // Natural growth is a flat production-per-head gain added on top of the
  // tile's productivity, growing by a constant amount each day.
  if (naturalGrowth > 0) {
    factors.push({ label: "Natural growth", amount: naturalGrowth });
  }
  if (battleDeficit > 0) {
    factors.push({ label: "Battle damage", amount: -battleDeficit });
  }
  return factors;
}

// Applies the `productionFactors` list to `base`, in order, never falling
// below zero.
export function productionFromFactors(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;
}

// The multiplier product of a `productionFactors` list, ignoring the absolute
// per-head terms (a port's flat production, natural growth, battle damage).
// This is what scales a tile's physical output.
export function productionMultiplier(factors) {
  let total = 1;
  for (const factor of factors) {
    if (factor.multiplier !== undefined) total *= factor.multiplier;
  }
  return total > 0 ? total : 0;
}