Battle-for-Tismo/tests/food_synthesis_test.js

import { TestCase } from "./framework/test_case.js";
import { smallState, cityOf } from "./framework/helpers.js";
import { key } from "../shared/hex.js";
import { RESOURCE_RULES } from "../shared/data.js";
import {
  foodNeedPerDay,
  tileFoodOutput,
  foodSynthesisEnergy,
  foodSynthesisMarginalEnergy,
  stockpileTarget,
  synthesisedFoodFor,
} from "../shared/resources.js";

const Q = RESOURCE_RULES.foodSynthesisQuadratic;

// The land's daily harvest in one region, exactly as the daily tick sums it.
function regionFood(state, city) {
  let total = 0;
  for (const coords of state.regionTiles(city)) {
    const k = key(coords.x, coords.y);
    if ((state.tilePopulation.get(k) || 0) <= 0) continue;
    total += tileFoodOutput(state.tiles[k]) * state._regionFoodMultiplier(city);
  }
  return total;
}

export class FoodSynthesisMathTest extends TestCase {
  test_energy_for_extra_food_is_quadratic() {
    this.assertApprox(foodSynthesisEnergy(0), 0);
    this.assertApprox(foodSynthesisEnergy(10), Q * 100);
    this.assertApprox(foodSynthesisEnergy(20), 4 * foodSynthesisEnergy(10));
  }

  test_the_marginal_tonne_costs_more_than_the_last() {
    this.assertApprox(foodSynthesisMarginalEnergy(0), 0);
    this.assertApprox(foodSynthesisMarginalEnergy(10), 2 * Q * 10);
    this.assertGreater(
      foodSynthesisMarginalEnergy(20), foodSynthesisMarginalEnergy(10),
      "diminishing returns: the next tonne costs more"
    );
  }

  test_a_region_grows_until_energy_meets_the_market_price() {
    const foodPrice = 5100;
    const energyPrice = 0.051;
    const breakEven = foodPrice / (2 * Q * energyPrice);
    this.assertApprox(synthesisedFoodFor(foodPrice, energyPrice, 1e6), breakEven);
    // A shortfall smaller than the break-even caps the extra food.
    this.assertApprox(synthesisedFoodFor(foodPrice, energyPrice, 10), 10);
    // Cheap energy grows past a larger shortfall; dear energy grows almost none.
    this.assertGreater(synthesisedFoodFor(foodPrice, 0.0001, 1e6), breakEven);
    this.assertApprox(
      synthesisedFoodFor(foodPrice, 1000, 1e6), foodPrice / (2 * Q * 1000)
    );
    this.assertApprox(synthesisedFoodFor(foodPrice, 1e9, 1e6), foodPrice / (2 * Q * 1e9));
  }

  test_no_synthesis_without_a_price_or_a_shortfall() {
    this.assertApprox(synthesisedFoodFor(5100, 0, 1000), 0);
    this.assertApprox(synthesisedFoodFor(0, 0.05, 1000), 0);
    this.assertApprox(synthesisedFoodFor(5100, 0.05, 0), 0);
    this.assertApprox(synthesisedFoodFor(5100, 0.05, -10), 0);
  }

  test_the_region_grows_whatever_the_market_cannot_supply() {
    const foodPrice = 5100;
    const energyPrice = 0.051;
    const shortfall = 10_000;
    const breakEven = foodPrice / (2 * Q * energyPrice);
    // No reachable supplier: grow the whole shortfall.
    this.assertApprox(synthesisedFoodFor(foodPrice, energyPrice, shortfall, 0), shortfall);
    // A market that covers only part: grow the rest beyond the break-even.
    this.assertApprox(
      synthesisedFoodFor(foodPrice, energyPrice, shortfall, 4000),
      shortfall - 4000
    );
    // A market that covers the affordable portion: grow only the break-even.
    this.assertApprox(
      synthesisedFoodFor(foodPrice, energyPrice, shortfall, 9000),
      breakEven
    );
    this.assertGreater(breakEven, 0);
  }
}

export class FoodSynthesisModelTest extends TestCase {
  test_a_region_short_of_food_forces_extra_from_energy() {
    const state = smallState();
    const city = cityOf(state, 0);
    // The generated region may open self-sufficient; strip its farmland so the
    // fixture is genuinely short, which is the point of the test.
    for (const coords of state.regionTiles(city)) {
      if (coords.x === city.coords.x && coords.y === city.coords.y) continue;
      state.tilePopulation.set(key(coords.x, coords.y), 0);
    }
    const need = foodNeedPerDay(state.getCityEconomy(city).population);
    const shortfall = need - regionFood(state, city);
    this.assertGreater(shortfall, 0, "the fixture region opens short of food");
    // Hold the reserve full so the test isolates the day's ration: with the
    // pantry a month deep, only the meal the land cannot grow is forced.
    state.getCityResourceStock(city).food = stockpileTarget(need);
    // Cheap energy against a dear market: force as much as the shortfall allows.
    state.setResourcePrice("energy", 0.00001);
    state.setResourcePrice("food", 1e9);
    state._tickResources();
    const extra = state._foodSynthesis.get(city.id) || 0;
    this.assertApprox(extra, shortfall, 1, "the whole shortfall is grown");
  }

  test_a_region_grows_extra_to_refill_an_empty_reserve() {
    const state = smallState();
    const city = cityOf(state, 0);
    // A self-sufficient region with an empty pantry still wants its month back.
    this.assertGreater(regionFood(state, city), 0, "the region has farmland");
    state.getCityResourceStock(city).food = 0;
    // The reserve is dearer to force than the land, but cheap energy against a
    // dear market makes the extra worth growing.
    state.setResourcePrice("energy", 0.00001);
    state.setResourcePrice("food", 1e9);
    state._tickResources();
    const extra = state._foodSynthesis.get(city.id) || 0;
    this.assertGreater(extra, 0, "an empty reserve drives synthesis above the harvest");
    this.assertGreater(
      state.getCityResourceStock(city).food, regionFood(state, city),
      "the store rises toward the reserve instead of hugging the day's harvest"
    );
  }

  test_a_region_buys_instead_when_energy_is_dearer_than_food() {
    const state = smallState();
    const city = cityOf(state, 0);
    state.setResourcePrice("energy", 1e9);
    state.setResourcePrice("food", 1);
    state._tickResources();
    this.assertApprox(state._foodSynthesis.get(city.id) || 0, 0);
  }

  test_the_extra_food_lands_in_the_region_s_store() {
    const state = smallState();
    const city = cityOf(state, 0);
    state.setResourcePrice("energy", 0.00001);
    state.setResourcePrice("food", 1e9);
    state._tickResources();
    const produced = state.getCivResourceSummary(0).production.food;
    this.assertGreater(
      produced, regionFood(state, city),
      "the nation's food production includes the forced extra"
    );
  }
}