Battle-for-Tismo/tests/roads_test.js

import { TestCase } from "./framework/test_case.js";
import { smallState } from "./framework/helpers.js";
import { buildRoadNetwork, greedySpanner, tileRoadCost } from "../shared/roads.js";
import { ROADS, TERRAIN_TILES } from "../shared/data.js";
import { key, parseKey } from "../shared/hex.js";

export class RoadsTest extends TestCase {
  test_road_cost_grows_exponentially_with_terrain() {
    const plains = TERRAIN_TILES.find((t) => t.terrainType === "Land");
    const hills = TERRAIN_TILES.find((t) => t.terrainType === "Hills");
    const mountain = TERRAIN_TILES.find((t) => t.terrainType === "Mountain");
    const sea = TERRAIN_TILES.find((t) => t.terrainType === "Sea");
    this.assertApprox(tileRoadCost(plains), Math.pow(ROADS.costBase, 1));
    this.assertApprox(tileRoadCost(hills), Math.pow(ROADS.costBase, 1.8));
    this.assertApprox(tileRoadCost(mountain), Math.pow(ROADS.costBase, 5));
    this.assertGreater(tileRoadCost(mountain), tileRoadCost(hills) * 8, "mountains dwarf hills");
    this.assertGreater(tileRoadCost(hills), tileRoadCost(plains), "hills cost more than plains");
    this.assertFalse(Number.isFinite(tileRoadCost(sea)), "the sea cannot carry a road");
    this.assertEqual(tileRoadCost(sea, true), 0, "a city tile is free");
  }

  test_cities_start_with_a_road_and_are_connected_by_the_network() {
    const state = smallState(["france", "britain", "poland"], 12345, { citiesPerCiv: 3 });
    const cityKeys = state.cities.map((city) => key(city.coords.x, city.coords.y));
    for (const city of state.cities) {
      this.assertTrue(
        city.improvements.includes(ROADS.improvementName),
        "a city is founded with a road"
      );
    }
    for (const cityKey of cityKeys) this.assertTrue(state.roads.has(cityKey));
    this.assertGreater(state.roads.size, cityKeys.length, "roads also cross the land");

    // Following roads from the first city must reach every other city.
    const seen = new Set([cityKeys[0]]);
    const queue = [parseKey(cityKeys[0])];
    while (queue.length > 0) {
      const coords = queue.pop();
      for (const neighbour of state.topology.neighbours(coords.x, coords.y)) {
        const nk = key(neighbour.x, neighbour.y);
        if (!state.roads.has(nk) || seen.has(nk)) continue;
        seen.add(nk);
        queue.push(neighbour);
      }
    }
    for (const cityKey of cityKeys) {
      this.assertTrue(seen.has(cityKey), `city ${cityKey} is reachable by road`);
    }
  }

  test_roads_level_the_movement_cost_across_terrain() {
    const state = smallState();
    const hill = state.landCells.find(
      (coords) => state.tiles[key(coords.x, coords.y)].terrainType === "Hills"
    );
    this.assertNotNull(hill, "the map has a hill");
    const unit = state._spawnUnit(hill, 0, state.protoUnits[0]);
    const before = state._tileTravelHours(unit, hill);
    state.roads.add(key(hill.x, hill.y));
    const after = state._tileTravelHours(unit, hill);
    this.assertLess(after, before, "a road makes the hill as cheap as plains");
    this.assertApprox(
      after,
      ROADS.movementCostMultiplier / state._effectiveSpeedAt(unit, hill),
      1e-9
    );
  }

  test_greedy_spanner_drops_links_the_others_already_cover() {
    // Four collinear points. The direct long links are covered by the chain of
    // unit links, so only the three short ones survive.
    const edges = [];
    for (let a = 0; a < 4; a++) {
      for (let b = a + 1; b < 4; b++) {
        edges.push({ a, b, cost: b - a, path: [] });
      }
    }
    edges.sort((x, y) => x.cost - y.cost);
    const chosen = greedySpanner(edges, 2);
    this.assertSize(chosen, 3, "only the short links are kept");
    for (const edge of chosen) this.assertEqual(edge.cost, 1);
  }

  test_the_network_is_sparse() {
    const state = smallState(["france", "britain", "poland", "slovenia"], 12345, { citiesPerCiv: 4 });
    const network = buildRoadNetwork(state.cities, state.topology, state.tiles);
    const cityKeys = state.cities.map((city) => key(city.coords.x, city.coords.y));
    const allPairs = (state.cities.length * (state.cities.length - 1)) / 2;
    this.assertGreater(allPairs, 6, "several candidate links exist");
    this.assertGreater(network.size, cityKeys.length, "roads cross the land");
    // 16 cities would need 120 links if every pair were connected; the spanner
    // stays far below that even counting the tiles between cities.
    this.assertLess(network.size, allPairs * 20, "the network stays sparse");
  }
}