import { content } from "@deadhead/content";
import { describe, expect, it } from "vitest";
import { economicDistance, fuelCost, routeDistance } from "../src/index";

const { config } = content;
const courier = content.shipModel("courier")!;
const earth = content.location("earth")!;
const moon = content.location("moon")!;
const { referenceMillionKm: ref, exponent } = config.economicDistance;

describe("economic distance (decision 0.5.84)", () => {
  it("leaves an Earth–Moon length leg unchanged", () => {
    expect(economicDistance(ref, config)).toBeCloseTo(ref);
  });

  it("grows more slowly than distance past the reference, and keeps order", () => {
    expect(economicDistance(130, config)).toBeLessThan(130);
    expect(economicDistance(130, config)).toBeGreaterThan(economicDistance(60, config));
    // Doubling the distance multiplies it by 2^exponent.
    expect(economicDistance(20, config) / economicDistance(10, config)).toBeCloseTo(2 ** exponent);
  });

  it("is the plain distance with an exponent of 1", () => {
    const linear = { ...config, economicDistance: { referenceMillionKm: ref, exponent: 1 } };
    expect(economicDistance(130, linear)).toBeCloseTo(130);
  });
});

describe("fuel cost", () => {
  it("costs more Earth→Moon than Moon→Earth for the same ship", () => {
    const t = Date.parse("2100-01-01T00:00:00Z");
    const distance = routeDistance(earth, moon, t);
    expect(fuelCost(courier, earth, distance, config)).toBeGreaterThan(
      fuelCost(courier, moon, distance, config),
    );
  });

  it("scales with economic distance", () => {
    expect(fuelCost(courier, earth, 10, config) / fuelCost(courier, earth, 5, config)).toBeCloseTo(
      2 ** exponent,
    );
  });

  it("matches a hand calculation", () => {
    // Economic distance of 0.5M km × 200 credits/M km × Earth multiplier 2.1.
    const expected = ref * (0.5 / ref) ** exponent * 200 * 2.1;
    expect(fuelCost(courier, earth, 0.5, config)).toBeCloseTo(expected);
  });
});