import { describe, expect, it } from "vitest";
import { createRng, deriveSeed } from "../src/index";

const sequence = (seed: number, length = 1000) => {
  const rng = createRng(seed);
  return Array.from({ length }, () => rng.next());
};

describe("seeded RNG", () => {
  it("produces the same 1,000 values for the same seed", () => {
    expect(sequence(42)).toEqual(sequence(42));
  });

  it("produces different sequences for different seeds", () => {
    expect(sequence(42)).not.toEqual(sequence(43));
  });

  it("keeps next() in [0, 1)", () => {
    for (const value of sequence(7, 10_000)) {
      expect(value).toBeGreaterThanOrEqual(0);
      expect(value).toBeLessThan(1);
    }
  });

  it("keeps int() within inclusive bounds and reaches both ends", () => {
    const rng = createRng(1);
    const seen = new Set<number>();
    for (let i = 0; i < 1000; i++) {
      const value = rng.int(1, 5);
      expect(value).toBeGreaterThanOrEqual(1);
      expect(value).toBeLessThanOrEqual(5);
      seen.add(value);
    }
    expect([...seen].sort()).toEqual([1, 2, 3, 4, 5]);
  });

  it("picks only list elements and throws on an empty list", () => {
    const rng = createRng(3);
    const list = ["a", "b", "c"];
    for (let i = 0; i < 100; i++) {
      expect(list).toContain(rng.pick(list));
    }
    expect(() => rng.pick([])).toThrow();
  });

  it("derives different child seeds for different labels", () => {
    expect(deriveSeed(42, "board")).not.toBe(deriveSeed(42, "names"));
    expect(deriveSeed(42, "board")).not.toBe(deriveSeed(43, "board"));
    expect(deriveSeed(42, "board")).toBe(deriveSeed(42, "board"));
  });
});