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

/** A device clock the test can set, forward or back. */
function device(start: number) {
  let time = start;
  return { now: () => time, set: (t: number) => (time = t) };
}

describe("device clock (Step 14.1, decision 0.5.88)", () => {
  it("returns device time plus the developer offset", () => {
    const d = device(1_000_000);
    const clock = new DeviceClock(d.now, { offsetMs: 5_000 });
    expect(clock.now()).toBe(1_005_000);
    clock.advance(60_000);
    expect(clock.now()).toBe(1_065_000);
  });

  it("never runs backward when the device clock is set back", () => {
    const d = device(2_000_000);
    const clock = new DeviceClock(d.now);
    expect(clock.now()).toBe(2_000_000);
    d.set(1_500_000);
    expect(clock.now()).toBe(2_000_000);
    expect(clock.lastTimeSeen).toBe(2_000_000);
  });

  it("reflects a forward move at once", () => {
    const d = device(2_000_000);
    const clock = new DeviceClock(d.now);
    clock.now();
    d.set(9_000_000);
    expect(clock.now()).toBe(9_000_000);
  });

  it("starts from a save's last time seen when the device is behind it", () => {
    const d = device(1_000);
    const clock = new DeviceClock(d.now, { lastTimeSeen: 5_000 });
    expect(clock.now()).toBe(5_000);
    clock.restore(4_000);
    expect(clock.now()).toBe(5_000);
    clock.restore(7_000);
    expect(clock.now()).toBe(7_000);
  });

  it("refuses to move backward through the developer offset", () => {
    expect(() => new DeviceClock(() => 0).advance(-1)).toThrow(RangeError);
  });
});